THE EFFECTS OF A SECONDARY-TREATED BLEACHED KRAFT MILL EFFLUENT ON AQUATIC ORGANISMS AS ASSESSED BY SHORT-TERM AND LONG-TERM LABORATORY TESTS

The chronic effects of secondary-treated effluent from a bleached kraf t mill were assessed by means of long-term and short-term laboratory t ests. In the long-term test, the effects of the effluent on the life c ycle of fathead minnows (Pimephales promelas) were studied. In this ex periment, which began with the egg; stage and continued through to sex ual maturity and reproduction, the fish were exposed in the laboratory to well water (control) and five concentrations (viz., 1.25, 2.5, 5, 10, or 20%) of effluent for 275 days. The effluent concentrations did not significantly affect the hatching of the eggs, the mortality of th e hatched fish, the incidence of visible morphological abnormalities, the mortality and the hatchability of the first generation eggs and la rvae, and the weights of minnows at various stages of development. Bas ed on a conservative evaluation of the data, a significant finding of this work was that effluent concentrations greater than or equal to 2. 5% caused lower egg production as well as changes in the gender balanc e (i.e., increased numbers of individuals with male secondary sexual c haracteristics) of the fish. Further work is required to understand th e causes and ecological significance of these findings. Two short-term tests, each lasting 7 days, were also run. In one, even 100% effluent did not reduce the survival or growth of minnow larvae, correctly pre dicting the lack of effluent effects on similar endpoints in the long- term test. In the other short-term test, while the survival of Cerioda phnia was also unaffected by 100% effluent, their reproductive capacit y was reduced, but only at effluent concentrations an order of magnitu de greater than those affecting the reproduction of minnows in the lon g-term test. (C) 1995 Academic Press, Inc.