A LABORATORY EXPOSURE PROCEDURE FOR SCREENING PULP AND PAPER-MILL EFFLUENTS FOR THE POTENTIAL OF CAUSING INCREASED MIXED-FUNCTION OXIDASE ACTIVITY IN FISH

To better understand the relationships between pulp manufacturing proc esses and mixed function oxidase (MFO) enzyme induction in fish, a pra ctical and standardized exposure procedure is required. This study was undertaken to develop a laboratory-based exposure procedure to quanti fy the relative MFO induction potencies of different types of pulp and paper mill effluents. One major consideration in developing the proce dure was to ensure that the protocol las practical so that tests could be performed in a short time, with small volumes of effluents and usi ng simple experimental conditions. A series of concentration-response and time-course experiments were conducted to find the minimum time an d effluent concentration which could distinguish the ability of differ ent effluents to cause significant MFO induction in rainbow trout in t he laboratory. Experiments were also conducted to determine the effect s of biotic and abiotic factors such as loading density, fish size and feeding regime. This study showed that the exposure of rainbow trout in the laboratory to 10% concentration of secondary-treated effluent f or 96 h caused significant increases in hepatic MFO activity. The magn itude of MFO induction was comparable to other field and laboratory ob servations. While fish size, lending density and feeding regime were f ound to affect the test results, consistent responses within a laborat ory using this protocol are possible, provided that these factors are standardized. Therefore, the short-term exposure approach described in this paper could be a relevant tool for assessing the ability of diff erent types of pulp and paper mill effluents to cause MFO induction in fish.