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A. Dick Vethaak,¹ Johan G. Jol,¹ André Meijboom,² Martin L. Eggens,³ Tristan ap Rheinallt,⁴ Peter W. Wester,⁵ Ton van de Zande,³ André Bergman,³ Norbert Dankers,² Freek Ariese,⁶ Rob A. Baan,⁷ James M. Everts,⁸ Antoon Opperhuizen,⁹ and Joop M. Marquenie¹⁰

¹Ministry of Transport, Public Works and Water Management, Directorate-General of Public Works and Water Management, National Institute for Coastal and Marine Management/RIKZ, Middelburg, The Netherlands; ²Research Institute for Nature Management, Department of Estuarine Ecology, Den Burg,The Netherlands; ³National Institute for Coastal and Marine Management/RIKZ, Haren, The Netherlands; ⁴Port Wemysss, Isle of Islay, United Kingdom; ⁵National Institute of Public Health and Environmental Protection, Laboratory for Pathology, Bilthoven, The Netherlands; ⁶Institute for Environmental Studies, Free University of Amsterdam, Amsterdam, The Netherlands; ⁷Organisation for Applied Scientific Research/TNO, Nutrition and Food Research Institute, Rijswijk, The Netherlands; ⁸Food and Agriculture Organisation, Dakar, Senegal; ⁹National Institute for Coastal and Marine Management/RIKZ, The Hague, The Netherlands; ¹⁰The Netherlands Oil Company, Assen, The Netherlands

Abstract

Disease development in flounder (Platichthys flesus) was studied over a period of 3 years in three large mesocosms (40 m x 40 m x 3 m) . Two of the mesocosms contained clean sand and the third, sharing a common water circulation with one of the clean-sand mesocosms, was stocked with contaminated dredged spoil. In this way, one of the clean-sand mesocosms was indirectly polluted via the water phase, and analysis of contaminant concentrations in sediments and flounder tissues showed that it had a status intermediate between the other two. Random samples of the flounder populations from the indirectly polluted and reference mesocosms were examined every 2 months for epidermal diseases (lymphocystis, skin ulcers, fin rot) and then released. In addition, every 6 months, random samples of fish from all three mesocosms were sacrificed for histological and chemical investigation. With regard to the development of epidermal disease, the results showed little difference between the reference mesocosm and the indirectly polluted mesocosm, with the exception that lymphocystis was significantly elevated in the indirectly polluted mesocosm. Although pollution may be a risk factor in the etiology of this disease, such a relationship would probably be obscured under field conditions due to variation arising from other factors. Histopathological analysis of the livers revealed in total four cases of hepatocellular adenoma (1.5% of sampled populations) in fish from the polluted mesocosms, the first occurring after 2.5 years of exposure in fish from the indirectly polluted mesocosm. Furthermore, several other liver lesions, including foci of cellular alteration and hydropic vacuolated lesions, developed during the course of the experiment before tumor formation was apparent. Prevalences of these conditions were very much lower in the reference mesocosm than in the two polluted mesocosms. Densities of melanomacrophage centers in the liver showed a similar trend. The findings clearly indicate that long-term exposure to chemically contaminated dredged spoil can induce liver neoplasia and other liver lesions in flounder at contaminant levels comparable to those found in the natural environment. Key words: biomarker, disease induction, fish disease, flounder (Platichthys flesus) , liver neoplasia, marine pollution, mesocosm. Environ Health Perspect 104:1218-1229 (1996)

Address correspondence to A.D. Vethaak, National Institute for Coastal and Marine Management/ RIKZ, Ecotoxicology Section, Grenadierweg 31, PO Box 8039, 4330 EA Middelburg, The Netherlands.

Thanks are due to Marie-José Steenwinkel (TNO) , Joke Robinson, and Jan Hoekman (RIVM) for excellent technical assistance.

Received 11 April 1996 ; accepted 22 July 1996.