Effect of cooling water chlorination on entrained selected copepods species

Abstract

Abstract Laboratory experiments were conducted to assess the effects of chlorine on copepods. Three copepod groups (Calanoida, Cyclopoida and Harpacticoida) and copepod naupliar stages were collected from coastal water to assess their tolerance to chlorine. Percentage mortality of the different groups of copepods and the naupliar stages were assessed after 5, 15, 30, 45 and 60 min of exposure to chlorine residuals of 0.2, 0.5, 0.8 and 1.0 mg/l. Mortality increased with increase in exposure time and concentration of the biocide. Calanoids were relatively more tolerant to chlorine compared to the other groups. Chlorine toxicity may be classified in chronological order as calanoids > cyclopoids > harpacticoids > naupliar stages. Continuous chlorination (with total chlorine residuals of 0.1 − 0.3 mg/l at the discharge) is the general practices adopted in desalination and power stations. Considering this, results of the present study indicate expected percentage mortality of the different groups as: Calanoids 7.9%, cyclopoids 11.1%, harpacticoids 10.2% and naupliar stages − 21.6%. Therefore, mortalities of copepods in cooling water circuits are not only due to physical entrapment and entrainment processes but also due to cooling water circulation. As copepods play a vital role in marine food chains, further studies will evaluate the effect of copepods mortalities on coastal communities.