Urinary mutagenicity assays: a problem arising from the presence of histidine associated growth factors in XAD-2 prepared urine concentrates, with particular relevance to assays carried out using the bacterial fluctuation test.

The appearance of mutagenic activity in urine samples from a group of nurses and from unexposed individuals has been investigated using the bacterial fluctuation test. Apparent mutagenic activity was seen in samples from all subjects and did not appear to be related to any specific occupational or environmental exposure. This activity seems to be related to the presence of histidine or histidine-related auxotrophic growth factors in the urine concentrates, not completely removed by the recommended XAD-2 column procedure. It is suggested that the reliance on XAD-2 columns for the removal of histidine may produce spurious results when using this assay to screen populations for exposure to mutagenic chemicals.