Myriophyllum spp. in ecological risk assessment: A case study with haloacetic acids

This thesis describes the utility of Myriophyllum spp. ecological risk assessment. Myriophyllum sibiricum and M. spicatum are rooted aquatic macrophytes occurring in a variety of ecosystems as natural and invasive species. M. sibiricum has been recommended as a new test species for the registration of pesticides in North America. There is a paucity of field level testing with these plants and laboratory to field testing. Studies were conducted to evaluate the ability of these plants to develop and exhibit toxicity from haloacetic acid (HAA) exposure under field conditions using microcosms. Myriophyllum spp. developed well under field conditions and were comparable in their sensitivity to toxicants under both laboratory and field conditions. Pigments were the least sensitive endpoints as compared to morphological endpoints such as mass and root measures. Laboratory data was a reasonable surrogate for effects observed in the field with these plants. HAAs were found to degrade readily, with the exception of trifluoracetic and chlorodifluoroacetic acids, and be relatively non-toxic to aquatic macrophytes. Using toxicity data from both field and laboratory tests to create effect measure distributions for these plants, HAAs were deemed to not pose a significant risk to these organisms under current environmental conditions. The use of effect measure distributions in the risk assessment process is promising, especially for threatened ecosystems and species. Overall, the use of Myriophyllum spp in ecological risk assessment holds substantial benefits for protecting aquatic environments.