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Toshihiro Horiguchi, Mitsuhiro Kojima, Fumihiko Hamada, Akira Kajikawa, Hiroaki Shiraishi, Masatoshi Morita, and Makoto Shimizu

¹National Institute for Environmental Studies, Tsukuba-shi, Ibaraki, Japan; ²Intercraft Co. Ltd., Musashino-shi, Tokyo, Japan; ³Tottori Prefectural Sea Farming Association, Tohaku-gun, Tottori, Japan; ⁴Tottori Prefectural Fisheries Experimental Station, Tohaku-gun, Tottori, Japan; ⁵The University of Tokyo, Bunkyo-ku, Tokyo, Japan

Abstract
We histopathologically examined gonads and chemically determined organotin compounds in tissues of the ivory shell, Babylonia japonica. Imposex (a superimposition of male-type genital organs on females) occurred in approximately 80-90% of B. japonica specimens that we examined, with the penis and vas deferens both well developed. No oviduct blockage by vas deferens formation was observed. Ovarian spermatogenesis and suppressed ovarian maturation were observed in the females that exhibited imposex, although no histopathological abnormalities were found in males. Tissue distributions of organotin compounds [tributyltin (TBT) , triphenyltin (TPhT) , and their metabolites] were different for butyltins and phenyltins ; a remarkably high accumulation of TBT was observed in the ctenidium, osphradium, and heart, whereas high concentrations of TPhT were detected in the ovary and digestive gland. More than one-third of TBT accumulated in the digestive glands of both males and females, followed by the testis, ctenidium, muscle, and heart tissues in males and in the muscle, ovary, ctenidium, and head tissues (including the central nervous system ganglia) in females. In both males and females, more than half of total TPhT accumulated in the digestive glands, followed by the gonads. The next highest values were in the muscle, ctenidium, and heart tissues in males and in the muscle, oviduct, and head tissues in females. Both TBT and TPhT concentrations in the gonads were positively correlated with penis length in females. Our findings strongly suggest that reproductive failure in adult females accompanied by imposex, possibly induced by TBT and TPhT from antifouling paints, may have caused the marked decline of B. japonica populations in Japan. Key words: imposex, ovarian spermatogenesis, population decline, reproductive failure, suppressed ovarian maturation, tributyltin, triphenyltin. Environ Health Perspect 114(suppl 1) :13-19 (2006) . doi:10.1289/ehp.8047 available via http://dx.doi.org/ [Online 21 October 2005]

This article is part of the monograph "The Ecological Relevance of Chemically Induced Endocrine Disruption in Wildlife."

Address correspondence to T. Horiguchi, National Institute for Environmental Studies, Endocrine Disruptors and Dioxin Research Project, Ecological Effect Research Team, 16-2, Onogawa, Tsukuba, Ibaraki, 305-8506, Japan. Telephone: 81 29 850 2522. Fax: 81 29 850 2673/2870. E-mail: thorigu@nies.go.jp

We are grateful to H. Hirose, Nihon University, Japan, for her cooperation and helpful suggestions on histopathological examination of gonads.

This study was partially supported by grants from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

M.K. is employed by Intercraft Co. Ltd. F.H. is employed by Prefecturial Sea Farming Association. The remaining authors declare they have no competing financial interests.

Received 31 January 2005 ; accepted 11 July 2005.