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2I - High-tiered Studies (MO7/8) Effects of two silvicultural herbicides on larval amphibians in Canada: an in situ approach. Wojtaszek, Barbara1, Thompson, Dean2, Staznik, Bozena2, Chartrand, Derek2, Buscarini, Teresa, Stephenson, Gerald1, 1 University of Guelph, Guelph, Ontario, Canada2 Canadian Forest Service, Sault Ste. Marie, Ontario, Canada ABSTRACT- In situ aquatic enclosures were deployed in two different wetland sites in Northern Ontario, Canada to investigate the effects of forest-use herbicides glyphosate (Vision®) and triclopyr (Release®) on northern leopard frog (Rana pipiens) and green frog (R. clamitans) larvae. Larvae were assessed for mortality, behavioural and growth responses during exposure to various concentrations of each product. By 96 hours post-treatment, complete larval mortality was observed in most enclosures treated at levels higher than worst-case scenario concentrations as calculated by Canadian regulatory authorities (EEC). However, only minimal mortality was observed at concentrations approximating those detected in real-world application scenarios. The wetland sites differed substantially in effects observed for either herbicide, consistent with known toxicological and environmental behaviours. For example, larval morality due to Release® was higher in the more acidic (pH Key words: herbicide, amphibian, silviculture, ecotoxicology |
6), eutrophic wetland, while Vision® showed greater deleterious effects in the higher pH, more oligotrophic wetland. R. pipiens larvae were especially sensitive to the sublethal effects (avoidance response) of Release®, suggesting potentially greater susceptibility to predation. Effects of herbicides on larval growth were site and species-dependent. In relation to their respective EEC values, Vision® appeared to be generally less toxic to larvae than Release®. In natural environments, overall amphibian larval response may result from both direct and indirect mechanisms (e.g. anoxia, food deprivation) and may be significantly affected by interactions with both biotic (e.g. sorption to macrophytes / periphyton) and abiotic factors (e.g. pH x herbicide). Impacts of herbicides on periphyton biomass accumulation and resultant effects upon larval amphibian growth is also explored.