Aquatic Toxicology 68 (2004) 75–85 Pentachlorophenol (PCP) bioaccumulation and effect on heat production on salmon eggs at different stages of development Kimmo A. Mäenpää ∗ , Olli-Pekka Penttinen, Jussi V.K. Kukkonen Department of Biology, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland Received 16 April 2003; received in revised form 26 October 2003; accepted 13 February 2004 Abstract In this study, pentachlorophenol (PCP) bioaccumulation and its effect on heat dissipation was studied in eggs of the lake salmon (Salmo salar m. sebago). In bioaccumulation studies, the eggs were exposed to low concentrations (0.051–0.056 mol/l, 13.583–14.915) of waterborne [ 14 C]-labeled PCP at two developmental stages: (1) 3 weeks after fertilization, and (2) just before hatching. The effect of PCP on egg heat dissipation was measured by a microcalorimeter after exposing the eggs to gradual concentrations (0–0.992 mol/l) of PCP for 48 h. After both the bioaccumulation and heat dissipation experiments, the eggs were dissected and the concentrations of PCP in tissue were determined separately for eggshell, yolk and embryo. The bioaccumulation studies showed that PCP accumulates more in the eggs at the late developmental stage. Bioconcentration factors (BCF) for different tissues were 3–42 times higher for the eggs at the late developmental stage compared with the eggs that were incubated only for 3 weeks. In early developmental stage, the eggshell adsorbs a large portion of the chemical. In late developmental stage, the actual embryo accumulated both proportionately and totally more than other dissected tissues in the beginning of the exposure, but eventually the yolk accumulated highest total amount of the chemical. A probable reason for the higher PCP body burden in the late developmental stage is that the respiration rate and metabolic activity of the embryo increases as it grows. The salmon eggs responded to an exposure to PCP with an elevated rate of heat dissipation. The threshold concentration above which the embryo heat dissipation was amplified was 29.64 mol/kg embryo wet weight (ww) or 0.28 mol/l. The highest embryo heat production was measured at the exposure concentration of 0.992 mol/l. At higher exposure concentrations the heat dissipation decreased. The basic findings of the study are that PCP accumulates in growing embryonic tissue and is able to change the physiology of developing embryo. © 2004 Elsevier B.V. All rights reserved. Keywords: Bioaccumulation; Critical body residue; Egg; Heat dissipation; Microcalorimeter; Pentachlorophenol; Salmon ∗ Corresponding author. Tel.: +358-13-251-3545/358-40-5576172; fax: +358-13-251-3590. E-mail address: kimmo.maenpaa@joensuu.fi (K.A. Mäenpää). 1. Introduction The spawn may expose fish to xenobiotics dissolved in aquatic environment, and an uptake of lipophilic chemicals, such as pentachlorophenol (PCP), is to be expected in the eggs. The embryogenesis is among the most sensitive phases of fish life (von Westernhagen, 0166-445X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2004.02.004