Some toxic effects of dimethyl sulfoxide in salmon and trout

Abstract

Acute toxicity data showed DMSO to be relatively harmless to four species of salmonids with LD 50's as follows: chinook salmon, 12 g/kg; sockeye salmon, 13 g/kg; coho salmon, 16 g/kg; and rainbow trout, 17 g/kg. All other experiments were performed on coho salmon. A daily sequence of intraperitoneal injections of 7.1 g/kg/day or more for 28 consecutive days produced significant mortalities. Hematologic changes consisted of a marked increase in polychromatocytes, plus slight and moderate degeneration of red blood cells and white blood cells, respectively. Histopathologic changes were noted in the kidney, liver, spleen, and pancreas. Median tolerance limits (TLm), established for cohos at intervals of 24, 48, 72, and 96 hours, were 7.2, 5.5, 4.9, and 4.6% DMSO, respectively. In addition, lethal exposure times (LET 50's), defined as the time required to kill half the population at a specified concentration and temperature, were recorded over an extended range of concentrations (0.01–16%) at 12° and at temperatures of 2° and 22° at 0, 8, 12, and 16% concentrations. No mortality occurred at the 2% concentration or less when fish were immersed for a 100-day period (12°). Survival time was affected inversely by concentration and temperature. Abnormal hematocrits, abnormal blood cell morphology as well as certain cellular alterations in gill, kidney, liver, brain, and spleen were observed following subjection to DMSO at high concentrations and/or after prolonged exposure. DMSO incorporated in a standard ration did not cause mortalities at the levels fed (0.01–20.0%). Diet consumption varied inversely with DMSO concentration. Reduced hematocrit values were noted in fish fed 12 and 18% DMSO in diet. Histopathology at these same two levels was limited to gill lamellae and consisted of edema and cellular hypertrophy. The injection, immersion, and ingestion experiments showed a safe level for yearling coho salmon, under these experimental conditions, of 2.8 g of DMSO per kilogram of body weight per day for 28 days, 1% v/v for 100 days, and 1% v/w for 16 weeks, respectively. These fish would tolerate higher concentrations of DMSO for a shorter period of time and recover rapidly when removed from DMSO.