Problems and prospects in the utilization of cytogenetics to estimate exposure at toxic chemical waste dumps.

In mammalian cells, one of the most sensitive indicators of exposure to mutagenic carcinogens has been the induction of cytogenetic effects, chromosome aberrations and sister chromatid exchanges (SCEs). Some mutagens, such as ionizing radiations that induce double-strand breaks in DNA are very efficient at inducing chromosome aberrations and can induce them at all stages of the cell cycle. Some other physical mutagens, such as ultraviolet light, cannot induce breaks directly, but form lesions in DNA that lead to the production of chromatid aberrations later when the cells proceed to the S phase. Although a few chemical mutagens can induce double-strand breaks in DNA and thus are radiomimetic or X-raylike, the majority are like ultraviolet light in that they form lesions that are not converted to aberrations until the cells enter S. Unlike X-rays and the few radiomimetic chemicals, these S-dependent agents, be they physical or chemical, are able to induce SCEs very efficiently. In fact, cells exposed to these agents often show large increases in SCEs at doses as low as 1/100 that required to show increases in chromosome aberrations.