Maloney Erin M, Morrissey Christy A, Headley John V, Peru Kerry M, Liber Karsten
Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Environ Toxicol Chem. 2017 Nov;36(11):3091-3101. doi: 10.1002/etc.3878. Epub 2017 Jul 26.
Extensive agricultural use of neonicotinoid insecticide products has resulted in the presence of neonicotinoid mixtures in surface waters worldwide. Although many aquatic insect species are known to be sensitive to neonicotinoids, the impact of neonicotinoid mixtures is poorly understood. In the present study, the cumulative toxicities of binary and ternary mixtures of select neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) were characterized under acute (96-h) exposure scenarios using the larval midge Chironomus dilutus as a representative aquatic insect species. Using the MIXTOX approach, predictive parametric models were fitted and statistically compared with observed toxicity in subsequent mixture tests. Single-compound toxicity tests yielded median lethal concentration (LC50) values of 4.63, 5.93, and 55.34 μg/L for imidacloprid, clothianidin, and thiamethoxam, respectively. Because of the similar modes of action of neonicotinoids, concentration-additive cumulative mixture toxicity was the predicted model. However, we found that imidacloprid-clothianidin mixtures demonstrated response-additive dose-level-dependent synergism, clothianidin-thiamethoxam mixtures demonstrated concentration-additive synergism, and imidacloprid-thiamethoxam mixtures demonstrated response-additive dose-ratio-dependent synergism, with toxicity shifting from antagonism to synergism as the relative concentration of thiamethoxam increased. Imidacloprid-clothianidin-thiamethoxam ternary mixtures demonstrated response-additive synergism. These results indicate that, under acute exposure scenarios, the toxicity of neonicotinoid mixtures to C. dilutus cannot be predicted using the common assumption of additive joint activity. Indeed, the overarching trend of synergistic deviation emphasizes the need for further research into the ecotoxicological effects of neonicotinoid insecticide mixtures in field settings, the development of better toxicity models for neonicotinoid mixture exposures, and the consideration of mixture effects when setting water quality guidelines for this class of pesticides. Environ Toxicol Chem 2017;36:3091-3101. © 2017 SETAC.
新烟碱类杀虫剂产品在农业中的广泛使用导致了全球地表水中存在新烟碱类混合物。尽管已知许多水生昆虫物种对新烟碱类敏感，但对新烟碱类混合物的影响却知之甚少。在本研究中，以幼虫摇蚊Chironomus dilutus作为代表性水生昆虫物种，在急性（96小时）暴露情景下，对选定新烟碱类（吡虫啉、噻虫胺和噻虫嗪）的二元和三元混合物的累积毒性进行了表征。使用MIXTOX方法，拟合了预测参数模型，并在随后的混合物测试中与观察到的毒性进行了统计比较。单化合物毒性测试得出吡虫啉、噻虫胺和噻虫嗪的半数致死浓度（LC50）值分别为4.63、5.93和55.34μg/L。由于新烟碱类的作用方式相似，浓度相加累积混合物毒性是预测模型。然而，我们发现吡虫啉 - 噻虫胺混合物表现出反应相加剂量水平依赖性协同作用，噻虫胺 - 噻虫嗪混合物表现出浓度相加协同作用，吡虫啉 - 噻虫嗪混合物表现出反应相加剂量比依赖性协同作用，随着噻虫嗪相对浓度的增加，毒性从拮抗作用转变为协同作用。吡虫啉 - 噻虫胺 - 噻虫嗪三元混合物表现出反应相加协同作用。这些结果表明，在急性暴露情景下，不能使用相加联合活性的常见假设来预测新烟碱类混合物对C. dilutus的毒性。事实上，协同偏差的总体趋势强调需要进一步研究新烟碱类杀虫剂混合物在田间环境中的生态毒理学效应，开发更好的新烟碱类混合物暴露毒性模型，以及在制定此类农药的水质准则时考虑混合物效应。《环境毒理学与化学》2017年；36:3091 - 3101。© 2017 SETAC。
