IMMUNOTOXICITY STUDIES IN MINK (MUSTELA-VISON) CHRONICALLY EXPOSED TODIETARY BLEACHED KRAFT PULP-MILL EFFLUENT

The immunotoxic potential of bleached kraft pulp mill effluent (BKME) to cell-mediated immunity in mink (Mustela vison) was investigated Oct ober 1993 through May 1994. For 26 weeks, 20 mink were fed a diet base d upon fish caught within 6 km downstream of a bleached kraft mill in Saskatchewan, Canada. Water for this group contained 25% softwood-run BKME. Twenty control mink were fed nutritionally matched diets based u pon fish from lakes receiving no municipal or industrial effluent and tap water. Using in vitro and in vivo immunotoxicity assays, the proli ferative response of mink peripheral blood mononuclear cells (PBMC) to mitogens was optimal, at 72 hr with 10 mu g/ml Concanavalin A, 1/80 d ilution pokeweed mitogen, and 1/80 dilution phytohemagglutinin. Bacter ial cell wall Escherichia coli lipopolysaccharide did not stimulate mi tosis of the mink PBMC. No difference (P < 0.05) in PBMC proliferation was seen between the control and BKME-exposed mink with any of the mi togens used. Delayed type hypersensitivity (DTH), a cell mediated resp onse, was assessed in mink vaccinated with live bacille Calmette-Gueri n (BCG) and then challenged by intradermal toe web injection with 200 mu g of sonicated BCG approximately 6 weeks later. The DTH response in the BKME-exposed mink was impaired based upon assessment using skin t hickness measurements, histopathological assessment and image analyzer technology. This decreased response is evidence for suboptimal immune function associated with BKME exposure, which could affect the compet itive fitness of piscivorous mammals naturally exposed to BKME.