Changes in Blood Chemistry and Blood Cell Morphology in Coho Salmon (Oncorhynchus kisutch) Following Exposure to Sublethal Levels of Total Residual Chlorine in Municipal Wastewater

Abstract

Yearling coho salmon (Oncorhynchus kisutch) were exposed for 12 wk to either 0.3, 1.1, or 3.6% chlorinated municipal sewage treatment plant effluent with seawater diluent (average salinity 28‰)under continuous flow conditions. The maximum safe concentration of effluent lies between 0.3 and 1.1% (average total residual chlorine (TRCl₂) content 0.003 and 0.009 mg/liter, respectively). Effluent concentrations of 0.3% produced no discernible effects on the fish. Concentrations of 1.1 and 3.6% (average content of TRCl₂ 0.030 mg/liter) resulted in reductions of hemoglobin and hematocrit to levels indicative of anemia. Observations of the erythrocytes revealed lysed and degenerating cells, increased numbers of circulating immature cells, and abnormal cells. These hematological effects are attributed to the oxidative nature of TRCl₂.