DERMAL ABSORPTION OF 3 WATERBORNE CHLOROETHANES IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) AND CHANNEL CATFISH (ICTALURUS-PUNCTATUS)

In vivo estimates of xenobiotic chemical flux across the dermal surfac e of intact fish were obtained by measuring chemical loss from venous blood to expired water. An experimental system was developed to separa te the dermal route of exposure from all other routes. The system was then used to measure dermal absorption of tetrachloraethane (TCE), pen tachloroethane (PCE), and hexachloroethane (HCE) in channel catfish (I ctalurus punctatus) and rainbow trout (Oncorhynchus mykiss), two fish with very different skin anatomies. The kinetics of accumulation varie d among chemicals, but for each compound were similar among species. T CE accumulated rapidly, reaching steady state in blood within as hr. S teady state was not reached in 48 hr with PCE or HCE, although blood l evels of PCE were probably close to steady-state values. Dermal Aux es timates (based on branchial efflux) for TCE, PCE, and HCE were two to four times greater in catfish than in trout. Arterial blood concentrat ions of each compound were three to sis times greater in catfish. Thes e observations are indicative of greater flux across catfish skin, aug mented by higher blood:water chemical partitioning. Trout skin is cove red with scales and has no taste buds, while catfish skin does not pos sess scales and has numerous taste bud papillae. Both scales and taste bud papillae originate in the dermis and extend to the skin surface t hrough the epidermis. In catfish these taste buds mag offer channels t hrough which chemicals diffuse across the epidermis to the more vascul arized dermis. A comparison of dermal and branchial uptake was made by estimating zero-time dermal and branchial fluxes for all three chloro ethanes. The mean dermal fluxes for TCE, PCE, and HCE ranged from 1.4 to 2.8, 1.8 to 3.6,and 1.4 to 3.2% of the total flux (branchial plus d ermal) in rainbow trout and channel catfish, respectively. This resear ch demonstrates that dermal absorption of waterborne chemicals occurs in large adult fish and results in distribution kinetics similar to th ose observed in inhalation exposures. Compared to branchial uptake, th e dermal route of exposure appears to be relatively unimportant in lar ge fish. It may, however, be very important in smaller fish and for ju veniles of larger species. (C) 1996 Society of Toxicology