Dermal absorption of three waterborne chloroethanes in rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus)

In vivo estimates of xenobiotic chemical flux across the dermal surface of intact fish were obtained by measuring chemical loss from venous blood to expired water. An experimental system was developed to separate the dermal route of exposure from all other routes. The system was then used to measure dermal absorption of tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE) in channel catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus mykiss), two fish with very different skin anatomies. The kinetics of accumulation varied among chemicals, but for each compound were similar among species. TCE accumulated rapidly, reaching steady state in blood within 48 hr. Steady state was not reached in 48 hr with PCE or HCE, although blood levels of PCE were probably close to steady-state values. Dermal flux estimates (based on branchial efflux) for TCE, PCE, and HCE were two to four times greater in catfish than in trout. Arterial blood concentrations of each compound were three to six times greater in catfish. These observations are indicative of greater flux across catfish skin, augmented by higher blood:water chemical partitioning. Trout skin is covered with scales and has no taste buds, while catfish skin does not possess scales and has numerous taste bud papillae. Both scales and taste bud papillae originate in the dermis and extend to the skin surface through the epidermis. In catfish these taste buds may offer channels through which chemicals diffuse across the epidermis to the more vascularized dermis. A comparison of dermal and branchial uptake was made by estimating zero-time dermal and branchial fluxes for all three chloroethanes. 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 dermal) in rainbow trout and channel catfish, respectively. This research demonstrates that dermal absorption of waterborne chemicals occurs in large adult fish and results in distribution kinetics similar to those observed in inhalation exposures. Compared to branchial uptake, the dermal route of exposure appears to be relatively unimportant in large fish. It may, however, be very important in smaller fish and for juveniles of larger species.