TOXICITY OF SEWAGE-SLUDGE TO MARINE ORGANISMS - A REVIEW

Results of laboratory, mesocosm, and field studies on the toxicity of sewage sludge to marine organisms are summarised The 24 taxa tested included adults, juveniles, larvae, embryos, sperm and algal zoospores. These toxicity studies are discussed in relation to sewage sludge dispersion and dilution, and observed effects in the field. The 96 h LC50 averages for sewage sludges ranged from 20% wet volume of sludge in seawater for polychaetes (Malacoceros fuliginosus and Scolelepis squamata) to 0.0003% for shrimp larvae (Crangon crangon). One third of the tests reviewed found minimum toxic concentrations of less than or equal to 0.1%. The cause of toxicity cannot be attributed to any single component, but contaminants from industrial wastes can be a significant factor. There is no indication of any build up of toxicity in the studies. Components of sewage can be utilised by phytoplankton, zooplankton, detrivorous invertebrates, and ingested by fish. Bioaccumulation of contaminants can occur through the diet. In general, dilution after dumping at sea is less than 0.1% (1 in 1000) within 30 min and 0.01% within 1 h. Based on these figures, acute toxicity is unlikely to occur at ecologically significant or detectable levels at dump sites. However, at some dump sites chronic effects due to organic enrichment are evident as changes in the species richness, relative abundance, and biomass of macroinvertebrate species.