Histopathological effects of petroleum hydrocarbons and heavy metals on the American oyster (Crassostrea virginica) from Tabasco, Mexico

Oyster tissues may be affected by the concentration of ions in the water (i.e. salinity) and by contaminants such as petroleum hydrocarbons and heavy metals. Oyster populations from three coastal lagoons (Mecoacan, Camen and Machona) in the Mexican state of Tabasco, in the southern Gulf of Mexico, were sampled for pollution studies during June, September and November 1992 and May 1993, No statistically significant relationships were found between the concentration of contaminants in the body tissues of organisms and their shell length, soft tissue weight and particulate matter; however, a significant correlation was found between condition index and salinity (r = -0.72). Generally, the lowest weights, shell lengths and indices of condition were found in Mecoacan. The concentrations of cadmium and zinc were inversely related to salinity (r = -0.52 and r = -0.32, respectively), so a riverine input is suspected. On average, 63% of the individual oysters showed histopathological lesions, which can be related to salinity and to the concentrations of cadmium and the unresolved fraction of hydrocarbons (UCM). The response of each of the tissues analysed was different. The percentage of individuals with damage in the digestive diverticulum increased linearly with UCM (r = 0.71), but in a saturation-response fashion (r = B-0 - B-0/(1 + X(B1)), r = 0.66) with cadmium, The percentage of individuals, with damage in the gills increased linearly with weight (r = 0.68), cadmium (r = 0.60) and UCM (r = 0.60). The lesions in the connective tissue decreased Linearly (r = -0.82) with salinity, but increased in a saturation-response way (r = 0.83) with cadmium. Finally, the percentage of individuals with lesions in the digestive tube decreased linearly with salinity (r = -0.59). Only the damage to the gills and digestive diverticula were dependent on gonadal maturity, while damage to the connective tissue was dependent on the sex of the individual.