Background

OECD TG 309 “Aerobic Mineralisation in Surface Water” (OECD Test Guideline 309 (2004)) is currently used in regulation for the assessment of the persistence of chemicals in surface water. The test is performed in a batch under defined conditions. Processes which might be relevant for the fate of a chemical in surface water like direct and indirect photolysis are not addressed. In order to study the impact of sunlight on the fate in surface water, pendimethalin, a herbicidal active substance with known sensitivity to aqueous photolysis, was used. This was tested in an experiment based on OECD 309, but scaled up to 900 L size with a 1.40 m water column and irradiated with special lamps in order to monitor the fate of the substance at different water depths, in comparison to dark controls.

Results

Pendimethalin degraded significantly under the applied test conditions. The test setups with exposure to simulated sunlight showed a significant faster degradation compared to the dark experiments. Application of 900 g sediment (1% of test system) to the test system further increased the degradation rate. In the simulated sunlight setups a faster degradation was observed in the upper water layer, hence, the concentration of the photolysis products were highest in the upper water layer, where the highest light intensity was measured. With decreasing light intensity in deeper water layers photolysis products were still detected at a water depth of 125 cm. Mineralisation up to 22% of the applied radioactivity was observed. In the dark controls neither significant amounts of photolysis products nor any mineralisation were detected. Among the different sampling depths no significant differences were observed. It was further observed that the dark controls became anaerobic at the end of the incubation time. This has been observed previously in standard laboratory tests according to OECD 309.

Conclusions

The study proves that for a substance sensitive to photolysis like pendimethalin, exposure to simulated sunlight leads to a significantly reduced degradation half-life (DegT₅₀) in surface water compared to the dark control. In the standard test according to OECD guideline 309 the influence of photolytical degradation is not considered and thus the laboratory test can lead to the overestimation of the persistence of a chemical in surface water and consequently to a false-positive evaluation in the overall PBT assessment (ECHA Guidance on Information Requirements and Chemical Safety Assessment 2004), when only the results of the standard OECD 309 study are considered.

中文翻译：

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根据OECD TG 309的放大实验，模拟日光对地表水中二甲戊乐灵降解的影响

背景

经合组织TG 309“地表水中的需氧矿化”（经合组织测试指南309（2004年））目前用于规章中，以评估地表水中化学物质的持久性。在定义的条件下分批执行测试。没有解决可能与地表水中化学物质的命运有关的过程，例如直接和间接光解。为了研究日光对地表水中命运的影响，使用了对水光分解敏感性已知的除草活性物质二甲戊灵。在基于OECD 309的实验中对此进行了测试，但与深色对照相比，它在1.40 m的水柱上可放大至900 L，并用特殊的灯照射，以监测该物质在不同水深下的命运。

结果

在应用的测试条件下，二甲戊乐灵显着降解。与黑暗实验相比，暴露在模拟阳光下的测试装置显示出明显更快的降解。将900 g沉积物（测试系统的1％）添加到测试系统中，可进一步提高降解速度。在模拟的日光设置中，在上部水层中观察到了更快的降解，因此，光解产物的浓度在上部水层中最高，在那里测量到最高的光强度。随着更深水层中光强度的降低，仍在125 cm水深处检测到光解产物。观察到矿化度高达所施加放射性的22％。在黑暗对照中，未检测到大量的光解产物或任何矿化。在不同的采样深度之间，未观察到显着差异。进一步观察到，黑暗的对照在孵育时间结束时变成厌氧的。以前在根据OECD 309的标准实验室测试中已经观察到了这一点。

结论

这项研究证明，对于诸如戊二甲戊灵这样对光解敏感的物质，与黑暗对照相比，暴露于模拟阳光下会导致地表水中降解半衰期（DegT ₅₀）大大降低。在根据OECD准则309进行的标准测试中，未考虑光解降解的影响，因此实验室测试可能导致高估了地表水中化学物质的持久性，并因此导致整个PBT评估中的假阳性评估（仅考虑标准OECD 309研究的结果时，《 ECHA信息要求和化学安全评估指南2004》。