MEASURING THE POTENCY OF PULP-MILL EFFLUENTS FOR INDUCTION OF HEPATICMIXED-FUNCTION OXYGENASE ACTIVITY IN FISH

A bioassay protocol was optimized for measuring the potency of effluen ts or waterborne chemicals for inducing mixed-function oxygenase (MFO) activity of rainbow trout (Oncorhynchus mykiss). Measurements of etho xyresorufin O-deethylase (EROD) can be made with an established endpoi nt assay using large volumes of reagents and tissue. However, a new ki netic microplate assay offers significant savings in time, reagents, a nd sample volumes. Data are distributed lognormally and must be log tr ansformed before statistical analyses. EROD activity increases with ex posure time to pulp mill effluent and a 4-d exposure provides a near-m aximal response. Optimum fish size conforms to standard practices in f ish toxicology; loading rates should not exceed 1 g of fish per liter of test solution per day. Feed should be withheld from Lest fish 48 h before testing to reduce the variance of measured activity, and anaest hetizing fish with MS-222 does not affect their response to MFO induce rs. Pulp mill effluents do not lose their potency during 2-3 wk of exp osure at temperatures ranging from -20 to 13 degrees C, whether stored in plastic or glass. Steel containers were associated with slight los ses in potency. Bioassays of MFO induction in fish exposed to liquid e ffluents are practical and conform to standard practice for testing th e lethality of waterborne chemicals. The results are sufficiently prec ise that differences among means based on five fish per treatment can be discriminated statistically when activity changes by threefold or m ore.