Lead redistribution in a mine soil treated with three manures and incubated at two different temperatures

The study of heavy metals’ redistribution between different fractions allows to know their bioavailability and mobility in soils. Soil samples were collected from a lead mine in Hamadan provinces, NW Iran. In a factorial experiment soil was treated with cow, sheep and poultry manures (20?g?kg^?1 soil) separately and incubated near field capacity at 10°C and 37°C. An untreated soil (as control) was also incubated at the same temperatures. After 0 and 120 days, a sequential extraction scheme was used to fractionate Pb of incubated samples into soluble-exchangeable (Sol-Exch), organic matter associated (AOM), carbonates associated (ACar), and residual (Res) forms. Soil Pb in Sol-Exch and AOM fractions were increased by manure application significantly. The AOM and ACar forms of Pb were higher in soils treated with the manures and incubated in lower temperature. In contrast, the Sol-Exch and Res chemical forms of Pb were higher in the soils incubated at 37°C. These results may be related to the higher calcium carbonate dissolution and organic matter decomposition because of better biological activity in the soils incubated in higher temperature. The increase of the Res fraction (stable form) in this condition may resulted in lower toxicity and mobility in soil environment.     

Mercury contamination in agricultural soils from abandoned metal mines classified by geology and mineralization

Lead (Pb) contents and partition in soils collected from eleven vegetable-growing lands in Fujian Province, China, were investigated using a modification of the BCR (Community Bureau of Reference) sequential extraction procedure coupled with the Pb isotope ratio technique. Pb contents in Chinese white cabbage (B. Chinensis L.) grown on the lands for this study were also measured. Results showed that Pb concentrations in fifty samples of topsoil ranged from 456 to 21.5 mg kg⁻¹, with each mean concentration of six sampling lands exceeding the national standard (50 mg kg⁻¹); while Pb concentrations in edible portions of thirty-two vegetable samples ranged from 0.009 to 2.20 mg kg⁻¹, with four sampling sites exceeding the national sanitary standard (0.2 mg kg⁻¹). A significant correlation (r = 0.971, P < 0.01) of Pb contents in the acid-extractable fractions by BCR approach and the vegetables was observed, which indicates that the acid-extractable Pb is useful for evaluating the metal bioavailability for plants and potential risk for human health in soils. The determination of lead isotope ratios in different chemical forms of soils by BCR sequential extraction procedures provides useful information on the Pb isotopic composition associated with different soil fractions (especially in the acid-extractable fractions), and the result is helpful for the further study on controlling and reducing Pb contamination in vegetable-growing soils.     

The effects of soil properties and temperature on the adsorption isotherms of lead on some temperate and semiarid surface soils of Iran

Sorption of metal ions by soil and clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The aim of this work was to study the retention mechanisms of Pb ions on different soil samples. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with temperate and semiarid climates. The adsorption isotherms of Pb on the soils have been studied at 15, 27 and 37°C. The adsorption data for different soils were fitted into Langmuir and Freundlich models. Temperate soil samples had higher clay content, cation exchange capacity, dichromate (oxidable) organic carbon, total Kjeldahl-nitrogen, biological activity, amorphous and crystalline Fe and Al, but semiarid soil samples had higher sand content, pH, equivalent calcium carbonate, available P and K. Lead adsorption data obtained from semiarid soils against those obtained from temperate soils were better fitted in both Langmuir and Freundlich models. Langmuir constants Q ₀ for Pb adsorption in semiarid soils were considerably lower than those for Pb adsorption in temperate soils. However, the binding energy (K _L) of Pb and Freundlich constant n were higher for data of semiarid soils. The effect of temperature on the Pb adsorption was positive especially in temperate soils; however, soil properties had higher effects on Pb adsorption.     

Seasonal Variations and Chemical Forms of Heavy Metals in Soils and Dusts from the Satellite Cities of Seoul, Korea

This research investigated heavy metal pollution of soils and dusts in two representative satellite cities of Seoul, Korea and studied the seasonal variations in metal concentrations through the rainy season and the chemical forms of metals using a sequential extraction analysis. The metal dispersion pattern was illustrated to match with urban structure. Soil and dust samples were collected from the cities of Uijeongbu and Koyang, which are the northern and northwestern satellite cities of Seoul (the capital), before and after rainy season. Concentrations of Cu, Pb and Zn were higher than those of the world averages for soils, and their levels decreased after rain, particularly in highly contaminated samples. Relatively high pH values were found in roadside soils, but no seasonal variation was found after the rainy season. The three metals (Cu, Pb and Zn) in soils and dusts were associated with various chemical fractions of soils and dusts as distinguished by the sequential extraction scheme, and a strong similarity of metal association between soils and dusts was found, which indicates that airborne dust may be a principle source of soil contamination. Copper is uniformly distributed, and Pb is largely associated with the reducible phase. There is an appreciable proportion of total Zn in the exchangeable/water-acid soluble fraction. After the rainy season, the most soluble fractions in soils and dusts were leached away. In terms of mobility and bioavailability of metals in soils and dusts, the order Zn >> Cu > Pb is suggested. Geographical variations of total metals corresponded well with urbanised areas of cities, especially the industrial complex and major motorways.     

外源铅铜镉在长三角和珠三角农业土壤中的转化

选择了我国经济发达地区的长江三角洲和珠江三角洲10个代表性农业土壤，采用室内培养和化学分级方法研究了加入外源铅、铜、镉在土壤中的动态变化及转化趋势，探讨了碳酸钙、粉煤灰、猪粪和钢渣等土壤改良剂对土壤重金属形态的影响。结果表明，随着土壤重金属负荷的提高，土壤中交换态重金属的比例增大，残余态比例下降，有效性提高，对环境威胁增大。当重金属加入最较低时，重金属优先向氧化物结合态、有机质结合态转化；而当加入最较高时，向交换态和碳酸盐结合态转化的比例明皿增加。pH和土壤组分对重金属在土壤中的转化有显著的影响，土壤pH下降可使交换态Cd、Cu、Pb的比例递增。加入碳酸钙、粉煤灰、猪粪和钢渣等改良剂可显著地降低土壤中交换态重金属比例，增加其它形态的重金属比例。     

污染土壤中有机质结合态重金属的研究

用物理与化学相结合的方法研究了2个污染土壤剖面中有机质结合重金属（Cd、Cu、Pb和Zn）的分布，把有机质相结合态重金属分为颗粒状有机质（POM）结合的重金属和与细土腐殖质结合的重金属。结果表明，土壤POM对重金属有明品的富集作用，其中〉2mmPOM重金属Cd、Cu、Pb和Zn的富集系数分别在1．4～3．2、2．5～2．6、2．8—3．9和3．0～3．9之间；而0．05～2mmPOM重金属Cd、Cu、Pb和Zn的富集系数分别在2．7～7．8、3．2～6．4、3．2～9．3和3．2～5．6之间，0．05～2mmPOM组分中重金属的平均富集高于〉2mmPOM组分。POM中重金属的富集程度与土壤重金属的积累呈正相关。有机质结合态重金属占土壤重金属总最的比例随土壤有机质积累而增高，表土层约40％以上的重金属以有机质结合态存在。     

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH₂OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl₂ extractable fraction. A large proportion of Cu was bound to the acidic H₂O₂ extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier’s procedure, and the order of mobility was Zn > Cd > Cu  > Pb.     

Effects of salinity on the transformation of heavy metals in tropical estuary wetland soil

Tropical estuary wetlands are important for aquaculture and wildlife. However, many of them receive large amounts of anthropogenic heavy metals annually. Here, the transformation of spiked heavy metals, namely, Cd, Cr, Cu, Ni, Pb, and Zn, and the effects of salinity on their transformation in wetland soils after an eight-month-long incubation under moisture-saturation conditions were studied in the Pearl River estuary in China. Cd exhibited high mobility and bioavailability, with 12.2% to 25% Cd existing in the exchangeable fraction. Other heavy metals primarily existed in the reducible and oxidisable forms, and less than 2% were bound to the exchangeable fraction. Compared with the controls, contents of none of the metals associated with residual forms were significantly altered. These results imply that most exchangeable metals, except for Cd, transformed into other stable fractions through an eight-month-long ageing process, but not into the residual fraction. Thus, transformation from non-residual to residual forms was very slow in the tropical estuary wetland environment. Addition of NaCl increased the exchangeable fractions of Cd, Pb, and Zn, suggesting that increased soil salinity induced by flood tides during the dry season may enhance their mobility.     

Lead availability in soils from Portugal’s Centre Region with special reference to bioaccessibility

Previous environmental biomonitoring studies indicated higher environmental lead (Pb) pollution levels at the districts of Aveiro and Leiria (Portugal). In evaluating the risk for human health, which is associated with contaminated soils after oral uptake, total soil concentrations have generally been held against criteria established from toxicological studies based upon the assumption that the uptake of the contaminant is similar in the toxicological studies and from the soils assessed. This assumption is not always valid, as most toxicological studies are carried out with soluble forms of the contaminants, whereas many soil contaminants are or become embedded in the soil matrix and thus exhibit limited availability. This study intends to estimate the soluble fraction of Pb in the soils from central Portugal, and to assess the bioaccessibility of Pb and, hence, infer exposure and risk for human health. Yet, as the physical–chemical properties of the soil exert some control over the solubility of Pb in the surface environment, the relation between such soil properties and the estimated soluble and/or bioaccessible fractions of Pb is also investigated. Other objective, with a more practical nature, was to give some contribution to find a suitable in vitro mimetic of the gastrointestinal tract environment. The results indicate relatively low total metal concentrations in the soils, even if differences between regions were observed. The Aveiro district has the higher total Pb concentration and the metal is in more soluble forms, that is, geoavailable. Soils with higher concentrations of soluble Pb show higher estimates of bioaccessible Pb. Soil pH seems to influence human bioaccessibility of Pb.     

Quantification and fractionation of mercury in soils from the Chatian mercury mining deposit,southwestern China

Contents of total Hg and Hg fraction, organic matter, pH, grain size and chemical composition were measured to investigate the pollution characteristics and binding behavior of Hg in soils collected from the Chatian Hg mining deposit (CMD), southwestern China. The average concentration of Hg concentration in the CMD soils was 155 and 1,315 times higher than that in control soils and Chinese soils, respectively, suggesting that the CMD soils were heavily contaminated by the element. The finding was confirmed by Müller geoaccumulation index assessment with 75% very seriously polluted, 6.25% highly to very highly polluted and 18.75% moderately to highly polluted. Hg sources in the region were natural and anthropogenic: in addition to the pedogenic process and original geochemical situation, human mining–refining activities have also seriously impacted the redistribution of Hg in soils, especially in paddy soils. Based on the BCR protocol, soil Hg was divided into exchangeable (EXC), amorphous Fe–Mn oxides (AFe–MnOX), organic-crystalline iron oxides (OM-CFe) and residual (RES) fraction. The average percentage of the four fractions in the CMD followed the trend: RES (85.77%) > OM-CFe (12.44%) > AFe–MnOX (0.93%) ≥ EXC (0.86%), suggesting that the majority proportion of soil Hg in the study area remained of residual form inside the soil mineral matrix. However, their concentrations and percentages significantly varied among different locations and land use types. Soil physico-chemical parameters were key factors affecting the presence of Hg fraction. Generally, Hg fraction concentrations were positively correlated with the sand contents and soil pH values, which was presumably due to the basic anthropogenic input of Hg-containing materials and their similarity to sand in physical characteristics. However, organic matter caused adsorption–fixation and reduction–volatilization to coexist, which had opposite effects on Hg concentrations in soil, consequently exhibiting its dual nature.     

Metal fractionation of cadmium, lead and arsenic of geogenic origin in topsoils from the Marrancos gold mineralisation, northern Portugal

The Marrancos gold mineralisation has a chemical assemblage of Fe–As–Se–Bi–Au–Ag–Te–(Cu–Pb–Zn–Sn–W). The −200 mesh of 144 topsoil samples was analysed by ICP–MS to determine total contents of 53 elements that include potentially harmful elements like Cd, As and Pb. The soil geochemistry shows that some trace elements occur in considerably high concentrations. On the basis of data for total metal concentrations, 10 topsoil samples were selected to carry out a metal fractionation study using a selective extraction method. A set of four leaches of increasing strength was used sequentially in the soil samples. Across the study area, there is some evidence of past mining and exploration activity, indicating that these soils may be locally disturbed. The shallow mineralised quartz veins were exploited for gold by the Romans. Several galleries were constructed during the 2nd World War, probably for the exploration of quartz–cassiterite–wolframite veins. However, the main mineralised body in depth was never explored. The results of metal fractionation show different partitions for the three elements. Total Cd concentrations in these soils are low, with a median value of 0.1 mg/kg. In average, 12% of total Cd is adsorbed by clays and/or co-precipitated with carbonates, and 19% is bounded to Fe–Mn oxyhydroxides. However, the low concentrations indicate that the metal does not represent an immediate risk to human health. For Pb, metal fractionation shows that, on average, 22% of Pb is adsorbed by amorphous Fe and Mn oxides, but the samples from the northern part of the area have the major fractions of Pb in soluble forms. The low probability of exposure in this part of the study area decreases the risk posed by this heavy metal. Total As concentrations in the Marrancos soils are extremely high. A large area has As concentrations above 1,000 mg/kg. For As, metal fractions in the sulphide phase vary between 84 and 98% in the studied samples. But one sample has 20% of total As in easily reducible forms, corresponding to a partial concentration of 1,800 mg/kg that has a high probability of being bioavailable. The most labile As forms occur at the southern part of the area, where the probability of exposure is higher and the risk of human health increases in the same order. From the three studied potentially harmful elements, As is certainly the element of concern.     

Assessment of bioaccessibility and exposure risk of arsenic and lead in urban soils of Guangzhou City,China

Soil ingestion is an important human exposure pathway of heavy metals in urban environments with heavy metal contaminated soils. This study aims to assess potential health risks of heavy metals in soils sampled from an urban environment where high frequency of human exposure may be present. A bioaccessibility test is used, which is an in vitro gastrointestinal (IVG) test of soluble metals under simulated physiological conditions of the human digestion system. Soil samples for assessing the oral bioaccessibility of arsenic (As) and lead (Pb) were collected from a diverse range of different land uses, including urban parks, roadsides, industrial sites and residential areas in Guangzhou City, China. The soil samples contained a wide range of total As (10.2 to 61.0 mg kg⁻¹) and Pb (38.4 to 348 mg kg⁻¹) concentrations. The bioaccessibility of As and Pb in the soil samples were 11.3 and 39.1% in the stomach phase, and 1.9 and 6.9% in the intestinal phase, respectively. The As and Pb bioaccessibility in the small intestinal phase was significantly lower than those in the gastric phase. Arsenic bioaccessibility was closely influenced by soil pH and organic matter content (r ² = 0.451, p < 0.01) in the stomach phase, and by organic matter, silt and total As contents (r ² = 0.604, p < 0.001) in the intestinal phase. The general risk of As and Pb intake for children from incidental ingestion of soils is low, compared to their maximum doses, without causing negative human health effects. The exposure risk of Pb in the soils ranked in the order of: industrial area/urban parks > residential area/road side. Although the risk of heavy metal exposure from direct ingestion of urban soils is relatively low, the risk of inhalation of fine soil particulates in the air remains to be evaluated.     

Phosphates for Pb immobilization in soils: a review

In its soluble ionic forms, lead (Pb) is a toxic element occurring in waters and soils mainly as the result of human activities. The bioavailability of lead ions can be decreased by complexation with various materials in order to decrease their toxicity. Pb chemical immobilization using phosphate addition is a widely accepted technique to immobilize Pb from aqueous solution and contaminated soils. The application of different P amendments cause Pb in soils to shift from forms with high availability to the most strongly bound Pb fractions. The increase of Pb in the residual or insoluble fraction results from formation of pyromorphite Pb₅(PO₄)₃X where X = F, Cl, Br, OH, the most stable environmental Pb compounds under a wide range of pH and Eh natural conditions. Accidental pyromorphite ingestion does not yield bioavailable lead, because pyromorphite is insoluble in the intestinal tract. Numerous natural and synthetic phosphates materials have been used to immobilize Pb: apatite and hydroxyapatite, biological apatite, rock phosphate, soluble phosphate fertilizers such as monoammonium phosphate, diammonium phosphate, phosphoric acid, biosolids rich in P, phosphatic clay and mixtures. The identification of pyromorphite in phosphate amended soils has been carried out by different non destructive techniques such as X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray absorption fine structure, transmission electron microscopy and electron microprobe analysis. The effectiveness of in situ Pb immobilization has also been evaluated by selective sequential extraction, by the toxicity leaching procedure and by a physiologically based extraction procedure simulating metal ingestion and gastrointestinal bioavailability to humans. Efficient Pb immobilization using P amendments requires increasing the solubility of the phosphate phase and of the Pb species phase by inducing acid conditions. Although phosphorus addition seems to be highly effective, excess P in soil and its potential effect on eutrophication of surface water, and the possibility of As enhanced leaching remains a concern. The use of mixed treatments may be a useful strategy to improve their effectiveness in reducing lead phyto- and bioavailability.     

Bioavailability of trace metals in brownfield soils in an urban area in the UK

Thirty-two brownfield sites from the city of Wolverhampton were selected from those with a former industrial use, wasteland or areas adjacent to industrial processes. Samples (<2 mm powdered soil fraction) were analysed, using inductively coupled plasma–atomic emission spectrometry (ICP–AES) for 20 elements. Loss on ignition and pH were also determined. A five-step chemical sequential extraction technique was carried out. Single leach extraction with 0.12 M hydrochloric acid of Pb, Cu and Zn in soil was determined as a first approximation of the bioavailability in the human stomach. Some of the sites were found to have high concentrations of the potentially toxic elements Pb, Zn, Cu and Ni. The partitioning of metals showed a high variability, however a number of trends were determined. The majority of Zn was partitioned into the least chemically stable phases (steps 1, 2 and 3). The majority of Cu was associated with the organic phase (step 4) and the majority of Ni was fractionated into the residue phase (step 5). The majority of Pb was associated with the residue fraction (step 5) followed by Fe–Mn oxide fraction (step 3). The variability reflects the heterogeneous and complex nature of metal speciation in urban soils with varied historic histories. There was a strong inverse linear relationship between the metals Ni, Zn and Pb in the readily exchangeable phase (step 1) and soil pH, significant at P < 0.01 level. There was a significant increase (P < 0.05) in the partitioning of Cu, Ni and Zn into step 4 (the organic phase) in soils with a higher organic carbon content (estimated by loss on ignition). Copper was highly partitioned into step 4 as it has a strong association with organics in soil but this phase was not important for the partitioning of Ni or Zn. The fractionation of Ni, Cu and Zn increased significantly in step 3 when the total metal concentration increases (P < 0.01). The Fe–Mn oxide fraction becomes more important in soils elevated in these metals, possibly due to the scavenging of metals by oxides. Cu and Pb extracted by HCl was statistically similar to the sum of the metals in steps 1 to 4 (P < 0.01) and HCl available Zn was statistically similar to the sum of Zn in steps 1 to 3 (P < 0.01). Step 4 (the organic phase) was not an important phase for Zn, so it was concluded that any Cu, Zn and Pb present in soil in a nonresidue phase would be potentially available for uptake into the human system once soil has been ingested.     

Geochemical distribution,bioavailability and potential toxicity of some trace metals in a complex micro-tidal estuary,Southwest India

The spatial and temporal variations of some trace metals in the surface sediments of Cochin Estuary were analyzed along with their geochemical associations to identify the possible sources, bioavailability and the health risks posed by them. The dominance of kaolinite and suggested that clay minerals distribution is influenced by sediment sorting. Total metal analysis revealed enrichment for Cd, Pb and Zn due to anthropogenic activities. The speciation analysis established that notwithstanding the large availability, carbonate as well as organic and sulfides bound fractions showed negligible associations with most of the metals. Hydrous Fe–Mn oxides appeared to play a major role in controlling the fate and transport of these metals in the sediments of Cochin Estuary. Lower contribution of the residual fractions for Cd (21%–26%), Pb (<60%) and Zn (24%–42%) indicated an obvious increase of other geochemical fractions. Risk assessment analysis revealed that regardless of total concentration, none of the analyzed metals were at safe levels in the estuary as appreciable percentages were found to be associated with mobile geochemical forms. The speciation study conspicuously established that the metals originating from non-geogenic sources are largely associated with the labile fractions and hence are more detrimental to the aquatic biota.     

Assessing geochemical influence of traffic and other vehicle-related activities on heavy metal contamination in urban soils of Kerman city,using a GIS-based approach

Heavy metal pollution caused by traffic activities is increasingly becoming a great threat to urban environmental quality and human health. In this paper, soils of Kerman urban and suburban areas were collected to assess the potential effects of traffic and other vehicle-related pollution by heavy metal accumulation in soils. Eighty-six samples were collected along streets and from residential and rural sectors, as well as vehicle-related workshops from depth of 0–5 and 15–20 cm and analyzed by flame atomic absorption spectrometry (FAAS) for heavy metals (Cd, Cr, Cu, Pb, Sn and Zn), as well as major elements (Al, Ca, Fe and Mn). Several hot-spot areas were identified in the composite geochemical maps produced based on Geographical Information System (GIS) technology. The majority of the hot-spot areas were identified to be vehicle-related workshops, fuel stations and road junctions. The most polluted hot-spot in the study area was located in soils close to a car battery processing workshop in the southwestern part of Kerman city, with concentrations of Cd (0.32 mg/kg), Cr (169 mg/kg), Cu (250 mg/kg), Pb (5,780 mg/kg), Sn (27.2 mg/kg) and Zn (178 mg/kg) of 1, 8.5, 8.3, 230, 13.5 and 3 times more than the relevant mean concentrations in natural soils, respectively. Traffic pollution has resulted in significant accumulation of heavy metals in soils and sediments, and that level of accumulation varied remarkably among elements. Based on X-ray diffraction analysis, most parts of soils and sediments of the Kerman basement consist of calcite and clay minerals. Abundance of clay minerals and medium to alkaline pH causes low mobility of heavy metals in soils of Kerman.     

Distribution of contaminant trace metals inadvertently provided by phosphorus fertilisers: movement,chemical fractions and mass balances in contrasting acidic soils

The frequent use of phosphorus (P) fertilisers accompanied by nitrogen and potassium sources may lead to a serious long-term environmental issue because of the presence of potentially hazardous trace metals (TM) in P fertilisers and unknown effects on the TM chemical fractions in agricultural soils. A 16-month-long column experiment was conducted to investigate the mobility and chemical forms of Cd, Cu, Cr, Ni, and Zn introduced into a Mollisol and an Andisol through surface incorporation (0–2 cm) of triple superphosphate (TSP) fertiliser. The effects of urea and potassium chloride (KCl) applications were investigated as well. After 15 cycles of 300-mm irrigation, TSP addition increased the 4 M HNO₃ extractable TM concentration in the upper (0–5 cm) section of soils. Beyond this depth, metals showed no significant mobility, with minimal leaching losses (<?1.9%, 25-cm depth). The TM chemical forms in the 0–5 cm section were significantly (p?<?0.01) affected by the soil type and fertilisers addition. Cadmium, Ni, and Zn were the elements which appeared in a larger proportion (up to 30%) in the most labile fraction (KNO₃ extractable) in fertilised soils. The impact of urea depended on the nitrification-related changes in soil pH, while fertilisation with KCl tended to increase the KNO₃ fraction of most metals probably due to K⁺ exchange reactions. Chromium remained minimally affected by the urea and KCl applications since this contaminant is strongly bound to the less labile solid phases. The low mobility of TM was governed mainly by their interaction with the solid phases rather than by their speciation at soil pH. The mass balance showed that the geochemical processes underwent in time by the P fertiliser increased the amount of TM extracted by the chemical fractionation scheme, therefore the reaction period of TSP with soil particles should be taken into account for evaluating TM availability. Long-term soil fertilisation could inadvertently contribute to an increased concentration and availability of these P fertilisers-born contaminants in the cultivated layer of acidic soils.     

Assessing Cd,Pb, Zn human bioaccessibility in smelter-contaminated agricultural topsoils (northern France)

The extractability of Cd, Pb, and Zn was investigated in contaminated agricultural topsoils located in an area highly affected by the past atmospheric emissions of two smelters in northern France in order to assess their mobility and human bioaccessibility. The determination of Cd, Pb, and Zn bioaccessibility (Unified Barge Method, in vitro test) was made to evaluate the absolute trace element (TE) bioavailability. The results highlighted differences in bioaccessibility between Cd, Pb, and Zn (Cd > Pb > Zn). The mean values of the bioaccessible fractions of Cd, Pb, and Zn during the gastric phase were 82, 55, and 33%, respectively, of the pseudototal concentrations, whereas during the gastrointestinal phase, the bioaccessible fractions of metals decreased to 45, 20, and 10%, respectively. Stepwise multiple regression analysis showed that human bioaccessibility was affected by various physicochemical parameters (i.e., sand, carbonates, organic matter, assimilated P, free Al oxides, and pseudototal Fe contents). Sequential extractions were performed as an indication of the TE availability in these soils. Cadmium occurred in the more available fractions, Pb was mostly present as bound by oxides, and a significant contribution to the pseudototal Zn concentration was defined as the unavailable residual form related to the crystalline structures of minerals. The concepts of bioavailability and bioaccessibility are important for quantifying the risks associated with exposure to environmental pollutants and providing more realistic information for human health.     

Environmental impact of historical harbour city Zadar (Croatia) on the composition of marine sediments and soils

Large amounts of oyster shells are produced as a by-product of shellfish farming in coastal regions without beneficial use options. Accordingly, this study was conducted to evaluate the potential for the use of waste oyster shells (WOS) containing a high amount of CaCO₃ to improve soil quality and to stabilize heavy metals in soil. To accomplish this, an incubation experiment was conducted to evaluate the ability of the addition of 1–5 wt% WOS to stabilize the Pb (total 1,246 mg/kg) and Cd (total 17 mg/kg) in a contaminated soil. The effectiveness of the WOS treatments was evaluated using various single extraction techniques. Soil amended with WOS was cured for 30 days complied with the Korean Standard Test method (0.1 M·HCl extraction). The Pb and Cd concentrations were less than the Korean warning and countermeasure standards following treatment with 5 wt% WOS. Moreover, the concentrations of Cd were greatly reduced in response to WOS treatment following extraction using 0.01 M·CaCl₂, which is strongly associated with phytoavailability. Furthermore, the soil pH and exchangeable Ca increased significantly in response to WOS treatment. Taken together, the results of this study indicated that WOS amendments improved soil quality and stabilized Pb and Cd in contaminated soil. However, extraction with 0.43 M·CH₃COOH revealed that remobilization of heavy metals can occur when the soil reaches an acidic condition.     

The influence of physicochemical parameters on bioaccessibility-adjusted hazard quotients for copper,lead and zinc in different grain size fractions of urban street dusts and soils

When the hazard quotient for ingestion (HQI) of a trace element in soil and dust particles is adjusted for the element’s bioaccessibility, the HQI is typically reduced as compared to its calculation using pseudo-total element concentration. However, those studies have mostly used bulk particles (<2 mm or <250 µm), and the reduction in HQI when expressed as bioaccessible metal may not be similar among particle size fractions, the possibility probed by the present study of street dusts and soils collected in Tehran. The highest Cu, Pb and Zn near-total concentrations occurred in the finest particles of dusts and soils. Bioaccessible concentrations of Cu, Pb and Zn in the particles (mg kg^?1) were obtained using simple bioaccessibility extraction test (SBET). The bioaccessibility (%) did not vary much among near-total concentrations. In the bulk (<250 µm) sample, the bioaccessible concentration of Cu and Pb increased as the pH of sample increased, while Zn bioaccessibility (%) in the bulk particles was influenced by organic matter and cation exchange capacity. X-ray diffraction identified sulfide and sulfate minerals in all of the size-fractionated particles, which are insoluble to slightly soluble in acidic conditions and included most of the Cu and Pb in the samples. The only Zn-bearing mineral identified was hemimorphite, which would be highly soluble in the SBET conditions. The calculated HQI suggested potential non-carcinogenic health risk to children and adults from ingestions of soils and dusts regardless of particle size consideration, in the order of Zn > Pb ≥ Cu. The HQI calculated from near-total metal was not much different for particle size classes relative to bulk particles; however, the bioaccessibility percent-adjusted HQI for Pb was higher for the smaller particles than the bulk. This work is novel in its approach to compare HQI for a bulk sample of particles with its composite particle size fractions.