Electron microscope autoradiographic examination of uptake behavior of lipophilic chemicals into fish gill

Juvenile carp (Cyprinus carpio) were exposed to fenvalerate and to an oligomer with molecular weights of 420 and 2,000-50,000 and log Po/w values of 6.4 and more than 14, respectively, and uptake behavior into gill tissues was observed by electron microscope autoradiography. It was qualitatively demonstrated that fenvalerate was absorbed into gill tissues and localized in membrane systems of each cell. On the other hand, no absorption was observed for the oligomer, even in the external membrane of pavement cells. These results suggest that absorption of the oligomer is limited by low diffusion into membranes due to its very high molecular weight, resulting in no bioconcentration in fish. The significance of log Po/w in uptake behavior is also verified from the distribution behavior of fenvalerate.