The aim of the present study was to examine whether effluents from an oil refinery with new "best available technology" for the effluent treatment may contain estrogenic substances. Standard municipal sewage has been shown to contain such compounds (Purdom et al. 1994), but few, if any studies have been carried out on highly purified refinery effluent. For comparison, and as a positive control, studies of municipal sewage were also done. Vitellogenin is produced in the liver of female fish and is the precursor of egg proteins. Its production is induced by estrogens (Tata and Smith 1979) and is normally not synthesised by immature fish or males. As an indicator of estrogenic compounds in these effluents, we used the increase in plasma vitellogenin concentrations in male rainbow trout (O n c o r h y n c u s m y k i s s) after and during exposure (Sumpter and Jobling 1995, Purdom et al. 1994)
MATERIALS AND METHODSThe effluent from the ESSO -Slagentangen Oil Refinery was chosen because the toxicity of process chemicals and effluents from this refinery has been studied (Riisberg et al 1996;Roseth et al 1996). This refinery is located at the outlet of the Oslofjord where the hydrodynamic conditions seem to be satisfactory, and no serious impact on water quality has been recorded (Jensen et al. 1992). T h e treatment works receive waste water from the oil refining process, drainage and ballast water. The three streams are mixed and stored in a large tank in order to smooth out variation in salinity. Thereafter the effluent is purified by skimming and sedimentation before being fed into the biological treatment system. This last section is a BIOX™ plant and has an aerobic and an anaerobic compartment. It was introduced in 1993 in order to meet the legal specifications for phenolics and "oil in water". According to typical routine analysis carried out at the refinery, 105 m 3 /hour-of effluent are produced, containing < 1 mg/L dissolved oil, and ca. 0.2 mg/L phenolics. The total organic carbon (TOC) is 16 mg/L, whereas NH 3 plus N H 4 ' is < 0.1 mg/L. The municipal sewage plant receives domestic waste water from Oslo. It is located at Bekkelaget at the inner part of the Oslofjord. TOC was 23.2 mg/L and NH 3 plus NH 4 ' , 24.9 mg/L. Rainbow trout (mean weight 350 g) of both sexes purchased from a commercial fish farm were used in the experiments. Both immature and mature fish were employed. The fish were anaesthetized with Correspondence to: J. Stenersen