Centre for Advanced Research in Environmental Genomics (CAREG), Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
Fisheries and Oceans Canada, Freshwater Institute, Winnipeg, Manitoba R3T 2N6, Canada.
Aquat Toxicol. 2014 Sep;154:291-303. doi: 10.1016/j.aquatox.2014.05.025. Epub 2014 May 28.
Glyphosate-based herbicides are currently the most commonly used herbicides in the world. They have been shown to affect survival, growth, development and sexual differentiation of tadpoles under chronic laboratory exposures but this has not been investigated under more environmentally realistic conditions. The purpose of this study is (1) to determine if an agriculturally relevant exposure to Roundup WeatherMax®, a relatively new and understudied formulation, influences the development of wood frog tadpoles (Lithobates sylvaticus) through effects on the mRNA levels of genes involved in the control of metamorphosis; (2) to compare results to the well-studied Vision® formulation (containing the isopropylamine salt of glyphosate [IPA] and polyethoxylated tallowamine [POEA] surfactant) and to determine which ingredient(s) in the formulations are responsible for potential effects on development; and (3) to compare results to recent field studies that used a similar experimental design. In the present laboratory study, wood frog tadpoles were exposed to an agriculturally relevant application (i.e., two pulses) of Roundup WeatherMax® and Vision® herbicides as well as the active ingredient (IPA) and the POEA surfactant of Vision®. Survival, development, growth, sex ratios and mRNA levels of genes involved in tadpole metamorphosis were measured. Results show that Roundup WeatherMax® (2.89 mg acid equivalent (a.e.)/L) caused 100% mortality after the first pulse. Tadpoles treated with a lower concentration of Roundup WeatherMax® (0.21 mg a.e./L) as well as Vision® (2.89 mg a.e./L), IPA and POEA had an increased condition factor (based on length and weight measures in the tadpoles) relative to controls at Gosner stage (Gs) 36/38. At Gs42, tadpoles treated with IPA and POEA had a decreased condition factor. Also at Gs42, the effect on condition factor was dependent on the sex of tadpoles and significant treatment effects were only detected in males. In most cases, treatment reduced the normal mRNA increase of key genes controlling development in tadpoles between Gs37 and Gs42, such as genes encoding thyroid hormone receptor beta in brain, glucocorticoid receptor in tail and deiodinase enzyme in brain and tail. We conclude that glyphosate-based herbicides have the potential to alter mRNA profiles during metamorphosis. However, studies in natural systems have yet to replicate these negative effects, which highlight the need for more ecologically relevant studies for risk assessment.
草甘膦类除草剂是目前世界上使用最广泛的除草剂。研究表明，在慢性实验室暴露下，草甘膦类除草剂会影响蝌蚪的存活、生长、发育和性别分化，但在更接近实际环境的条件下，这一现象尚未得到研究。本研究的目的是：(1) 确定一种农业相关的暴露于新型的研究较少的农达 WeatherMax®制剂是否会通过影响参与变态发育的基因的 mRNA 水平来影响林蛙蝌蚪 (Lithobates sylvaticus) 的发育；(2) 将结果与研究较为充分的 Vision®制剂(含有草甘膦异丙胺盐[IPA]和聚氧化乙撑牛脂胺[POEA]表面活性剂)进行比较，并确定制剂中的哪些成分可能对发育产生影响；(3) 将结果与最近使用类似实验设计的野外研究进行比较。在本实验室研究中，林蛙蝌蚪暴露于农业相关的应用(即两次脉冲)的农达 WeatherMax®和 Vision®除草剂以及 Vision®的活性成分(IPA)和 POEA 表面活性剂。测量了蝌蚪的存活率、发育、生长、性别比例和参与变态发育的基因的 mRNA 水平。结果表明，农达 WeatherMax®(2.89 毫克酸当量(a.e.)/升)在第一次脉冲后导致 100%的死亡率。用较低浓度的农达 WeatherMax®(0.21 毫克 a.e./升)以及 Vision®(2.89 毫克 a.e./升)、IPA 和 POEA 处理的蝌蚪在 Gosner 阶段(Gs)36/38 时与对照组相比具有更高的条件因子(基于蝌蚪的长度和重量测量)。在 Gs42 时，用 IPA 和 POEA 处理的蝌蚪的条件因子降低。同样在 Gs42 时，条件因子的影响取决于蝌蚪的性别，只有在雄性中才检测到显著的处理效果。在大多数情况下，处理会降低 Gs37 到 Gs42 期间控制蝌蚪发育的关键基因的正常 mRNA 增加，例如脑甲状腺激素受体β、尾巴糖皮质激素受体和脑和尾巴脱碘酶基因。我们得出的结论是，草甘膦类除草剂有可能改变变态发育过程中的 mRNA 谱。然而，在自然系统中的研究尚未复制这些负面影响，这凸显了进行更具生态相关性的研究以进行风险评估的必要性。
