Pablo Fleur, Hyne Ross V
Department of Environment and Climate Change, Centre for Ecotoxicology, Lidcombe, NSW, Australia.
Arch Environ Contam Toxicol. 2009 Apr;56(3):525-35. doi: 10.1007/s00244-008-9251-1. Epub 2008 Oct 21.
A model mesocosm system was used to simulate the effect of endosulfan entering a waterway from episodic events such as accidental overspray or in runoff water containing contaminated sediment following storm events. The fate of technical endosulfan applied to a 24-stream mesocosm was compared in experiments where the pesticide was applied either directly as water contamination or after being pre-bound to sediment. The flow of water through the streams was discontinued for a 10-12 h period following the pesticide application. Following the water application, only approximately 3% of endosulfan remained in the streams after 4 days and then was not detectable after 7 days. In contrast, after application pre-bound to sediment, approximately 33% of the endosulfan remained in the streams after 4 days and 14% after 7 days. Additionally, with the sediment-bound application, the proportion of endosulfan was higher in the substrate (11%) after 7 days than in the overlying water (3%), and approximately 1% was oxidised to the sulphate form. The dissipation of endosulfan in the water column of both experiments followed a two-parameter exponential decay model characterised by a relatively fast first-order single-phase process. In sediment of both experiments and the gravel of the sediment-dosing experiment, the dissipation of endosulfan followed more closely a four-parameter bi-exponential decay model characterised by first-order kinetics of two fractions: the first fraction dissipates quickly, and in the longer term the second fraction dominates the overall dissipation with a slower rate. In the gravel section of the water-dosing experiment, endosulfan dissipation was characterised by relatively very slow two-parameter exponential decay. The overall dissipation rates of the alpha- and beta-endosulfan isomers were significantly higher in the water-dosing than in the sediment-dosing experiment, except in the gravel section of the mesocosm. The uptake of the endosulfan into passive samplers constructed from polyethylene membrane bags containing trimethylpentane solvent (TRIMPS) placed in the overlying water was linear. In contrast, TRIMPS buried in sediment failed to uptake endosulfan from the sediment substrate, indicating that short-term deployment of passive samplers can only be used to determine time-weighted average concentrations of bioavailable chemicals in the water column. A 34-h LC50 of 2.8 microg/l [95% confidence interval (CI) 1.5-4.2 microg/l] for juveniles of the native fish Macquaria ambigua was obtained when exposed during the water-dosing experiment. This study demonstrated that the pulse entry of sediment contaminated with endosulfan into a receiving waterway was more persistent compared with direct aqueous contamination and the endosulfan would be bioavailable to pelagic organisms following a gradual partitioning to the water column.
一个模型中宇宙系统被用于模拟硫丹从偶然的过度喷洒等突发事件进入水道，或在暴雨事件后随含有受污染沉积物的径流进入水道的影响。在实验中，比较了应用于24条溪流中宇宙的工业用硫丹的归宿，其中农药要么直接作为水污染施加，要么预先与沉积物结合后施加。在施加农药后，水流在溪流中中断10 - 12小时。在施加水之后，4天后只有约3%的硫丹残留在溪流中，7天后则检测不到。相比之下，预先与沉积物结合施加后，4天后约33%的硫丹残留在溪流中，7天后为14%。此外，对于与沉积物结合的施加方式，7天后硫丹在底质中的比例（11%）高于上覆水中的比例（3%），且约1%被氧化为硫酸盐形式。两个实验中水柱中硫丹的消散均遵循双参数指数衰减模型，其特征为相对快速的一级单相过程。在两个实验的沉积物以及沉积物加药实验的砾石中，硫丹的消散更符合四参数双指数衰减模型，其特征为两个组分的一级动力学：第一组分快速消散，从长期来看第二组分以较慢速率主导总体消散。在加水实验的砾石部分，硫丹消散的特征为相对非常缓慢的双参数指数衰减。除了在中宇宙的砾石部分，α - 和β - 硫丹异构体的总体消散速率在加水实验中显著高于沉积物加药实验。硫丹被吸收到置于上覆水中的由含有三甲基戊烷溶剂（TRIMPS）的聚乙烯膜袋构建的被动采样器中呈线性关系。相比之下，埋在沉积物中的TRIMPS未能从沉积物底质中吸收硫丹，这表明被动采样器的短期部署只能用于确定水柱中生物可利用化学物质的时间加权平均浓度。在加水实验期间暴露时，本地鱼类麦氏麦鳕幼鱼的34小时半数致死浓度（LC50）为2.8微克/升[95%置信区间（CI）1.5 - 4.2微克/升]。这项研究表明，与直接水污染相比，受硫丹污染的沉积物脉冲式进入受纳水道更具持久性，并且硫丹在逐渐分配到水柱后对浮游生物具有生物可利用性。
