The quantification and distribution of pollution Pb at a woodland in rural south central Ontario, Canada

Lead concentrations and Pb isotope ratios were measured in the forest floor, mineral soil and vegetation at a white pine and a sugar maple stand in a woodland in south central Ontario. Lead concentrations decreased and 206Pb/207Pb ratios increased with mineral soil depth reflecting the mixing of pollution and natural Pb sources. Lead concentrations and 206Pb/207Pb ratios at 20-30 cm depth were approximately 6-7 mg/kg and 1.31-1.32, respectively. Assuming an integrated 206Pb/207Pb ratio in deposition over time of 1.18, estimated from lichen measurements and published data for the region, approximately 65% of Pb in the surface (0-1 cm) mineral soil is from anthropogenic sources. Approximately 90% of pollution Pb is found in the 0-10 cm soil layer (Ah) and less than 3% of the pollution Pb is present in the forest biomass and mull-type forest floor combined. Despite low Pb concentrations in vegetation (<2.5 mg/kg), we estimate that between 65 and 100% of the Pb in vegetation and approximately 75% of the Pb in the forest floor is from pollution sources. In total, the pollution Pb burdens at the pine and maple stands are estimated to be 860 and 750 mg/m2, respectively.     

Isotopic characterisation of lead in contaminated soils from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria

Soil samples from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria contained very high concentrations of cadmium, lead and zinc (up to 140, 4900 and 5900 mg kg(-1), respectively). A roadside soil in a relatively uncontaminated area also contained high concentrations of the same metals (24, 1550 and 1870 mg kg(-1), respectively) indicating that the transport of ores could be a source of contamination. Even though the lead isotope ratios in all the samples fell within a very narrow range (for example, 1.186-1.195 for (206)Pb/(207)Pb), the samples could be differentiated into three distinct groups: ores ((206)Pb/(207)Pb and (208)Pb/(207)Pb ratios of 1.1874-1.1884 and 2.4755-2.4807, respectively), current deposition (1.1864 and 2.4704-2.4711, respectively) and local background (1.1927-1.1951 and 2.4772-2.4809, respectively). Although most of the current deposition has its origin in the ores used at the smelter, up to 12% could be from other sources such as petrol lead.     

Metal contamination in the lichen Alectoria sarmentosa near the copper smelter of Murdochville, Québec

Lichens were used to evaluate the metal pollution in a forest ecosystem around the smelter of Murdochville, Canada. As reached values 5.8 times higher in the smelter vicinity than in the 'background' sites. This enrichment was 2 times higher for 3 metals (Cu, Cd and Pb). The highest As, Ba, Cd, Cu, and Pb concentrations in lichens were 4, 112, 1, 23, 50 and 952mg/kg respectively. Contamination declined exponentially with increasing distance from the smelter and was related to elevation and slope exposition to the smelter flux. (206)Pb/(207)Pb and (206)Pb/(204)Pb ratios were low close to the smelter (1.16 and 18), but increased with distance to constant values (1.19 and 18.7) and showed an inverse correlation with lead concentrations. Forest contamination was detectable up to 30km from the smelter.     

The Pb pollution fingerprint at Lochnagar: the historical record and current status of Pb isotopes

Ratios of 206Pb/207Pb in a Lochnagar sediment core slowly decline from c. 1.32 at 140 cm to c. 1.23 at 9 cm, and then rapidly decline to c. 1.15 at the surface. Ninety percent of the Pb in the surface sediments can be attributed to anthropogenic sources. The 206Pb/207Pb ratio data imply that catchment peat surface contains a higher fraction of anthropogenic Pb than the sediment surface. The 206Pb/207Pb ratios in the surface of the sediment core are consistent with ratios in trapped sediments collected annually between 1998 and 2003. However, there is no significant decline in these recent samples suggesting that the reduction in atmospheric Pb emissions has not yet been recorded by the sediments due to Pb inputs from the catchment. As catchment peats store about 840 kg previously deposited anthropogenic Pb since 1860, it is likely that catchment inputs will continue to affect future 206Pb/207Pb ratios.     

Effect of recent climate change on Arctic Pb pollution: a comparative study of historical records in lake and peat sediments

Historical changes of anthropogenic Pb pollution were reconstructed based on Pb concentrations and isotope ratios in lake and peat sediment profiles from Ny-?lesund of Arctic. The calculated excess Pb isotope ratios showed that Pb pollution largely came from west Europe and Russia. The peat profile clearly reflected the historical changes of atmospheric deposition of anthropogenic Pb into Ny-?lesund, and the result showed that anthropogenic Pb peaked at 1960s-1970s, and thereafter a significant recovery was observed by a rapid increase of (206)Pb/(207)Pb ratios and a remarkable decrease in anthropogenic Pb contents. In contrast to the peat record, the longer lake record showed relatively high anthropogenic Pb contents and a persistent decrease of (206)Pb/(207)Pb ratios within the uppermost samples, suggesting that climate-sensitive processes such as catchment erosion and meltwater runoff might have influenced the recent change of Pb pollution record in the High Arctic lake sediments.     

Distribution and fractionation of phosphorus, cadmium, nickel, and lead in calcareous soils amended with composts

Composts improve organic carbon content and nutrients of calcareous soils but the accumulation and distribution of phosphorus and heavy metals among various fractions in soil may vary under the south Florida conditions. The accumulation of P, Cd, Ni, and Pb with depth and the distribution of water soluble, exchangeable, carbonate, Fe-Mn oxides, organic and residual forms of each element were investigated in soils amended with municipal solid waste (MSW) compost, co-compost and biosolids compost and inorganic fertilizer (as control). Total concentrations of P, Cd, Ni, and Pb were higher in the 0-22 cm soil layers and decreased considerably in the rock layers. These elements were in the decreasing order of P > Pb > Ni > Cd. Amounts of water soluble and exchangeable forms of P, Cd, Ni and Pb were negligible at 0-22 cm soil depths except for Cd in the 10-22 cm depth. Amending calcareous soil with either organic or inorganic amendments rendered phosphorus, nickle and lead in the residual form followed by Fe-Mn oxides form in the 0-10 and 10-22 cm soil layers. Cadmium was predominantly in the Fe-Mn oxides fraction followed by the residual and carbonate forms in both soil layers. A significant positive correlation was found between various organic carbon fractions and organic forms of P, Cd and Pb in the surface soil layer. Soil amended with MSW compost had higher concentration of Cd in the organic fraction whereas, co-compost and MSW compost amended soil had higher concentrations of organic Ni fraction in the 0-10 cm soil layer.     

Trace metal contamination of sediments in an e-waste processing village in China

This study examined trace metal contamination of sediments in Guiyu, China where primitive e-waste processing activities have been carried out. It was found that some river sediments in Guiyu were contaminated with Cd (n.d.-10.3mg/kg), Cu (17.0-4540mg/kg), Ni (12.4-543mg/kg), Pb (28.6-590mg/kg), and Zn (51.3-324mg/kg). The (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios of the Pb-contaminated sediments of Lianjiang (1.1787+/-0.0057 and 2.4531+/-0.0095, respectively) were lower than those of Nanyang River (1.1996+/-0.0059 and 2.4855+/-0.0082, respectively), indicating a significant input of non-indigenous Pb with low (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios. Copper, Pb and Zn in the non-residual fractions noticeably increased in the contaminated sediments compared to those in the uncontaminated sediments. A genuine concern is associated with potential transport of the contaminated sediments downstream and enhanced solubility and mobility of trace metals in the non-residual fractions.     

Heavy metals in agricultural soils of the Pearl River Delta,South China

There is a growing public concern over the potential accumulation of heavy metals in agricultural soils in China owing to rapid urban and industrial development and increasing reliance on agrochemicals in the last several decades. Excessive accumulation of heavy metals in agricultural soils may not only result in environmental contamination, but elevated heavy metal uptake by crops may also affect food quality and safety. The present study is aimed at studying heavy metal concentrations of crop, paddy and natural soils in the Pearl River Delta, one of the most developed regions in China. In addition, some selected soil samples were analyzed for chemical partitioning of Co, Cu, Pb and Zn. The Pb isotopic composition of the extracted solutions was also determined. The analytical results indicated that the crop, paddy and natural soils in many sampling sites were enriched with Cd and Pb. Furthermore, heavy metal enrichment was most significant in the crop soils, which might be attributed to the use of agrochemicals. Flooding of the paddy soils and subsequent dissolution of Mn oxides may cause the loss of Cd and Co through leaching and percolation, resulting in low Cd and Co concentrations of the paddy soils. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the Fe-Mn oxide and residual fractions, while Zn was predominantly found in the residual phase. A significant percent fraction of Cu was bound in the organic/sulphide and residual phases. Based on the 206Pb/207Pb ratios of the five fractions, it was evident that some of the soils were enriched with anthropogenic Pb, such as industrial and automobile Pb. The strong associations between anthropogenic Pb and the Fe-Mn oxide and organic/sulphide phases suggested that anthropogenic Pb was relatively stable after deposition in soils.     

Atmospheric lead deposition to Okefenokee Swamp, Georgia, USA

Contamination of the environment from atmospheric deposition during the twentieth century is pervasive even in areas ostensibly considered pristine or remote from point sources. In this study, Pb concentrations in a 210Pb-dated peat core collected from the Okefenokee Swamp, GA were used to assess historical contaminant input via atmospheric deposition. Lead isotope ratios were determined by dynamic reaction cell ICP-MS (DRC-ICP-MS). Increases in Pb concentration occurred in the late nineteenth century and a marked rise in Pb concentrations pre-dated the widespread use of leaded gasoline within the US. The 206Pb/207Pb ratios of 1.19 during this period were consistent with coal combustion emissions. A later increase in Pb concentration, concurrent with a trend toward more radiogenic 206Pb/207Pb ratios in gasoline is consistent with an increased input of Pb from leaded gasoline emissions. However, it appears that coal combustion emissions remain a major source of Pb to the Okefenokee.     

Contamination and source differentiation of Pb in park soils along an urban-rural gradient in Shanghai

Urban soil Pb contamination is a great human health risk. Lead distribution and source in topsoils from 14 parks in Shanghai, China were investigated along an urban-rural gradient. Topsoils were contaminated averagely with 65 mg Pb kg⁻¹, 2.5 times higher than local soil background concentrations. HCl-extracts contained more anthropogenic Pb signatures than total sample digests as revealed by the higher ^207/206Pb and ^208/206Pb ratios in extracts (0.8613 ± 0.0094 and 2.1085 ± 0.0121 versus total digests 0.8575 ± 0.0098 and 2.0959 ± 0.0116). This suggests a higher sensitivity of HCl-extraction than total digestion in identifying anthropogenic Pb sources. Coal combustion emission was identified as the major anthropogenic Pb source (averagely 47%) while leaded gasoline emission contributed 12% overall. Urbanization effects were observed by total Pb content and anthropogenic Pb contribution. This study suggests that to reduce Pb contamination, Shanghai might have to change its energy composition to clean energy.     

Historical reconstruction of atmospheric lead pollution in central Yunnan province, southwest China: an analysis based on lacustrine sedimentary records

Atmospheric lead (Pb) pollution during the last century in central Yunnan province, one of the largest non-ferrous metal production centers in China, was reconstructed using sediment cores collected from Fuxian and Qingshui Lakes. Lead concentrations and isotopic ratios (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) were measured in sediment cores from both lakes. The operationally defined chemical fractions of Pb in sediment core from Fuxian Lake were determined by the optimized BCR procedure. The chronology of the cores was reconstructed using ²¹⁰Pb and ¹³⁷Cs dating methods. Similar three-phase variations in isotopic ratios and enrichment factors of Pb were observed in the sediment cores from both lakes. Before the 1950s, the sediment data showed low ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios and enrichment factors (EFs?=?~1), indicating that the sedimentary Pb was predominantly of lithogenic origin. However, these indices were increased gradually between the 1950s and the mid-1980s, implying an atmospheric Pb deposition. The EFs and isotopic ratios of Pb reached their peak during recent years, indicating aggravating atmospheric Pb pollution. The average anthropogenic Pb fluxes since the mid-1980s were estimated to be 0.032 and 0.053 g m^?2 year^?1 recorded in Fuxian and Qingshui cores, respectively. The anthropogenic Pb was primarily concentrated in the reducible fraction. Combining the results of Pb isotopic compositions and chemical speciations in the sediment cores and in potential sources, we deduced that recent aggravating atmospheric Pb pollution in central Yunnan province should primarily be attributed to regional emissions from non-ferrous metal production industries.     

Distribution and Fractionation of Phosphorus,Cadmium, Nickel,and Lead in Calcareous Soils Amended with Composts

Abstract

Composts improve organic carbon content and nutrients of calcareous soils but the accumulation and distribution of phosphorus and heavy metals among various fractions in soil may vary under the south Florida conditions. The accumulation of P, Cd, Ni, and Pb with depth and the distribution of water soluble, exchangeable, carbonate, Fe–Mn oxides, organic and residual forms of each element were investigated in soils amended with municipal solid waste (MSW) compost, co-compost and biosolids compost and inorganic fertilizer (as control). Total concentrations of P, Cd, Ni, and Pb were higher in the 0–22 cm soil layers and decreased considerably in the rock layers. These elements were in the decreasing order of P ? Pb > Ni > Cd. Amounts of water soluble and exchangeable forms of P, Cd, Ni and Pb were negligible at 0–22 cm soil depths except for Cd in the 10–22 cm depth. Amending calcareous soil with either organic or inorganic amendments rendered phosphorus, nickle and lead in the residual form followed by Fe–Mn oxides form in the 0–10 and 10–22 cm soil layers. Cadmium was predominantly in the Fe–Mn oxides fraction followed by the residual and carbonate forms in both soil layers. A significant positive correlation was found between various organic carbon fractions and organic forms of P, Cd and Pb in the surface soil layer. Soil amended with MSW compost had higher concentration of Cd in the organic fraction whereas, co-compost and MSW compost amended soil had higher concentrations of organic Ni fraction in the 0–10 cm soil layer.     

Pb isotopes as tracers of mining-related Pb in lichens, seaweed and mussels near a former Pb-Zn mine in West Greenland

Identification of mining-related contaminants is important in order to assess the spreading of contaminants from mining as well as for site remediation purposes. This study focuses on lead (Pb) contamination in biota near the abandoned ‘Black Angel Mine’ in West Greenland in the period 1988-2008. Stable Pb isotope ratios and total Pb concentrations were determined in lichens, seaweed and mussels as well as in marine sediments. The results show that natural background Pb (²⁰⁷Pb/²⁰⁶Pb: 0.704-0.767) and Pb originating from the mine ore (²⁰⁷Pb/²⁰⁶Pb: 0.955) have distinct isotopic fingerprints. Total Pb in lichens, seaweed, and mussels was measured at values up to 633, 19 and 1536 mg kg⁻¹ dry weight, respectively, and is shown to be a mixture of natural Pb and ore-Pb. This enables quantification of mining-related Pb and shows that application of Pb isotope data is a valuable tool for monitoring mining pollution.     

Isotope ratios of lead in Japanese women’s hair of the twentieth century

Introduction  

Isotope ratios of lead (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) in Japanese women’s hair of the twentieth century were measured to evaluate lead contamination of human proximate environment of those days.     

Trace metal distribution in sediments of the Pearl River Estuary and the surrounding coastal area, South China

Surface sediments and sediment cores collected at the Pearl River Estuary (PRE) and its surrounding coastal area were analysed for total metal concentrations, chemical partitioning, and Pb isotopic compositions. The distribution of Cu, Cr, Pb, and Zn demonstrated a typical diffusion pattern from the land to the direction of the sea. Two hotspots of trace metal contamination were located at the mixed zone between freshwater and marine waters. The enrichment of metals in the sediments could be attributed to the deposition of the dissolved and particulate trace metals in the water column at the estuarine area. The similar Pb isotopic signatures of the sediments at the PRE and its surrounding coastal area offered strong evidence that the PRE was a major source of trace metals to the adjacent coastal area. Slightly lower (206)Pb/(207)Pb ratios in the coastal sediments may indicate other inputs of Pb in addition to the PRE sources, including the inputs from Hong Kong and other parts of the region.     

Atmospheric Pb isotopic composition and trace metal concentration as revealed by epiphytic lichens:: an investigation related to two altitudinal sections in Eastern France

During Fall 1996, epiphytic lichens were collected along altitudinal sections in two areas of France (the Vosges mountains in the North-East, and the Alps, in Haute-Savoie) in order to verify any geographic distribution of atmospheric metals on a small scale. These lichens have various Pb isotopic compositions (²⁰⁶Pb/²⁰⁷Pb=1.126–1.147) which are correlated with the altitude of sampling. Lichens sampled near valleys display isotopic ratios significantly less radiogenic than those sampled at several hundred to thousand meters of altitude. In the Vosges sections, Pb concentrations and isotopic compositions of lichens may be used to define three zones: (1) valley: Pb-rich and non-radiogenic ratios, (2) transition: low-Pb and intermediate isotopic compositions, (3) mountain: heterogeneous Pb concentrations but more radiogenic and homogeneous Pb isotopic composition. Other metals (Zn, Cu, Cd, As), when normalised one to another, are not fractionated between these zones and display homogeneous relative abundance along the altitudinal sections of both sites. Variation of ²⁰⁶Pb/²⁰⁷Pb ratios with altitude is interpreted in terms of mixing of at least two pollution sources: one being the petrol (leaded and/or unleaded) combustion, and the other being of industrial origin. The latter is characterised by a more radiogenic isotopic composition. The Pb isotopic composition of flue gas residues from different municipal solid waste combustors in the Rhine valley and in other areas of France would suggest that these plants might be an important source of industrial Pb in the atmosphere. If the average industrial Pb in France has a ²⁰⁶Pb/²⁰⁷Pb close to 1.15, between 60 and 80% of the total Pb in lichens from the Rhine valley would come from gasoline combustion, whereas 85–90% of the Pb would have an industrial origin in lichens from higher altitude in the Vosges mountains. Although lichens from the Alps were collected at higher altitude, the percentage of industrial Pb for these lichens would be slightly lower (65%). Major winds and convection winds in the different valleys must then play an important role in term of distribution of atmospheric Pb in function of altitude.     

Pb isotope ratios of lake sediments in West Greenland: inferences on pollution sources

Lead (Pb), like many other pollutants, is carried into the Arctic by long-range atmospheric transport from industrial centers at lower latitudes. Unlike other pollutants, Pb can be used to assess emission source regions through the use of stable Pb isotope analyses. Using sediment cores from 17 lakes (three profiles and 14 top/bottom sample pairs) in the Søndre Strømfjord (Kangerlussuaq) region, West Greenland (67°N), this study assesses the extent and origin of Pb pollution along a 150 km transect between the Inland Ice and Davis Strait. Like ice core analyses from the interior of Greenland, the isotope analyses suggest pre-industrial contamination, although significant concentration changes in the lake sediments do not occur until the 18th/19th centuries, with the maximum concentrations occurring about 1970. Compared to the background, the Pb concentrations in recent sediments have increased about 2.5-fold, with slightly higher enrichments towards the coast, where annual precipitation is highest. For all of the lakes, there is a major decline in the ²⁰⁶Pb/²⁰⁷Pb ratio in the recent sediments (mean 1.218±0.030) as compared to deeper sediments (mean 1.365±0.084). Using a Pb isotope mixing model, we calculated an excess Pb isotope ratio, i.e. the isotope ratio necessary to produce the observed declines in recent sediments. While studies of atmospheric aerosols in the high Arctic (²⁰⁶Pb/²⁰⁷Pb ratio ∼1.16) have indicated that Russian emissions (²⁰⁶Pb/²⁰⁷Pb ratio ∼1.15–1.16) are a dominant source of arctic pollution, the excess Pb ratios of the lake sediments in the Søndre Strømfjord region (²⁰⁶Pb/²⁰⁷Pb ratio ∼1.14–1.15), in the low Arctic, suggest that W Europe (²⁰⁶Pb/²⁰⁷Pb ratio ∼1.14) is also a major emission source for this region.     

Lead contamination of the Seine River, France: geochemical implications of a historical perspective

Four sediment cores collected in the Seine River basin and dated between 1916 and 2003 were analyzed for lead concentrations and isotopic composition. In all four cores, the measured Pb concentration (up to 460 mg kg⁻¹) lies significantly above the natural background (27-40 mg kg⁻¹), although a significant decrease (down to 75 mg kg⁻¹) was observed during the second half of the 20th century which can be explained by the reduction of lead emissions. The ²⁰⁶Pb/²⁰⁷Pb ratio measured in these samples indicates that the main source of Pb used in the Paris conurbation is characterized by a “Rio Tinto” signature (defined as ²⁰⁶Pb/²⁰⁷Pb = 1.1634 ± 0.0001). A high contribution, up to 25%, from the leaded gasoline (characterized by ²⁰⁶Pb/²⁰⁷Pb = 1.08 ± 0.02) is revealed in the Seine River downstream Paris, indicating that lead from the leaded gasoline is preferentially released to the river.The dominating Pb signature in the Paris conurbation that is currently sampled through incinerators fumes (²⁰⁶Pb/²⁰⁷Pb = 1.1550 ± 0.0005) and waste water treatment plant (²⁰⁶Pb/²⁰⁷Pb = 1.154 ± 0.002), represents a mixture of highly recycled lead from the Rio Tinto mine and lead from leaded gasoline (imprinted by the low ²⁰⁶Pb/²⁰⁷Pb of the Broken Hill mine). This signature is called “urban” rather than “industrial”, because it is clearly distinct from the Pb that is found in areas contaminated by heavy industry, i.e. the heavy industries located on the Oise River which used lead from European ores characterized by high ²⁰⁶Pb/²⁰⁷Pb ratios (∼1.18-1.19) and possibly a minor amount of North American lead (²⁰⁶Pb/²⁰⁷Pb ratios > 1.20). The “urban” signature is also found in a rural area upstream of Paris in the 1970’s. At the Seine River mouth in 2003, Pb with an urban signature represents 70% of the total Pb sediment content, with the 30% remaining corresponding to natural Pb.     

Characteristics of lead geochemistry and the mobility of Pb isotopes in the system of pedogenic rock–pedosphere–irrigated riverwater–cereal–atmosphere from the Yangtze River delta region,China

Knowledge of the characteristics of Pb and its isotopic transfer in different compartments is scant, especially for the mobility of Pb isotopes in the geochemical cycle. The present study characterizes differential Pb transport mechanism and the mobility of Pb isotopes in the pedogenic parent rock–pedosphere–irrigated riverwater–cereal–atmosphere system in the Yangtze River delta region, by determining Pb concentration and Pb isotopic ratios of pedogenic parent rocks, fluvial suspended particle matter, tillage soils, soil profiles, irrigated riverwater, fertilizer, Pb ore, cereal roots and grains. The results show that Pb isotopes in the geochemical cycle generally follow the equation of ²⁰⁸Pb/²⁰⁶Pb = −1.157 × ²⁰⁶Pb/²⁰⁷Pb + 3.46 (r² = 0.941). However, Pb isotopes have different mobility in different environmental matrixes. Whereas in the pedosphere, the heavier Pb (²⁰⁸Pb) usually shows stronger mobility relative to the lighter Pb, and is more likely to transfer into soil exchangeable Pb fraction and carbonates phase. The lighter Pb shows stronger transfer ability from soil to cereal grain via root compared to the heavier Pb. However, the cereal grains have lower ²⁰⁶Pb/²⁰⁷Pb and higher ²⁰⁸Pb/²⁰⁶Pb ratios than root and tillage soil, similar to the airborne Pb and anthropogenic Pb, implying that a considerable amount of Pb in cereal grains comes from the atmosphere. The estimate model shows that 16.7–52.6% (average: 33.5%) of Pb in rice grain is the airborne Pb.     

Leaching of heavy metals from contaminated soils using EDTA

Ethylenediaminetetraacetic acid (EDTA) extraction of Zn, Cd, Cu and Pb from four contaminated soils was studied using batch and column leaching experiments. In the batch experiment, the heavy metals extracted were virtually all as 1:1 metal-EDTA complexes. The ratios of Zn, Cd, Cu and Pb of the extracted were similar to those in the soils, suggesting that EDTA extracted the four heavy metals with similar efficiency. In contrast, different elution patterns were obtained for Zn, Cd, Cu and Pb in the column leaching experiment using 0.01 M EDTA. Cu was either the most mobile or among the most mobile of the four heavy metals, and its peak concentration corresponded with the arrival of full strength EDTA in the leachate. The mobility of Zn and Cd was usually slightly lower than that of Cu. Pb was the least mobile, and its elution increased after the peaks of Cu and Zn. Sequential fractionations of leached and un-leached soils showed that heavy metals in various operationally defined fractions contributed to the removal by EDTA. Considerable mobilisation of Fe occurred in two of the four soils during EDTA leaching. Decreases in the Fe and Mn oxide fraction of heavy metals after EDTA leaching occurred in both soils, as well as in a third soil that showed little Fe mobilisation. The results suggest that the lability of metals in soil, the kinetics of metal desorption/dissolution and the mode of EDTA addition were the main factors controlling the behaviour of metal leaching with EDTA.