Incomplete Recovery in a Coastal Fish Community Exposed to Effluent from a Modernized Swedish Bleached Kraft Mill

Between 1982 and 1987, many abnormalities were reported in a Baltic coastal fish community exposed to bleached kraft mill effluent. Perch (Perca fluviatilis) was selected as a sentinel species. Local recruitment was significantly reduced owing to high larval mortality associated with gonad malfunctions and low embryo quality. Adult abundance was low near the mill outfall and the community was poor in species. After 1984, the toxicity of the effluent was reduced by substituting chlorine dioxide for molecular chlorine which resulted in lower amounts of organochlorine waste, while other effluent variables remained relatively unchanged. In 1992 the use of chlorine was discontinued. A follow-up study on fish showed that many previously documented abnormalities were absent, e.g., symptoms of external disease, lower rate of sexual maturation, and reduced relative gonad size. The number of species had increased, and the fish community resembled a more normal species assemblage. However, perch embryos produced in the effluent area remained smaller than those in a local reference area and larval survival was low. Consequently, although reduced organochlorine waste discharge had resulted in environmental improvement, recovery in the perch population was incomplete.