Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, 86001, USA; International Rice Research Institute, Los Baños, Philippines.
International Rice Research Institute, Los Baños, Philippines; Natural Resource Institute, University of Greenwich, Chatham Maritime, Kent, UK.
Environ Pollut. 2021 Mar 1;272:115955. doi: 10.1016/j.envpol.2020.115955. Epub 2020 Nov 6.
Identifying the adverse impacts of pesticide exposure is essential to guide regulations that are protective of wildlife and human health. Within rice ecosystems, amphibians are valuable indicators because pesticide applications coincide with sensitive reproductive and developmental life stages. We conducted two experiments using wild cane toads (Rhinella marina) to test 1) whether environmentally relevant exposure to a commercial formulation of butachlor, an acetanilide herbicide used extensively in rice, affects amphibian development and 2) whether cane toad tadpoles are capable of acclimatizing to sub-lethal exposure. First, we exposed wild cane toads to 0.002, 0.02, or 0.2 mg/L of butachlor (Machete EC), during distinct development stages (as eggs and hatchlings, as tadpoles, or continuously) for 12 days. Next, we exposed a subset of animals from the first experiment to a second, lethal concentration and examined survivorship. We found that cane toads exposed to butachlor developed slower and weighed less than controls, and that development of the thyroid gland was affected: exposed individuals had smaller thyroid glands and thyrocyte cells, and more individual follicles. Analyses of the transcriptome revealed that butachlor exposure resulted in downregulation of transcripts related to metabolic processes, anatomic structure development, immune system function, and response to stress. Last, we observed evidence of acclimatization, where animals exposed to butachlor early in life performed better than naïve animals during a second exposure. Our findings indicate that the commercial formulation of butachlor, Machete EC, causes thyroid endocrine disruption in vertebrates, and suggest that exposure in lowland irrigated rice fields presents a concern for wildlife and human health. Furthermore, we establish that developmental assays with cane toads can be used to screen for adverse effects of pesticides in rice fields.
确定农药暴露的不良影响对于指导保护野生动物和人类健康的法规至关重要。在水稻生态系统中，两栖动物是有价值的指标，因为农药的施用与敏感的生殖和发育生命阶段相吻合。我们使用野生甘蔗蟾蜍（Rhinella marina）进行了两项实验，以测试 1）环境相关暴露于广泛用于水稻的乙酰苯胺类除草剂丁草胺的商业制剂是否会影响两栖动物的发育，以及 2）甘蔗蟾蜍蝌蚪是否能够适应亚致死暴露。首先，我们将野生甘蔗蟾蜍暴露于 0.002、0.02 或 0.2 mg/L 的丁草胺（Machete EC）中，在不同的发育阶段（作为卵和孵化后的幼体，作为蝌蚪或连续暴露）中暴露 12 天。接下来，我们从第一个实验中选择一部分动物暴露于第二个致死浓度，并检查存活率。我们发现，暴露于丁草胺的甘蔗蟾蜍发育较慢，体重较轻，并且甲状腺发育受到影响：暴露个体的甲状腺较小，甲状腺细胞和单个滤泡较多。转录组分析表明，丁草胺暴露导致与代谢过程、解剖结构发育、免疫系统功能和应激反应相关的转录物下调。最后，我们观察到适应的证据，即早期暴露于丁草胺的动物在第二次暴露时的表现优于天真的动物。我们的研究结果表明，商业制剂丁草胺（Machete EC）会导致脊椎动物的甲状腺内分泌干扰，并表明在低地灌溉水稻田中暴露于农药会对野生动物和人类健康造成关注。此外，我们建立了甘蔗蟾蜍的发育测定可用于筛选稻田中农药的不良影响。
