DDT: effect of continuous exposure on ATPase activity in fish, Pimephales promelas

Fat head minnows, 45-days old, were continuously exposed to DDT using continuous water flow and constant temperature conditions. Exposures were to 0.5 and 2.0 ppb of DDT in water, and combinations of the two concentrations with 50 ppm in food, and 50 ppm in food alone, using C1 4-DDT in food. Brain homogenates were analyzed for enzyme activity from fish treated for 56, 118, 225, and 266 days; and gill analysis was made at 225 and 226 days exposure. Enzyme reductions were greatest in oligomycin-sensitive (mitochondrial) Mg2+ ATPase, with pronounced effects (over 50% inhibition) at the 266th sampling day. In contrast, Na+-K+ ATPase and oligomycin-insensitive Mg2+ ATPase activities were activated by as much as 28% and 40%, respectively. Mitochondrial Mg2+ ATPase of fish brain has been inhibited to the greatest extent in previously reported in vitro studies. All three ATPase enzymes were reduced in gill tissue sampled at the 266th day, with mitochondrial Mg2+ ATPase showing the greatest decline.