Problems in monitoring mutagenicity of human urine.

Blue-cotton (-rayon) adsorbable fractions of human urines were examined for mutagenicity in Salmonella typhimurium TA98 with metabolic activation. Ingestion of cooked beef caused significant increases in urinary mutagenicity that were comparable to that caused by cigarette smoking. When a sample obtained after ingestion of cooked beef was passed through a carboxymethyl cellulose column, the mutagenicity of the eluate was found to be almost one order of magnitude greater than that of the original sample, suggesting the presence of antimutagenic factors in the sample. The oleic acid content of the sample was not great enough to account for this phenomenon. Other urine samples subjected to column fractionation were found to contain the putative antimutagenic factors. This finding further confounds the monitoring of urinary mutagenicity.