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Cadmium dispersal on a raised heathland in the Peak District National Park adjacent to a major trunk road

Cadmium dispersal on a raised heathland in the Peak District National Park adjacent to a major... Volume 4 † Number 2 † June 2011 10.1093/biohorizons/hzr017 ......................................................................................................................................................................................................................................... Research article Cadmium dispersal on a raised heathland in the Peak District National Park adjacent to a major trunk road Andrew Pickett* Staffordshire University, 22 Russell Street, Newcastle-under-Lyme, Staffs, UK. * Corresponding author: Email: andypickett@live.co.uk Supervisor: Professor John Dover, Staffordshire University, 22 Russell Street, Newcastle-under-Lyme, Staffs, UK. ........................................................................................................................................................................................................................................ Heavy metals are naturally present in soils as trace elements but deposition from vehicle wear and tear increases concentrations found adjacent to highways and has been shown to disperse further in relation to traffic volume. The heavy metal cadmium (Cd), used in the manufacture of tyres, has toxic effects on some plant species, with soil acidity being a major factor in plant Cd uptake. In this study, levels of Cd in soil and root material from Calluna vulgaris were investigated along with soil pH on wet heather moorland in the Peak District National Park. In December 2009, samples were collected from 10 transects extending up to 125 m from a trunk road that has a daily vehicle use .23 000. The peat substrate of the study site was found to be highly acidic (mean pH+ S.D.: 3.44+ 0.119). Reported Cd concentrations in peat core samples (50–200 mm depth) are within the UK rural soil distribution range (0.1–1.8 mg kg ), but increase progressively up to 85 and 125 m on either side of the road probably assisted by the wind. Root samples from C. vulgaris showed a degree of Cd accumulation (mean+ S.D.: 17.78 mgg + 9.338) compared with normal concentrations in plants from unpolluted soils (0.1 mgg ). Coupled with data from previous research, results from this study suggest that increased soil Cd concentrations could affect the competitive balance between C. vulgaris and other moorland plants such as Molinia caerulea. Advances in analytical techniques allowing a better understanding of plant responses to metal toxicity are also discussed. Key words: cadmium, traffic pollution, heathland, Calluna vulgaris, Peak District National Park. Submitted September 2010; accepted March 2011 ........................................................................................................................................................................................................................................ Potential traffic-derived pollutants include polyaromatic Introduction hydrocarbons, volatile organic compounds, heavy metals Highway run-off contains numerous potential environmental and particulates such as rubber from tyres, nitrogen oxides, pollutants that can adversely affect fauna and flora adjacent ammonia and nitrous acid. Heavy metals are normal con- to roads, the effects of which have been shown to extend a stituents of soil horizons as trace elements for which flora 1 –3 greater distance from increased daily vehicle use. The dis- have locally adapted with regard to ion uptake, increased con- persal of vehicle emissions and particulates from wear and centrations are persistent however, remaining in an undis- tear also varies from place to place being influenced by turbed environment for decades. Derived from vehicle wear factors such as wind direction, local climate, topography and tear, some of the most frequently reported metals are 4,5 and seasonal salt applications in severe winter weather. zinc (Zn) and cadmium (Cd) used in tyre manufacture; It has been estimated that 5.4% of Sites of Special copper, manganese and chromium from brake systems; also 4,9 Scientific Interest (SSSIs) in England lie partly within iron, aluminium and nickel from engine component wear. 200 m of a major road. In terms of nature conservation, a Cd uptake in plants better understanding of pollutant effects on vegetation assemblages could help to develop techniques for use in the Cd is a relatively rare element in terms of crustal abundance, management of valued semi-natural habitats. but it is of concern as it is highly toxic to most prokaryotic ......................................................................................................................................................................................................................................... 2011 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 149 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... and eukaryotic organisms, entering the food chain through suggested that this may be as a result of transformations animal grazing or crop harvesting on plants that have accu- carried out by metal-mobilizing and acid-producing 10 33 mulated Cd via root uptake. Humans are more vulnerable bacteria. to Cd accumulation in organs from contaminated food than 11,12 grazing stock due to their longer life span. Cd solubility Calluna vulgaris in water can facilitate rapid distribution in the environment In this study, root samples from Heather (Calluna vulgaris) and entry into the food chain via crop plants has caused were used to assess Cd uptake in the dominant higher serious problems to human health in China and fatalities in 13,14 plant species native to the area. It has been suggested that the mid-20th century Japan. More recent observations C. vulgaris is dependent on an association with the ectomy- of Cd burden in herbivores carried out in Norway have corrhizal fungi Hymenoscyphus ericae for survival on acidic either noted a ‘certain relationship’ with environmental 15,16 and/or heavy metal-polluted soils in the UK, by reducing Cd concentrations or found a weak or absent 17,18 heavy metal uptake. Over recent decades though, despite relationship. this defence mechanism, C. vulgaris has been experiencing Small amounts of Cd are taken in by higher plants directly a loss of cover in favour of Purple Moor grass (Molinia caer- from the atmosphere; movement into plant cells is normally ulea) due to eutrophication, although it is unclear whether gained by way of micronutrient transporters in root epider- 2þ Cd is a factor in this process. mal cells. Due to the high mobility and solubility of Cd ions, entry to cortical tissue via transmembrane carriers 2þ 2þ 2þ 2þ 2þ used to uptake Ca ,Fe ,Mg ,Cu and Zn occurs Aims and objectives 19,20 readily and can reach the xylem when complexed with 21 The main aim of this project was to ascertain the extent of Cd organic acids or phytochelatins. Adverse effects of Cd dispersal in soil and plant material adjacent to a major road in accumulation in plants include reduction in photosynthesis, 22 an ESA characterized by strong acidity, surface water and sub- water and nutrient uptake, disruption of cell transport pro- 23,24 strate with high organic matter content. The objectives were to cesses and inhibition of enzyme activities and affects 25 ascertain the local peat substrate pH value, compare available general root and shoot growth. Normal Cd concentrations 21 11 soil and root sample Cd concentrations in order to evaluate the in plants have been published as 0.1 mgg . effect of local conditions on the potential toxic effect of Cd to Cd availability to plants is influenced by a number of C. vulgaris. Also, using a further understanding of the pro- factors such as amount of water in the soil which increases 2þ cesses that influence plant Cd uptake and drawing on recent activity of hydrated Cd ions, whereas elevated concen- research, a further aim was to investigate whether Cd may trations of Zn and Fe can compete for root uptake of diva- be a factor affecting the competitive balance between lent cations. Organic matter content of the soil is inversely C. vulgaris and M. caerulea. related to plant Cd uptake as it is effective in keeping Cd unavailable by complexion with agents in humic sub- 26,27 stances but the most important factor in controlling 28,29 uptake of heavy metals is pH. A linear relationship has Materials and Methods been shown between soil pH decreasing and Cd uptake Site description increasing, the more naturally acidic substrate providing a greater level of toxic effect. The study area is a raised wet heathland, designated an SSSI, in the South-West Peak District with an annual precipitation Raised heathland in the peak district of 140 cm/year and comprises ombrotrophic peat 0.5–2 m An acidic substrate is a characteristic of the upland blanket thick (Peak District ). Through this locality the A537 peat moorlands which cover around 8% of land area in the Buxton to Macclesfield trunk road, which has a minimum UK, contributing 10–15% of the total global resource. predicted daily vehicle use of 23 708 in 2011 The Peak District National Park, situated in north-central (Highways ), cuts across a sloping heather moorland England, contains two environmentally sensitive areas between Wildboarclough and Upper Hartington Quarter (ESAs), characterized by extensive heather moorland and over a height difference of 545–470 m through 2 km south- 31 37 blanket bog habitats. Payments are made to land managers west to north-east. The section through Wildboarclough is to maintain these ecologically important landscapes, con- exposed to prevailing south-westerly winds over a large taining a number of SSSIs, and listed in the EU Habitats area of surface water named Tinkerspit Gutter, an area Directive (92/43/EEC) as ‘Special Areas of Conservation’ likely to experience hydrological mobilization of Cd, (SAC) and Special Protection Areas. sloping down to the source of the River Goyt over a distance Recent research in the southern Pennines has raised of 2 km. The landowner, United Utilities, granted permission concern regarding further acidification of the environment, to carry out sampling following consultation with the tenant, showing a highly acidic pH level (3.00–3.14), it was Lord Derby and Natural England. ......................................................................................................................................................................................................................................... 150 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Sampling soil: water suspension. Each of the 16 suspensions was shaken for 15 min using a Bibby Stuart Scientific SF1 Flask C. vulgaris root and peat core sampling from transects Shaker (300 oscillations/minute) and analysed for pH running perpendicular to the A537 was carried out in using a Mettler Toledo Seven Multi-digital pH meter cali- December 2009. Using two permanent traffic signs on brated with standard solutions at pH 4, 7 and 9. either side of the road as an arbitrary origin at grid reference 37 38 SJ 004 716, a random number generator set at 0–1000 (maximum 1 km distance) was used to assign starting Peat samples (chelation using ethylene-diamine- points in metres for seven transects on the north (N) and tetraacetic acid) three transects on the south (S) side of the A537 as shown in Fig. 1. A greater number of samples were taken from the Following the method published in Rowell, peat samples north side of the main road due to the direction of the were oven dried overnight at 758C and ground to 2mm decreasing gradient and prevailing wind direction. Peat particle size using a brass sieve, available Cd was core samples to a depth of 200 mm below the surface were then extracted from each sample using 0.5 M collected using a hardened carbon/steel peat auger at four ethylene-diamine-tetraacetic acid (EDTA). 3  5 aliquots points along each transect (5, 45, 85 and 125 m) and from each sample (mean+ S.D.: 5.012 g+ 0.0202) were retained in sealed sample bags (n ¼ 40) for later analysis. then transferred to 250 ml conical flasks to which 50 ml Root samples were collected on the north side of the A537 (mean+ S.D.: 49.89 ml+ 0.153) of 0.5 M EDTA disodium only, due to limited resources, from five transects at four salt dehydrate (pH 7) was added and stirred for 1 h using sample points along each transect (5, 45, 85 and 125 m) a Bibby Stuart Scientific SF1 Flask Shaker set at 300 oscil- and retained in sealed sample bags (n ¼ 20) for later analysis. lations/minute. Samples were then filtered using Whatman Sample sizes were limited in order to minimize disturbance no.541 hardened, ashless filter papers; solutions were on the ESA, however the locations were recorded so that then retained for later analysis by atomic absorbance future analyses could be compared. spectrophotometry. Sampling handling and chemical analyses Root samples (acid digestion) Area pH value Using the procedure set out in Milner and Whiteside, root samples were dried at 408C for 48 h, crushed to pass Soil samples were selected at random (n ¼ 16) from the 40 through a 0.7 mm brass sieve and the resulting powder samples obtained and pH was determined using a 1:10 oven dried at 1058C overnight. 0.2 g of each sample was then weighed into a long-necked Kjeldhal flask to which 1.0 ml sulphuric acid (H SO :S.G. ¼ 1.84), 5 ml nitric 2 4 acid (HNO :S.G. ¼ 1.42) and 1 ml perchloric acid (HClO : 72%) were added. The mixture was then heated gently until the initial reaction subsided and then boiled until white sulphuric acid fumes appeared and then for a further 15 min. The digest was then transferred to 100 ml volumetric flask, made up to 100 ml with deionized water and retained for later analysis by atomic absorbance spectrophotometry. Available soil Cd concentration analysis Available soil Cd concentration for each sample solution was determined using graphite furnace atomic absorbance spec- trophotometry (Unicam 939 AA spectrometer, GF90 furnace, FS90 auto-sampler) with deuterium lamp back- ground correction and ammonium nitrate (NH NO :5 mg 4 3 ml ) matrix modifier. Each run of samples was preceded by calibration using Cd standard solutions (10, 20, 30, 40 21 21 and 50 ng ml ), results given in ng ml were converted Figure 1. Sketch map of the study area showing positions of transects to sample concentration values for root and soil of mgg adjacent to the A537. Origin point of measurements recorded at grid refer- 37 21 ence SJ 004 716 was two permanent traffic warning signs. and mg kg , respectively. ......................................................................................................................................................................................................................................... 151 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... Results Area pH From the 16 random soil samples, the study site was found to have a highly acidic pH (mean+ S.D.: 3.44+ 0.119). No significant trend was observed in pH values recorded on either side of the road or in proximity to the road. Soil Cd concentration Available Cd concentrations derived from peat samples taken along transects running perpendicular to the north (down- ward sloping) side of the A537 are summarized in Fig. 2. Median values, when viewed with interquartile ranges (boxes), show a steady increase as the distance from the Figure 3. Soil available Cd concentrations (mg kg ) from samples (n ¼ road increases from 5 m to 125 m. Within each distance 35) taken along transects perpendicular to the south side of the A537. group, a large variation in concentrations can be observed Boxplots show median, first and third quartiles along with minimum and with notable data skewness at 5 and 85 m. maximum values. Results from analysis of samples taken along transects on the south side of the A537 shown in Fig. 3 illustrate a greater increase in available Cd concentrations than on the north side from 5 m to 85 m with a marked decrease at 125 m. Interquartile and total ranges within each distance group describe a large variation of values and a significant degree of data skewness. Overall range across all distance groups ¼ 0.12–1.20 mg 21 21 kg , overall mean+ S.D. ¼ 0.54 mg kg + 0.222. Root Cd concentrations Median, quartiles and range values for Cd concentration derived from collected C. vulgaris root samples, at distances from the A537, are summarized in Fig. 4. A considerable variation in root Cd concentration was recorded within each distance group, particularly at 45 m from the road where the Cd burden range ¼ 10.85–42.03 mgg . Figure 4. Root Cd burden in C. vulgaris (mgg ) from samples (n ¼ 20) taken at distances along transects perpendicular to the north side of the A537. Boxplots show median, first and third quartiles along with minimum and maximum values. Overall root mean Cd concentration+ S.D.: 17.78 mgg + 9.338. Soil/root Cd association The strength of association between soil and root sample Cd concentrations was not significant (r ¼ 20.800 (20); P  0.2), results in this study showing a negative relationship. Discussion The highly acidic condition of the study site reported in this Figure 2. Soil available Cd concentrations (mg kg ) from samples (n ¼ paper (mean+ S.D.) 3.44+ 0.119 compares well with pre- 84) taken along transects perpendicular to the north side of the A537. vious research in the southern Pennines carried out by Boxplots show median, first and third quartiles along with minimum and maximum values. Linton et al. who reported a pH range of 3.00–3.14 over ......................................................................................................................................................................................................................................... 152 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... 21 21 Table 1. Soil (mg kg ) and root (mgg ) Cd concentrations with six sites. This has strong implications for the flora in the area regard to distance as pH has been shown to be one of the most important 11 29 factors, if not the most important factor, in determining Distance from A537 (m) the bioavailability of Cd in soils to plants. Studies by Kou 42– 44 5 45 85 125 et al., Sappin-Didier et al., and Tsalidas et al. each ................................................................................................................ observed an increase in plant Cd uptake with a corresponding Soil Cd concentration decrease in pH, although two studies in Canada point out the North importance of the substrate organic content. Sauve et al. A1 0.12 0.53 0.68 0.77 observed that organic matter had a high sorption affinity for A2 0.36 0.4 0.74 0.76 Cd, which was as much as 30 times higher than mineral A3 0.2 0.39 0.73 0.83 soil, another study carried out in Canada showed that 46 B1 0.12 0.7 0.73 0.28 organic matter was the primary sorbent for heavy metals. B2 0.54 0.63 0.82 0.3 In this study, available Cd in soil concentrations reported B3 0.14 0.55 0.86 0.28 (overall range: 0.12–1.20 mg kg ) are within the UK rural C1 0.42 0.48 1.01 0.85 soil distribution range (0.1–1.8 mg kg ) published in the UK Soil and Herbage Pollutant Survey, although the C2 0.52 0.42 1.01 0.87 overall mean Cd concentration found in this study C3 0.39 0.4 0.69 0.6 (0.499 mg kg ) was higher than the mean UK rural and D1 0.54 0.39 0.44 0.61 urban soil concentrations (0.39 and 0.49 mg kg , respect- D2 0.63 0.39 0.55 0.57 ively). It should be noted that figures published by this D3 0.56 0.44 0.5 0.91 survey show extracts refluxed with Aqua Regia, which E1 0.5 0.31 0.52 0.8 would normally be considerably higher than those found E2 0.44 0.34 0.44 0.63 using the EDTA method employed in this study. Overall, E3 0.45 0.47 0.55 0.58 available Cd concentrations were observed to be higher F1 0.24 0.48 0.41 0.52 between 85 and 125 m, with the trend implying that F2 0.26 0.36 0.3 0.54 additional sampling over 125 m on the north side of the F3 0.25 0.35 0.32 0.46 road may have shown a further increase. These data G1 0.59 0.43 0.4 0.63 support previous research on the consequences of traffic pol- lutant dispersal carried out by Angold who examined plant G2 0.69 0.43 0.43 0.72 species composition adjacent to the A31 in Hampshire (12 h G3 0.68 0.2 0.63 0.77 traffic flow ¼ 35 000) observing a ‘maximum edge effect’ of South 200 m from the dual carriageway. Results from this study are A1 0.69 0.35 0.96 0.7 also substantiated by in their analysis of vegetation health A2 0.61 0.23 0.82 0.72 adjacent to the M62 in northern England (mean motor A3 0.29 0.21 0.88 0.63 vehicle flow ¼ 74 000 per day) and the M40 (mean motor B1 0.3 0.89 0.39 0.77 vehicle flow ¼ 94 000 per day), concluding that background B2 0.27 0.85 0.49 0.71 levels of motor vehicle pollutants were likely to be reached B3 # 0.67 0.53 0.68 within 50–100 m of the road (Table 1). C1 0.16 0.76 1.2 0.56 Available Cd concentrations in the peat substrate on the C2 0.15 0.54 1 0.39 north side of the A537 showed a steady increase over the C3 0.16 0.8 0.68 0.59 sampling distance from 5 to 125 m, which would follow the descending slope away from the road combined with the Root Cd concentration surface water characteristic of this particular area. Whilst Sample 5 m 45 m 85 m 125 m variability of concentrations within distance groups was NA 25.15 42.03 9.2 16.48 high, overall increases were observed to follow the downward NB 12.98 10.88 15.63 9.55 gradient that has few erosion runnels or hillocks to prevent NC 14.34 13.74 27.86 14.98 ground-level wind. It is possible in this case that the prevailing ND 23.38 32.21 10.09 5.87 highly acidic conditions in the soil at the study site reduce the NE 19.54 7.97 18.69 26.42 Cd binding effect of humic substances within the substrate 2þ thereby increasing the solubility of Cd ions that are at the 125 m sampling point. The gradient on this side of the leached from the roadside area, being carried over 125 m by road is a gradual incline which somewhat contradicts the the surface hydrology. The trend of Cd transport on the 2þ explanation of Cd ions being transported by surface south side of the road showed a larger increase from 5 to waters. These data presented in this paper support an 85 m than on the north side with a decrease being observed ......................................................................................................................................................................................................................................... 153 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... explanation that pollutants from vehicles are dispersed by contaminated soils has been ascribed largely to a heavy infec- wind to a greater degree than by surface water, the elevated tion by mycorrhizal fungi, often observed in the roots of these 52,10 and open perspective of the landscape being subject to seaso- species that reduces heavy metal uptake. Despite this nal strong winds from a north-easterly and south-westerly defence mechanism, C. vulgaris has been observed to exhibit direction. In their study assessing the effects of two motor- a darker colour in new growth near to a road and a general 50 49 ways in Germany (64 000 and 103, 300 vehicles per day) decrease in abundance, whereas grass species such as also suggested an impact of wind, observing an edge effect M. caerulea and Deschampsia flexuosa appear to be more tol- extending up to 230 m downwind and 80 m upwind of the erant in polluted soils and are abundant in many parts of the roads, with particulates decreasing in concentration over a Peak District. In D. flexuosa, a very low uptake of Cd has shorter distance than gaseous constituents. been observed at varying levels of metal contamination and The total biomass of C. vulgaris root material analysed Cd concentrations have been reported for M. caerulea shoots was 4.0 g in total due to the sample size (n ¼ 20) and the that are 10-fold higher than C. vulgaris analysed in the same 10,53 mass of individual root samples digested (0.2 g), the results research. The spread of M. caerulea at the expense of therefore give an indication of plant uptake rather than moorland heather due to eutrophication from deposition of hard evidence of potential toxic effect from Cd. Cd concen- pollutants derived from anthropomorphic activities has been trations extracted from root samples of C. vulgaris root reported in a number of northern European countries over 54 –56,30 showed a high degree of variation within each distance the last three decades. An established complete group, particularly at 45 m, the trend of Cd burden dropping canopy of C. vulgaris can compete successfully with off between 45 and 85 m. Across all four distance groups, a M. caerulea even with an increased availability of nutrients degree of Cd accumulation in the root biomass was observed in the medium term yet dispersal of traffic-borne eutrophica- that is higher than the normal concentration in plants from tion and pollution increases the competitive ability of 21 11 58,49 unpolluted soils (0.1 mgg ) but lower than concen- M. caerulea, particularly near to the roadside. The combi- trations derived from metal hyperaccumulator plants nation of biotic factors influencing the success of in situ plant 21 11 (100 mgg ). Comparison of Cd concentration in soil populations are numerous and dynamic but a better under- and root material from each sample point implied a negative standing of individual stress tolerances within species may correlation, although more data would be required to draw help in developing techniques for conservation strategies. any serious conclusions from this. Along with many other The response of plants to increasing concentrations of factors, this could mean that the organic matter content of heavy metals can now be more fully understood through the peat substrate is binding with Cd making it less available analysis of gene expression of the metal transporter gene for plant uptake further from the road. HMA4, which is essential for root to shoot transport and a It has been accepted for a number of years that metal non- key determinant of the metal hyperaccumulation pheno- hyperaccumulator plants show a progressive build up of type. A comparison of the level of expression in the flower- heavy metals in root systems, whereas hyperaccumulators ing plants Arabidopsis halleri (a metal hyperaccumulator) are able to transport absorbed toxic metals to the above- and A. thaliana (a metal non-tolerant) displayed a higher ground biomass, therefore a comparison of root, shoot level of expression of the HMA4 transporter gene in and leaf Cd concentrations in C. vulgaris would be useful in the hyperaccumulator. The significant role of this gene assessing the plants ability to thrive in metal-contaminated expression in metal transport has been further demonstrated soils. In their study in Norway, Brekken and Steinnes ana- by a single gene transfer of HMA4 into the non-accumulator lysed Cd concentration in leaves, shoots and twigs from A. thaliana, increasing its shoot metal uploading. C. vulgaris, observing minimal transfer of background soil A number of other mechanisms and processes have been Cd levels (1–3 mg kg ) to the above-ground biomass of the reported within plants that enhance metal tolerance and 21 21 plant (twigs ¼ 0.1 mgg ; leaves/shoots ¼ 0.05 mgg ) accumulation such as chelation of metal ions and subsequent which, when coupled with data from this research showing a compartmentalization in vacuoles, increased enzyme activity 60 –62 degree of accumulation in C. vulgaris root, suggests that it is and expression of the AtPCS1 gene. Research into plant a metal non-accumulator. In the same study, a seasonal metal tolerance mechanisms over the last decade has mainly trend in metal uptake was observed that also has importance focused on cash crops, biotechnology could also aid con- with the findings of this study in that the highest concen- servation efforts by allowing greater knowledge of environ- trations of Cd were reported from samples collected in mental processes. Metal tolerance may well be one of the summer with a 51% decrease being observed in autumn many factors affecting dominance between Heather and samples, therefore concentrations derived for this research Purple Moor grass and indeed between other plant species. (from samples collected in winter) would be expected to be In Germany, the moss Hylocomium splendens has been the lowest of annual Cd burden in C. vulgaris. observed to contain Cd levels three times higher than the The success of C. vulgaris and other ericaceous species such background level of ,0.1 mgg which could aid this as Vaccinium as colonists of acidic and heavy metal species with regard to competitive ability with other ......................................................................................................................................................................................................................................... 154 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... bryophytes. In a delicately balanced ecosystem such as the Author biography raised wet heathland surveyed in this study, further knowl- A.P. is 45 years old and gained direct entry into year 2 of a BSc edge of responses to metal pollution exhibited by character- (Hons) Biology degree course at Staffordshire University in istic species (ericaceous shrubs, graminoids and bryophytes) 2008 having carried out his first year in Biological Sciences could be very useful to land managers when assessing the at Wolverhampton University in 2000/01. His main interests best way to conserve moorland floral assemblage. are conservation of biodiversity and semi-natural landscapes It is considered that phytoremediation, the use of hyperac- along with the chemistry of life processes. A.P. believes these cumulator plants to transfer metals to plant tissue which is interests are shown through in the project, which he enjoyed then harvested, would not be sustainable or practical for carrying out immensely, the results allowing a good discussion landscape scale remediation. The most promising research and the opportunity to compare with previously published examines the potential of tying Cd up in the soil, making articles. Following graduation A.P. has now begun a it less available for plant uptake. Pierzynski and P.G.C.E. course at Manchester Metropolitan University in Hettiarachchi have listed several forms of phosphorus order to pursue a career teaching science in secondary schools. that could achieve this. Technological advances in analysis and microscopic techniques are generating new knowledge that professionals involved in conservation could manipulate to achieve their aims. References 1. 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Bradley R, Burt AJ, Read DJ (1982) The biology of mycorrhizae in the Econ 57: 259–275. Ericaceae 8: the role of mycorrhizal infection in heavy metal resistance. 32. Rothwell JJ, Evans MG, Daniels SM, Allott TEH (2007) Baseflow and stormflow New Phytol 91: 197–209. metal concentrations in streams draining contaminated peat moorlands in 53. Gjengedal E (1992) Uptake and mobility of metals in naturally growing plant the Peak District National Park (UK). J Hydrol 341: 90–104. species in catchments subjected to long-term changes in soil acidification. 33. Linton PE, Shotbolt L, Thomas AD (2007) Microbial communities in long- Doctoral Thesis. Norway: University of Trondheim, AVH. term heavy metal contaminated ombotrophic peats. Water Soil Air Pollut 54. Hansen K (1976) Ecological studies in Danish heathland vegetation. Dansk 186: 97–113. Bot Arch 81: 7–116. 34. Bradley R, Burt AJ, Read DJ (1981) Mycorrhizal infection and resistance to 55. Damblon F (1992) Paleobotanical analysis of Eriophorum and heavy metal toxicity in Calluna vulgaris. Nature 292: 335–337. Molinia tussocks as a means of reconstructing recent history of 35. Peak District National Park Authority (2001) Study Area factsheet 20: The undisturbed mires in the Haute-Ardenne, Belgium. Rev Paleobot Palynol Goyt Valley [online]. March 2001. http://www.peakdistrict-nationalpark. 273–288. info/studyArea/factsheets/media/goytmap2.gif 56. Berendse F, Schmidtz M, De Visser W (1994) Experimental manipulation of (accessed 22 May 2010). succession in heathland ecosystems. Ocealogica 100: 38–44. 36. Highways Agency Area Study (2003) Predicted Daily Vehicle Use on 57. Aerts R (1989) Above ground biomass and nutrient dynamics of Calluna vul- Motorways and Major Roads. http://www.highways.gov.uk/roads/ garis and Molinia caerulea in a dry heathland. Oikos 56: 31–38. projects/4998.aspx. 58. Aerts R, Berendse F, Klerk NM, Bakker C (1990) Root production and root 37. Ordnance Survey (2008) Explorer Map: OL24. Southampton: Ordnance turnover in two dominant species of wet heathlands. Ocealogica 81: Survey. 374–378. 38. Beswick KM, Choularton TW, Inglis DWF, Dove AJ, Fowler D (2003) Influences 59. Hanikenne M, Talke IN, Haydon MJ et al. (2008) Evolution of hyperaccu- on long term trends in ion concentration and deposition at Holme Moss. mulation required cis-regulatory changes and triplication. Nature 453: Atmospheric Environment 37: 1927–1940. 391–395. 39. Random. org. (2009) Random Number Generator [online]. http//www. 60. Bennett LE, Burkhead JL, Hale KL et al. (2003) Analysis of transgenic Indian random.org/ (accessed 1 December 2009). mustard plants for phytoremediation of metal-contaminated mine tailings. J 40. Rowell DL (1994) Soil Science: Methods and Applications. Essex: Pearson Environ Qual 32: 432–440. Education Ltd. ......................................................................................................................................................................................................................................... 156 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... 61. Zhu YL, Pilon-Smits EHA, Tarun SA, Weber SU, Jouanin L, Terry N (1999) 63. Steinnes E, Hanssen JE, Rambaek JP, Vogt NB (1994) Atmospheric deposition Cadmium tolerance and accumulation in Indian Mustard is enhanced by of trace elements in Norway: temporal and spatial trends studied by moss overexpressing g-glutamylcysteine synthetase. Plant Physiol 121: analysis. Water Soil Air Pollut 74: 121–140. 1169–1177. 64. Pierzynski GM, Hettiarachchi GM (2002) Method for in situ immobilization 62. Gasic K, Korban SS (2007) Transgenic Indian Mustard (Brassica jucea) plants and reduction of metal bioavailability in contaminated soils, sediments expressing an Arabidopsis phytochelatin synthase (AtPCS1) exhibit and wastes. United States Patent No. 6,383,128. Date of Patent: May 7, enhanced As and Cd tolerance. Plant Mol Biol 64: 361–369. 2002. 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Cadmium dispersal on a raised heathland in the Peak District National Park adjacent to a major trunk road

Bioscience Horizons , Volume 4 (2) – Jun 1, 2011

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Volume 4 † Number 2 † June 2011 10.1093/biohorizons/hzr017 ......................................................................................................................................................................................................................................... Research article Cadmium dispersal on a raised heathland in the Peak District National Park adjacent to a major trunk road Andrew Pickett* Staffordshire University, 22 Russell Street, Newcastle-under-Lyme, Staffs, UK. * Corresponding author: Email: andypickett@live.co.uk Supervisor: Professor John Dover, Staffordshire University, 22 Russell Street, Newcastle-under-Lyme, Staffs, UK. ........................................................................................................................................................................................................................................ Heavy metals are naturally present in soils as trace elements but deposition from vehicle wear and tear increases concentrations found adjacent to highways and has been shown to disperse further in relation to traffic volume. The heavy metal cadmium (Cd), used in the manufacture of tyres, has toxic effects on some plant species, with soil acidity being a major factor in plant Cd uptake. In this study, levels of Cd in soil and root material from Calluna vulgaris were investigated along with soil pH on wet heather moorland in the Peak District National Park. In December 2009, samples were collected from 10 transects extending up to 125 m from a trunk road that has a daily vehicle use .23 000. The peat substrate of the study site was found to be highly acidic (mean pH+ S.D.: 3.44+ 0.119). Reported Cd concentrations in peat core samples (50–200 mm depth) are within the UK rural soil distribution range (0.1–1.8 mg kg ), but increase progressively up to 85 and 125 m on either side of the road probably assisted by the wind. Root samples from C. vulgaris showed a degree of Cd accumulation (mean+ S.D.: 17.78 mgg + 9.338) compared with normal concentrations in plants from unpolluted soils (0.1 mgg ). Coupled with data from previous research, results from this study suggest that increased soil Cd concentrations could affect the competitive balance between C. vulgaris and other moorland plants such as Molinia caerulea. Advances in analytical techniques allowing a better understanding of plant responses to metal toxicity are also discussed. Key words: cadmium, traffic pollution, heathland, Calluna vulgaris, Peak District National Park. Submitted September 2010; accepted March 2011 ........................................................................................................................................................................................................................................ Potential traffic-derived pollutants include polyaromatic Introduction hydrocarbons, volatile organic compounds, heavy metals Highway run-off contains numerous potential environmental and particulates such as rubber from tyres, nitrogen oxides, pollutants that can adversely affect fauna and flora adjacent ammonia and nitrous acid. Heavy metals are normal con- to roads, the effects of which have been shown to extend a stituents of soil horizons as trace elements for which flora 1 –3 greater distance from increased daily vehicle use. The dis- have locally adapted with regard to ion uptake, increased con- persal of vehicle emissions and particulates from wear and centrations are persistent however, remaining in an undis- tear also varies from place to place being influenced by turbed environment for decades. Derived from vehicle wear factors such as wind direction, local climate, topography and tear, some of the most frequently reported metals are 4,5 and seasonal salt applications in severe winter weather. zinc (Zn) and cadmium (Cd) used in tyre manufacture; It has been estimated that 5.4% of Sites of Special copper, manganese and chromium from brake systems; also 4,9 Scientific Interest (SSSIs) in England lie partly within iron, aluminium and nickel from engine component wear. 200 m of a major road. In terms of nature conservation, a Cd uptake in plants better understanding of pollutant effects on vegetation assemblages could help to develop techniques for use in the Cd is a relatively rare element in terms of crustal abundance, management of valued semi-natural habitats. but it is of concern as it is highly toxic to most prokaryotic ......................................................................................................................................................................................................................................... 2011 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 149 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... and eukaryotic organisms, entering the food chain through suggested that this may be as a result of transformations animal grazing or crop harvesting on plants that have accu- carried out by metal-mobilizing and acid-producing 10 33 mulated Cd via root uptake. Humans are more vulnerable bacteria. to Cd accumulation in organs from contaminated food than 11,12 grazing stock due to their longer life span. Cd solubility Calluna vulgaris in water can facilitate rapid distribution in the environment In this study, root samples from Heather (Calluna vulgaris) and entry into the food chain via crop plants has caused were used to assess Cd uptake in the dominant higher serious problems to human health in China and fatalities in 13,14 plant species native to the area. It has been suggested that the mid-20th century Japan. More recent observations C. vulgaris is dependent on an association with the ectomy- of Cd burden in herbivores carried out in Norway have corrhizal fungi Hymenoscyphus ericae for survival on acidic either noted a ‘certain relationship’ with environmental 15,16 and/or heavy metal-polluted soils in the UK, by reducing Cd concentrations or found a weak or absent 17,18 heavy metal uptake. Over recent decades though, despite relationship. this defence mechanism, C. vulgaris has been experiencing Small amounts of Cd are taken in by higher plants directly a loss of cover in favour of Purple Moor grass (Molinia caer- from the atmosphere; movement into plant cells is normally ulea) due to eutrophication, although it is unclear whether gained by way of micronutrient transporters in root epider- 2þ Cd is a factor in this process. mal cells. Due to the high mobility and solubility of Cd ions, entry to cortical tissue via transmembrane carriers 2þ 2þ 2þ 2þ 2þ used to uptake Ca ,Fe ,Mg ,Cu and Zn occurs Aims and objectives 19,20 readily and can reach the xylem when complexed with 21 The main aim of this project was to ascertain the extent of Cd organic acids or phytochelatins. Adverse effects of Cd dispersal in soil and plant material adjacent to a major road in accumulation in plants include reduction in photosynthesis, 22 an ESA characterized by strong acidity, surface water and sub- water and nutrient uptake, disruption of cell transport pro- 23,24 strate with high organic matter content. The objectives were to cesses and inhibition of enzyme activities and affects 25 ascertain the local peat substrate pH value, compare available general root and shoot growth. Normal Cd concentrations 21 11 soil and root sample Cd concentrations in order to evaluate the in plants have been published as 0.1 mgg . effect of local conditions on the potential toxic effect of Cd to Cd availability to plants is influenced by a number of C. vulgaris. Also, using a further understanding of the pro- factors such as amount of water in the soil which increases 2þ cesses that influence plant Cd uptake and drawing on recent activity of hydrated Cd ions, whereas elevated concen- research, a further aim was to investigate whether Cd may trations of Zn and Fe can compete for root uptake of diva- be a factor affecting the competitive balance between lent cations. Organic matter content of the soil is inversely C. vulgaris and M. caerulea. related to plant Cd uptake as it is effective in keeping Cd unavailable by complexion with agents in humic sub- 26,27 stances but the most important factor in controlling 28,29 uptake of heavy metals is pH. A linear relationship has Materials and Methods been shown between soil pH decreasing and Cd uptake Site description increasing, the more naturally acidic substrate providing a greater level of toxic effect. The study area is a raised wet heathland, designated an SSSI, in the South-West Peak District with an annual precipitation Raised heathland in the peak district of 140 cm/year and comprises ombrotrophic peat 0.5–2 m An acidic substrate is a characteristic of the upland blanket thick (Peak District ). Through this locality the A537 peat moorlands which cover around 8% of land area in the Buxton to Macclesfield trunk road, which has a minimum UK, contributing 10–15% of the total global resource. predicted daily vehicle use of 23 708 in 2011 The Peak District National Park, situated in north-central (Highways ), cuts across a sloping heather moorland England, contains two environmentally sensitive areas between Wildboarclough and Upper Hartington Quarter (ESAs), characterized by extensive heather moorland and over a height difference of 545–470 m through 2 km south- 31 37 blanket bog habitats. Payments are made to land managers west to north-east. The section through Wildboarclough is to maintain these ecologically important landscapes, con- exposed to prevailing south-westerly winds over a large taining a number of SSSIs, and listed in the EU Habitats area of surface water named Tinkerspit Gutter, an area Directive (92/43/EEC) as ‘Special Areas of Conservation’ likely to experience hydrological mobilization of Cd, (SAC) and Special Protection Areas. sloping down to the source of the River Goyt over a distance Recent research in the southern Pennines has raised of 2 km. The landowner, United Utilities, granted permission concern regarding further acidification of the environment, to carry out sampling following consultation with the tenant, showing a highly acidic pH level (3.00–3.14), it was Lord Derby and Natural England. ......................................................................................................................................................................................................................................... 150 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Sampling soil: water suspension. Each of the 16 suspensions was shaken for 15 min using a Bibby Stuart Scientific SF1 Flask C. vulgaris root and peat core sampling from transects Shaker (300 oscillations/minute) and analysed for pH running perpendicular to the A537 was carried out in using a Mettler Toledo Seven Multi-digital pH meter cali- December 2009. Using two permanent traffic signs on brated with standard solutions at pH 4, 7 and 9. either side of the road as an arbitrary origin at grid reference 37 38 SJ 004 716, a random number generator set at 0–1000 (maximum 1 km distance) was used to assign starting Peat samples (chelation using ethylene-diamine- points in metres for seven transects on the north (N) and tetraacetic acid) three transects on the south (S) side of the A537 as shown in Fig. 1. A greater number of samples were taken from the Following the method published in Rowell, peat samples north side of the main road due to the direction of the were oven dried overnight at 758C and ground to 2mm decreasing gradient and prevailing wind direction. Peat particle size using a brass sieve, available Cd was core samples to a depth of 200 mm below the surface were then extracted from each sample using 0.5 M collected using a hardened carbon/steel peat auger at four ethylene-diamine-tetraacetic acid (EDTA). 3  5 aliquots points along each transect (5, 45, 85 and 125 m) and from each sample (mean+ S.D.: 5.012 g+ 0.0202) were retained in sealed sample bags (n ¼ 40) for later analysis. then transferred to 250 ml conical flasks to which 50 ml Root samples were collected on the north side of the A537 (mean+ S.D.: 49.89 ml+ 0.153) of 0.5 M EDTA disodium only, due to limited resources, from five transects at four salt dehydrate (pH 7) was added and stirred for 1 h using sample points along each transect (5, 45, 85 and 125 m) a Bibby Stuart Scientific SF1 Flask Shaker set at 300 oscil- and retained in sealed sample bags (n ¼ 20) for later analysis. lations/minute. Samples were then filtered using Whatman Sample sizes were limited in order to minimize disturbance no.541 hardened, ashless filter papers; solutions were on the ESA, however the locations were recorded so that then retained for later analysis by atomic absorbance future analyses could be compared. spectrophotometry. Sampling handling and chemical analyses Root samples (acid digestion) Area pH value Using the procedure set out in Milner and Whiteside, root samples were dried at 408C for 48 h, crushed to pass Soil samples were selected at random (n ¼ 16) from the 40 through a 0.7 mm brass sieve and the resulting powder samples obtained and pH was determined using a 1:10 oven dried at 1058C overnight. 0.2 g of each sample was then weighed into a long-necked Kjeldhal flask to which 1.0 ml sulphuric acid (H SO :S.G. ¼ 1.84), 5 ml nitric 2 4 acid (HNO :S.G. ¼ 1.42) and 1 ml perchloric acid (HClO : 72%) were added. The mixture was then heated gently until the initial reaction subsided and then boiled until white sulphuric acid fumes appeared and then for a further 15 min. The digest was then transferred to 100 ml volumetric flask, made up to 100 ml with deionized water and retained for later analysis by atomic absorbance spectrophotometry. Available soil Cd concentration analysis Available soil Cd concentration for each sample solution was determined using graphite furnace atomic absorbance spec- trophotometry (Unicam 939 AA spectrometer, GF90 furnace, FS90 auto-sampler) with deuterium lamp back- ground correction and ammonium nitrate (NH NO :5 mg 4 3 ml ) matrix modifier. Each run of samples was preceded by calibration using Cd standard solutions (10, 20, 30, 40 21 21 and 50 ng ml ), results given in ng ml were converted Figure 1. Sketch map of the study area showing positions of transects to sample concentration values for root and soil of mgg adjacent to the A537. Origin point of measurements recorded at grid refer- 37 21 ence SJ 004 716 was two permanent traffic warning signs. and mg kg , respectively. ......................................................................................................................................................................................................................................... 151 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... Results Area pH From the 16 random soil samples, the study site was found to have a highly acidic pH (mean+ S.D.: 3.44+ 0.119). No significant trend was observed in pH values recorded on either side of the road or in proximity to the road. Soil Cd concentration Available Cd concentrations derived from peat samples taken along transects running perpendicular to the north (down- ward sloping) side of the A537 are summarized in Fig. 2. Median values, when viewed with interquartile ranges (boxes), show a steady increase as the distance from the Figure 3. Soil available Cd concentrations (mg kg ) from samples (n ¼ road increases from 5 m to 125 m. Within each distance 35) taken along transects perpendicular to the south side of the A537. group, a large variation in concentrations can be observed Boxplots show median, first and third quartiles along with minimum and with notable data skewness at 5 and 85 m. maximum values. Results from analysis of samples taken along transects on the south side of the A537 shown in Fig. 3 illustrate a greater increase in available Cd concentrations than on the north side from 5 m to 85 m with a marked decrease at 125 m. Interquartile and total ranges within each distance group describe a large variation of values and a significant degree of data skewness. Overall range across all distance groups ¼ 0.12–1.20 mg 21 21 kg , overall mean+ S.D. ¼ 0.54 mg kg + 0.222. Root Cd concentrations Median, quartiles and range values for Cd concentration derived from collected C. vulgaris root samples, at distances from the A537, are summarized in Fig. 4. A considerable variation in root Cd concentration was recorded within each distance group, particularly at 45 m from the road where the Cd burden range ¼ 10.85–42.03 mgg . Figure 4. Root Cd burden in C. vulgaris (mgg ) from samples (n ¼ 20) taken at distances along transects perpendicular to the north side of the A537. Boxplots show median, first and third quartiles along with minimum and maximum values. Overall root mean Cd concentration+ S.D.: 17.78 mgg + 9.338. Soil/root Cd association The strength of association between soil and root sample Cd concentrations was not significant (r ¼ 20.800 (20); P  0.2), results in this study showing a negative relationship. Discussion The highly acidic condition of the study site reported in this Figure 2. Soil available Cd concentrations (mg kg ) from samples (n ¼ paper (mean+ S.D.) 3.44+ 0.119 compares well with pre- 84) taken along transects perpendicular to the north side of the A537. vious research in the southern Pennines carried out by Boxplots show median, first and third quartiles along with minimum and maximum values. Linton et al. who reported a pH range of 3.00–3.14 over ......................................................................................................................................................................................................................................... 152 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... 21 21 Table 1. Soil (mg kg ) and root (mgg ) Cd concentrations with six sites. This has strong implications for the flora in the area regard to distance as pH has been shown to be one of the most important 11 29 factors, if not the most important factor, in determining Distance from A537 (m) the bioavailability of Cd in soils to plants. Studies by Kou 42– 44 5 45 85 125 et al., Sappin-Didier et al., and Tsalidas et al. each ................................................................................................................ observed an increase in plant Cd uptake with a corresponding Soil Cd concentration decrease in pH, although two studies in Canada point out the North importance of the substrate organic content. Sauve et al. A1 0.12 0.53 0.68 0.77 observed that organic matter had a high sorption affinity for A2 0.36 0.4 0.74 0.76 Cd, which was as much as 30 times higher than mineral A3 0.2 0.39 0.73 0.83 soil, another study carried out in Canada showed that 46 B1 0.12 0.7 0.73 0.28 organic matter was the primary sorbent for heavy metals. B2 0.54 0.63 0.82 0.3 In this study, available Cd in soil concentrations reported B3 0.14 0.55 0.86 0.28 (overall range: 0.12–1.20 mg kg ) are within the UK rural C1 0.42 0.48 1.01 0.85 soil distribution range (0.1–1.8 mg kg ) published in the UK Soil and Herbage Pollutant Survey, although the C2 0.52 0.42 1.01 0.87 overall mean Cd concentration found in this study C3 0.39 0.4 0.69 0.6 (0.499 mg kg ) was higher than the mean UK rural and D1 0.54 0.39 0.44 0.61 urban soil concentrations (0.39 and 0.49 mg kg , respect- D2 0.63 0.39 0.55 0.57 ively). It should be noted that figures published by this D3 0.56 0.44 0.5 0.91 survey show extracts refluxed with Aqua Regia, which E1 0.5 0.31 0.52 0.8 would normally be considerably higher than those found E2 0.44 0.34 0.44 0.63 using the EDTA method employed in this study. Overall, E3 0.45 0.47 0.55 0.58 available Cd concentrations were observed to be higher F1 0.24 0.48 0.41 0.52 between 85 and 125 m, with the trend implying that F2 0.26 0.36 0.3 0.54 additional sampling over 125 m on the north side of the F3 0.25 0.35 0.32 0.46 road may have shown a further increase. These data G1 0.59 0.43 0.4 0.63 support previous research on the consequences of traffic pol- lutant dispersal carried out by Angold who examined plant G2 0.69 0.43 0.43 0.72 species composition adjacent to the A31 in Hampshire (12 h G3 0.68 0.2 0.63 0.77 traffic flow ¼ 35 000) observing a ‘maximum edge effect’ of South 200 m from the dual carriageway. Results from this study are A1 0.69 0.35 0.96 0.7 also substantiated by in their analysis of vegetation health A2 0.61 0.23 0.82 0.72 adjacent to the M62 in northern England (mean motor A3 0.29 0.21 0.88 0.63 vehicle flow ¼ 74 000 per day) and the M40 (mean motor B1 0.3 0.89 0.39 0.77 vehicle flow ¼ 94 000 per day), concluding that background B2 0.27 0.85 0.49 0.71 levels of motor vehicle pollutants were likely to be reached B3 # 0.67 0.53 0.68 within 50–100 m of the road (Table 1). C1 0.16 0.76 1.2 0.56 Available Cd concentrations in the peat substrate on the C2 0.15 0.54 1 0.39 north side of the A537 showed a steady increase over the C3 0.16 0.8 0.68 0.59 sampling distance from 5 to 125 m, which would follow the descending slope away from the road combined with the Root Cd concentration surface water characteristic of this particular area. Whilst Sample 5 m 45 m 85 m 125 m variability of concentrations within distance groups was NA 25.15 42.03 9.2 16.48 high, overall increases were observed to follow the downward NB 12.98 10.88 15.63 9.55 gradient that has few erosion runnels or hillocks to prevent NC 14.34 13.74 27.86 14.98 ground-level wind. It is possible in this case that the prevailing ND 23.38 32.21 10.09 5.87 highly acidic conditions in the soil at the study site reduce the NE 19.54 7.97 18.69 26.42 Cd binding effect of humic substances within the substrate 2þ thereby increasing the solubility of Cd ions that are at the 125 m sampling point. The gradient on this side of the leached from the roadside area, being carried over 125 m by road is a gradual incline which somewhat contradicts the the surface hydrology. The trend of Cd transport on the 2þ explanation of Cd ions being transported by surface south side of the road showed a larger increase from 5 to waters. These data presented in this paper support an 85 m than on the north side with a decrease being observed ......................................................................................................................................................................................................................................... 153 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... explanation that pollutants from vehicles are dispersed by contaminated soils has been ascribed largely to a heavy infec- wind to a greater degree than by surface water, the elevated tion by mycorrhizal fungi, often observed in the roots of these 52,10 and open perspective of the landscape being subject to seaso- species that reduces heavy metal uptake. Despite this nal strong winds from a north-easterly and south-westerly defence mechanism, C. vulgaris has been observed to exhibit direction. In their study assessing the effects of two motor- a darker colour in new growth near to a road and a general 50 49 ways in Germany (64 000 and 103, 300 vehicles per day) decrease in abundance, whereas grass species such as also suggested an impact of wind, observing an edge effect M. caerulea and Deschampsia flexuosa appear to be more tol- extending up to 230 m downwind and 80 m upwind of the erant in polluted soils and are abundant in many parts of the roads, with particulates decreasing in concentration over a Peak District. In D. flexuosa, a very low uptake of Cd has shorter distance than gaseous constituents. been observed at varying levels of metal contamination and The total biomass of C. vulgaris root material analysed Cd concentrations have been reported for M. caerulea shoots was 4.0 g in total due to the sample size (n ¼ 20) and the that are 10-fold higher than C. vulgaris analysed in the same 10,53 mass of individual root samples digested (0.2 g), the results research. The spread of M. caerulea at the expense of therefore give an indication of plant uptake rather than moorland heather due to eutrophication from deposition of hard evidence of potential toxic effect from Cd. Cd concen- pollutants derived from anthropomorphic activities has been trations extracted from root samples of C. vulgaris root reported in a number of northern European countries over 54 –56,30 showed a high degree of variation within each distance the last three decades. An established complete group, particularly at 45 m, the trend of Cd burden dropping canopy of C. vulgaris can compete successfully with off between 45 and 85 m. Across all four distance groups, a M. caerulea even with an increased availability of nutrients degree of Cd accumulation in the root biomass was observed in the medium term yet dispersal of traffic-borne eutrophica- that is higher than the normal concentration in plants from tion and pollution increases the competitive ability of 21 11 58,49 unpolluted soils (0.1 mgg ) but lower than concen- M. caerulea, particularly near to the roadside. The combi- trations derived from metal hyperaccumulator plants nation of biotic factors influencing the success of in situ plant 21 11 (100 mgg ). Comparison of Cd concentration in soil populations are numerous and dynamic but a better under- and root material from each sample point implied a negative standing of individual stress tolerances within species may correlation, although more data would be required to draw help in developing techniques for conservation strategies. any serious conclusions from this. Along with many other The response of plants to increasing concentrations of factors, this could mean that the organic matter content of heavy metals can now be more fully understood through the peat substrate is binding with Cd making it less available analysis of gene expression of the metal transporter gene for plant uptake further from the road. HMA4, which is essential for root to shoot transport and a It has been accepted for a number of years that metal non- key determinant of the metal hyperaccumulation pheno- hyperaccumulator plants show a progressive build up of type. A comparison of the level of expression in the flower- heavy metals in root systems, whereas hyperaccumulators ing plants Arabidopsis halleri (a metal hyperaccumulator) are able to transport absorbed toxic metals to the above- and A. thaliana (a metal non-tolerant) displayed a higher ground biomass, therefore a comparison of root, shoot level of expression of the HMA4 transporter gene in and leaf Cd concentrations in C. vulgaris would be useful in the hyperaccumulator. The significant role of this gene assessing the plants ability to thrive in metal-contaminated expression in metal transport has been further demonstrated soils. In their study in Norway, Brekken and Steinnes ana- by a single gene transfer of HMA4 into the non-accumulator lysed Cd concentration in leaves, shoots and twigs from A. thaliana, increasing its shoot metal uploading. C. vulgaris, observing minimal transfer of background soil A number of other mechanisms and processes have been Cd levels (1–3 mg kg ) to the above-ground biomass of the reported within plants that enhance metal tolerance and 21 21 plant (twigs ¼ 0.1 mgg ; leaves/shoots ¼ 0.05 mgg ) accumulation such as chelation of metal ions and subsequent which, when coupled with data from this research showing a compartmentalization in vacuoles, increased enzyme activity 60 –62 degree of accumulation in C. vulgaris root, suggests that it is and expression of the AtPCS1 gene. Research into plant a metal non-accumulator. In the same study, a seasonal metal tolerance mechanisms over the last decade has mainly trend in metal uptake was observed that also has importance focused on cash crops, biotechnology could also aid con- with the findings of this study in that the highest concen- servation efforts by allowing greater knowledge of environ- trations of Cd were reported from samples collected in mental processes. Metal tolerance may well be one of the summer with a 51% decrease being observed in autumn many factors affecting dominance between Heather and samples, therefore concentrations derived for this research Purple Moor grass and indeed between other plant species. (from samples collected in winter) would be expected to be In Germany, the moss Hylocomium splendens has been the lowest of annual Cd burden in C. vulgaris. observed to contain Cd levels three times higher than the The success of C. vulgaris and other ericaceous species such background level of ,0.1 mgg which could aid this as Vaccinium as colonists of acidic and heavy metal species with regard to competitive ability with other ......................................................................................................................................................................................................................................... 154 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... bryophytes. In a delicately balanced ecosystem such as the Author biography raised wet heathland surveyed in this study, further knowl- A.P. is 45 years old and gained direct entry into year 2 of a BSc edge of responses to metal pollution exhibited by character- (Hons) Biology degree course at Staffordshire University in istic species (ericaceous shrubs, graminoids and bryophytes) 2008 having carried out his first year in Biological Sciences could be very useful to land managers when assessing the at Wolverhampton University in 2000/01. His main interests best way to conserve moorland floral assemblage. are conservation of biodiversity and semi-natural landscapes It is considered that phytoremediation, the use of hyperac- along with the chemistry of life processes. A.P. believes these cumulator plants to transfer metals to plant tissue which is interests are shown through in the project, which he enjoyed then harvested, would not be sustainable or practical for carrying out immensely, the results allowing a good discussion landscape scale remediation. The most promising research and the opportunity to compare with previously published examines the potential of tying Cd up in the soil, making articles. Following graduation A.P. has now begun a it less available for plant uptake. Pierzynski and P.G.C.E. course at Manchester Metropolitan University in Hettiarachchi have listed several forms of phosphorus order to pursue a career teaching science in secondary schools. that could achieve this. Technological advances in analysis and microscopic techniques are generating new knowledge that professionals involved in conservation could manipulate to achieve their aims. References 1. 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Journal

Bioscience HorizonsOxford University Press

Published: Jun 1, 2011

Keywords: cadmium traffic pollution heathland Calluna vulgaris Peak District National Park

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