Toxicities of 2,2',4,4'- and 3,3',4,4-tetrachlorobiphenyls to house flies at different ages and enzyme levels.

Two tetrachlorobiphenyls (2,2',4,4'-tetraCB and 3,3',4,4'-tetraCB) had different effects on the longevity of adult female house flies (Musca domestica), depending on enzyme levels at dosing. Twenty-four-hour acute toxicities of the two tetrachlorobiphenyls were also compared with one trichlorobiphenyl (2,2',5-triCB) at different enzyme levels. 2,2',4,4'-tetraCB killed more than 90% of the flies within 12 h at the highest dose (1,667 ppm, micrograms/g); however, the toxicity of the moderate dose (1,250 ppm) was age-dependent and greater in 1- and 15-day-old flies and lower in 5-day-old flies. Daily mortality patterns of the lower doses (390 and 833 ppm) were similar to the control. LT50s (time for 50% death) were also different in different age groups at the moderate dose. The toxicity of 3,3',4,4'-tetraCB was similar to the control in all age groups, with a slight increase in the early mortalities and a decrease in the LT50s at the highest (1,200 ppm) dose. The twenty-four-hour lethality of 2,2',4,4'-tetraCB was very high, even at the lower doses in 1- and 15-day-old flies. Lower doses were least toxic at day 5, when the levels of cytochrome P450 enzymes were at the highest. On the other hand, the acute toxicity of 2,2',5-triCB increased from 5 and 15% in 1- and 15-day-old flies, respectively, to about 50% in 5-day-old flies, suggesting bioactivation of 2,2',5-triCB. The acute toxicity of 3,3',4,4'-tetraCB was negligible in all ages of house flies.