Comparing Deterministic and Probabilistic Risk Assessments. A case study at a closed steel mill in southern Sweden (7 pp)

Background, Aims and Scope   Contaminated land is a high priority environmental problem in most of Europe and North-America. Sweden is no exception and generic guideline values have been developed for the initial assessment, but site-specific assessments are also needed. The generic guideline values are not applicable when the exposure conditions are different from the typical Swedish conditions or when the site contains a particularly sensitive ecosystem. The Swedish guideline values have, like in many other countries, been set by using deterministic point estimates for all variables and constants in the used multimedia model. The same approach is common also for site-specific assessments, and a limitation is that it fails to quantify variability and uncertainty. Probabilistic risk assessment provided a method to deal with this problem. Variability and uncertainty in the input parameters (variables or constants) are described by probability distributions, and likewise the output (risk or exposure) is presented as a probability distribution. A substantial number of probabilistic risk assessments for contaminated land at sites in North America, Europe and Asia have been published. However, an extensive review of the literature did not identify any study where probabilistic risk assessment was applied to a site contaminated by an iron or steel industry. Here we will describe such a case, where we have compared a deterministic point estimate with a probabilistic risk assessment for six elements and benzo[a]pyrene. Methods   The site had different metallurgical plants in operation for more than 100 years. Most parts of the steel mill were closed by the mid 1980s, and today the site is used by small-sized enterprises. The soil is contaminated with metals from the previous industrial operations. The present owner plans to develop the site and has therefore initiated extensive investigations of soil contamination. Sixty-two soil samples collected between 1997 and 2000 provided a good coverage of the whole site, and were analyzed for the content of different elements and polycyclic aromatic hydrocarbons (PAH). The exposure assessments were focused on six elements with high concentrations compared to the generic guideline values; arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn). In addition, benzo[a]pyrene was included due to the high toxicity and comparatively high concentrations. Variability and uncertainty were characterized in a Monte Carlo simulation of exposures (10 000 iterations), and the exposures were evaluated with two land use scenarios; less sensitive use and sensitive use. Results and Discussion   The deterministic point estimates and the probabilistic estimates of the 95th percentile are in approximately the same ranges in the scenario of less sensitive land use. It is only the exposure for arsenic that is slightly above the toxicological reference value (TRV) in the deterministic assessment. In the probabilistic assessment, the exposure for all elements is below the TRV. The results for sensitive land use are applicable to a scenario where the site is developed for general housing. The deterministic point estimates and the probabilistic estimates of the 95th percentile are also here in approximately the same ranges, but the exposure exceeds the TRV for arsenic, cadmium and lead. Drinking water, vegetables grown on site and soil ingestion are the major exposure pathways for this scenario. In this assessment, the estimated intake distributions are applicable to a randomly selected individual. The probability distributions used here to characterize the different soil parameters are typically representing both variability and uncertainty, and the same is true the majority of the exposure variables. We therefore decided not to attempt to separate variability and uncertainty at this stage, but with additional data from a more in-depth site investigation it might be possible to achieve this. Conclusions and Outlook   To the best of our knowledge, this study is the first report on a probabilistic risk assessment on a former iron and steel works site. The materials handled by this industry were less toxic than for many other metallurgical operations, but contaminants may still severely limit the options for future land use. This case study shows that probabilistic exposure estimates for a set of soil contaminants can be quite similar to deterministic point estimates. The main difference is instead to be found in the additional information obtained with the probabilistic assessment. The sensitivity analyses show pathways and input variables that contribute most to variations in the total intake of each contaminant, e.g. dermal contact and ingestion of soil, vegetables and drinking water. This information can be used both in the planning of future land use and for active measures to reduce current exposure. The probabilistic assessment also provides information on the magnitude of exposure and the margin of safety. This information may facilitate risk communication between decision-makers and stakeholders. The presentation of results from probabilistic risk assessments is only briefly discussed in the literature and here we see a need for research and opportunities for enhancement. The choice of data analytical tools may then be of importance, since more complex multimedia models are rather difficult to decipher when implemented within traditional spreadsheet software. Some of the research needs are identified here and in a previous review article in this journal.     

Use of the BCR three-step sequential extraction procedure for the study of the partitioning of Cd, Pb and Zn in various soil samples

A slightly modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (BCR) for analysis of sediments was successfully applied to soil samples. Contaminated soil samples from the lead and zinc mining area in the Mezica valley (Slovenia) and natural soils from a non-industrial area were analysed. The total concentrations of Cd, Pb and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS). Total metal concentrations in natural soils ranged from 0.3 to 2.6 mg kg^-1 for Cd, from 20 to 45 mg kg^-1 for Pb and from 70 to 140 mg kg^-1 for Zn, while these concentrations ranged from 0.5 to 35 mg kg^-1 for Cd, from 200 to 10000 mg kg^-1 for Pb and from 140 to 1500 mg kg^-1 for Zn in soils from contaminated areas. The results of the partitioning study applying the slightly modified BCR three-step extraction procedure indicate that Cd, Pb and Zn in natural soils prevails mostly in sparingly soluble fractions. Cd in natural soils is bound mainly to Fe and Mn oxides and hydroxides, Pb to organic matter, sulphides and silicates, while Zn is predominantly bound to silicates. In contaminated soils, Cd, Pb and Zn are distributed between the easily and sparingly soluble fractions. Due to the high total Cd, Pb and Zn concentrations in contaminated soil close to the smelter, ! and their high proportions in the easily soluble fraction (80% of Cd, 50% of Pb and 70% of Zn), the soil around smelters represents an environmental hazard.     

混合菌降解土壤中多环芳烃的试验研究

PAHs生物降解程度受多种因素影响。通过筛选驯化PAHs降解菌,研究混合菌对土壤中菲、芘、苯并（a）蒽、苯并（b）荧蒽、苯并（k）荧蒽、茚并（1,2,3-cd）芘的生物降解性能,并考察污染时间对土壤中PAHs降解效果的影响。结果表明,筛选的混合菌具有很强的PAHs降解能力,缩短了PAHs生物降解的半衰期,且PAHs起始降解速率较快,之后趋于平缓。27d内土壤中的菲、芘、苯并（a）蒽、苯并（b）荧蒽、苯并（k）荧蒽、茚并（1,2,3-cd）芘的平均降解率分别为98.14%、89.97%、88.47%、63.55%、65.24%、60.49%,其中菲在5d之内的降解率高于93%。污染210d的土壤中各PAHs的起始降解速率高于污染50d的土壤,因此污染时间越长,PAHs生物降解的停滞期越短。     

水稻和不同品种苋菜间作对水稻产量、根区速效养分及砷累积的影响

【目的】探究水稻与苋菜间作对水稻产量、根区速效养分及水稻各部位吸收累积As的影响。【方法】通过小区试验研究水稻单作(对照)、水稻与圆叶白苋菜间作、水稻与籽粒苋间作、水稻与红苋菜间作条件下水稻产量、根际土壤速效养分与有机质含量、As累积量的变化。【结果】4个处理水稻收获期地上部、地下部、谷壳和糙米中As含量均表现为:水稻与圆叶白苋菜间作水稻与籽粒苋间作水稻与红苋菜间作水稻单作。与对照相比,水稻与圆叶白苋菜间作显著提高了水稻地上部、地下部、谷壳和糙米As含量,增幅分别为88.50%、65.38%、68.25%和45.45%;对土壤As的提取量为5.44 mg·m~(-2),显著高于对照,为对照的1.67倍;水稻单株生物量显著高于对照、与红苋菜间作和与籽粒苋间作,地上部生物量比对照提高63.79%。与水稻单作相比,间作处理水稻单位面积产量比对照显著下降,间作中单位面积产量最高的为与圆叶白苋菜间作,为对照的59.15%;间作处理水稻根际土壤速效养分、有机质含量均有不同程度的增加。【结论】水稻与苋菜间作,水稻单位面积产量降低,地上部、地下部、谷壳和糙米中As含量以及根区土壤速效养分与有机质含量显著提高。水稻与圆叶白苋菜间作能从As污染土壤中提取最多的As,生产出的苋菜符合国家安全标准,为最优方案。     

水泥-过磷酸钙复合材料固化铅污染土的浸出和力学特性

水泥是铅污染土固稳修复常用的固化剂,在修复重度铅污染土时效果较差。而过磷酸钙在稳定铅污染土方面具有溶出风险低、长期稳定性好和环境安全性高的优点。为了研究水泥-过磷酸钙复合材料固化后铅污染土的浸出和力学特性,采用水泥-过磷酸钙复合材料对铅污染土进行固化/稳定化处理,通过浸出试验、无侧限抗压强度试验和渗透试验对固化前后的铅污染土固化体进行浸出和力学特性变化特征对比分析,分别探讨了水泥和过磷酸钙添加量对固化土浸出和力学特性的影响规律。结果表明:水泥可显著改善铅污染土的强度和渗透特性,当水泥的添加量从5%增加到30%时,固化土的抗压强度从0.56 MPa增加到4.78 MPa;渗透系数从8.2×10-7cm/s减小到2.2×10-8cm/s。但水泥在固稳高浓度铅污染土效果较差,当水泥的添加量从5%增加到30%时,固化土的浸出浓度从56.3 mg/L减少到19.8 mg/L,固化土的浸出浓度远高于我国危险废弃物鉴别标准(GB/T 5085.3—2007)。过磷酸钙可显著降低污染土中铅的浸出特性,固化土的浸出浓度从43.5 mg/L减少到0.17mg/L;但过磷酸钙会降低固化土的力学性能。随着过磷酸钙添加量从1%增加到5%,固化土的抗压强度从1.17MPa降低到0.42 MPa;渗透系数从3.0×10-7cm/s增加到1.3×10-6cm/s。因此,在铅污染土实际工程中应根据实际的场地工况和修复目标,合理选择水泥和过磷酸钙的配比,保证修复后的铅污染土强度特性和浸出特性均满足修复标准。     

腐殖酸强化脱硫石膏改良油污盐碱土壤的研究

以腐殖酸为表面活性剂进行了脱硫石膏改良油污盐碱土壤的土柱实验,研究了不同洗盐条件下土壤渗透性能、电导率和pH值的变化规律。研究结果表明,油污显著影响脱硫石膏改良盐碱土壤的效果,淋洗前后油污土壤的碱化度仅从42.78%下降到37.72%;而加入腐殖酸表面活性剂后,油污盐碱土壤碱化度由42.78%下降到23.20%,淋出液电导率值显著增高,且pH值有所变化,证明加入腐殖酸表面活性剂可显著强化脱硫石膏改良油污盐碱土壤。     

基于专利文献分析的土壤污染修复技术发展现状与展望

为明确土壤污染修复技术在世界范围的研究布局和发展态势,基于德温特专利创新索引数据库(Derwent Innovation Index,DII)对2005—2013年土壤污染修复技术专利进行了计量学统计,并探讨了该技术的研究布局、研究重点及发展趋势。结果显示,世界范围内土壤污染修复技术涉及的专利申请量逐渐增长,土壤污染修复技术研究较为活跃。中国是该技术领域主要的专利申请国,也是最大的技术来源国,其专利数量从2005年逐年上升,尤其是2009年以后呈现快速上升趋势。土壤污染修复技术相关专利涉及的学科领域呈现交叉趋势,技术布局广泛,主要涉及化学、仪器与仪表、工程学、水资源学等方面。土壤污染修复领域主题词聚类分析显示,土壤砷、镉、铅、铬污染是该领域的研究热点,土壤污染物的稳定固化、植物修复、电动化修复、添加调理剂、土壤淋洗、离子束、分离回收等是可供采用的重要技术,并且2010年以后,污染物稳定固化、植物修复、添加调理剂修复技术的研发活动更为活跃。基于以上研究,认为今后应加强研发高效经济的土壤污染修复技术,注重已有专利成果的转化,促进专利的市场应用,使其发挥更大的社会和经济效益。     

某蓄电池厂铅污染土壤稳定化修复工程药剂筛选研究

依据某蓄电池厂土壤铅污染的基本情况,在修复工程实施前,开展了稳定化固化药剂的筛选试验。在试验过程中采用了石灰、水泥、磷酸二氢钠、磷酸二氢铵、磷酸二氢钙、磷酸氢钙、磷酸三钙、磷酸、磷肥等9 种药剂,分别进行了铅污染土壤稳定化试验。针对低浓度污染土壤,采用10%石灰、20%石灰、10%水泥、20%的水泥、10%的磷酸二氢钙、10%磷酸三钙、20%磷酸三钙、10%磷酸二氢铵、20%磷酸二氢铵和20%的磷酸可以达到修复目标。针对高浓度污染土壤,当添加20%的水泥、20%的磷酸氢钙、10%磷酸三钙、20%磷酸三钙、10%磷酸二氢铵、20%磷酸二氢铵、10%磷酸和20%磷酸可以达到修复目标。从修复成本考虑,建议采用水泥作为稳定化药剂,低浓度污染土壤的添加量为10%,高浓度污染土壤的添加量为20%。     

森林土壤表层土的生态毒性评估

A series of 9 soil samples were taken at a timber treatment site in SW France where Cu sulphate and chromated copper arsenate (CCA) have been used as wood preservatives (Sites P1 to P9) and one soil sample was collected at an adjacent site on the same soil type (Site P10). Copper was a major contaminant in all topsoils, varying from 65 (Soil P5) to 2600 mg Cu kg^-1 (Soil P7), exceeding background values for French sandy soils. As and Cr did not accumulate in soil, except at Site P8 (52 mg As kg^-1 and 87 mg Cr kg^-1) where CCA-treated posts were stacked. Soil ecotoxicity was assessed with bioassays using radish, lettuce, slug Arion rufus L., and earthworm Dendrobaena octaedra (Savigny). There were significantly differences in lettuce germination rate, lettuce leaf yield, radish root and leaf yields, slug herbivory, and earthworm avoidance. An additional bioassay showed higher negative impacts on bean shoot and root yields, Rhizobium nodule counts on Bean roots, and guaiacol peroxidase activity in primary Bean leaves for soil from Site P7, with and without fertilisation, than for soil from Site P10, despite both soils having a similar value for computed free ion Cu²⁺ activity in the soil solution (pCu²⁺). Beans grown in soil from Site P7 that had been fertilised showed elevated foliar Cu content and phytotoxic symptoms. Soils from Sites P7 (treatment plant) and P6 (storage of treated utility poles) had the highest ecotoxicity, whereas soil from Site P10 (high organic matter content and cation exchange capacity) had the lowest. Except at Site P10, the soil factor pCu²⁺ computed with soil pH and total soil Cu could be used to predict soil ecotoxicity.     

石油污染土壤的微生物修复研究进展

在污染土壤修复技术中,微生物修复成本低廉、操作简单、修复效果好,是一类环境友好的绿色技术,在当前最具应用前景.对石油污染土壤的微生物修复技术及其影响因素进行了全面评述,并针对该方法的局限性对其研究重点进行了展望.