Biochemical and histological biomarkers by the adult crucian carp (Carassius carassius (L.)) living in a biologically treated pulp mill effluent were studied. Enocell pulp mill in Uimaharju, Finland, discharges its effluents through a waste water pond to the River Pielisjoki. This pond harbours an introduced crucian carp population that apparently reproduces on site. The objective of the present study was to measure possible hormonal effects of treated pulp mill effluent on crucian carps living in a wastewater pond. Adult fish were collected for analysis by traps. A reference population was sampled from a small natural pond. Blood and bile samples were taken for analyses of hemoglobin, hematocrit, testosterone, triiodothyronine (T3), thyroxine (T4), vitellogenin, organic chlorine compounds, resin acids and neutral wood-based compounds. In addition, a histological analysis of male gonads was made.
The exposed fish had higher concentration of organic chlorine compounds, resin acids and β-sitosterol in bile compared to the reference fish. The same compounds could also be found in sediment of the wastewater pond. The exposed male fish had higher liver somatic index (LSI), lower gonad somatic index (GSI), lower haemoglobin and haemocrit, but higher T3 than in the reference fish. In addition, in an average, increased plasma testosterone concentration and decreased thyroxin (T4) levels were found in the exposed male fish. No vitellogenin production was found in the exposed male fish and some females showed decreased vitellogenin levels. The histological structure of the gonads in the exposed males was normal. The results suggest more anti-estrogenic than estrogenic effects of pulp mill effluents on the crucian carp.