Skin and liver diseases induced in flounder (Platichthys flesus) after long-term exposure to contaminated sediments in large-scale mesocosms.

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 population) 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.

Cadmium kinetics in freshwater clams (Unionidae) under field and laboratory conditions.

Cadmium dosing experiments were carried out with the freshwater clam Unio pictorum in flow-through micro-streams in order to obtain additional information on the kinetics of cadmium accumulation and elimination. Accumulation of cadmium in the kidney was rapid and within 3 weeks a concentration factor of 6000 was found. During elimination (29 weeks), the organs lose about one-third of their cadmium content rather rapidly, but no further elimination occurs. It can be concluded that the process of Cd accumulation is rapid and almost irreversible.

Bioassay and biomonitoring assessments of contaminant mobility from dredged material.

The Clean Water Act in the United States requires that the environmental evaluation of dredged material prior to its discharge must include the effects of the proposed disposal environment on the bioaccumulation of contaminants in the food chain. Although the total amount of contaminated material is relatively small when the national dredging program is considered, a significant effort is expended to ensure that, through the application of predictive tests prior to dredging, the contaminated material is deposited in a manner that will result in minimum contaminant mobility. There also has been a necessity to conduct studies and develop management plans in relation to the potential movement of contaminants at disposal sites constructed before the hazardous nature of many contaminants were known. Three case studies illustrate some of the bioassay and biomonitoring procedures currently being applied by the Corps of Engineers.