不同含磷化合物修复铅污染土壤后的人体健康风险评价

磷酸盐钝化铅是铅污染土壤的重要修复技术之一.但磷酸盐修复土壤铅污染后,土壤铅对人体的健康风险仍缺乏系统研究.本研究通过向铅污染土壤添加五种不同的含磷化合物(KH_2PO_4、NH_4H_2PO_4、CaHPO_4,植酸和卵磷脂),分析了其对铅污染土壤的钝化效果,运用in vitro和SHIME模型评估修复后土壤铅对人体的健康风险.结果表明,添加含磷化合物30 d后,五种处理均有效降低了铅的DTPA和CaCl_2可提取态,分别降低了62.5%—66.5%和27.8%—49.5%,其中植酸和CaHPO_4处理效果较好,卵磷脂处理效果较差.5种处理中,铅的生物可给性在胃、小肠和结肠阶段有显著差异,分别为8.67%—9.31%、0.88%—1.55%、2.06%—2.76%,由于受pH的影响,铅在胃阶段生物可给性最高且各处理之间差异不明显,在小肠阶段KH_2PO_4处理土壤铅的生物可给性最低,卵磷脂处理铅的生物可给性最高,结肠阶段NH_4H_2PO_4处理土壤铅的生物可给性最低,卵磷脂处理铅的生物可给性最高.结肠阶段铅的生物可给性均高于小肠阶段的,可见肠道微生物促进了土壤中Pb的溶出,提高了铅的生物可给性,增加了人体的健康风险.在添加同等含量的含磷化合物修复铅污染土壤后,KH_2PO_4处理对人体健康风险最小,卵磷脂最大.     

有机肥对铅在土壤中形态分配的影响

为了解铅污染商品有机肥对培养土壤中铅形态的影响以及低铅含量有机肥对外源铅污染土壤中铅形态分配的影响,在海南采集了4种商品有机肥样品,进行有机肥与土壤铅污染的老化培养实验.结果表明,原土壤中重金属铅主要以交换态(33.43%)和残渣态(30.03%)存在,随着海藻有机肥(HK01)和羊粪有机肥(DF01)施肥量的增加,处理土壤中交换态铅的比例显著降低(P0.05),有机结合态从9.56%提高到22.05%.外源铅(250 mg·kg-1)污染土壤中以交换态(36.21%)、铁锰态(27.03%)和碳酸盐结合态铅(23.54%)为主;随着有机肥料添加量的增大,格瑞龙有机肥处理后,污染土壤中的交换态铅的比例有所下降,添加量为10%时比例最低为27.80%;有机结合态和残渣态铅的比例上升,在20%时比例最大为13.68%、13.35%.鱼蛋白豆粕有机肥处理的土壤中交换态铅和碳酸盐结合态铅比例下降,在添加量为20%时比例分别降低到11.75%和11.89%,铁锰氧化物结合态铅变化不显著;铅主要转入有机结合态铅和残渣态,平均增长比例分别为8.42%、3.03%.施用有机肥经过足够长时间的老化均会使土壤中的有效性高的铅转化成稳定态的铅,因此有机肥对铅污染的土壤的修复作用较大.但是由于重金属铅的移动性差,会累积在土壤表层,施用有机肥前还是要经过检测,选用相对安全的有机肥改良土壤.     

土壤中铅的吸附-解吸行为研究进展

铅是重要的土壤重金属污染元素之一，了解铅在土壤中的物理化学行为，有利于预防和修复土壤的铅污染。土壤中铅的吸附-解吸行为，依吸附机理的不同，分为专性吸附和非专性吸附。土壤铅吸附的机理还存在不同的观点，如水解吸附／非水解吸附机理，单分子吸附／双分子吸附机理等。影响土壤中铅吸附-解吸行为的主要因素，有土壤矿物组成、土壤有机质、pH、温度、竞争离子等。文章最后对描述土壤铅吸附过程的主要数学方程(Langmuir方程、Freundlich方程和Temkin方程)作了论述。     

腐殖酸对土壤铅赋存形态的影响

通过室内培养试验,深入探讨了不同用量腐殖酸,对铅污染土壤中铅各形态的影响.结果表明,腐殖酸各处理均能显著降低土壤中铅的交换态(EX-),碳酸盐结合态(Cob-)和铁锰氧化物结合态(FeMn-)的含量,而有机结合态(Ob-)铅和残渣态(Res-)铅的含量则显著提高.施用腐殖酸有效地降低了铅的活性,且影响程度随腐殖酸用量的增加而显著增加.腐殖酸对土壤中铅离子的各形态含量随时间的变化的影响表现为,在培养040 d期间,随培养时间的延长交换态铅含量无明显变化,残渣态铅含量显著降低,其它三种形态均呈增加趋势;培养40 d后,随培养时间的延长各形态的含量均无显著变化.综合考虑认为施入10%质量比的腐殖酸即可显著降低铅的活性,从而可达到较好的修复效果.     

天然沸石对番茄及土壤中铅的影响

为探索沸石对轻度铅污染土壤的修复效果及农业安全生产可行性,利用盆栽试验研究了不同沸石添加量及不同沸石粒级等因素对不同生长时期番茄（Solanum lycopersicum）植株铅质量分数、累积量和土壤铅质量分数的影响。结果表明,添加天然沸石可提高土壤有效铅质量分数,不同程度地增加番茄地上部生物量,具有提高番茄茎叶铅质量分数及积累量、果实产量的趋势,也具有降低收获期根部铅质量分数及积累量的趋势。18g·kg-1是提高地上部生物量,抑制土壤铅污染、茎叶和根部铅积累的最佳沸石添加量,但有促进果实铅积累的趋势;沸石添加量为10g·kg-1则在提高土壤有效铅质量分数的同时可抑制果实铅的积累。中粒级沸石可抑制果实铅积累,大粒级为削减根部铅积累量促进茎叶铅积累的最佳沸石粒级,小粒级沸石则可抑制收获期茎叶铅的积累。     

壳聚糖辅助下玉米修复铅污染土壤能力的研究

为了研究壳聚糖辅助下玉米(ZeamaysL.)对铅污染土壤的修复能力,采用L9(34)正交试验进行研究,考虑了4因素3水平,4因素为土壤铅含量、壳聚糖含量、壳聚糖溶液pH值以及加入壳聚糖后的提取时间.研究结果表明,加入壳聚糖会造成玉米生长停滞,甚至死苗,原因在于壳聚糖属于天然高分子有机物,会造成土壤板结,阻碍植物吸收水分,同时壳聚糖将土壤中的大量重金属溶出,造成玉米重金属中毒.加入壳聚糖后,玉米对铅的吸收较对照结果有很大提高,壳聚糖能够促进铅元素从土壤向植物体内转移,但壳聚糖促进铅元素从玉米地下部分向地上部分转移的能力较弱;综合壳聚糖的促进效果,在土壤铅含量为1.8g·kg-1,壳聚糖含量为5mmol·kg-1(土),壳聚糖溶液pH值为4.5,提取时间为7天的条件下,有利于促进铅在玉米地上部分的吸收.     

沈阳市加杨(Populus Candensis)叶铅污染的空间分布

实地调查采样、结合GIS技术进行室内综合分析,系统研究了沈阳市加杨叶铅污染的空间分布状况.结果表明,沈阳市加杨(Populus canadensis)叶铅质量分数是0.68～106.767 mg·kg-1,平均值是17.416 mg·kg-1,是对照点叶铅质量分数的15.18倍.叶铅污染较严重.叶铅质鼍分数空间分异大,已形成4个高浓度中心.不同功能区加杨叶铅质量分数由大到小的顺序是:工业区,商业区,二类混合区,居民文教区,一类混合区,对照区.与点状污染源距离越远,叶铅质量分数越小.加杨叶铅质量分数和土壤相关性极其显著,这说明沈阳市实行无铅汽油之后,植物叶铅主要来自土壤.     

浑河冲洪积平原土壤及浅层地下水中铅的分布特征

为探讨浑河冲洪积扇土壤及浅层地下水中铅的含量、来源及其分布特征,对研究区50个土壤样品、5个地表水样品和22个浅层地下水样品进行了铅含量分析.结果表明,研究区土壤、地表水和浅层地下水均受到了一定程度的铅污染.表层土壤铅含量较高,在17.72—114.46 mg.kg-1之间,受人为污染影响较大;随土壤深度的增加铅含量呈现逐渐降低的趋势,其迁移规律与铬、砷、铜等重金属密切相关,受土壤性质和有机质含量的影响较大,为研究区土壤和浅层地下水环境风险评价及污染防治提供了科学依据.     

铅锌冶炼厂渣堆场周边土壤铅污染特征

金属冶炼过程留下的废渣经过雨水冲刷及渗滤液等的作用使残留在废渣中的重金属发生迁移转化,导致渣堆场下及周边土壤受到重金属污染。了解冶炼厂渣堆场下及周边土壤重金属污染状况对场地修复及土地利用规划均有重大意义。本研究调查了湖南某铅锌冶炼厂渣堆场0~4 km内三个采样区0~20 cm表层土壤及0~100 cm深度土壤中铅的污染状况,采用单项污染指数法进行铅污染评价,并分析了铅纵向迁移随深度变化和横向迁移随距离变化的分布特征。结果表明,铅锌冶炼厂渣堆场下及周边0~1 km范围内土壤受到了铅污染,渣堆场下、距渣堆场10 m处及1 km处表层土壤中重金属铅的质量分数分别可达775.25、645.33和309.80 mg·kg^-1,超过了当地土壤中铅的背景值,也超过了土壤二级质量标准甚至三级质量标准。三个采样区的铅污染指数分别为2.6、2.1及1.03,污染等级均为Ⅱ级,污染程度为轻度污染。三个采样区土壤中铅污染主要集中于0~20 cm土壤层中,铅的质量分数分别达775.25,645.33和309.80 mg·kg^-1,20~100 cm土壤层中铅的质量分数低于0~20 cm的,分别在88.48~120.96 mg·kg-1、235.01~380.16 mg·kg^-1及309.80~59.32 mg·kg^-1之间。渣堆场下土壤中的铅从0~20cm土壤层往下至20~100cm土壤层迁移量远小于距渣场10 m处及1 km处的。三个采样区表层0~20 cm土壤层中铅的变化规律为距渣堆场0 m（渣堆场下）〉距渣堆场10 m〉距渣堆场1 km〉距渣堆场4 km,质量分数随距离增加而降低。20~40 cm及40~60 cm土壤层中铅的变化规律为距渣堆场10 m〉距渣堆场1 km〉距渣堆场0 m处（渣堆场下）〉距渣堆场4 km,60~80 cm及80~100 cm土壤层的变化规律为距渣堆场10 m〉距渣堆场0 m处（渣堆场下）〉距渣堆场1 km〉距渣堆场4 km,铅的质量分数随距离的增加先升高后降低。     

蜂窝煤灰渣和磷肥结合修复铅污染贫磷潮土的研究（Remediation of Lead Polluted Chaotu Soil with Low Phosphorus Availability by Application of Honeycomb Briquette Combustion Residue and Phosphorus Fertilizer）

利用蜂窝煤灰渣和磷肥结合稳定铅污染贫磷(Olsen-P=2.50mg·kg-1)潮土中铅的可行性.采用盆栽试验,设置0和500mg·kg-1两个Pb用量,灰渣用量分别为干土质量的0%和2%,P:Pb分别为0和4.种植黑麦草,植物生长85d后收获,测定植物产量、土壤DTPA-Pb、Olsen-P含量、pH值和电导率(EC).结果表明,在两个Pb用量及两个P:Pb比例下,加入灰渣后,土壤的DTPA-Pb含量均降低,平均降低5.61%.其中加铅未加磷处理灰渣效果达到0.05的显著水平,各加Pb处理中,同时加入磷肥和灰渣处理土壤的DTPA-Pb含量最低;加入灰渣后处理土壤中的Olsen-P含量均增加,平均增加了2.71mg·kg-1,各处理土壤pH值上升约0.1个单位,加入灰渣也导致各处理土壤的EC增加.各处理条件下加入灰渣后植物产量均减小.在未加磷土壤中加入Pb后,土壤Olsen-P含量显著增加(p<0.05),表明高铅有效性下,植物可能通过根系分泌物增加了土壤磷的有效性.以上结果表明,蜂窝煤灰渣有可能用于降低污染土壤中铅的有效性,但其对植物生长的抑制作用需要克服.     

土壤中铜的生物可给性及其对人体的健康风险评价

为了研究土壤中铜的生物可给性与土壤理化性质之间的相互关系以及人体无意摄入土壤铜的风险,采集我国一些地区的15个土壤样品,利用in vitro方法研究了这些土壤中铜的生物可给性及其对人体的健康风险。结果表明,有2个土壤样品中铜的含量高过我国土壤环境质量标准的三级标准,有8个土壤样品中铜的含量高过二级标准;土壤中铜的溶解态浓度及其生物可给性变化很大,胃肠阶段铜的溶解态含量分别为5.2~308.8 mg·kg~(-1)和5.9~348.5 mg·kg~(-1),平均值分别为74.8 mg·kg~(-1)和82.0 mg·kg~(-1);而铜的生物可给性分别为183%~66.6%和213%~77.4%,平均值分别为442%和51.1%。胃阶段铜的生物可给性与土壤有机质和pH呈显著正相关,而与粘粒呈显著负相关,与铁铝氧化物有显著相关性;小肠阶段铜的生物可给性与土壤有机质和pH呈显著正相关,与土壤中总铜和锰氧化物含量呈显著负相关。如以胃阶段为判断,无意摄人土壤中铜对儿童的TDI(tolerable daily intake)贡献率除浙江富阳为2.51%外,有12个土壤样品低于1.00%,最低为0.11%。如以小肠阶段为判断,无意摄入土壤中铜对儿童的TDI贡献率除浙江富阳和浙江台州的土壤分别为2.83%和2.01%,另有12个土壤样品低于1.00%。可见,对于本研究中大多数土壤,通过口部无意摄入土壤中铜的对人体并没有很高的风险。     

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.     

土壤中金属的生物可给性及其动态变化的研究

土壤中金属的生物可给性常应用于人体健康风险评价,如能准确地判定土壤中金属在胃肠阶段不同时间的溶出动态,研究者就可以更好地分析其对人体的健康风险。本文采集5种不同地区的重金属污染的土壤,利用改进的PBET方法,分别在胃阶段的20、40、60、80 min以及小肠阶段的1、2、3、4、5 h时取样并分析,探究土壤中8种金属元素（As、Al、Cd、Cr、Fe、Mn、Ni、Pb）的生物可给性和溶出动态,探讨造成金属溶出动态变化的影响因素,对其溶出机理进行初步探究。研究结果表明,Fe、Al的生物可给性较低,并且在胃肠阶段差异较小。与胃阶段相比,土壤中Pb、Cd的生物可给性在小肠阶段明显降低,而As、Mn、Cr、Ni的生物可给性在小肠阶段均升高。升幅最大的两个元素是Ni、Cr,其小肠阶段的平均生物可给性分别升高61.4%、29.9%。在溶出量随时间变化方面,在胃阶段,假定1 h时溶出率为100%。20 min时,土壤中Fe、Ni的平均溶出率较低,分别为59.3%、56.8%,其他6种金属元素的平均溶出率在71.2%~79.5%。As、Cd、Pb的溶出速率是先快后慢,Cr和Ni的溶出速率是先慢后快,而Fe、Mn、Al的溶出速率基本保持不变。在小肠阶段,假定4 h时溶出率为100%。Al、As、Cd、Mn的溶出率基本不变。1 h时,土壤中Cr（土壤A除外）、Ni的平均溶出率最低,分别为31.5%、32.7%,而5 h时,Fe、Cr、Ni的溶出率还在升高。由此可见,土壤中不同金属元素的生物可给性以及溶出动态是有明显差异的。     

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.     

Enrichment and solubility of trace metals associated with magnetic extracts in industrially derived contaminated soils

Magnetic fractions (MFs) in industrially derived contaminated soils were extracted with a magnetic separation procedure. Total, soluble, and bioaccessible Cr, Cu, Pb and Zn in the MFs and non-magnetic fractions (NMFs) were analyzed using aqua regia and extraction tests, such as deionized water, toxicity characteristic leaching procedure (TCLP), and gastric juice simulation (GJST) test. Compared with the non-magnetic fractions, soil MFs were enriched with Fe, Mn, Pb, Cd, Cr, Cu, and Ni. Extraction tests indicated that soil MFs contained higher water, TCLP, and GJST-extractable Cr, Cu, Pb, and Zn concentrations than the soil NMFs. The TCLP-extractable Pb concentration in the MFs exceeded the USEPA hazardous waste criteria, suggesting that soil MFs have a potentially environmental pollution risk. Solubility of trace metals was variable in the different extraction tests, which has the order of GJST?>?TCLP?>?water. TCLP test showed Cu and Zn were more mobile than Cr and Pb while bioaccessibility of trace metal defined by GJST test showed the order of Cu?≈?Cr?≈?Zn?>?Pb. These findings suggested that the MFs in the industrially derived contaminated soils had higher possibility of polluting water bodies, and careful environmental impact assessment was necessary.     

小白菜的干鲜状态对其铅的生物可给性的影响(Effects of Dry and Fresh States of Brassica chinensis on the Oral Bioaccessibility of Lead)

为了研究小白菜的干鲜状态对其铅的生物可给性的影响,设置了对照(不添加铅,本底值为32.37mg·kg-1)、300mg·kg-1和500mg·kg-13种土壤铅浓度处理的盆栽实验,并将收获的小白菜分别以干样和鲜样进行基于生理学的invitro人工胃肠模拟实验,测定其中铅的生物可给性.结果表明:栽种2个月后,小白菜铅含量分别达到0.38mg·kg-1、4.55mg·kg-1和12.50mg·kg-1(干重),对铅的富集系数分别为0.012、0.015和0.025,可能存在较高的健康风险.invitro实验表明:样品干鲜状态、铅浓度处理以及二者的交互效应是影响铅的生物可给性的重要因素.无论干样还是鲜样,铅在胃阶段和小肠阶段的溶解态量均随样品铅含量的增加而线性增加;对于同一铅浓度处理,鲜样中铅的生物可给性无论在胃阶段还是小肠阶段均显著高于干样(p<0.01).使用干样进行健康风险评价可能会低估小白菜中的铅对人体的健康风险.     

The relationship between soil geochemistry and the bioaccessibility of trace elements in playground soil

A total of 32 samples of surficial soil were collected from 16 playground areas in Madrid (Spain), in order to investigate the importance of the geochemistry of the soil on subsequent bioaccessibility of trace elements. The in vitro bioaccessibility of As, Co, Cr, Cu, Ni, Pb and Zn was evaluated by means of two extraction processes that simulate the gastric environment and one that reproduces a gastric?+?intestinal digestion sequence. The results of the in vitro bioaccessibility were compared against aqua regia extractions (“total” concentration), and it was found that total concentrations of As, Cu, Pb and Zn were double those of bioaccessible values, whilst that of Cr was ten times higher. Whereas the results of the gastric?+?intestinal extraction were affected by a high uncertainty, both gastric methods offered very similar and consistent results, with bioaccessibilities following the order: As?=?Cu?=?Pb?=?Zn?>?Co?>?Ni?>?Cr, and ranging from 63 to 7?%. Selected soil properties including pH, organic matter, Fe and CaCO₃ content were determined to assess their influence on trace element bioaccessibility, and it was found that Cu, Pb and Zn were predominantly bound to organic matter and, to a lesser extent, Fe oxides. The former fraction was readily accessible in the gastric solution, whereas Fe oxides seemed to recapture negatively charged chloride complexes of these elements in the gastric solution, lowering their bioaccessibility. The homogeneous pH of the playground soils included in the study does not influence trace element bioaccessibility to any significant extent except for Cr, where the very low gastric accessibility seems to be related to the strongly pH-dependent formation of complexes with organic matter. The results for As, which have been previously described and discussed in detail in Mingot et al. (Chemosphere 84: 1386–1391, 2011), indicate a high gastric bioaccessibility for this element as a consequence of its strong association with calcium carbonate and the ease with which these bonds are broken in the gastric solution. The calculation of risk assessments are therefore dependant on the methodology used and the specific environment they address. This has impacts on management strategies formulated to ensure that the most vulnerable of society, children, can live and play without adverse consequences to their health.     

典型农耕区黑土和沼泽土团聚体颗粒中重金属的分布特征解析

了解重金属在土壤中的富集特征是其风险评价和土壤修复的基础。分别以黑龙江省典型的农耕黑土和沼泽土为研究对象,采用干筛法获得〉4000、4000～2000、2000～1000、1000～250、250～53和〈53衄16个粒级的土壤团聚体颗粒组。利用等离子质谱（ICP-MS）测定了本土和各级团聚体颗粒中Cr、Cd、As和Pb的含量,并对其颗粒组分布特征及对有机碳的响应进行了解析。研究表明,2种土壤中的重金属Cr、Cd和Pb的富集因子均大于1,而As则存在明显的流失。除了黑土中的As和Pb外,其他重金属随着团聚体粒径的增加而呈现富集减弱的趋势。其中,cr和cd主要趋向分布在粉．黏团聚体（〈53wn）颗粒中;Pb在黑土中易赋存于1000～2000μm大团聚体中,在沼泽土中则富集于53～250μm的微团聚体中;As不但趋向被吸附在53～250μm的微团聚体中,而且在黑土中也容易被吸附在〉l000μm的大团聚体中。金属质量负载计算表明,大粒径颗粒组对土壤中重金属含量的总体贡献较大。土壤中有机碳含量均随着团聚体粒径减小而升高,cr和Cd分布与颗粒有机碳含量正相关,黑土中As的分布与颗粒中有机碳含量负相关而在沼泽土中呈弱正相关,Pb的分布则与有机碳含量均无明显的相关性。     

Effect of red mud addition on the fractionation and bio-accessibility of Pb,Zn and As in combined contaminated soil

Using soil incubation experiments, the effect of red mud addition on the fractionation and bioaccessibility of Pb, Zn and As in combined contaminated soil was studied. The results showed that red mud addition could significantly decrease the concentration of HOAc-extractable Pb and Zn in soil. Compared with the control, 5% red mud addition could significantly reduce the concentrations of HOAc-extractable Pb and Zn in soil after 1, 2 and 3 months of incubation [62.5, 65.3 and 73.5% decrease (Pb), 56.7, 65.8 and 67.4% decrease (Zn)]. Whereas adding red mud could remarkably increase the concentrations of specific absorbed As and residual As in soil. The result of a simple bioavailability extraction test (SBET) indicated that all treatments with red mud addition markedly reduced the concentration of bioaccessible Zn but increased the concentration of bioaccessible As in soil, while having little effect on the concentration of bioaccessible Pb in soil. After 3 months incubation, all treatments including 1, 2 and 5% red mud addition reduced the concentration of bioaccessible Zn by 53.1–56.7% compared with the control, but increased the concentration of bioaccessible As by 1.81–6.25 times. The results suggested that red mud is an additive with potential for the remediation soil contaminated soil by combinations of heavy metals, although it should be added based on the different heavy metals in the soil. Combined use of red mud and hyperaccumulators to remediate heavy metal contaminated soil needs further study.     

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.