Department of Biomedical Sciences and Veterinary Public Health, Swedish University of Agricultural Sciences, Box 7028, 750 07, Uppsala, Sweden.
Environ Monit Assess. 2019 Jun 21;191(7):454. doi: 10.1007/s10661-019-7590-1.
It is well-known that the metamorphosis process in amphibians is dependent on thyroid hormones. Laboratory studies have shown that several environmental contaminants can affect the function of thyroid hormones leading to alterations in the amphibian metamorphosis. The basic idea of the present study was to elucidate if the amphibian metamorphosis might be a useful tool as biomarker for effect-based environmental monitoring, examining wild tadpoles for potential thyroid hormone disruption. A laboratory test was performed to identify the responses from exposure to 6-propylthiouracil (PTU), which has a well-known mechanism on the thyroid system, on Swedish tadpoles from the Rana genus. This was followed by an environmental monitoring study where tadpoles of Rana arvalis, R. temporaria, and Bufo bufo were sampled from various sites in Sweden. Morphological data such as body weight, histopathological measurements of the thyroid glands, and environmental parameters were recorded. The results revealed that Rana tadpoles respond similar as other amphibians to PTU exposure, with interrupted development and increased size relative to the developmental stage. Data on some wild tadpoles showed similar features as the PTU exposed, such as high body weight, thus suggesting potential thyroid disrupting effects. However, histological evaluation of thyroid glands and pesticide analyses of the water revealed no clear evidence of chemical interactions. To a minor degree, the changes in body weight may be explained by natural circumstances such as pH, forest cover, and temperature. The present study cannot fully explain whether the high body weights recorded in some tadpoles have natural or chemical explanations. However, the study reveals that it is clearly achievable to catch tadpoles in suitable stages for the use in this type of biomonitoring and that the use of these biomarkers for assessment of thyroid disruption seems to be highly relevant.
众所周知，两栖动物的变态过程依赖于甲状腺激素。实验室研究表明，几种环境污染物会影响甲状腺激素的功能，导致两栖动物变态的改变。本研究的基本思路是阐明两栖动物的变态是否可以作为基于效应的环境监测的有用工具，检查野生蝌蚪是否存在潜在的甲状腺激素破坏。进行了一项实验室测试，以确定暴露于 6-丙基硫氧嘧啶 (PTU) 时的反应，PTU 对甲状腺系统有明确的作用机制，测试对象为来自瑞典林蛙属的蝌蚪。随后进行了一项环境监测研究，在瑞典的不同地点采集了林蛙、欧林蛙和牛蛙的蝌蚪。记录了形态学数据，如体重、甲状腺的组织病理学测量值和环境参数。结果表明，与其他两栖动物一样，林蛙蝌蚪对 PTU 暴露的反应相似，发育中断，相对于发育阶段的大小增加。一些野生蝌蚪的数据显示出与 PTU 暴露相似的特征，例如体重高，因此表明可能存在甲状腺破坏作用。然而，对甲状腺组织的组织学评估和对水的农药分析并未显示出明确的化学相互作用的证据。在较小程度上，体重的变化可能可以用自然情况（如 pH 值、森林覆盖率和温度）来解释。本研究不能完全解释一些蝌蚪中记录的高体重是自然原因还是化学原因造成的。然而，该研究表明，显然可以捕获处于适合这种类型生物监测的阶段的蝌蚪，并且使用这些生物标志物评估甲状腺破坏似乎具有高度相关性。
