In vitro estimates of bioaccessible nickel in field-contaminated soils, and comparison with in vivo measurement of bioavailability and identification of mineralogy

This study determined nickel (Ni) bioaccessibility in weathered smelter-contaminated soils, separately for particle-sized fractions using two in vitro methods: simulated gastrointestinal digestion (PBET) and PBET followed by absorption by Caco-2 cells. Relative bioavailability of Ni in soils was determined in vivo using rats, validating in vitro estimates; a mineralogical basis of variation in bioavailability/bioaccessibility among soils was explored. In vitro assays identified the same difference in bioaccessibility for Ni among particle size fractions. PBET estimates were more precise, thus likely to be more useful in discerning differences among soils. In vivo bioavailability for Ni was below limit of detection for the small soil particles, and 31% and 56% for the larger particles. The relative bioavailability calculated from this work suggests that risk from ingesting Ni-contaminated soils could be overestimated by between 2- and 50-fold if the estimates of exposure are not adjusted for the lower bioavailability of weathered Ni originating from smelter emissions. The overestimation that would occur by using total Ni is greatest for the particle size that is most likely to adhere to the hands of children, demonstrating the importance of particle-size separation of soils for bioavailability determination and risk assessment.     

Evaluation of metal concentrations in edible vegetables grown in compost amended soil

Agricultural uses of compost usually have a positive effect on the yield of vegetable crops for human consumption. However, compost that contains heavy metals can transfer these components to soils and plants. To evaluate the contamination levels of metals in soil, compost, and edible vegetables, the Mn, Zn, Pb, Cd, Cu, and Ni total contents were measured. Metal availability in soils, as well as other variables – the pH, CEC (cation exchange capacity), total nitrogen, organic carbon, particle size distribution and mineralogy of the clay fraction – were examined in the soil samples. The analysed compost samples were produced from urban solid waste, cattle manure, and edible vegetable and tree pruning residues. The values of pH, CEC, total nitrogen, organic matter, exchangeable hydrogen and carboxylic groups were measured in the compost samples. Of the six metals examined in the soils, in general, Mn and Zn attained the highest concentrations, followed by Cu. Relatively high Mn, Zn, Cu, Cd and Pb concentrations were found in the soils. Metal concentrations extracted with DTPA were below the critical levels in soils, i.e. the levels above which toxicity is likely. In general, Zn, Pb, Cd, Cu and Ni concentrations in compost were lower than those reported by other workers, while Mn levels were within the range for this metal in compost. The results showed that there was an effect of the vegetable type (p < 0.01) for all the parameters examined. High Pb concentrations were found in lettuce and chive as compared with the tolerance limit for this metal in fresh vegetables in Brazil. Cadmium concentrations were also enhanced in the fresh vegetables compared with the typical concentrations of metals in plants. Zinc, Cu, Cd, and Ni concentrations were lower than the tolerance limits established for foods by the Brazilian legislation.     

Assessment of fly ash-aided phytostabilisation of highly contaminated soils after an 8-year field trial: part 1. Influence on soil parameters and metal extractability

Sustainable management of large surface areas contaminated with trace elements is a real challenge, since currently applied remediation techniques are too expensive for these areas. Aided phytostabilisation appears to be a cost efficient technique to reduce metal mobility in contaminated soils and contaminated particle spread. In this context, this study aimed at evaluating the long-term efficiency of aided phytostabilisation on former agricultural soils highly contaminated with trace elements. The influence of afforestation and fly ash amendments to reduce metal mobility was investigated. Before being planted with a tree mix, the study site was divided into three plots: a reference plot with no amendment, the second amended with silico-aluminous fly ash and the third with sulfo-calcic fly ash. After eight years, some soil physico-chemical parameters, including cadmium (Cd), lead (Pb) and zinc (Zn) extractability were modified. In particular, pH decreased on the whole site while organic carbon content increased. The alteration of these parameters influencing trace element mobility is explained by afforestation. Over time, concentrations of CaCl₂-extractable metals increased and were correlated with the soil pH decrease. In the amended soils, extractable Cd, Pb and Zn concentrations were lower than in the reference soil. The results indicated that the two fly ashes buffered natural soil acidification due to vegetation development and limited trace element mobility and thus could limit their bioavailability. For long-term phytostabilisation, special attention should be focused on the soil pH, metal mobility and phytoavailability analysis.     

The impact of increased oxygen conditions on metal-contaminated sediments part II: effects on metal accumulation and toxicity in aquatic invertebrates

The present study evaluated the effect of increasing oxygen concentrations in overlying surface water on the accumulation and toxicity of sediment-bound metals in the aquatic invertebrates Lumbriculus variegatus, Asellus aquaticus and Daphnia magna. A 54 days experiment using three experimental treatments (90% O₂ in overlying surface water, 40% O₂ and a non-polluted control) was conducted. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured in the superficial sediment layer (0-1 cm). At each time point, accumulated metal levels as well as the available energy stores were measured in L. variegatus and A. aquaticus and each time D. magna was exposed to surface water in a 24 h toxicity test. Additionally metallothionein-like protein (MTLP) induction was quantified in L. variegatus. Oxygen induced changes in sediment AVS resulted in faster accumulation of metals from contaminated sediments in A. aquaticus, while no differences in toxicity in this species were observed. Ag, Cr, As and Co accumulation as well as toxicity in water exposed D. magna were clearly enhanced after 54 days, caused by oxidation of metal-sulfide complexes. Due to their feeding and burrowing behaviour, metal accumulation and toxicity in L. variegatus was not influenced by geochemical characteristics. Nevertheless, a rapid induction of MTLP was observed in both the 90% O₂ and the 40% O₂ treatment. The present study showed that elevated oxygen concentrations in overlying surface water can directly enhance metal accumulation and toxicity in aquatic invertebrates, however this is highly dependent on the organisms ecology and most dominant metal exposure route (water vs. sediment).     

Use of sequential ASE extraction to evaluate the bioavailability of DDT and its metabolites to wheat roots in soils with various organic carbon contents

An accelerated solvent extraction (ASE) procedure using water, n-hexane and a mixture of n-hexane and acetone as solvents in sequence was developed and tested to evaluate the bioavailability of DDT and its metabolites including p,p'-DDT, o,p'-DDT, p,p'-DDE, and p,p'-DDD (SigmaDDTs) to wheat uptake from soils characterized by varied organic carbon contents. Results indicated that the extractability of SigmaDDTs with water was enhanced considerably in the presence of water soluble organic carbon (WSOC), while the amount of SigmaDDTs extracted with n-hexane was negatively correlated to the content of water insoluble organic carbon (WIOC). The interaction between SigmaDDTs and WIOC also reduced the bioavailability of the pesticides to wheat roots during uptake. There was a good positive correlation between the amount of SigmaDDTs extracted by n-hexane and the amount of SigmaDDTs accumulated in wheat roots, suggesting some potential for the use of the n-hexane ASE-extracted fraction as an indicator of SigmaDDTs' bioavailability to plant uptake. As such, the three sequentially extracted fractions may be viewed as representing the mobile, bioavailable, and fixed pools of SigmaDDTs in the soil.     

Maximum likelihood mixture estimation to determine metal background values in estuarine and coastal sediments within the European Water Framework Directive

Some of the recently derived European Directives, such as the Water Framework and Marine Strategy, have, as ultimate aims, to achieve concentrations of hazardous substances in the marine environment near background values. Hence, the determination of natural background levels, in marine sediments, is highly relevant. The present study proposes the use of the maximum likelihood mixture estimation (MLME) to determine regional background levels and upper threshold of metal concentration, with the Basque Country as a case study (with a data set of 575 samples, from estuarine and littoral areas, including both intertidal and subtidal sediments). The heuristic procedure is applied with unimodal data distributions (Cd, Cr, Fe and Ni) and the mixture density estimations, based upon maximum likelihood, are carried out with polypopulational data distributions (As, Cu, Mn, Hg, Pb and Zn). The upper limits of the distribution are proposed, as the limits between 'High Status' and 'Good Status' (according to the Water Framework Directive terminology). The regional upper limits were 0.45 microg g(-1) for Cd, 71 microg g(-1) for Cr, 53,542 microg g(-1) for Fe, 57 microg g(-1) for Ni, 24 microg g(-1) for As, 64 microg g(-1) for Cu, 447 microg g(-1) for Mn, 0.27 microg g(-1) for Hg, 66 microg g(-1) for Pb, and 248 microg g(-1) for Zn. The results from this study can assist further in the determination of sediment reference conditions, to assess chemical status, within the above-mentioned directives; likewise, it will be studied as a useful methodology in determining regional metal backgrounds in other European countries.     

Antagonistic Action of Fe and Mn in Mediterranean-Type Plants Irrigated with Wastewater Effluents Following Biological Treatment

The present study examined the ability of certain Mediterranean plants to absorb Mn ++ when irrigated with wastewater effluents following treatment, the relative absorption of Fe ++ and Mn ++ , as well as the endurance of such plants to high Mn ++ concentrations in the water used for their irrigation. The experimental plants used in the study were Olea europaea , Nerium oleander and Geranium sp . These plants were irrigated with secondary treatment wastewater effluents, with water commonly used for irrigation in the area, and with water enriched with high concentrations of Mn ++ . The results showed that irrigation of the plants with wastewater treatment effluents resulted in slightly elevated concentrations of Mn ++ and Fe ++ in the leaves, the roots, and in the soil. On the contrary, irrigation with water enriched with high concentrations of Mn ++ (as high as 1000 mg/L) resulted in correspondingly high Mn ++ concentrations in the plants under study. The accumulation of Mn ++ was much higher in the roots than in the leaves of these plants. In the case of Mn ++ enriched water irrigation, the corresponding concentrations of Fe ++ in the roots, in the leaves, and in the soil indicated the existence of strong antagonism between these two elements. All plants exhibited tolerance to high concentrations of Mn ++ .     

Remediation of arsenic contaminated soils by iron-oxide application, evaluated in terms of plant productivity, arsenic and phytotoxic metal uptake

Four iron-bearing additives, selected for known or potential ability to adsorb anions, were evaluated for their effectiveness in attenuation of arsenic (As) in three soils with different sources of contamination (canal dredgings, coal fly ash deposits, and low-level alkali waste). Amendments used were lime, goethite (alpha-FeOOH) (crystallised iron oxide) and three iron-bearing additives, iron grit and iron (II) and (III) sulphates plus lime, which result in 'de novo' iron oxide formation in soils. Each was applied to the test soils at a rate of 1% w/w. A series of plant growth trials were conducted on the equilibrated, amended soils using spinach (Spinacia oleracea) and tomato (Lycopersicon esculentum) as test crops. These were grown in the contaminated soils for a period of three months in controlled glasshouse conditions. Evaluation of the potential of the amendments as immobilising agents was determined by plant growth (biomass) and elemental accumulation in plant tissues, indicating the bioavailability of As and other heavy metals following amendment. Goethite produced the most promising results in terms of reduction of plant shoot As content. It was concluded that, whilst Fe-oxides may be used as effective in situ amendments to attenuate As in soils by reducing its bioavailability, their effects on plant growth require careful consideration. In addition, soil-plant transfer of As was not completely halted by any amendment.     

Trace elements in home-produced eggs in Belgium: Levels and spatiotemporal distribution

The purpose of this study was to evaluate the levels of arsenic, cadmium, lead, copper and zinc in home-produced eggs, soils and kitchen waste samples of private chicken owners in Belgium, and to determine spatiotemporal differences in trace element contents in eggs. Eggs were sampled in all provinces of Belgium in autumn 2006 and spring 2007. A total number of 59 private chicken owners participated in the study. Trace elements were determined by inductively coupled plasma-mass spectrometry except for mercury, which was determined by atomic absorption of mercury vapour. The mean fresh weight concentrations in eggs in autumn and spring respectively were < 8.0 and < 8.0 µg/kg for arsenic, 0.5 and < 0.5 µg/kg for cadmium, 116 and 74 µg/kg for lead, 0.43 and 0.52 mg/kg for copper, 20.3 and 19.2 mg/kg for zinc, and 3.15 and 4.44 µg/kg for mercury. Analysis of variance determined significant differences in some trace element concentrations in eggs among seasons and regions in Belgium. Average concentrations of arsenic, cadmium and mercury corresponded well with values measured in other countries, while copper and zinc concentrations were within the same order of magnitude as in other countries. Average lead concentrations were high compared to concentrations in eggs from other countries and correlated well with lead concentrations in soil, indicating that the soil is an important source. Other sources of trace elements in eggs might be home-grown vegetables and forage (grass and herbs), and indirectly, air pollution.     

Relationships among total recoverable and reactive metals and metalloid in St. Lawrence River sediment: bioaccumulation by chironomids and implications for ecological risk assessment

The availability and bioaccumulation of metals and metalloids, and the geochemical interactions among them, are essential to developing an ecological risk assessment (ERA) framework and determining threshold concentrations for these elements. The purpose of this study was to explore the relationships among total recoverable and reactive metals and metalloid in sediment and their bioaccumulation by chironomids. In the fall of 2004 and 2005, 58 stations located in the three fluvial lakes of the St. Lawrence River and its largest harbour area in Montreal, Canada, were sampled. Nine total recoverable and reactive metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and one metalloid (As) were measured in whole sediment using two extraction methods: HCl/HNO(3) and HCl 1N, respectively. The bioaccumulation of six metals (Cd, Cr, Cu, Ni, Pb and Zn) and As by chironomids was evaluated in a subset of 22 stations. Strong collinearities were observed between some total recoverable or reactive metal concentrations in sediment; two principal clusters, including collinear metals, were obtained. The first one included metals of mainly geological origin (Al, Cr, Fe, Mn, Ni), while the second one included As, Cd, Cu, Pb and Zn, which likely derive mainly from point sources of anthropogenic contamination. Each element also showed strong collinearity between their total recoverable and reactive forms (0.65< or =r < or =0.97). We can conclude that both chemical forms are equivalent for use in statistical models needed to explain biological responses and also in screening risk assessment. However, these relationships are not always proportional. Lower availability percentages were observed for Cd, Cu and Zn in the highly mixed-contaminated area of the Montreal Harbour, even though concentrations in sediment were higher. We observed a significant correlation (0.50< or =r < or =0.56) between concentrations in chironomids and concentrations of both total recoverable and reactive Cr and Pb in sediment. Arsenic was an exception, with accumulation by chironomids being highly related to reactive sediment concentrations. Finally, we observed variable influences of explanatory factors (e.g. sediment grain size, Al, Fe, Mn, S, TOC), depending on which metal or metalloid was being predicted in chironomids. In this context, it is difficult to choose a universal predictive method to explain the bioaccumulation of specific metals, and more research is still needed into normalization procedures that consider a combination of explanatory factors.     

Evaluation of trace metals bioavailability in Japanese river waters using DGT and a chemical equilibrium model

To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water. In this study, we employed the diffusive gradients in thin-films (DGT) to determine the bioavailability of metals (Ni, Cu, Zn, and Pb) in Japanese water systems. The DGT results were compared with a chemical equilibrium model (WHAM 7.0) calculation to examine its robustness and utility to predict dynamic metal speciation. The DGT measurements showed that biologically available fractions of metals in the rivers impacted by mine drainage and metal industries were relatively high compared with those in urban rivers. Comparison between the DGT results and the model calculation indicated good agreement for Zn. The model calculation concentrations for Ni and Cu were higher than the DGT concentrations at most sites. As for Pb, the model calculation depended on whether the precipitated iron(III) hydroxide or precipitated aluminum(III) hydroxide was assumed to have an active surface. Our results suggest that the use of WHAM 7.0 combined with the DGT method can predict bioavailable concentrations of most metals (except for Pb) with reasonable accuracy.     

Modeling metal bioaccumulation in a deposit-feeding polychaete from labile sediment fractions and from pore water

Estuarine sediments are often highly enriched in particle-reactive metal contaminants and because aquatic animals have often been shown to acquire metals predominantly from their diet, benthic animals feeding on deposited or resuspended sediments may also accumulate metals through this uptake pathway. Laboratory experiments were performed in which the surface deposit-feeding polychaete, Nereis succinea, was exposed to As(+ 5), Cd, and Cr(+ 3) in pore water or in estuarine sediments with and without enrichment with algal debris. These experiments generated metal uptake parameters (assimilation efficiency of ingested metal [AE], uptake rate constant of dissolved metal, efflux rate constants following dietary or aqueous metal exposures) used in a kinetic model of metal bioaccumulation. The model showed that > 97% of the body burden of these metals is accumulated through ingested sediment. The kinetic model was further modified to consider the geochemical fractionation of the metals in the sediments because metals bound to some fractions were shown to be unavailable to these polychaetes. The modified model substituted the AE term for each metal by the percentage of metal extracted in neutral and weak acid exchangeable fractions (termed “carbonex” fraction) multiplied by the slope of the regression between the metal AE and its fractionation in carbonex. The modified model generated predictions of As, Cd, and Cr body burdens in polychaetes at three different estuarine sites that matched independent field observations at these sites (r² = 0.84 for sediments without organic enrichment, r² = 0.87 with organic enrichment). Model predictions that relied on total metal concentrations showed weaker relationships (r² = 0.11-0.50). This study adds to the evidence for the dominance of dietary uptake of metals in aquatic animals and identifies a key sedimentary fraction of metals that can account for bioavailability of sediment-bound metals.     

Organic nitrogen transformations in a 4-stage Bardenpho nitrogen removal plant and bioavailability/biodegradability of effluent DON

Nitrogen species, specifically, the fate and occurrence of organic nitrogen (ON) within a 4-stage Bardenpho process bioreactor producing low total nitrogen (TN) effluents were investigated in this study. The results showed release of ON in primary anoxic zone and no ON release in the first aerobic zone of the process. The research included investigation of biodegradability/bioavailability of wastewater-derived effluent dissolved ON (DON). The final-effluent DON utilization was evaluated by two different bioassay protocols in the presence and absence of nitrate. About 28–57% of the effluent DON was bioavailable/biodegradable. Bioavailable (to algae and bacteria) DON (ABDON) and biodegradable (to bacteria) DON (BDON) results did not show significant differences in terms of quantity, but DON utilization rates by ABDON (0.13 day⁻¹) protocol were higher than that of the BDON (0.04 day⁻¹) protocol in the nitrate-removal samples. As a result, ABDON requires a shorter time to exert the bioavailable fraction due to symbiotic relationship between algae and bacteria. In the nitrate-containing samples, it appears that nitrate competes with labile DON as a nitrogen source to microorganisms in both ABDON and BDON protocols. The first order decay rate of DON in the presence of nitrate was 0.11 day⁻¹ and 0.02 day⁻¹ for ABDON and BDON, respectively.     

Dissolution of D2EHPA in liquid-liquid extraction process: implication on metal removal and organic content of the treated water

Effects of pH, extractant/diluent ratios, and metal concentrations on the extent of extractant dissolution during liquid-liquid extraction were investigated. Experimental result shows that D₂EHPA dissolution increases dramatically at pH above 4, leveling off at pH 6-7. The phenomenon is consistent with deprotonation of D₂EHPA and the domination of negatively charged D₂EHPA species at pH of higher than 4. Concentration of D₂EHPA in the aqueous phase, i.e., the extent of extractant dissolution, drops after addition of metal and decreases with increasing metal concentration. The amount of D₂EHPA ‘re-entering’ the organic phase is calculated to be 2.04 mol per mol of Cd added, which is quite closed to the stoichiometric molar ratio of 2 between D₂EHPA and Cd via ion exchange reaction. The effect of metal species on the extent of extractant/metal complexes re-entering is in the order of Cd≈Zn ＞ Ag, which might be coincident to the complexation stability of these metals with D₂EHPA. The extent of extractant dissolution in liquid-liquid extraction process depends on the type and concentration of metal to be removed, pH of aqueous phase, and extractant/diluent ratios.     

Surface adsorption of metals onto the earthworm Lumbricus rubellus and the isopod Porcellio scaber is negligible compared to absorption in the body

In terrestrial organisms, bioaccumulation is usually based on a summation of the amount of metal adsorbed to the body wall and absorbed into the body. The relative proportions of metal adsorption and absorption are usually not quantified. In this study, the distinction between adsorbed and absorbed metals was investigated in two different terrestrial species exposed to metals for 2 weeks. The earthworm Lumbricus rubellus was chosen as representative for organisms mainly taking up metals via the dermal route, and the isopod Porcellio scaber as an organism taking up metals mainly via the alimentary tract. Cross-sections of whole animals were made using a cryostat and accumulated metals were localized by means of a phosphor screen (autoradiography). Radiolabels were used to determine the distribution of metals over the different organs and to distinguish between adsorption and absorption. Cd in the earthworm was mainly found in tissues of the chloragogenous region, whereas Zn was also found in various other organs and in the connective tissue. In the isopod, both Cd and Zn were mainly located in the hepatopancreas. Adsorbed amounts of Cd and Zn were negligible compared to internalized Cd and Zn concentrations for both organisms. Consequently, when focusing on effects of metal uptake for the organism itself, there is no need to correct for adsorption. This suggests that adsorption to the epidermis is not a rate limiting step in metal uptake by soil invertebrates.     

Indium and thallium background contents in soils in China

The background values of indium and thallium in China are investigated. The distributive character of these elements in different soil types and 34 provinces (cities) are studied. Some conclusions can be obtained based on these results.     

A single bioavailability model can accurately predict Ni toxicity to green microalgae in soft and hard surface waters

The major research questions addressed in this study were (i) whether green microalgae living in soft water (operationally defined water hardness <10 mg CaCO₃/L) are intrinsically more sensitive to Ni than green microalgae living in hard water (operationally defined water hardness >25 mg CaCO₃/L), and (ii) whether a single bioavailability model can be used to predict the effect of water hardness on the toxicity of Ni to green microalgae in both soft and hard water. Algal growth inhibition tests were conducted with clones of 10 different species collected in soft and hard water lakes in Sweden. Soft water algae were tested in a ‘soft’ and a ‘moderately hard’ test medium (nominal water hardness = 6.25 and 16.3 mg CaCO₃/L, respectively), whereas hard water algae were tested in a ‘moderately hard’ and a ‘hard’ test medium (nominal water hardness = 16.3 and 43.4 mg CaCO₃/L, respectively). The results from the growth inhibition tests in the ‘moderately hard’ test medium revealed no significant sensitivity differences between the soft and the hard water algae used in this study. Increasing water hardness significantly reduced Ni toxicity to both soft and hard water algae. Because it has previously been demonstrated that Ca does not significantly protect the unicellular green alga Pseudokirchneriella subcapitata against Ni toxicity, it was assumed that the protective effect of water hardness can be ascribed to Mg alone. The log K_MgBL (= 5.5) was calculated to be identical for the soft and the hard water algae used in this study. A single bioavailability model can therefore be used to predict Ni toxicity to green microalgae in soft and hard surface waters as a function of water hardness.     

Metal-binding proteins and peptides in the aquatic fungi Fontanospora fusiramosa and Flagellospora curta exposed to severe metal stress

The production of thiol-containing proteins/peptides and its role in metal-binding was examined in the aquatic hyphomycetes Fontanospora fusiramosa and Flagellospora curta exposed to Cu, Cd, or Zn at concentrations inhibiting the biomass production in 80%. Heat-treated cell-free extracts were separated by size-exclusion chromatography and the thiol and metal content in the fractions was determined. F. curta, the species tolerant to metals, showed higher absolute levels of thiol compounds, which bound higher amounts of Cu and Cd than F. fusiramosa. Peptides with very low molecular weight (<9 kDa), most likely glutathione and phytochelatins, were the major Cu- and Zn-binding components in both species of aquatic hyphomycetes. In most cases, proteins with high molecular weight (>26 kDa) were induced by metal ions and they were the major Cd-binding component in both species. Proteins with characteristics of metallothioneins were also induced by exposure to metals in both species, but they showed a minor role in metal-binding, suggesting they might have other functions in fungal cells.     

Trace zinc and copper concentrations in roadside vegetation and surface soils: a measurement of local atmospheric pollution in Alice,South Africa

The concentration of zinc and copper in 180 grass and associated soil samples collected in triplicate samples were determined. The triplicate field data were averaged to yield mean soil and vegetation metal concentrations at each sample location. The zinc levels ranged from 7.0 ± 1.4(S.D.) — 134.8 ± 6.3(S.D.) μgg^‐1, dry weight, in grass and from 0.6 ± 0.2 (S.D.) — 119.5 ± 3.9 (S.D.) μgg^‐1, dry weight, in surface soils. The results showed that zinc contents are high close to the road traffic and fall off rapidly with distance from the road edge. Similar studies on copper gave lower values ‐1.0 ± 0.2(S.D.) — 8.1 ± 1.4(S.D.) μgg^‐1, dry weight in soil samples which did not show any correlation with distance from road traffic. Analysis of standard soil reference materials (SRM 2710) gave results (Zn, 6636.5 ± 43.7(S.D.); Cu, 2725 ± 49.1(S.D.)) which are found to be in good agreement with certified NIST values (Zn, 6952 ± 91; Cu, 2950 ± 130). Results of spiking experiments with vegetation gave high percentage recoveries for both elements (Zn, 96.6 ± 1.3(S.D.)% and Cu, 95.5 ± 0.5(S.D.)%). Blank determinations were done for background corrections.