Biomarkers of oxidative stress in freshwater clams (Corbicula fluminea) as mechanistic tools to evaluate the impairment of stream ecosystem health by lawn care pesticides
Conners, Deanna Erin
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Many chemicals including fertilizers, herbicides, insecticides and fungicides are routinely applied to lawns, and have the potential to leach into nearby aquatic ecosystems and adversely affect biota. The purpose of this dissertation was to develop sensitive biological markers of stress in freshwater clams (Corbicula fluminea) for use as mechanistic tools to evaluate the degradation of streams by turf contaminants. Many xenobiotics cause damage in aquatic organisms via oxidative stress mechanisms, therefore measurements of stress used in this study included antioxidants (superoxide dismutase, catalase, glutathione) and indicators of cellular (lipid peroxidation, DNA strand breaks) and physiological (condition index) oxidative damage. Clams exposed in situ to pesticide runoff from residential lawns and a golf course accumulated a variety of persistent metals and organic pesticides in their tissues. Concentrations of turf contaminants were typically highest in tissues of clams deployed in streams that drain residential properties of high socioeconomic status during times of heavy rain and in a stream draining a golf course. Clams exposed to turf contaminants exhibited transient signs of oxidative stress (i.e., elevated levels of superoxide dismutase, catalase, glutathione and lipid peroxidation), whereas condition indices were reduced only at high exposures. These results suggest that clams may be able to compensate for adverse cellular effects of pesticides but that energy required for amelioration can eventually affect physiological processes. A laboratory experiment was conducted to investigate if the observed effects on clam health were caused by turf chemicals accumulated by clams, and not by other contaminants that may co-occur in the streams but were not measured. Realistic concentrations of turf contaminants induced oxidative stress in laboratory-exposed clams, but not to the extent as observed in the field where exposures may have been more severe due to the presence of other contaminants. Together these data suggest that turf contaminants may be important contributors to the etiology of stress in freshwater clams from urbanized streams. Furthermore, these data when combined with other indicators of stream ecosystem health (e.g., community indices and ecosystem processes) highlight the utility of oxidative stress biomarkers in freshwater clams for use as mechanistic tools in biomonitoring.