根系分泌物及其在植物修复中的作用

 近年来环境污染日益严重,污染物在土壤植物中的行为引起了人们的高度关注。利用植物去除土壤水体等介质中污染物的植物修复是近10年来兴起的一项安全、廉价的技术,已成为污染生态学和环境生态学的研究热点,它通过植物吸收、根滤、稳定、挥发等方式清除环境中的重金属和有机污染物。国内外有关植物修复的研究报道和概述很多, 但对植物根系分泌物在植物修复中所起的作用及其机理少有述评。 本文从根系分泌物对土壤重金属和土壤有机污染物的去除作用出发,对根系分泌物的种类、数量及其在去除环境污染物中的作用机理和功能地位进行了总结,并借助研究事例对影响植物根系分泌的内外因子,如植物种类、营养胁迫、重金属胁迫、根际环境的理化性质、土壤微生物及其它环境因子进行了讨论。概言之,根系分泌物在修复污染土壤中的重金属途径是多种多样的,主要是通过调节根际pH值、与重金属形成螯合物、络合反应、沉淀、提高土壤微生物数量和活性来改变重金属在根际中的存在形态以及提高重金属的生物有效性,从而减轻它对环境的危害。在清除有机污染物时,根系分泌物中的酶可以对有机污染物进行直接降解,根系分泌物影响下的微生物也可以对有机污染物进行间接降解,且被认为是主要的降解途径。根系分泌物在植物修复过程中确实起着某些重要作用,今后应将这方面的研究重点放在某些特异性根系分泌物植物,尤其是某些重金属超富集植物资源的寻找、筛选上,通过室内实验和野外研究确定其根系分泌物对清除重金属和有机污染物的效率,证实超富集植物根系分泌物的特异性与污染物超富集的内在联系,找到污染土壤生态恢复和治理的有效方法并加以推广应用,如针对性地在被污染地大面积种植此类具特异性根分泌物植物,并辅以营林措施如修剪等,加快生物修复进程,提高修复效率。植物根系分泌物在植物修复过程中所具有的重要生态意义和可能应用前景,为污染生态学和化学生态学之间的联合研究开拓了全新的领域,今后将取得新的突破和重要进展。     

Regional distribution characteristics and ecological risk assessment of heavy metal pollution of different land use in an antimony mining area – Xikuangshan,China

Abstract

Mining activities have introduced various heavy metals and metalloids to surrounding soil environments, causing adverse impacts to the ecological environment system. The extremely high concentration of various heavy metals and metalloids make the Xikuangshan (Hunan, China) an excellent model to assess their ecological risk. In this study, the soil samples from 26 locations of different land use methods in four areas (smelting area, road nearby ore, mining area, and ore tailing area) in Xikuangshan with different levels of various heavy metals and metalloids (Sb, As, Pb, and Cd) were analyzed; in addition, the index of geo-accumulation and the potential ecological risk index were used to evaluate ecological risk. The results showed that the average contents of Sb, As, Pb, and Cd in all soil samples were 4368.222?mg·kg^?1, 40.722?mg·kg^?1, 248.013?mg·kg^?1, and 40.941?mg·kg^?1, respectively, implying serious contamination of compound pollution of heavy metals in soil. The concentration of heavy metals in soil among smelting area, road nearby ore, mining area, and ore tailing area showed significant distribution characteristics of region because different mining activities such as smelting, mining, transportation, and stacking caused different pollution intensity. Moreover, the contents of Sb in soil samples decreased successively in residue field, wasteland, forestland, sediment, grassland, and vegetable field, and the contents of Sb in vegetable-field and ecological restoration grassland were relatively low, which indicate that the method of grassland ecological restoration is an effective method to control antimony pollution in soil. The results of ecological risk assessment showed that the antimony mining area was seriously polluted by Sb, As, Pb, and Cd, and had strong ecological risk, and Sb and Cd were the most important pollution factors, which indicated that the pollution of Sb and Cd should be a major concern of relevant departments of environment and health.     

重金属复合污染对眼优角蚱代谢组的影响

【目的】对金属矿区和非金属矿区环境中生活的眼优角蚱Eucriotettix oculatus体内重金属含量及其代谢组进行分析,探究重金属复合污染对眼优角蚱体内重金属累积和代谢组的影响。【方法】使用ICP-MS法对眼优角蚱成虫体内重金属含量进行测定,同时采用基于 UPLC-MS/MS检测平台、自建数据库以及多元统计分析相结合的手段,对金属矿区和非金属矿区眼优角蚱成虫肠道中的代谢物进行差异分析,并利用 KEGG 数据库对差异代谢物进行注释以及通路富集分析。【结果】金属矿区眼优角蚱成虫体内9种重金属含量是非金属矿区的0.4~212.4倍。多元统计分析结果表明,金属矿区眼优角蚱成虫肠道中共有112种代谢物的含量发生了显著变化,主要为氨基酸类、脂肪酰类、有机酸类、核苷酸类、苯类等物质。KEGG注释及通路富集分析显示,可被注释到的显著差异代谢物共有49种,与代谢通路相关的显著差异代谢物有40种,富集最显著的通路是甲状腺激素合成通路、催产素信号通路、胆汁分泌通路、酪氨酸代谢通路。【结论】重金属复合污染环境中生存的眼优角蚱成虫体内有多类重金属累积,重金属可改变眼优角蚱肠道中的代谢物的组成,其中一些代谢物的改变可能是眼优角蚱适应重金属复合污染生境的策略。     

铜川煤矿区重金属污染对土壤微生物群落代谢和酶活性的影响

研究了陕西省铜川煤矿矿区的重金属污染状况以及不同程度的重金属污染对土壤微生物代谢、微生物群落功能以及土壤酶活性的影响.结果表明： 铜川矿区土壤中重金属Cu、Zn、Cd、Pb全量及有效量均显著高于非矿区土壤,其中Cd污染最为严重.采用Biolog方法结合主成分分析和聚类分析发现,随着污染程度的增加,不同土壤微生物群落间的代谢特征发生显著变化,而且这种变化主要体现在糖类和氨基酸类碳源的利用差异.在轻度、中度污染情况下,土壤微生物群落对碳源的利用表现出激活效应;而在重度污染的情况下,土壤微生物群落对碳源的利用表现出抑制效应.随着污染程度的增加,脲酶、蛋白酶、碱性磷酸酶和过氧化氢酶的活性均呈现降低的趋势,矿区土壤脲酶、蛋白酶、碱性磷酸酶和过氧化氢酶活性分别是非矿区土壤中相应酶活性的50.5%～65.1%、19.1%～57.1%、87.2%～97.5%、77.3%～86.0%;蔗糖酶和纤维素酶在中等污染程度以下的土壤中表现为激活效应,而在重度污染的土壤中表现为抑制效应.     

有机肥连续施用对菜田重金属行为的影响——基于地球化学模型研究

2017年起,农业部连续多年出台化肥减量增效行动工作方案,要求适当增加有机肥投入,发展循环农业。但连续施用的有机肥进入土壤后,会对土壤pH、有机质和重金属含量等产生影响,改变土壤重金属行为。科学评估有机肥料施用的影响至关重要。仅通过总含量评估重金属污染风险被认为是片面的,不同化学提取剂提取的重金属含量不能完全代表实际污染状况。地球化学模型具有良好的适用性,比传统的提取方法能够更全面地解释重金属的行为。在集约化农业种植区黄淮海平原,多次施用不同比例的粪源有机肥于旱地菜田,并引入地球化学模型,结合pH依赖性浸出试验,明确连续施肥对菜田土壤重金属行为的主要影响机制。研究发现,有机肥中的铜锌含量远高于土壤中的含量,施用后,它们在土壤中的淋溶浓度随着施用比例增加而显著增加,最多可超过十倍以上,并且活性大大增加,与施肥后溶解性有机物含量的升高呈正相关。不同处理条件下的土壤重金属浸出趋势相似：在中性pH下浸出浓度最低,然后逐渐向强酸和强碱增加,呈现出V型变化。地球化学模型LeachXS展示出较好的模拟结果,其模拟值与实测浓度具有良好的相关性(71.02%)。模拟结果显示,有机肥的施用不会明显改变重金...     

贵州省典型汞铊矿区周边农田土壤跳虫群落特征

大量的采矿活动导致矿区周边土壤重金属污染, 严重危害土壤生物安全。汞、铊等重金属元素毒性强, 相关污染的土壤生态风险鲜有研究。跳虫作为土壤环境变化指示生物, 能很好地反映土壤质量的健康状况。本研究以贵州省某汞铊矿区周边的农田土壤为研究对象, 按离矿区距离和作物类型设置4个采样区, 每个采样区种植2种作物, 每种作物农田设置3个样方。研究土壤跳虫群落结构和多样性及其影响因子。结果表明, 调查区内跳虫平均密度为12,000 ind./m²; 采样区距离矿区越近, 土壤重金属污染程度越大, 综合污染指数越高, 跳虫种数、密度、多样性和丰富度指数均呈先增加再降低的趋势; 环境因子分析表明重金属显著影响跳虫群落结构: Folsomides americanus、Isotomiella minor和Protaphorura encarpatus数量与汞、铊和砷含量呈负相关。高有机质含量能缓解重金属对土壤跳虫的影响, 但作物类型(玉米与薏仁)对土壤跳虫群落结构的影响无显著差异。本研究结果表明土壤有机质或能反向调节重金属污染对土壤跳虫群落的影响。     

From geochemical background determination to pollution assessment of heavy metals in sediments and soils

Establishing geochemical background concentrations to distinguish the natural background from anthropogenic concentrations of heavy metals in sediments and soils is necessary to develop guidelines for environmental legislation. Due to the fact that the background concentrations strongly depend on geological characteristics such as mineral composition, grain size distribution and organic matter content, several normalization methods have been developed. Empirical (geochemical), theoretical (statistical) and integrated methods (combining both empirical and theoretical methods) are the main approaches described in literature for determination of geochemical background concentrations. In this review paper, the different approaches as well as the main normalization methods for heavy metal concentrations in sediments and soils will be discussed. Both geochemical background concentrations and added risk level (maximum permissible addition) should be taken into account for setting up legal threshold limits. Moreover, different approaches to evaluate the pollution status of heavy metals in sediments and soils, from Sediment/Soil Quality Guidelines to quantitative indices (Geo-accumulation Index-I_geo, Enrichment Factor-EF, Pollution Load Index-PLI and Risk assessment Code-RAC) will be presented. Although guidelines to establish whether a sediment or soil is polluted or not are generally only related to total metal concentrations, the available/reactive pool i.e., availability/reactivity of metals should be taken into account for sediment/soil pollution assessment.     

城市地表灰尘中重金属的来源、暴露特征及其环境效应

地表灰尘是城市环境重金属的“源”、“汇”载体,与环境质量和人类健康有着密切关系.分析了城市地表灰尘重金属污染研究的意义,综述了国内外城市地表灰尘重金属地球化学行为研究进展,包括地表灰尘重金属来源、暴露特征及其影响因素分析、环境效应等方面.提出应加强时间序列及小尺度微观研究;地理因素对地表灰尘中重金属暴露特征、环境效应的影响机理研究.     

Pollution and ecological risk assessment of antimony and other heavy metals in soils from the world's largest antimony mine area,China

Xikuangshan is located in Lengshuijiang City, Hunan province, China. With intensive mining and metallurgical activities, large amounts of tailing containing heavy metals (in this study, the term “heavy metals” is used for both metals and metalloids) were introduced to the soils around the mine area. Those heavy metals including antimony and other heavy metals would pose huge risk to human health and ecological environment. With a view to providing information on the extent of contamination and potential ecological risk of heavy metals in the soils of this mine area, the total contents of antimony (Sb), manganese (Mn), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) in the soils were examined. The results revealed that the predominant pollutants in this area were Sb, Cd, and Zn with mean concentrations being 356.58, 9.98, and 486.42 mg kg^?1, 119.66, 117.41, and 5.17 times of the corresponding background values respectively. The pollution indices (Ps) indicated that the pollution levels of all sampling zones were serious including the control zones. The ecological risk levels of all heavy metals were very high on all the sampling zones except sampling zone 7 (as considerable), and Sb, Cd, and As were regarded as making great contribution to the risk indices (RI).     

Five heavy metals accumulation and health risk in a traditional Chinese medicine Cortex Moutan collected from different sites in China

This study assessed the concentrations of five heavy metals Pb, Cd, Cr, Cu and Zn in both soil and a traditional Chinese medicine Cortex Moutan collected from 6 typical sites, growing this medicine, in China. The potential health risks associated with those heavy metals were also assessed. It is shown that Cd content in soils from five of the six sites was higher than the environmental Quality Standard for Soils of China (EQSS). The cortex from a copper tailings area in Tongling (marked as TLC) accumulated much higher amounts of heavy metals than the other sites. Calculated pollution index implied that the herbs in TLC were mildly contaminated by Pb, Cd, and Cu. Hazard quotient (HQ) indicated the intake of Pb, Cd, Cr, Cu, and Zn was safe by cortex consumption, but noncarcinogenic and carcinogenic risks of all metals in Cortex Moutan in hillside near the copper tailings (marked as TLB) and TLC were higher. The results suggested more attention should be paid to the planting area near the mining tailing, and in order to ensure the quality of the herbal medicines, the regions where this herb is grown should be at distance from the mining tailing area.     

Geochemical baseline determination and pollution assessment of heavy metals in urban soils of Karachi,Pakistan

Karachi is one of the most populated urban agglomerations in the world. No categorical study has yet discussed the geochemical baseline concentrations of metals in the urban soil of Karachi. The main objectives of this study were to establish geochemical baseline values and to assess the pollution status of different heavy metals. Geochemical baseline concentrations of heavy metals were estimated using the cumulative frequency distribution (CDF) curves. The estimated baseline concentrations of Pb, Cr, Cu, Zn and Fe were 56.23, 12.9, 36.31, 123.03 and 11,776 mg kg⁻¹, respectively. The pollution status of heavy metals in urban soils was evaluated using different quantitative indices (enrichment factor–EF, Geo-accumulation Index–I_geo, and pollution index–PI). Enrichments factors of the selected heavy metals determined by using Fe as a normalizer showed that metal contamination was the product of anthropogenic activities. The urban soils of Karachi were found to have a moderate to moderately severe enrichment with Pb, whereas Cr and Cu has moderate and Zn has minor enrichment. I_geo results indicated moderate soil contamination by Pb at some of the sampling locations. PI for Pb, Cr, Cu and Zn was found in the range of 0.04–3.42, 0.19–1.55, 0.27–2.45 and 0.32–1.57, respectively. Large variations in PI values of Pb revealed that soil in those areas of the city which are influenced by intensive anthropogenic activities have exceptionally high concentrations of Pb. The findings of this study would contribute to the environmental database of the soil of the region and would also facilitate both at the local and the international scales, in a more accurate global environmental monitoring, which will eventually facilitate the development of management and remediation strategies for heavy metal contaminated urban soil.     

Exploiting the genetic and biochemical capacities of bacteria for the remediation of heavy metal pollution

The threat of heavy metal pollution to public health and wildlife has led to an increased interest in developing systems that can remove or neutralise its toxic effects in soil, sediments and wastewater. Unlike organic contaminants, which can be degraded to harmless chemical species, heavy metals cannot be destroyed. Remediating the pollution they cause can therefore only be envisioned as their immobilisation in a non-bioavailable form, or their re-speciation into less toxic forms. While these approaches do not solve the problem altogether, they do help to protect afflicted sites from noxious effects and isolate the contaminants as a contained and sometimes recyclable residue. This review outlines the most important bacterial phenotypes and properties that are (or could be) instrumental in heavy metal bioremediation, along with what is known of their genetic and biochemical background. A variety of instances are discussed in which valuable properties already present in certain strains can be combined or improved through state-of-the-art genetic engineering. In other cases, knowledge of metal-related reactions catalysed by some bacteria allows optimisation of the desired process by altering the physicochemical conditions of the contaminated area. The combination of genetic engineering of the bacterial catalysts with judicious eco-engineering of the polluted sites will be of paramount importance in future bioremediation strategies.     

藏中矿区重金属污染土壤的微生物活性变化

微生物几乎参与土壤中的一切生物及生物化学反应,土壤微生物活性可较敏感地反映土壤中生化反应的方向和强度,是探讨重金属污染生态效应的有效途径之一。通过野外调查与采样和室内分析,研究了藏中矿区重金属污染对土壤酶活性、基础呼吸、代谢商(qCO2)和可矿化N的影响。结果表明,矿区土壤受重金属Cu、Zn、Pb、Cd不同程度污染,使得土壤酶活性、可矿化N受到抑制,基础呼吸和qCO2则受到刺激。逐步多元回归分析表明,在Cu、Zn、Pb、Cd复合污染条件下,矿区土壤重金属复合污染对土壤微生物活性的影响是复杂的;主成分分析表明,土壤总体微生物活性指标能较好地反映拉屋矿区土壤重金属复合污染状况,可作为藏中矿区土壤环境质量评价及量化分类的有效指标。     

工矿区不同类型生物结皮对大气降尘重金属的富集规律及其影响因子

大气降尘是矿区土壤重金属的主要来源,而生物结皮对大气降尘重金属有显著的富集作用。为探究不同类型生物结皮对大气降尘重金属的富集规律及其影响因子,选取宁东典型火电厂周边生物结皮广布区作为试验样地,3类生物结皮作为研究对象,并以临近裸土作为对照,对比分析了生物结皮富集大气降尘过程中土壤理化性质、酶活性及重金属含量的变化,采用相关分析、冗余分析和方差分解方法探讨了不同类型生物结皮的结皮层(A层)和层下土壤(B层)重金属含量与其土壤物理、化学性质及酶活性之间的关系。结果表明：燃煤烟尘是矿区大气降尘重金属污染的主要来源,涉及重金属元素包括Cd、Cr、Hg、Pb、Zn、As。生物结皮对源自大气降尘的重金属元素均具有显著的富集作用,且在不同演替阶段生物结皮间的富集规律完全一致：藓结皮>混生结皮>藻结皮;重金属综合污染指数评价结果显示：生物结皮对重金属具有表层富集效应,表现为A层污染程度高于B层。不同类型生物结皮A、B层综合污染指数存在显著差异,排序为：藓结皮>混生结皮>藻结皮;和对照相比,三类生物结皮均能通过富集大气降尘增加其A、B层养分和细颗粒物含量并改善土壤质地。方差分解结...     

Transfection of siRNA into <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> (Rotifera)

Lake Taihu is one of the most contaminated lakes in China. Surface sediment data show that the northern area of the Lake has the worst heavy metals pollution, and high heavy metal concentrations were attributed to discharge of untreated and partially treated industrial waste water from cities to the north of the lake. To study geochemical features and pollution history of heavy metals, total content and chemical fractionations of Cu, Fe, Mn, Ni, Pb, and Zn were analyzed for core sediments from western Lake Taihu using the speciation extraction procedure, proposed by the Commission of the European Communities Bureau of Reference (BCR), together with grain size and organic carbon measurements. Results show that sediments are composed of organic-poor clayey-fine silts for Cores MS and DLS, and have similar geochemical features shown by heavy metals. Cu, Fe, Ni, and Zn mainly are associated with the residue fraction, Mn is concentrated in the exchangeable-carbonate and residue fractions, and Pb is concentrated in the Fe–Mn oxide fraction and organic-sulfide fraction. The fractions of Ni, Pb, and Zn bound to Fe–Mn oxide show significant correlations with Mn from the Fe–Mn oxide fraction, and the organic-sulfide fractions of Cu, Mn, Ni, Pb, and Zn are correlated with TOC. The increase of Cu, Mn, Ni, Pb and Zn content and percentage of extractable fractions in the upper layers of the sediments are correlated with anthropogenic input of heavy metals due to rapid industrial development. This coincides with rapid economic development in the Taihu basin since late 1970s. Heavy metals in the surface sediments have certain potential biological toxicity as shown by the higher SEM/AVS ratio.     

重庆溶溪锰矿区土壤重金属污染评价及植物吸收特征

对重庆溶溪锰矿尾渣堆积区土壤、优势植物以及周边农田土壤的重金属含量(Mn、Cd、Cu、Zn和Pb)进行测定分析,并以重庆市土壤背景值为评价标准,应用Hakanson潜在生态危害指数法对土壤中重金属的潜在生态危害进行了评价。结果表明:该锰矿尾渣堆积区土壤中Mn、Cd、Cu、Zn和Pb的平均含量分别为48382.5、3.91、79.97、131.23和80.68 mg/kg,受到Mn、Cd的严重污染,Mn为强或很强生态危害,Cd为极强生态危害,而Cu、Zn、Pb为轻微生态危害,各尾矿渣堆积区的综合潜在生态危害指数(RI)均远大于720,为极强生态危害。对优势植物重金属含量的分析显示,绝大部分植物地上部Mn、Cd含量都超出正常范围的上限值,而Cu、Zn和Pb含量基本都在正常范围内;根据植物对重金属的吸收特征,将植物分为三类:将重金属主要累积于地上部分的富集型,如垂序商陆(Phytolacca americana L.)和酸模叶蓼(Polygonum lapathifolium Linn.),适用于重金属复合污染土壤的植物修复;将重金属主要累积于根部的根部囤积型,如芒(Miscanthus sinensis Anderss.)和乌蕨(Stenoloma chusanum Ching);重金属含量较低的规避型,如黄花蒿(Artemisia annua L.)、长波叶山蚂蝗(Desmodium sequax Wall.)及钻形紫苑(Aster subulatus Michx.);后两种类型的植物可种植在重金属污染严重且使用价值相对较低的矿山废弃地上,同时规避型植物对于研究植物的重金属排斥机理具有重要价值。溶溪锰矿区周边农田土壤主要受到Cd的严重污染,Cd为很强或极强生态危害。     

Review: Nutritional ecology of heavy metals

The aim of this review is to focus the attention on the nutrition ecology of the heavy metals and on the major criticisms related to the heavy metals content in animal feeds, manure, soil and animal-origin products. Heavy metals are metallic elements that have a high density that have progressively accumulated in the food chain with negative effects for human health. Some metals are essential (Fe, I, Co, Zn, Cu, Mn, Mo, Se) to maintain various physiological functions and are usually added as nutritional additives in animal feed. Other metals (As, Cd, F, Pb, Hg) have no established biological functions and are considered as contaminants/undesirable substances. The European Union adopted several measures in order to control their presence in the environment, as a result of human activities such as: farming, industry or food processing and storage contamination. The control of the animal input could be an effective strategy to reduce human health risks related to the consumption of animal-origin products and the environmental pollution by manure. Different management of raw materials and feed, animal species as well as different legal limits can influence the spread of heavy metals. To set up effective strategies against heavy metals the complex interrelationships in rural processes, the widely variability of farming practices, the soil and climatic conditions must be considered. Innovative and sustainable approaches have discussed for the heavy metal nutrition ecology to control the environmental pollution from livestock-related activities.     

Nematodes as Sentinels of Heavy Metals and Organic Toxicants in the Soil

Field and laboratory research has repeatedly shown that free-living soil nematodes differ in their sensitivity to soil pollution. In this paper, we analyze whether nematode genera proved sensitive or tolerant toward heavy metals and organic pollutants in six long-term field experiments. We discuss overlaps between nematode physiological responses to heavy metals and to organic pollutants, which may explain why nematodes can exhibit co-tolerance toward several contaminants. We propose a simple method for separating direct effects of soil contamination on nematode populations from indirect effects mediated through the food chain. Finally, we analyze the extent to which nematodes exhibited consistent responses across the experiments analyzed. Our results show that (a) indirect effects of pollution were generally strong; (b) fewer nematode genera were tolerant than sensitive; (c) many genera, including practically all Adenophorea, exhibited a common response pattern to contaminants; and (d) several genera of the Secernentea exhibited differential tolerance toward particular pollutants. We conclude that bioindication of soil contamination should preferentially be based on tolerant, and less on sensitive, nematodes. We provide a list of nematode genera that may potentially serve as differential bioindicators for specific soil contaminants.     

Applying Mental Models to Qualitative Risk Assessment at the Tar Creek Superfund Site

Re-suspension of heavy metal residuals generated by former mining activities conducted at the Tar Creek Superfund site may result in exposures of nearby residents. Currently, remediation and mitigation activities include removal of yard soil containing high concentrations of heavy metals, removal of selected chat piles, and providing assistance for families with young children. Although these are important activities to reduce potential risks to Tar Creek residents, a qualitative assessment of the site that uses mental models identifies other potential contaminants of concern, transport, and exposure pathways that may require further investigation. Mental models structure judgments about hazards and risk by visually representing a contaminated site through the use of influence diagrams. A mental model was applied to the Mayer Ranch area of the Tar Creek Superfund site in Ottawa County, Oklahoma, to support a qualitative assessment of the health risks from heavy metals exposure. Documents were reviewed to develop influence diagrams illustrating the processes, interactions, and potential exposures that could subject a hypothetical individual recreating at Mayer Ranch to various health risks. The diagrams were modified to reflect expert judgments. The mental model includes four influence diagrams: source term, fate, and transport processes that may influence human health risks due to exposure to heavy metals; natural wetland processes that could remove heavy metals; net alkaline constructed wetland processes that could remove heavy metals; and potential future impacts from the removal of sediment and land development that could increase risk. Policies, regulations, and technologies that could most reduce the probability of exposures can be determined and evaluated by focusing on the environmental transport pathways and contaminants that pose the greatest potential risks and determining the difference between the risks. Also evident are the knowledge gaps with respect to the processes within wetlands.     

Spatial distribution and environmental risk assessment of heavy metals identified in soil of a decommissioned uranium mining area

Abstract

The spatial distribution of six heavy metals (Cd, As, Zn, Pb, Cr, and Cu) in the soil of a decommissioned uranium mining area was investigated and their potential environmental risk was assessed. Soil samples were collected along the main riversides enclosing the mining area. The heavy metal distribution was determined by geospatial interpolation. Pearson correlation coefficient and principal component analysis were used to locate the sources of pollution which are the mine ore as natural source, and dressing plants and tailing area from human activity. The results indicate that the average concentrations of As and Cd strongly exceed the recommended EQSS (Environmental Quality Standard for Soils of China) limits at all sampling sites, whereas Zn concentrations were found to be slightly over the limit only at sampling sites close to the mining area. The concentrations of Cr, Cu and Pb were all within the recommended limits. Environmental risk was assessed using the toxicity characteristic leaching procedure defining the degree to which extend the metal is released into the solution. High leaching rates were found only for Zn and Cd, suggesting that together with its high concentrations Cd is the most toxic metal around the mining area, followed by As.