Municipal wastewater treatment plant (WWTP) effluent is a primary source of pharmaceutical and personal care products (PPCPs) to the marine environment as most of these compounds are not fully removed during the treatment process. Continual discharge from treatment plants into coastal areas exposes organisms to a suite of PPCPs on a regular basis which may act as stressors. To understand effects of mixtures of PPCPs on wildlife, we conducted a lab experiment that exposed Pacific oysters to effluent from coastal WWTPs of different discharge capacities, to represent different population sizes in Oregon. Oysters were exposed weekly to effluent from two coastal wastewater treatment plants, processing <1 million gallons/day and >1 million gallons/day. Oysters were distributed across five treatment levels (effluent water in artificial seawater at ratios of 10:90 and 25:75 for each treatment plant, and a 0:100 control) with four tanks per treatment, each housing nine oysters for 12 weeks. At 6 and 12 weeks, oyster shell size, weight, condition index (ratio of dry tissue weight to dry shell weight), and feeding rate (algal clearance) were recorded. Effluent was collected weekly for the duration of the study to be analyzed for PPCPs.
Results/Conclusions
Mortality during the experiment was low (1.3%) and dispersed among treatments. Throughout the 12 weeks of exposure, there was no change in shell size in any treatment, indicating no detectable effects of effluent on shell growth. Preliminary analysis of condition index in the six-week sample using a one-way ANOVA revealed no significant differences in oyster health among treatments (p>.05). These results demonstrate that effluent may not affect oyster health, or that detection of effects may limited at the organism level for this species. The short time period of exposure (6 weeks) and the tendency of oysters to survive a wide range of environmental conditions could be possible drivers of this pattern. Pacific oysters are a prominent commercial aquaculture species in Oregon that could come in contact with PPCPs in effluent. The ability to detect effects of contamination is important for safe aquaculture, ecological functions provided by oysters, and human health. Further analysis of endpoints in the 12-week sample, and addition of PPCP concentrations in effluent, may reveal effects over a longer exposure period and/or provide information about specific compounds that wildlife are exposed to on a regular basis in areas with low coastal populations.