Histochemistry as a tool for examining possible pathologic cause-and-effect relationships between heavy metal and inflammatory lesions in oysters, Crassostrea virginica

Unexplained inflammatory lesions have been seen on many occasions in oysters ( Crassostrea virginica) that have been examined by histopathologic methods. Application of the Mallory's hematin and the rubeanic acid methods for demonstration of copper in histologic sections revealed strong staining reactions in granules of some, but not all, granular hemocytes. These cells were clearly involved as constituents of acute inflammatory lesions characterized by infiltration of arteries, occlusion of veins, and diapedesis through external epithelia of the mantle and gastrointestinal tract. Heavily contaminated sites (i.e. Raritan Bay, New Jersey) showed strong staining reactions in a large number of animals examined. Control sites such as Great Bay, New Jersey, showed much lighter reactions. Seasonal sampling in the New Jersey sites revealed the most intense involvement in the late summer with apparent decreasing staining intensities in the fall. Other species of bivalve mollusks ( Mytilus edulis and Mercenaria mercenaria) only showed significant staining reactions for heavy metal in kidney tissues with no evidence that heavily contaminated sites had higher levels. These results constitute preliminary evidence of a cause-and-effect relationship between a heavy metal contaminant (most probably copper) and inflammatory lesions in the oyster.