EFFECTS OF SEWAGE-SLUDGE ON MARINE FISH EMBRYOS AND LARVAE

Herring (Clupea harengus L.) eggs from three different spawning stocks and cod (Gadus morhua L.) eggs produced by laboratory broodstock were exposed to sewage sludge at concentrations ranging from 0.01 to 1.0%. At 0.1% sludge concentrations significant and reproducible toxic effects of sewage sludge were found for embryo viability, time of hatching, mortality during hatching, post-hatch larval survival and larval feeding. Some larvae were physically trapped by floccs of sludge. A delayed toxic effect occurred in one test. Variation in oxygen concentration, ammonia concentration and pH were monitored throughout the experiments and concentrations of metals measured in the raw sludge. While ammonia, chromium, copper and zinc levels were very high, and may have accounted for the toxic effects observed, other unmeasured toxicants may have been involved The limited information on sludge dilution at dump sites suggests that if toxic effects do occur, they would be confined to the dump site.