Abstract：
Large quantities of organochlorine pesticides (OCPs) have been used in tropical regions. The fate processes and risks of these legacy contaminants in the tropics are poorly understood. Herein, we investigated the occurrence of three classes of widely used OCPs and their metabolites in surface and core soil from five cities across Vietnam with a prevalent tropical monsoon climate and a long history of OCP application. We aimed to elucidate migration potentials, degradation conditions, and transformation pathways and assess current health risks of these contaminants. Generally, the concentrations of OCPs and metabolites in the soil core were slightly lower than those in surface soil except for hexachlorocyclohexane (HCH) isomers. 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane (p,p\'-DDT), 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p\'-DDE), the sum of dicofol and 4,4\'-dichlorobenzophenone (p,p\'-DBP), and 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (p,p\'-DDD) were the most abundant compounds in both surface and core soils. A uniform distribution of HCHs (the sum of α-, β-, γ-, and δ-HCH) at trace levels was found in almost all soils, serving as evidence of the lack of recent use of HCH pesticides. Higher concentrations of DDTs (the sum of DDT, DDD, and DDE) were observed in north-central Vietnamese soil, whereas appreciable concentrations of ENDs (the sum of α- and β-endosulfan and endosulfan sulfate) were only found in southern Vietnamese soils. Empirical diagnostic ratios indicated residuals of DDTs were mainly from technical DDT rather than dicofol, whereas aged HCHs could be explained by the mixture of lindane and technical HCH. Both historical applications and recent input explain DDTs and ENDs in Vietnamese soil. Total organic carbon performs well in preventing vertical migration of more hydrophobic DDTs and ENDs. The dominant transformation pathway of DDT in surface soil followed p,p\'-DDE→2,2-bis(4-chlorophenyl)-1-chloroethylene or p,p\'-DDMU→1,1-bis(4-chlorophenyl)ethylene or p,p\'-DDNU→p,p\'-DBP, whereas the amount of p,p\'-DDMU converted from p,p\'-DDD and p,p\'-DDE is similar in soil core. Non-cancer risks of OCPs and metabolites in all soils and cancer risks of those chemicals in core soils were below the safety threshold, whereas a small proportion of surface soil exhibited potential cancer risk after considering the exposure pathway of vegetable intake. This study implied that organic matter in non-rainforest tropical deep soils still could hinder the leaching of hydrophobic organic contaminants as in subtropical and temperate soils. When lands with a history of OCP application are used for agricultural purposes, dietary-related risks need to be carefully assessed.
摘要：
热带地区已使用了大量的有机氯农药（OCP）。人们对热带地区这些遗留污染物的命运过程和风险知之甚少。在这里，我们调查了越南五个热带季风气候普遍且OCP应用历史悠久的城市的表层和核心土壤中三类广泛使用的OCP及其代谢产物的发生。我们旨在阐明迁移潜力，降解条件，和转化途径，并评估这些污染物当前的健康风险。一般来说,除六氯环己烷（HCH）异构体外，土壤核心中的OCP和代谢物浓度略低于表层土壤中的OCP和代谢物浓度。2,2-双(4-氯苯基)-1,1,1-三氯乙烷(p，p\'-DDT)，2,2-双（4-氯苯基）-1,1-二氯乙烯（p，p\'-DDE)，三氯杀螨醇和4,4'-二氯二苯甲酮的总和(p，p\'-DBP)，和2,2-双（4-氯苯基）-1,1-二氯乙烷（p，p'-DDD）是表层和核心土壤中最丰富的化合物。HCHs的均匀分布(α-，β-,γ-,和δ-HCH）在几乎所有土壤中都发现了痕量水平，作为最近缺乏使用六氯环己烷农药的证据。较高浓度的滴滴涕(滴滴涕的总和，DDD,和DDE)在越南中北部土壤中观察到，而仅在越南南部土壤中发现了相当浓度的ENDs（α-和β-硫丹以及硫丹硫酸盐的总和）。经验诊断比表明滴滴涕的残留主要来自技术滴滴涕而不是三氯杀螨醇，而老化的六氯环己烷可以用林丹和工业六氯环己烷的混合物来解释。历史应用和最近的投入都解释了越南土壤中的DDTs和ENDs。总有机碳在防止更疏水的DDT和END的垂直迁移方面表现良好。DDT在表层土壤中的主要转化途径依次为p，p\'-DDE→2,2-双(4-氯苯基)-1-氯乙烯或p,p'-DDMU→1,1-双(4-氯苯基)亚乙基或p,p'-DDNU→p,p\'-DBP,而P的数量，p\'-从p转换的DDMU,p\'-DDD和p,p'-DDE在土芯中相似。所有土壤中OCPs和代谢物的非癌症风险和核心土壤中这些化学物质的癌症风险低于安全阈值。而在考虑蔬菜摄入的暴露途径后，一小部分表层土壤表现出潜在的癌症风险。这项研究表明，非热带雨林热带深层土壤中的有机物仍然会像亚热带和温带土壤一样阻碍疏水性有机污染物的浸出。当具有OCP应用历史的土地用于农业目的时，饮食相关风险需要仔细评估.
