The use of Serratia indica and Bacillus subtilis var. niger spores for tracing sewage dispersion in the sea.

Abstract

SummaryExperiments were conducted at 2 coastal sites to evaluate the suitability of Serratia indica and spores of Bacillus subtilis var. niger for tracing offshore and longshore dispersion of sewage released from submarine outfalls. Neither organism was found in the sea or the rivers studied prior to an experimental release and, whereas tracer spores persisted in the sea and the littoral zone for some days after release, S. indica disappeared within a few days. Where S. indica was released continuously from an outfall, it dispersed similarly to coli‐aerogenes bacteria. Both tracers were killed rapidly in seawater exposed to sunlight, but their mortality kinetics differed. Tracer spores did not die or germinate in the dark when suspended in sewage during 24 h or in seawater during 9 days, but death occured after 3 days in seawater exposed to sunlight. Spores dispersed offshore similarly to K82Br and to S. indica; because of this and their stability, it was thought that they could be used for measuring physical dilution independently of mortality. The continuous release of S. indica into the sea is suitable for measuring the pollution field around a discharge; adding single doses of either tracer yields information on dispersion processes and transit times to the shore.