Background

Macroinvertebrates in aquatic ecosystems are repeatedly exposed to pesticides during their life cycle. Effects of consecutive exposure during different life stages and possible synergistic effects are not addressed in the standardized hazard assessment. The present study investigated two environmentally relevant exposure scenarios in batch (microcosm) and artificial indoor stream (mesocosm) experiments using the larvae of the mayfly Rhithrogena semicolorata (grazer) and natural aufwuchs. Grazers were analysed regarding growth, physiological condition, and drift behaviour, while the aufwuchs was analysed in terms of biomass using the particulate organic carbon as well as the chlorophyll a content. The aim was to reveal direct and indirect effects of an herbicide exposure during autumn on juvenile grazers and an insecticide exposure during spring on semi-juvenile grazers.

Results

Direct and indirect effects were found in both exposure scenarios at environmentally relevant concentrations. In the herbicide exposure scenario with terbutryn, clear direct effects on the aufwuchs community with a LOEC of 0.38 µg L⁻¹ were found. Effect levels of grazers due to indirect effects were equal, with the overnight drift being the most sensitive grazer endpoint. In the insecticide exposure scenario, clear lethal and sub lethal effects of lambda-cyhalothrin were evident. Derived LC₅₀ values for the artificial indoor stream and batch experiment were 2.42 µg g⁻¹ OC (69 days) and 1.2 µg g⁻¹ OC (28 days), respectively. Sub lethal effects in terms of increased drift as well-reduced growth and triglyceride levels were found at concentrations of 1.4 and 0.09 µg g⁻¹ OC (LOECs). These results were confirmed by the batch experiment, which revealed effect values in the similar range. Finally, a clear indirect effect of the insecticide on the aufwuchs was evident in the batch experiment with an LOEC at 0.9 µg g⁻¹ OC.

Conclusion

Toxicity Exposure Ratios calculated with the derived effect values indicate a risk for the investigated grazer by both pesticides. Moreover, observed indirect effects during the herbicide exposure seem to be able to affect the grazers during a second exposure with an insecticide, due to reduced physiological conditions. We suggest further research with time-shifted exposure scenarios to gain a better understanding of the complex interactions of pesticides with the life cycle and the food webs of macroinvertebrates.

中文翻译：

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杀虫剂在其生命周期中对底栖食草动物的直接和间接影响。

背景

水生生态系统中的大型无脊椎动物在其生命周期中反复接触农药。标准化危害评估中未涉及不同生命阶段连续接触的影响和可能的协同效应。本研究使用蜉蝣Rhithrogena semicolorata的幼虫，在批次（微观世界）和人工室内流（中宇宙）实验中调查了两种与环境相关的暴露场景(grazer) 和自然 aufwuchs。对食草动物的生长、生理条件和漂移行为进行了分析，而使用颗粒有机碳和叶绿素 a 含量对 aufwuchs 的生物量进行了分析。目的是揭示秋季除草剂暴露对幼年食草动物的直接和间接影响，以及春季杀虫剂暴露对半幼年食草动物的直接和间接影响。

结果

在环境相关浓度的两种暴露情景中都发现了直接和间接影响。在使用特布林的除草剂暴露情景中，发现了对 aufwuchs 群落的明显直接影响，LOEC 为 0.38 µg L ^-1。由于间接影响，食草动物的影响水平相同，过夜漂移是最敏感的食草动物终点。在杀虫剂暴露情景中，λ-三氯氟氰菊酯的明显致死和亚致死效应是明显的。人工室内流和批次实验的衍生 LC ₅₀值为 2.42 µg g ^-1  OC（69 天）和 1.2 µg g ^-1OC（28天），分别。^{在 1.4 和 0.09 µg g -1}  OC (LOECs)的浓度下发现了在增加漂移方面的亚致死效应，因为生长和甘油三酯水平显着降低。这些结果通过批量实验得到证实，该实验揭示了相似范围内的效果值。^{最后，在 LOEC 为 0.9 µg g -1}  OC的批量实验中，杀虫剂对 aufwuchs 有明显的间接影响。

结论

使用衍生效应值计算的毒性暴露比表明两种农药对所研究的食草动物的风险。此外，由于生理条件降低，在除草剂暴露期间观察到的间接影响似乎能够在第二次暴露于杀虫剂期间影响食草动物。我们建议进一步研究时移暴露场景，以更好地了解农药与大型无脊椎动物的生命周期和食物网的复杂相互作用。