Department of Environmental Toxicology and Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX, 79409-1163, USA.
U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit and Departments of Natural Resources Management and Biological Sciences, Texas Tech University, Lubbock, TX, 79409-2120, USA.
Harmful Algae. 2018 Dec;80:130-139. doi: 10.1016/j.hal.2018.11.004. Epub 2018 Nov 17.
Glyphosate-based herbicides (GBH) are widely used around the globe. While generally toxic to phototrophs, organic phosphorus in glyphosate can become available to glyphosate-resistant phytoplankton and contribute to algal bloom development. Few studies have examined the effects of GBH on growth of eukaryotic microalgae and information for the toxic bloom-forming haptophyte, Prymnesium parvum, is limited. Using a batch-culture system, this study examined the effects on P. parvum growth of a single application of Roundup Weed and Grass Killer Super Concentrate Plus® (Roundup SC), Roundup Weed and Grass Killer Ready-to-Use III® (Roundup RtU), and technical-grade glyphosate at low concentrations [0-1000 μg glyphosate acid equivalent (ae) l]. Roundup formulations differ in the percent of glyphosate as active ingredient (Roundup SC, ∼50%; Roundup RtU, 2%), allowing indirect evaluation of the influence of inactive ingredients. Roundup SC enhanced exponential growth rate at 10-1000 μg glyphosate ae l, and a positive monotonic association was noted between Roundup SC concentration and early (pre-exponential growth) but not maximum cell density. Glyphosate and both Roundup formulations enhanced growth rate at 100 μg glyphosate l, but only Roundup SC and glyphosate significantly stimulated early and maximum density. This observation suggests the higher concentration of inactive ingredients and other compounds in Roundup RtU partially counteracts glyphosate-dependent growth stimulation. When phosphate concentration was varied while maintaining other conditions constant, addition of Roundup SC and glyphosate at 100 μg l influenced growth more strongly than equivalent changes in phosphate-associated phosphorus. It appears, therefore, that low doses of glyphosate stimulate growth by mechanisms unrelated to the associated small increases in total phosphorus. In conclusion, glyphosate and GBH stimulate P. parvum growth at low, environmentally relevant concentrations. This finding raises concerns about the potential contribution to P. parvum blooms by glyphosate-contaminated runoff or by direct application of GBH to aquatic environments.
草甘膦基除草剂（GBH）在全球范围内广泛使用。虽然草甘膦一般对光合生物有毒，但草甘膦中的有机磷可以被抗草甘膦的浮游植物利用，并有助于藻类大量繁殖。很少有研究调查 GBH 对真核微藻生长的影响，而关于有毒赤潮生物角毛藻的信息有限。本研究使用批量培养系统，调查了单一应用草甘膦制剂 Roundup Weed and Grass Killer Super Concentrate Plus®（Roundup SC）、Roundup Weed and Grass Killer Ready-to-Use III®（Roundup RtU）和技术级草甘膦对 P. parvum 生长的影响，浓度低至 [0-1000μg 草甘膦酸当量 (ae) l]。Roundup 制剂中草甘膦的有效成分百分比不同（Roundup SC，约 50%；Roundup RtU，2%），这允许间接评估非活性成分的影响。Roundup SC 在 10-1000μg 草甘膦 ae l 范围内增强了指数生长率，并且在 Roundup SC 浓度和早期（指数生长前）但不是最大细胞密度之间观察到正单调关联。草甘膦和两种 Roundup 制剂在 100μg 草甘膦 l 时均增强了生长率，但只有 Roundup SC 和草甘膦显著刺激了早期和最大密度。这一观察结果表明，Roundup RtU 中较高浓度的非活性成分和其他化合物部分抵消了草甘膦依赖性的生长刺激。当在保持其他条件不变的情况下改变磷酸盐浓度时，添加 100μg l 的 Roundup SC 和草甘膦对生长的影响比磷酸盐相关磷的等效变化更为强烈。因此，草甘膦的低剂量似乎通过与总磷相关的小增量无关的机制刺激生长。总之，草甘膦和 GBH 在低浓度下刺激 P. parvum 的生长，这些浓度在环境相关范围内。这一发现引起了人们对受草甘膦污染径流或直接向水生环境应用 GBH 可能对 P. parvum 大量繁殖的潜在贡献的关注。
