| Male-Biased Sex Ratios of Fish Embryos Near a Pulp Mill: Temporary Recovery after a Short-Term Shutdown D. G. Joakim Larsson and Lars Förlin Department of Zoology/Zoophysiology, Göteborg University, Göteborg, Sweden Abstract
In a previous study we showed that broods from the viviparous eelpout (Zoarces viviparus) were significantly male biased in 1998 in the vicinity of a large kraft pulp mill on the Swedish Baltic coast. One suggested hypothesis was that masculinizing compounds in the effluent were affecting gonadal differentiation of the embryos, resulting in skewed sex ratios. In this article, we present further evidence for a causal relationship between the exposure to the effluent and the male-biased sex ratios. Analyses of historical samples showed that the eelpout produced male-biased broods close to the mill in 1997 in addition to 1998. During 1999, the mill was shut down for 17 days, coinciding with the period when the gonads of the eelpout embryos differentiate. Subsequently, in the fall of 1999, the sex ratios were no longer male biased ; however, the following year (2000) , a significant male bias reappeared. Investigations at 13 sites for up to 4 years showed a relatively stable sex ratio around 50/50, with the exceptions by the mill and with few observations of deviating ratios at other sites. Several reports document endocrine disturbances in fish near pulp and paper mills, including the expression of male secondary sex characters in female fish. The repeatedly identified male bias at the investigated mill, the normalization after mill shutdown, and the reappearance the following year indicate that pulp mill effluents also can affect sex ratios of nearby fish. Key words: androgenic, endocrine disruptors, gonadal differentiation, masculinization, ovary, testis. Environ Health Perspect 110:739-742 (2002) . [Online 11 June 2002] http://ehpnet1.niehs.nih.gov/docs/2002/110p739-742larsson/ abstract.html Address correspondence to J. Larsson, Department of Physiology/Endocrinology, Sahlgrenska Academy, Göteborg University, Box 434, SE-405 30, Göteborg, Sweden. Telephone: +46-31-7733589. Fax: +46-31-7733531. E-mail: joakim.larsson@fysiologi.gu.se We thank H. Hällman, L. Strandell, G. Ericsson, and B. Löfnerts for help with sexing embryos, and all personnel from the Department of Fisheries, Institute of Coastal Research, and the Department of Zoology/Zoophysiology, Göteborg University, who were involved in sampling eelpout. These studies were supported by research grants from the Foundation for Strategic Environmental Research, the Swedish Environmental Protection Agency, the pulp mill industry, the Collaborative Virtual Education Program, Orvar and Gertrud Nybelins Foundation, and the Water Quality Association of the Bohus Coast. Received 31 July 2001 ; accepted 11 January 2002. Figure 1 was corrected on 29 July 2002.
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