EFFECTS OF A SECONDARY-TREATED THERMOMECHANICAL PULP-MILL EFFLUENT ONAQUATIC ORGANISMS AS ASSESSED BY SHORT-TERM AND LONG-TERM LABORATORY TESTS

The chronic effects of secondary-treated effluent from a thermomechani cal pulp (TMP) mill were assessed by means of long-term and short-term laboratory toxicity tests. The effluent used for the tests was sample d at a western Canadian mill using mostly softwoods and <10% recycled fiber as furnish. In the long-term test, the effects of the effluent o n the life cycle of fathead minnows (Pimephales promelas) were studied . In this experiment, which began with the egg stage and continued thr ough to sexual maturity and reproduction, the fish were exposed in the laboratory to well water (control) and five concentrations (1.25%, 2. 5%, 5%, 10%, or 20%) of effluent or 202 d. None of the effluent concen trations significantly affected!he hatching of the eggs, the mortality , weight, length, gonad size, gender balance, and reproduction of the hatched fish, the prevalence of gross morphological and histopathologi cal changes, and the hatchability of the first generation eggs. Two sh ort-term tests, each lasting 7 d, were also performed. In these tests, 100% effluent caused no change in the survival/growth of minnow larva e or in the survival/reproduction of Ceriodaphnia.