Dietary toxicity of picloram herbicide in rats.

The toxicity of orally administered technical-grade picloram was evaluated in male and female Fischer 344 rats. Dietary dose levels were up to 2000 mg/kg body weight (bw) X d for 2 wk, 500 mg/kg bw X d for 13 wk, or 200 mg/kg bw X d for 12 mo. Routine indices of toxicity were evaluated at all of the respective time periods. Body weight, food consumption, clinical chemistries, urinalyses, and hematological determinations were considered unaffected by treatment. The only treatment-related effect, regardless of the duration of exposure, was in the liver of both male and female rats. This was generally manifested as an increase in the liver-to-body weight ratio and slight hypertrophy and pallor of the centrilobular hepatocytes. These effects were consistently present in rats receiving 1000 mg/kg bw X d for 2 wk, 300 mg/kg bw X d for 13 wk, or 200 mg/kg bw X d for 6 or 12 mo. Similar effects were marginally evident for rats receiving 500 mg/kg bw X d for 2 wk, 150 mg/kg bw X d for 13 wk, or 60 mg/kg bw X d for 6 or 12 mo. At 60 mg/kg bw X d, the effects were not progressive from 6 to 12 mo. The no-observable-effect level (NOEL) was 20 mg/kg bw X d for male and female rats fed picloram for 12 mo.