The environmental fate of thymol,a novel botanical pesticide,in tropical agricultural soil and water

In this study, the environmental fate of thymol, including hydrolysis, aqueous photolysis, soil sorption and soil degradation, was studied under conditions that simulated the tropical agricultural environment. This study was undertaken to supply basic information for evaluating the environmental risks of applying this new botanical pesticide to tropical crop production. The results showed that the hydrolysis of thymol was pH-dependent and accelerated by acidic conditions and high temperatures. However, the hydrolysis rate was far lower than the aqueous photolysis rate, indicating that direct photolysis is an important dissipation pathway for thymol in water. The sorption of thymol by three tropical soils was consistently well described by the Freundlich model, and the sorption coefficients increased in the order sandy soil < loamy soil < clay soil, a characterization that depended on the organic carbon contents of the soil. The soil degradation rate of thymol decreased in the order sandy soil > loamy soil > clay soil, which has a negative correlation with the sorption of thymol in soils. We concluded that the degradation rates of thymol in tropical soil and water are fast: thymol in water is photodegraded (50%) by sunlight within 28 h, and the thymol in soils is degraded (50%) within 8.4 d. Therefore, the environmental risk to the surrounding soils and water of thymol application for tropical crop production is low.     

Influence of humic acid on the sorption of uranium(IV) to kaolin

Safety assessments for radioactive waste disposal require estimations of the migration of radionuclides in soils. The influence of humic acid (HA) on the sorption of uranium in its +4 oxidation state to kaolin has been examined from pH 4 to 8, with HA concentrations of 15–200 ppm. In the absence of HA, 20–40% of the U(IV) was in solution, with more sorption occurring at higher pH. The presence of HA solubilised up to 90% of the uranium with higher solubilities at higher HA concentrations and higher pH values. Uranium sorption was mapped against HA sorption, and it was found that there was a lower level of U(IV) sorption than can be accounted for by just measuring HA sorption. However, this effect got less marked as the pH rose. Sensitivity analysis indicated that the fraction of surface-bound HA is the controlling parameter for modelling in these systems.     

Field Studies on 32P Movement and P Leaching from Flooded Paddy Soils in the Region of Taihu Lake, China

Field experiments were done in two sites, Yixing and Changshu, Jiangsu province, China, to study P movement and leaching in flooded paddy soils. P movement in soil was investigated by using the KH₂ ³²PO₄ tracker method, and the amount of P leached from the soil layer in different depths was estimated by measuring P concentrations in the soil solution and saturated hydraulic conductivities in field. Determination was done about one month after P application. There was 46% and 42% of total ³²P retained in the 0–5cm layer of soil in the Yixing site and in the Changshu site respectively. The ³²P retained in the 25–30 cm layer was only about 1–2% of the total ³²P added. Furthermore, 8.01% of ³²P in the soil of Yixing site and 16.8% of ³²P in the soil of Changshu site was lost from the layer 0–30cm soil. The seasonal amounts of P leached from the top soil layer and from bottom layer are about 4.5–5.8% and 1.6–2.1% of the total P application, respectively. Changes of total P concentrations in soil solutions during rice growth showed that the fertilizer P applied before flooding of the paddy fields suffered a flash leaching loss and a slow leaching loss. We concluded that the fertilizer P could quickly move in the flooded paddy rice field and parts of it can enter into surface water and ground water. Unless the P application is well managed the risk of P loss and consequently environmental pollution exist.     

Phenanthrene adsorption by soils treated with humic substances under different pH and temperature conditions

The mobility of phenanthrene (PHE) in soils depends on its sorption and is influenced by either the existing soil humus or exogenous humic substances. Exogenous humic acids (HAs) were added to soil to enhance the amount of soil organic carbon (SOC) by 2.5, 5.0, and 10.0 g kg⁻¹. PHE desorption of the treated soils was determined at two pH levels (3.0 and 6.0) and temperatures (15 and 25 °C). Soil PHE adsorption was related to pH and the type and quantity of added HAs. Humic acid (HA) and fulvic acid (FA) derived from peat had different effects on adsorption of PHE. Adsorption increased at first and then decreased with increasing quantity of exogenous FA. When the soil solution pH (in 0.005 M CaCl₂) was 4.5 or 3.0, the turning points were 2.5 g FA kg⁻¹ at pH 3.0 and 5 g FA kg⁻¹ at pH 4.5. When soil solution pH was 6, the amount of adsorbed PHE was enhanced with increasing exogenous HAs (HA or FA) and amount of adsorption by soil treated with FA was higher than with HA. Adsorption of PHE in the FA treatment at 10.0 g kg⁻¹ was lower than the controls (untreated soil or treatment with HAs at 0 g kg⁻¹) when the soil solution pH was 3.0. This suggests that FA adsorbed by soil was desorbed at low pH and would then increase PHE solubility, and PHE then combined with FA. PHE adsorption was usually higher under lower pH and/or lower temperature conditions. PHE sorption fitted the Freundlich isotherm, indicating that exogenous humic substances influenced adsorption of phenanthrene, which in turn was affected by environmental conditions such as pH and temperature. Thus, exogenous humic substances can be used to control the mobility of soil PAHs under appropriate conditions to decrease PAH contamination.     

农田重金属污染原位钝化修复研究进展

污染土壤重金属原位钝化修复是通过向土壤中施加一些活性钝化修复材料,通过溶解沉淀、离子交换吸附、氧化还原、有机络合等反应来改变重金属在土壤中的赋存状态,降低土壤中重金属的有效浓度、迁移性和生物有效性。这种方法成本较低、操作简单、见效快且适合大面积推广,在重金属污染土壤修复中有着不可替代的作用。尤其对主要由污水灌溉、大气沉降等造成的农田土壤面源污染,一些具有吸附固定土壤中重金属离子特性的天然物质和工业副产品都可运用在实地的钝化修复中,且不同类型的钝化修复剂对重金属污染土壤的钝化修复效果各不相同。采用实验室评价和实地应用评价,一方面可以评估钝化修复材料对污染土壤中重金属离子的固定效率;另一方面可以评估钝化修复材料对土壤理化性状、养分状况和生物活性的影响。对重金属污染土壤原位钝化修复中不同来源的钝化剂进行了分类,目前广泛使用的钝化修复剂主要包括硅钙物质、含磷材料、有机物料、黏土矿物、金属及金属氧化物、生物碳及新型材料等,概述了它们各自对重金属污染土壤的钝化修复效果。从研究方法、评价指标、环境影响因子、钝化机制以及环境风险评价等方面分析了该领域的研究现状以及存在的主要问题,今后应重点关注钝化修复剂对土壤-作物系统的潜在环境风险以及钝化材料修复效果的田间长期稳定性评价。     

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.     

Biogeochemical transfer and dynamics of iodine in a soil–plant system

Radioactive iodide (¹²⁵I) is used as a tracer to investigate the fate and transport of iodine in soil under various leaching conditions as well as the dynamic transfer in a soil–plant (Chinese cabbage) system. Results show that both soils (the paddy soil and the sandy soil) exhibit strong retention capability, with the paddy soil being slightly stronger. Most iodine is retained by soils, especially in the top 10 cm, and the highest concentration occurs at the top most section of the soil columns. Leaching with 1–2 pore volume water does not change this pattern of vertical distributions. Early breakthrough and long tailing are two features observed in the leaching experiments. Because of the relatively low peak concentration, the early breakthrough is really not an environmental concern of contamination to groundwater. The long tailing implies that the retained iodine is undergoing slow but steady release and the soils can provide a low but stable level of mobile iodine after a short period. The enrichment factors of ¹²⁵I in different plant tissues are ranked as: root > stem > petiole > leaf, and the ¹²⁵I distribution in the young leaves is obviously higher than that in the old ones. The concentrations of ¹²⁵I in soil and Chinese cabbage can be simulated with a dual-chamber model very well. The biogeochemical behaviors of iodine in the soil-cabbage system show that cultivating iodized cabbage is an environmentally friendly and effective technique to eliminate iodine deficiency disorders (IDD). Planting vegetables such as cabbage on the ¹²⁹I-contaminated soil could be a good remediation technique worthy of consideration.     

Aluminum fractionation in acidic soils and river sediments in the Upper Mero basin (Galicia,NW Spain)

This study aims to determine aluminum fractions in the fine earth of acidic soils under different land uses (forest, pasture and cultivation) and in the river bed sediments of the headwater of the Mero River in order to identify and quantify Al-bearing phases to assess Al mobility and potential bioavailability (environmental availability) in the monitoring area. Sequential extraction is used to evaluate the Al partitioning into six fractions operationally defined: soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, aluminum bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction (aluminum within the crystal lattices of minerals). The mean concentration of total aluminum (24.01 g kg^?1) was similar for the three considered uses. The mean percentage of the aluminum fractions, both in soils and sediments, showed the following order: residual fraction ? amorphous compounds ≈ crystalline iron oxides > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter ≈ Mn oxides. However, in the soils, the amorphous compounds and water-soluble/exchangeable/specifically adsorbed fraction showed considerable differences between some types of uses, the percentage of aluminum linked to amorphous compounds being higher in forest soils (16% of total Al) compared to other uses (mean about 8% of total Al). The highest values of water-soluble/exchangeable/specifically adsorbed Al were also found in forest soils (mean 8.6% of the total Al versus about 4% of pasture and cultivation), which is consistent with the lower pH and higher organic matter content in forest soils. Nevertheless, the potentially bioavailable fraction (sum of the first three fractions) is low, suggesting very low geoavailability of this element in both soils and sediments; hence, the possibility to affect the crops and water quality is minimal.     

Elucidation of phosphorous sorption by calcareous soils using principal component analysis

This study was conducted to understand the mechanisms governing P-sorption and desorption by calcareous soils (up to 48% CaCO ₃). Batch experiments with KCl as background were carried out by adding varying amount of P up to 100 mgP.L^?1. The desorption percentage (%DES) results show that little P was released from the adsorbed phase. Principal component analysis was applied to evaluate the combined influence of soil components on P sorption. The complex P sorption process can be related to specific soil components by the following equation: P? sorption=?2.20 (CaCO ₃% )?0.04 (Fe? oxide)+0.04 (pHe)+11.02 (sand % )+3.35 (silt)?10.73 (clay)?1.24 (EC)?0.22 (OM)?0.81 (CEC)?1.93 (P? Olsen) (R²=0.9941, SSE=380). Sand% and clay% are the most significant variables for modelling P sorption data. The derived equation could be applied to predict P sorption in other soils that have similar compositions to those investigated herein. The degree of P saturation (DPS) threshold level for all soils was less than 3% except in the soil with the lowest iron oxide. All of the studied soils have exceeded the environmentally unacceptable P concentration except the soil with the lowest iron oxide content.     

Sorption and bioavailability of arsenic in selected Bangladesh soils

The bioavailability of arsenic (As) in the soil environment is largely governed by its adsorption–desorption reactions with soil constituents. We have investigated the sorption–desorption behaviour of As in four typical Bangladeshi soils subjected to irrigation with As-contaminated groundwater. The total As content of soils (160 samples) from the Laksham district ranged from <0.03 to approximately 43 mg kg⁻¹. Despite the low total soil As content, the concentration of As in the pore water of soils freshly irrigated with As-contaminated groundwater ranged from 0.01 to 0.1 mg l⁻¹. However, when these soils were allowed to dry, the concentration of As released in the pore water decreased to undetectable levels. Remoistening of soils to field moisture over a 10-day period resulted in a significant (up to 0.06 mg l⁻¹) release of As in the pore water of soils containing >10 mg As kg⁻¹ soil, indicating the potential availability of As. In soils containing <5 mg As kg⁻¹, As was not detected in the pore water. A comparison of Bangladeshi soils with strongly weathered long-term As-contaminated soils from Queensland, Australia showed a much greater release of As in water extracts from the Australian soils. However, this was attributed to the much higher loading of As in these Australian soils. The correlation of pore water As with other inorganic ions (P, S) showed a strongly significant (P < 0.001) relationship with P, although there was no significant relationship between As and other inorganic cations, such as Fe and Mn. Batch sorption studies showed an appreciable capacity for both As^V and As^III sorption, with As^V being retained in much greater concentrations than As^III.     

Is there a relationship between soil and groundwater toxicity?

Part IIA of the Environmental Protection Act 1990 requires environmental regulators to assess the risk of contaminants leaching from soils into groundwater (DETR, 1999). This newly introduced legislation assumes a link between soil and groundwater chemistry, in which rainwater leaches contaminants from soil into the saturated zone. As the toxicity of both groundwater and overlying soils is dependent upon the chemicals present, their partitioning and their bioavailability, similar patterns of soil, leachates and groundwater toxicity should be observed at contaminated sites. Soil and groundwater samples were collected from different contaminated land sites in an urban area, and used to determine relationships between soil chemistry and toxicity, mobility of contaminants, and groundwater chemistry and toxicity. Soils were leached using water to mimic rainfall, and both the soils and leachates tested using bioassays. Soil bioassays were carried out using Eisenia fetida, whilst groundwater and leachates were tested using the Microtox test system and Daphnia magna 48 h acute tests. Analysis of the bioassay responses demonstrated that a number of the samples were toxic to test organisms, however, there were no significant statistical relationships between soil, groundwater and leachate toxicity. Nor were there significant correlations between soil, leachates and groundwater chemistry.     

除草剂苯噻草胺在土壤中的吸附

对除草剂苯噻草胺在6种不同土壤中的吸附行为进行了研究。结果表明,土壤对苯噻草胺有较强的吸附性。在试验浓度范围内,苯噻草胺的土壤吸附行为可用线性吸附模型表征。土壤有机质是影响苯噻草胺吸附行为的重要因素,其吸附系数有随土壤有机质含量增高而增大的趋势。通过在线性吸附系数（Kd)和土壤有机质含量（OM％）之间构建的回归方程：Kd=2.6120 OM% 1.0746,可以预测苯噻草胺的Kd值,其预测的可靠性通过蒙特卡洛模拟得以检验。     

Effect of natural organic matter on arsenic release from soils and sediments into groundwater

Arsenic (As) contamination in groundwater has received significant attention recently. Natural and anthropogenic sources contribute to the worldwide occurrence of As contamination. As speciation is an important factor related to its toxic and mobile behavior. The release of As from soils and sediments into groundwater is governed by several geophysicochemical processes, of which, As sorption behavior is of principle significance. This review paper summarizes existing information regarding the effects of natural organic matter (NOM) on the fate and mobility of As species in the environment. NOM may enhance the release of As from soils and sediments into the soil solution, thereby facilitating As leaching into the groundwater. The main influencing mechanisms include competition for available adsorption sites, formation of aqueous complexes, and/or changes in the redox potential of site surfaces and As redox speciation. NOM may also serve as binding agents, thereby reducing As mobility. However, comparably little research has been performed on this aspect. Since most investigations have been done on purified minerals under laboratory conditions, further research involving various geological materials under natural environmental conditions is required. Development of proper geochemical conceptual models may provide means of predicting the role of NOM in arsenic leaching and/or immobilization.     

Sorption and desorption of pymetrozine on six Chinese soils

Pymetrozine is a selective insecticide with a unique chemical structure and mode to control hemipteran and homopteran. While pymetrozine has brought great benefits to crop production by killing insects, its residues in soil may have a detrimental effect on environment. Therefore, it is of great importance to investigate its behaviors in soil. In this study, the sorption and desorption of pymetrozine on six Chinese soils were investigated using a batch equilibrium approach to understand its mobile behavior in the soils. Both sorption and desorption isotherms of pymetrozine were in good agreement with the Freundlich model. The sorption coefficient K_F varied between 3.37 and 58.32 mL∙g⁻¹ and the sorption isotherms were nonlinear, with 1/n ranging from 0.57 to 0.91. A regression equation was proposed to predict the sorption of pymetrozine on six different soil samples: log K_F = 4.3708 − 4.5709 × log (pH in 0.01mol·L⁻¹ CaCl₂) + 0.4700 × log OC% + 0.0057 × sand (%) + 0.0022 × CEC(clay), with R² = 0.9982. The organic carbon content of soil positively affected the sorption of pymetrozine, but soil pH had a negative effect on the sorption. Additionally, effects of CaCl₂ concentration, soil to solution ratio and pesticide form were investigated. The sorption was promoted with an increase in soil to solution ratio and a decrease in CaCl₂ concentration. The possible variation of the five formulated products of pymetrozine was also investigated.     

Antioxidant enzyme activities of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in response to nonylphenols and degradation of nonylphenols by <Emphasis Type="Italic">M. aeruginosa</Emphasis>

The aim of this study was to examine the effects of chemical nonylphenols (NPs) on the antioxidant system of Microcystis aeruginosa strains. The degradation and sorption of NPs by M. aeruginosa were also evaluated. High concentrations of NPs (1 and 2 mg/l) were found to cause increases in superoxidase dismutase (SOD) and glutathione-S-transferase (GST) activities and in glutathione (GSH) levels. These results suggest that toxic stress manifested by elevated SOD and GST levels and GSH contents may be responsible for the toxicity of NPs to M. aeruginosa and that the algal cells could improve their antioxidant and detoxification ability through the enhancement of enzymatic and nonenzymatic prevention substances. The observed elevations in GSH levels and GST activities were relatively higher than those in SOD activities, indicating that GSH and GST contributed more in eliminating toxic effects than SOD. Low concentrations of NPs (0.05–0.2 mg/l) enhanced cell growth and decreased GST activity in algal cells of M. aeruginosa, suggesting that NPs may have acted as a protecting factor, such as an antioxidant. The larger portion of the NPs (>60%) disappeared after 12 days of incubation, indicating the strong ability of M. aeruginosa to degrade the moderate persistent NP compounds. The sorption ratio of M. aeruginosa after a 12-day exposure to low nominal concentrations of NPs (0.02–0.5 mg/l) was relatively high (>30%). The fact that M. aeruginosa effectively resisted the toxic effects of NPs and strongly degraded these pollutants indicate that M. aeruginosa cells have a strong ability to adapt to variations in environmental conditions and that low and moderate concentrations of organic compounds may favor its survival. Further studies are needed to provide detailed information on the fate of persistent organic pollutants and the survival of algae and to determine the possible role of organic pollutants in the occurrence of water blooms in eutrophic lakes.     

Geochemical speciation of trace metals in sediments of the northern Nile Delta Lake by sequential extraction technique

ABSTRACT

The present study was performed to investigate surface sediment samples from Lake Edku of the Nile Delta Lagoons, Egypt. The Lake is important for fishing in the region. The importance of research is to understand the mobility and bioavailability of each studied metal. The study was carried out on 10 sampling sites during 2017. The sediments were subjected to the technique of sequential extraction to examine the chemical forms of some trace metals (Fe, Mn, Zn, Cu, Pb and Ni). Five stage extractions were done as the following order: soluble and exchangeable, carbonate, iron and manganese oxides, organic matter fraction and residual fraction. Attained results from the five fractions showed variations in the concentrations of metal contents of different sites under study. The overall metal concentrations (%) in the initial four extractable fractions (exchangeable, carbonate, oxides and organic matter fractions) were assessed to configure the mobility of each studied metal. The risk assessment code (RAC) represents the summation of exchangeable and carbonate fractions, it was between low and medium risk for aquatic environment. The range percentage of RAC for the metals was in the following order: 1.8–13, 4–23.5, 15–26, 5.7–19.5, 9–25 and 4.8–18.2 for Fe, Mn, Zn, Cu, Pb and Ni, respectively. Approximately 30% of the total copper was associated to the organic fraction, which may represent a high mobility of copper in these sediments. The highest mobility of metals in the sediments could be confirmed by its bioavailability factor (BF), which was within the ranges of 0.32–0.61, 0.36–0.59, 0.64–0.83, 0.36–0.72, 0.37–0.62 and 0.52–0.78 for Fe, Mn, Zn, Cu, Pb and Ni, respectively. The BF exhibited the following order: Zn > Ni > Cu > Pb ≈ Mn?>?Fe. The high levels of BF for the studied metals may represent the potentiality for toxic metals to be easily released into the aquatic environment.     

Biosolids application affects the competitive sorption and lability of cadmium,copper, nickel,lead, and zinc in fluvial and calcareous soils

The objective of this research was to investigate the effects of biosolids on the competitive sorption and lability of the sorbed Cd, Cu, Ni, Pb, and Zn in fluvial and calcareous soils. Competitive sorption isotherms were developed, and the lability of these metals was estimated by DTPA extraction following their sorption. Sorption of all metals was higher in the fluvial than in the calcareous soil. Sorption of Cu and Pb was stronger than that of Cd, Ni, and Zn in all soils. Biosolids application (2.5%) reduced the sorption of all metals especially Cu and Pb (28–43%) in both soils (especially the calcareous soil) at the lower added metal concentrations (50 and 100 mg L^?1). However, it increased the sorption of all metals especially Pb and Cu in both soils (especially the calcareous soil; 15.5-fold for Cu) at the higher added concentrations (250 and 300 mg L^?1). Nickel showed the highest lability followed by Cd, Zn, and Pb in both soils. Biosolids increased the lability of the sorbed Ni in the fluvial soils at all added concentrations and the lability of Cd, Pb, and Zn at 50 mg L^?1, but decreased the lability of Cd, Pb, and Zn at 250 and 300 mg L^?1 in both soils. We conclude that at low loading rate (e.g., 50 mg L^?1) biosolids treatment might increase the lability and environmental risk of Cd, Cu, Pb, and Zn. However, at high loading rate (e.g., 300 mg L^?1) biosolids may be used as an immobilizing agent for Cd, Cu, Pb, Zn and mobilizing agent for Ni.     

Diphenylarsinic acid sorption mechanisms in soils using batch experiments and EXAFS spectroscopy

• DPAA sorption data was found to fit the Freundlich equation. • K_f was significantly positive correlated with oxalate-extractable Fe₂O₃. • Ligand exchange was the main mechanism for DPAA sorption on soils. • Bidentate binuclear and monodentate mononuclear DPAA bonds were identified. Diphenylarsinic acid (DPAA) is a phenyl arsenic compound derived from chemical warfare weapons. Macroscopic and microscopic work on DPAA sorption will provide useful information in predicting the partitioning and mobility of DPAA in the soil-water environment. Here, batch experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to investigate the sorption mechanisms of DPAA. The DPAA sorption data from 11 soil types was found to fit the Freundlich equation, and the sorption capacity, K_f, was significantly and positively correlated with oxalate-extractable Fe₂O₃. The K_f values of eight of the 11 untreated soils (1.51–113.04) significantly decreased upon removal of amorphous metal (hydr)oxides (0.51–13.37). When both amorphous and crystalline metal (hydr)oxides were removed from the untreated soils, the K_f values either decreased or slightly increased (0.65–3.09). Subsequent removal of soil organic matter from these amorphous and crystalline metal (hydr)oxide-depleted samples led to further decreases in K_f to 0.02–1.38, with only one exception (Sulfic Aquic-Orthic Halosols). These findings strongly suggest that ligand exchange reactions with amorphous metal (hydr)oxides contribute most to DPAA sorption on soils. EXAFS data provide further evidence that DPAA primarily formed bidentate binuclear (²C) and monodentate mononuclear (¹V) coring-sharing complexes with As-Fe distances of 3.34 and 3.66 Å, respectively, on Fe (hydr)oxides. Comparison of these results with earlier studies suggests that ²C and ¹V complexes of DPAA may be favored under low and high surface coverages, respectively, with the formation of ¹V bonds possibly conserving the sorption sites or decreasing the steric hindrance derived from phenyl substituents.     

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.     

兽用抗生素在土壤环境中的行为及其生态毒理效应研究进展

目前全球至少有70%左右的抗生素被用于畜牧业和水产养殖业,这些抗生素大多不能被动物完全吸收,以母体或代谢物的形式排出动物体外的抗生素约占用药量的40～90%,排出体外的抗生素大多随粪便等进入环境尤其是土壤环境中并在其中累积.为了明确兽用抗生素对环境中生物等的影响,合理评价兽用抗生素的环境风险,论文就土壤环境中兽用抗生素的来源,兽用抗生素在土壤环境中的吸附、迁移、降解以及对环境中生物的影响等方面进行了综述,在此基础上提出了今后的重点研究方向.