Toxicokinetics of monochloroacetic acid: a whole-body autoradiography study

Monochloroacetic acid (MCA) is a toxic chemical used as a herbicide and in the synthesis of various organic compounds. MCA has also been shown to be present in chlorinated drinking waters. In order to understand the mechanism of MCA toxicity, we studied the tissue distribution of [1-¹⁴C]MCA in rats, by whole-body autoradiography technique. Male Sprague-Dawley rats were given a tracer dose of [1-¹⁴C]MCA [6.8 μg/100 g (40 μCi) body weight] by tail vein and euthanized at different time intervals (5 min, 1, 4, 12, 24 and 48 h). The animals were embedded in carboxymethyl cellulose and frozen immediately. Frozen animals were sectioned and processed using whole-body autoradiographic techniques. Analysis of developed sections showed that at 5 min, there was a rapid accumulation of ¹⁴C-activity in the kidney cortex and stomach walls. The radioactivity was rapidly removed from the circulation. There was high accumulation of ¹⁴C-activity in the myocardial tissues. The liver was also loaded with MCA and/or its metabolites. After 1 h following administration of [¹⁴C]MCA, radioactivity was extensively excreted into the small intestinal lumen. The accumulation of ¹⁴C-activity in the brain, thymus, salivary glands and tongue was prominent at 1 h. After 4 h the liver and other tissues started to eliminate most of the radioactivity. Contrary to other tissues, however, the central nervous system, thymus and pancreas started to accumulate the radioactivity at later time periods. These observations suggest the accumulation of MCA and/or its metabolites into hydrophilic tissues at earlier time periods and into lipophilic tissues at later times.