Early life‐stage mortalities of Japanese medaka (Oryzias latipes) exposed to polychlorinated diphenyl ethers

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Abstract
Polychlorinated diphenyl ethers (PCDEs) are a group of compounds that resemble polychlorinated dibenzofurans in structure that have been detected at ppb concentrations in fish from the Great Lakes. The objective of this project was to determine the toxicological significance of PCDE residues in fish. PCDE congener 77 (3,3′,4,4′‐tetrachlorodiphenyl ether), congener 71 (2,3′,4′,6‐tetrachlorodiphenyl ether), congener 118 (2,3′,4,4′,5‐pentachlorodiphenyl ether), and congener 105 (2,3,3′,4,4′‐pentachlorodiphenyl) were tested for toxicity with early life stages (ELS) of Japanese medaka, Oryzias latipes. These embryotoxicity data showed that the mono‐ortho congeners 105 and 118 and the non‐ortho congener 77 were embryotoxic to medaka. However, the toxic equivalency factors (TEFs) estimated for congeners 105, 77, and 118 relative to 2,3,7, 8‐TCDD were relatively low at 0.00056, 0.00003, and 0.00001, respectively. PCDE compounds were isolated in a fraction prepared from a bulk extract of Lake Ontario lake trout. In this fraction, congeners 99 (2,2′,4,4′,5‐pentaCDE), 153 (2,2′,4,4′,5,5′‐hexaCDE), 154 (2,2′,4,4′,5,6′‐hexaCDE), and 163 (2,3,3′,4′,5, 6‐hexaCDE) comprised 81.3% of total PCDEs, while congeners 77, 71, 118, and 105 comprised only 1.1% of total PCDEs. The LC50 for embryotoxicity of this fraction was equivalent to 15.5 ng/ml of total PCDEs. Toxicopathic lesions noted in medaka embryos exposed to either individual PCDEs or the lake trout extract included vascular hemorrhage but no edematous lesions. Medaka fry did not exhibit symptoms of hyperexcitability prior to death, as has been noted for ELS of lake trout exhibiting “swim‐up syndrome.” These data indicate that PCDEs in Lake Ontario lake trout have the potential to induce toxic effects in early life stages of fish. However, the medaka mortalities were not consistent with observations of either “blue‐sac disease” or swim‐up syndrome observed in some natural populations of Great Lakes salmonids.

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