Heavy metal contamination of the soils used for stocking raw materials in the former ILVA iron-steel industrial plant of Bagnoli (southern Italy)

The total contents and the chemical and mineralogical forms of the metals Fe, Al, Cu, Co, Cr, Pb, Zn, Ni and Mn in the horizons of a soil profile, representative of an area devoted to stocking raw materials in the dismantled iron-steel industrial plant of ILVA of Bagnoli (Naples), were studied by physical and chemical methods. The geological setting of the study area is the result of volcanic activity in the Phlegrean Fields, a group of polygenic volcanoes to the west of Naples, which give rise to the parent soil material. Soil morphology appeared to be strongly disturbed by the occurrence and stratification of materials used in the industrial process. Fine sediments illuviation down the profile resulted in the occurrence of silt and clay coatings. The total contents of Cu, Co, Cr, Pb, Zn and Ni, in the whole soil samples, especially in the surface layers, were above the regulatory levels (Cu 120, Co 20, Cr 150, Pb 100, Zn 150, Ni 120 mg kg(-1)) stated by the Italian Ministry of Environment for soils in public, private and residential areas, and below the levels (Cu 600, Co 250, Cr 800, Pb 1000, Zn 1500, Ni 500 mg kg(-1)) outlined for soils and subsoils of industrial and commercial areas (Gazzetta Ufficiale della Repubblica Italiana, 1999). Speciation of heavy metals and the determination of the different chemical pools in the fraction < 2 mm identified the large presence of elements trapped in the mineralogical structure of oxides and silicates and occluded in easily reducible manganese or iron oxides. A constant amount of Cu was associated with organic compounds. A significant amount of Zn (> 20%) was extracted in diluted acetic acid solution, indicating that the element was present in a more readily and potentially available form. In the clay fraction (< 2 microm) heavy metals were associated with both amorphous and crystalline iron forms. The presence of iron-rich clay coatings was evident in the illuvial pores of deeper horizons. Enrichment in Cu, Co, Cr and Zn of the coatings was observed. Possible translocation of metals down through the soil profile mainly bound to fine particles of relatively inert forms of iron is hypothesised. The dispersion in water of the clay fraction resulted in an average percentage dispersion of approximately 20% with a peak of 41.7% at 68-72 cm depth. Magnetite, goethite, hematite, calcite and quartz mixed with K-feldspars, clynopyroxenes and mica occurred in the coarse sand fractions (2-0.2 mm) of the soil samples from all the surface horizons. Talcum and goethite together with clay minerals at 1.4 nm, kaolinite and illite were found in the clays (< 2 microm).     

Arsenic solubility and distribution in poultry waste and long-term amended soil

The purpose of this study was to quantify the solubility and distribution of As among solid-phase components in poultry wastes and soils receiving long-term poultry waste applications. Arsenic in the water-soluble, NaOCl-extractable (organically bound), NH(2)OH x HCl-extractable (oxide bound) and residual fractions were quantified in an Upper Coastal Plain soil (Neshoba County, MS) that received annual waste applications. After 25 years, As in the amended soil had a mean of 8.4 mg kg(-1) compared to 2.68 mg kg(-1) for a non-amended soil. Arsenic in the amended soil was mainly in the residual fraction (72% of total), which is generally considered the least bioavailable fraction. Arsenic in poultry waste samples was primarily water-soluble (5.3-25.1 mg kg(-1)), representing 36-75% of the total As. To assess the extent of spatial heterogeneity, total As in a 0.5-ha area within the long-term waste-amended field was quantified. Soil surface samples were taken on 10-m grid points and results for total As appeared negatively skewed and approximated a bimodal distribution. Total As in the amended soil was strongly correlated with Fe oxides, clay and hydroxy interlayered vermiculite concentrations, and negatively correlated with Mehlich III-P, mica and quartz contents.     

Heavy metal pollution associated with mining activity in the Kouh-e Zar region,NE Iran

The Kouh-e Zar mining area is located in the central part of the “Khaf–Bardaskan” volcanic-plutonic zone, NE Iran. Mining activity has resulted in pollution of soil and water resources by potentially toxic elements including arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), antimony (Sb), nickel (Ni) and zinc (Zn). In this study, the major source of heavy metal pollution and elucidating the probable environmental risks associated with this area were determined by quantifying pollution in soils and water resources. Concentrations of Cd, Cr, Cu, Pb and Zn in the Kouh-e Zar mining area varied in the range of 5–470, 33–442, 25–5125, 81.15–12,096.27 and 55–4210 mg/kg, respectively. The geo-accumulation index for Cd in all samples was extremely high (I_geo > 5) and the enrichment factor also shows an extremely high amount (EF > 40), both representing evidence for highly polluted soil in the area. However, the coefficients of aqueous migration (K_x) of Cd, Cr, Cu, Pb and Zn were K_x < 0.1, so they are classified as “least mobile and inert” grade. Also, the heavy metals tend to remain in soil (solid environment). Cluster analysis (CA) determined the lithogenic origin for Zn, Cu, Cr and Cd, and the anthropogenic origin (mining activity) for Pb in the soils of the mining area. The concentrations of Cd, Cu, Pb and Zn in water are controlled by free Fe and Mn oxy-hydroxide content in the soils. Both water–rock interaction and mining activity have contributed to pollution in the area.

     

中国红土的微结构和工程性质

为了研究红土的高强度、低压缩和高孔隙的工程特性,我们系统地分析了我国各类红土的物理力学性质,物质成分和微结构特征。我们发现红土强度主要来源于粒间残存或新生的化学键力、晶质氧化铁的胶结力和胶态含水氧化铁的影响。长期处于湿润条件下,赋存于孔隙溶液中的游离胶态氧化铁,虽能对粘土表面斥力起一定抑制作用,但还是不能完全阻止红粘土的胀缩行为。     

Earthworms as colonisers: Primary colonisation of contaminated land, and sediment and soil waste deposits

This paper reviews the role of earthworms in the early colonisation of contaminated soils as well as sediment and waste deposits, which are worm-free because of anthropogenic activities such as open-cast mining, soil sterilisation, consistent pollution or remediation of contaminated soil. Earthworms live in close interaction with their soil environment and are able to change it considerably by their burrowing and litter comminuting behaviour.While earthworms have been studied extensively, several questions still remain unanswered such as:What are the characteristics of successful early colonisers?Do they function well in dispersal, individual establishment or population growth?Do the negative environmental conditions in these kinds of anthropogenic soils hamper colonization or are these colonizers relatively resistant to it?To what extent does colonization change the characteristics of the colonized substrate?In short, do earthworms impact the soil?In this paper, the characteristics that make earthworms successful colonisers are briefly described as well as which species are the most successful and under what circumstances, and what do earthworms contribute to the total process of succession. We propose that it is not so much eco-type or r-K strategy that govern success and succession of earthworm colonisation but rather environmental flexibility not only towards pH, desiccation, and temperature but also towards contaminants such as heavy metals. Moreover, the formation of an organic litter layer, in close connection with re-vegetation of the area, is essential for establishing earthworm populations, which, at first, are mainly superficially and shallow active species. The burrowing and organic matter digesting activity of these earthworms changes the upper soil to a well mixed humus layer suitable for deep burrowing earthworm species.     

矿区土壤重金属污染现状及对策

介绍了矿区土壤重金属污染的现状、污染特点、污染来源，同时提出了相应的治理对策，指出植物修复是一种有前途的土壤污染治理技术。     

Biodegradation and chiral stability of fipronil in aerobic and flooded paddy soils

Microbiological degradation of the racemic mixture, the enantiopure R- and S-fipronil was examined under both aerobic and flooded conditions in three Chinese paddy soils. The degradation kinectics and enantiomer fraction (EF) were determined by means of high-performance liquid chromatography (HPLC) with chiral Chiralcel OD-H column, while desulfinyl, sulfone and sulfide derivatives were monitored by reversed phase HPLC with diode array detection (DAD). The degradation/transformation of enantiomers of fipronil in the three live soils under aerobic and flooded conditions generally complied with the first-order kinetics (R2 > or = 0.94). The calculated t1/2 values of the enantiomers of fipronil ranged between 21 and 34 days for aerobic incubation experiments and between 8 and 19 days under flooded conditions incubation, respectively. The calculated EF values of fipronil during the incubation time were all close to 0.5, indicating that the degradation/transformation of fipronil was almost nonenantioselective. The main metabolites of fipronil formed in the incubation experiments were sulfone and sulfide derivatives by oxidative and reductive processes, respectively. The oxidative pathway seemed more active. Under flooded conditions, S-fipronil was preferentially degraded in the three soil samples used. The main metabolite was determined as fipronil sulfide. In control experiments, almost no removal of enantiomers of fipronil was observed indicating that the degradation of fipronil in the paddy soil used was attributed to microbial mediated processes under both aerobic and flooded conditions. In addition, no enantiomerization of fipronil was observed in the soil samples examined under both aerobic and flooded conditions. These results for major differences in the degradation of the enantiomers as well as the formation of toxic metabolites may have some implications for better environmental and ecological risks assessment for chiral pesticides.     

Trace element partitioning and soil particle characterisation around mining and smelting areas at Tharsis, Ríotinto and Huelva, SW Spain

Trace elements may present an environmental hazard in the vicinity of mining and smelting activities. However, the factors controlling trace element distribution in soils around ancient and modern mining and smelting areas are not always clear. Tharsis, Ríotinto and Huelva are located in the Iberian Pyrite Belt in SW Spain. Tharsis and Ríotinto mines have been exploited since 2500 B.C., with intensive smelting taking place. Huelva, established in 1970 and using the Flash Furnace Outokumpu process, is currently one of the largest smelter in the world. Pyrite and chalcopyrite ore have been intensively smelted for Cu. However, unusually for smelters and mines of a similar size, the elevated trace element concentrations in soils were found to be restricted to the immediate vicinity of the mines and smelters, being found up to a maximum of 2 km from the mines and smelters at Tharsis, Ríotinto and Huelva. Trace element partitioning (over 2/3 of trace elements found in the residual immobile fraction of soils at Tharsis) and soil particles examination by SEM-EDX showed that trace elements were not adsorbed onto soil particles, but were included within the matrix of large trace element-rich Fe silicate slag particles (i.e. 1 mm ? at least 1 wt.% As, Cu and Zn, and 2 wt.% Pb). Slag particle large size (1 mm ?) was found to control the geographically restricted trace element distribution in soils at Tharsis, Ríotinto and Huelva, since large heavy particles could not have been transported long distances. Distribution and partitioning indicated that impacts to the environment as a result of mining and smelting should remain minimal in the region.     

Evaluation of mercury pollution in cultivated and wild plants from two small communities of the Tapajós gold mining reserve, Pará State, Brazil

This study examines the total Hg contamination in soil and sediments, and the correlation between the total Hg concentration in soil and vegetables in two small scale gold mining areas, S?o Chico and Creporizinho, in the State of Para, Brazilian Amazon. Total Hg values for soil samples for both study areas are higher than region background values (ca. 0.15 mg/kg). At S?o Chico, mean values in soils samples are higher than at Creporizinho, but without significant differences at alpha<0.05 level. S?o Chico's aboveground produce samples possess significantly higher values for total Hg levels than samples from Creporizinho. Creporizinho's soil-root produce regression model were significant, and the slope negative. Creporizinho's soil-aboveground and root wild plants regression models were also significant, and the slopes positives. Although, aboveground:root ratios were >1 in all of S?o Chico's produce samples, soil-plant parts regression were not significant, and Hg uptake probably occurs through stomata by atmospheric mercury deposition. Wild plants aboveground:root ratios were <1 at both study areas, and soil-plant parts regressions were significant in samples of Creporizinho, suggesting that they function as an excluder. The average total contents of Hg in edible parts of produces were close to FAO/WHO/JECFA PTWI values in S?o Chico area, and much lower in Creporizinho. However, Hg inorganic small gastrointestinal absorption reduces its adverse health effects.     

Chemical analysis and X-ray diffraction assessment of stabilized expansive soils

The long-term viability of many construction projects is heavily dependent on the soundness of the underlying subgrade soil which needs to be capable of supporting loads from structures without undergoing excessive deformation or volume changes. However, in certain locations geotechnical engineers face repeated problems in the design of substructures due to the presence of expansive soils. Light structures are especially susceptible to damage in such situations which can result in cracks in walls, beams, columns and on-grade slabs. One extensively used way of overcoming such problems is to improve the soil by stabilizing it with cement and/or lime which prevents this unwanted behavior. Most previous research conducted on expansive soils focused on studying the effects of treatment on the physical properties of the soil without detailed examination of the physicochemical mechanism of the process, although some studies surveyed the effect of the treatment using cement and lime on the mineralogical composition and newly formed pozzolanic compounds. In this research the mineralogical changes due to lime and cement additions to two different expansive soils from Saudi Arabia, in particular, were investigated using X-ray diffraction. The results of this work indicate that addition of lime or cement to the soils tested resulted in the formation of pozzolanic compounds, namely, calcium silicate hydrate and calcium aluminate hydrate together with calcite (CaCO₃). The soil improvements are compared for cement and lime. Changes in potassium, aluminum and silicon were also determined and interpreted in terms of the soil mineralogy. It was concluded that pozzolanic compounds play a significant role in reducing the swelling and increasing the strength.     

Arsenic extractability in soils in the areas of former arsenic mining and smelting, SW Poland

Arsenic (As) concentrations in soils and waste material in two areas of former As mining and processing: Z?oty Stok (Z?ote Mts.) and Zele?niak (Kaczawskie Mts.), SW Poland, were measured to assess levels and environmental risk associated with possible increases in arsenic mobility under changing pH and redox conditions. Twenty six soil samples were collected from 12 sites, and represented a broad spectrum of soil properties and parent material origin, including natural soils, mine spoils, slags and tailings. Arsenic species were examined using a sequential extraction technique. The changes in As solubility were determined from extraction test solutions adjusted to solution pH values varying from 2 to 8. The effects of reducing conditions on As mobility were examined in incubation tests. Most of soils demonstrated extremely high concentrations of As, both of natural and anthropogenic origin. Total As concentrations in all samples were in the range 100-43,500 mg/kg. Sequential extraction techniques suggested that the main species of As in all soils were those bound to iron (Fe) oxides, in particular amorphous ones, whereas the contributions of mobile and specifically sorbed As forms were relatively low. In tailings and tailings-affected alluvial soils, As occurred mainly in residual forms, however these soils also had considerable amounts of mobile As. In all other soils, mobile As forms were very low. Arsenic mobilization could be possible at extremely low or high pH conditions (pH<2 or pH>8), and this may be of particular practical importance in the case of tailings, which are highly alkaline. High pH promotes solubilization of As forms in reducing conditions, whereas in neutral and acidic soils the risk of As release under reducing conditions is limited.     

Plant-available lead and other metals in British garden soils

An account is given of an investigation of the fertility status and heavy metal content of garden soils in England and Wales and the availability to and uptake of lead by radish generally, and by potatoes in two villages of contrasting epidemiological history. Intentional interference (i.e., cultivation) of gardens by man has resulted in a generally high level of fertility, but inadvertent additions of lead and other metals have resulted in many garden soils being contaminated. There are regional differences in fertility but not in heavy metal content. In rural areas, uncontaminated soils were associated with allotments and new gardens, and lead contamination was identified in urban and industrial areas as a result of pollution from vehicle exhausts, industry, mining and miscellaneous sources. Mature gardens in rural areas were also contaminated by lead and evidence is presented to support a hypothesis of increasing pollution with time, perhaps due to coal ash from chimneys. Radish absorbed soil lead and certain gardens produced plants the lead content of which was close to or above the legal limit of 2 mg/kg Pb. Potato was a weaker absorber of lead but plant contents still reflected lead contamination of soil. Consumption of vegetables from contaminated gardens could account for an appreciable proportion of the maximum safe daily intake of lead.     

Distribution of natural and anthropogenic thallium in the soils in an industrial pyrite slag disposing area

The total concentrations combined with the chemical speciation of thallium (Tl) were examined in order to track the distribution of natural and anthropogenic Tl in the soils in an industrial pyrite slag disposing area. Their geochemical behaviors in the soils were further discussed. Soil samples were collected from three soil profiles adjacent to a large open-disposed pile of industrial Tl-rich pyrite slag, and from one soil profile in the background area. The results show that the soil contamination with Tl derived from slag (slag-Tl) is generally limited; slag-Tl was mainly accumulated in the upper part (< 16.5 cm) of the vicinal soils of the slag pile and shows large variation in concentration among different sampling sites. Basically, the soils surrounding the slag pile within 5 m are more Tl-contaminated than those under the slag pile and those far away from the slag pile. In respect of the concentrations of total Tl, the deeper soils of the studied profiles seem to be uncontaminated. However, the percentages of Tl in the easily reducible fraction indicate that these soils have been actually contaminated by slag-Tl. Natural Tl and anthropogenic Tl are distributed differently among the soil components in the studied soils. Natural Tl in the background soils is predominantly hosted in the residual fraction ( approximately 98%), while anthropogenic Tl was significantly incorporated into the more labile fractions of the soil (up to approximately 80%), especially in the acid-extractable fractions and easily reducible fraction (up to approximately 30% and approximately 45%, respectively). Detailed analysis of speciation data of Tl suggests that despite being predominantly controlled by the degree of Tl pollution, the distribution of slag-Tl in the soils can be further affected by the general differences in soil properties. In this study, the order for preferential immobilization of anthropogenic Tl among major soil components can be roughly summarized as: Tl(III) carbonates and hydroxides > Mn oxide-hydroxides > Fe oxide-hydroxides > adsorption sites on the surface of soil, while the order can be significantly mediated by the pH conditions in the soils. The correlations between the fractions of Tl in the slag and in the soils indicate that the anthropogenic Tl in the soils in the studied slag disposing area should be mainly derived from the dissolved slag-Tl that was leached by rainwater rather than from the washed-out particles of slag.     

An assessment of cement-PFA and lime-PFA used to stabilize clay-size materials

Difficulties in construction operations are often associated with clay soils. However, the engineering behaviour of such soils can be improved by stabilizing them with the addition of small amounts of cementitious materials. Nonetheless because clay soils possess a range of mineralogical compositions some are more easy to estabilize than others. In order to investigate this problem, three of the principal components found in clays, namely, kaolinite, montmorillonite and quartz, were chosen. These three components were treated with varying amounts of cement plus PFA. and lime plus PFA. PFA was used as an extender with cement and with lime to evaluate how effective such mixtures are when used to stabilize clay soils. The addition of PFA reduces the cost of the stabilizing agent. Because stabilization of clay soils most frequently has been used in connection with road construction, kaolinite, montmorillonite and quartz were subjected to the types of test used in the design procedure for roadways, that is, consistency limit tests, compaction tests, California bearing ratio tests, unconfined compressive tests, and tests to determine Young's modulus. Except for those samples used for assessment of consistency limits, the others were prepared with optimum values of moisture content and maximum dry density. Those samples used for unconfined compression and modulus of elasticity measurements were cured for different periods of time. The results of the various tests were examined to see if there was an optimum amount for a particular addition which would bring about maximum enhancement of engineering performance of the components concerned. Generally mixtures of cement and PFA or lime and PFA did not give as good results as when cement and lime were used on their own. Also those mixtures with the highest proportions of cement and of lime usually gave the better improvement in values. Nevertheless it may be worth making some sacrifice in soil improvement to obtain the saving in cost that the use of PFA brings.     

Distribution and mobility of arsenic in soils of a mining area (Western Spain)

High levels of total and bioavailable As in soils in mining areas may lead to the potential contamination of surface water and groundwater, being toxic to human, plants, and animals. The soils in the studied area (Province of Salamanca, Spain) recorded a total As concentration that varied from 5.5 mg/kg to 150 mg/kg, and water-soluble As ranged from 0.004 mg/kg to 0.107 mg/kg, often exceeding the guideline limits for agricultural soil (50 mg/kg total As, 0.04 mg/kg water-soluble As). The range of As concentration in pond water was < 0.001 μg/l-60 μg/l, with 40% of samples exceeding the maximum permissible level (10 μg/l) for drinking water. Estimated bioavailable As in soil varied from 0.045 mg/kg to 0.760 mg/kg, around six times higher than water-soluble As fraction, which may pose a high potential risk in regard to its entry into food chain. Soil column leaching tests show an As potential mobility constant threatening water contamination by continuous leaching. The vertical distribution of As through soil profiles suggests a deposition mechanism of this element on the top-soils that involves the wind or water transport of mine tailings. A similar vertical distribution of As and organic matter (OM) contents in soil profiles, as well as, significant correlations between As concentrations and OM and N contents, suggests that type and content of soil OM are major factors for determining the content, distribution, and mobilization of As in the soil. Due to the low supergenic mobility of this element in mining environments, the soil pollution degree in the studied area is moderate, in spite of the elevated As contents in mine tailings.     

采煤塌陷区土地复垦与重构土壤质量研究

中国人多地少,土地资源短缺,再加上每年因采煤塌陷的土地甚多,矿区人地关系矛盾突出。实施土地复垦工程是缓和矿区"矿—粮"矛盾的重要措施,同时也是建立稳定煤矿区生态系统的主要措施。本文在探讨矿区土地复垦技术的基础上,研究了复垦后重构土壤的质量演变。结果表明:现有的矿区土地复垦技术主要有非充填式复垦和充填式复垦两大类;重构土壤的容重、含水量、耕作阻力,以及土壤养分和污染性状等,与自然农业土壤相比均存在相异的发展过程。     

Environmental contamination and seasonal variation of metals in soils,plants and waters in the paddy fields around a PbZn mine in Korea

The objective of this study is to investigate the extent and degree of heavy metal contamination of paddy fields influenced by metalliferous mining activity. Paddy soils, rice plants and irrigation waters were sampled along six traverse lines in the vicinity of the mine and nearby control site. Soil samples were taken 30, 80 and 150 days after rice transplanting, to study seasonal variation of their chemical properties and heavy metal concentrations. Sampling of rice plants and irrigation waters was also undertaken with seasons. The analysis of the samples were carried out using ICP-AES for 25 elements including Cd, Cu, Pb and Zn. Physical and chemical properties of soils (pH, loss-on-ignition, cation exchange capacity and texture) and waters (pH, Eh and temperature) were also measured. The properties of soils were similar to the average Korean soils, with the exception of some samples taken in the vicinity of the mine. Concentrations of Cd, Cu, Pb and Zn in paddy soils, rice plants and irrigation waters sampled in the immediate vicinity of the mine were relatively high due to the seepage of metals from mining dump sites. Although there was variation between sampling sites, soil pH values under reducing conditions were on average higher than those under oxidising conditions. Relatively low content of organic matter and low cation exchange capacity of soils were found at 80 days after rice transplanting (P < 0.05). No seasonal variations in metal concentrations were found in paddy soils throughout the period of the rice growing, in which soils ranged from flooded reducing conditions through most of the growing season to drained oxidising conditions before and at harvest. Relatively high metal concentrations were found in the rice stalks and leaves under oxidising conditions. The sequential extraction analysis of selected soil samples confirmed that high proportions of exchangeable fractions of the metals were found under oxidising conditions. It was shown that Cd and Zn concentrations in rice leaves and stalks and rice grain increased with increasing metal concentrations in paddy soils to a greater extent than for Cu and Pb. This difference in uptake is in agreement with the greater proportions of Cd and Zn, compared with Cu and Pb, in the exchangeable soil fraction extracted with MgCl₂. Average daily intake from locally grown rice by the residents was estimated to be 121 μg Cd and 126 μg Pb. Thus, long-term metal exposure by regular consumption of the rice poses potential health problems to residents in the vicinity of the mine, although no adverse health effects have as yet been observed.     

Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.     

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: I. Soil ingestion, soil-metal partitioning and potential availability to pasture herbage and livestock

This paper first evaluates the relative importance of the soil-plant-animal and soil-animal pathways of Zn, Cu and (especially) Pb investigated over a 15-month study period at 12 floodplain sites located within and downstream of the mineralised and historic mining area of mid-Wales, and secondly considers the implications of a sequential extraction procedure (SEP) undertaken on soils of varying particle size sampled from the study locations. Generally, very good agreement was found between the chemical partitioning of the three metals for each of the physical soil fractions subjected to the SEP. The availability of Pb to pasture vegetation, especially at the contaminated sites, is indicated with its associations with the more soluble (i.e. exchangeable and Fe/Mn oxide) soil phases, yet soil and/or plant barriers effectively restrict above-ground herbage concentrations of this metal. Consequently, with sheep ingesting soil at rates varying according to season from 0.1% to 44% or more of dry matter intake, the soil-animal pathway accounts for the majority of Pb consumption through most of the year, and at moderately and highly contaminated sites significant quantities of relatively soluble soil-Pb can be ingested at rates exceeding safety threshold limits.