Sequential histopathologic, hematologic, and blood chemistry changes induced in mice by a technical and a purified preparation of 2,4,5‐trichlorophenoxy acetic acid

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Abstract
Maternal mice were given 2,4,5‐trichlorophenoxyacetlc acid (2,4,5‐T) on days 6 through 14 of pregnancy in a teratologic study at the National Center for Toxicological Research. Sick or moribund mice sacrificed after 4–8 doses of 120 mg/kg 2,4,5‐T often showed severe myocardial lesions, hypocellularity of the bone marrow, and depletion of lymphocytes in the thymus, spleen, or lymph nodes. Healthy mice sacrificed on day 17, 11 days after treatment began, showed few or no severe lesions. To determine if lesions earlier in gestation contributed significantly to an increase in fetal abnormalities in the healthy 17‐day survivors, dihybrid cross F2 pregnant and nonpregnant mice received by gavage 0, 60, or 120 mg/kg 2,4,5‐T on days 6 through 14 of pregnancy. One group received a technical preparation containing 97.9 ± 0.4% 2,4,5‐T; another received a purified preparation containing 99 ± 0.3% 2,4,5‐T. Mice were sacrificed when they became moribund and at 6, 24, and 30 hr, as well as at 4, 6, 8, and 11 days after beginning treatment. Almost all mice given 60 mg/kg and many given 120 mg/kg 2,4,5‐T appeared normal at sacrifice either early or late in pregnancy and showed little or no pathologic changes. Mice that became ill or moribund often showed severe lesions; few survived 11 days. Severe myocardial lesions were seen in 26 of 70 moribund mice given the technical 2,4,5‐T and 24 of 33 given the purified preparation of 2,4,5‐T. The moribund mice, particularly those given the purified compound, also showed a high incidence of lesions in other organs and marked hematological and blood chemistry changes. These findings indicate that the lesions are primarily due to 2,4,5‐T rather than to impurities in the technical preparation; also impaired maternal health is not the primary cause of the increase in fetal abnormalities.