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Schistosomiasis and the Chlorination of Sewage Effluent

A study was undertaken in Puerto Rico to determine the effect of chlorine at different dosage levels on the hatched and unhatched miracidium of Schistosoma mansoni. Results indicate that in sewage effluent with a BOD between 25 and 45 mg per liter, the free-swimming miracidium is killed in 1 or 2 minutes when the 30-minute chlorine residual is 0.2 mg per liter. From three experiments each employing 13 dosage levels to secondary sewage effluent (pH range 7.0–9.0, BOD range 20–48 mg per liter), the highest chlorine dosage tolerated for 15 minutes by the unhatched miracidium was an initial 2.0 mg per liter and a 15-minute residual of 0.9 mg per liter. No unhatched miracidia in effluent survived an initial dosage of 2.4 mg per liter with a 15-minute residual of 1.5 mg per liter or above. Primary sewage treatment effluent with a higher BOD (115 mg per liter) required a higher chlorine dosage (11.3 mg per liter initial, 8.5 mg per liter residual at 15 minutes).

The writer believes that chlorination at a level sufficiently high to give a 15-minute residual of at least 2.5 mg per liter would be of value in ridding sewage effluent in Puerto Rico of viable S. mansoni eggs and miracidia.

^* Present address: Department of Zoology, Montana State University, Missoula, Montana.