The health consequences of chronic low concentration exposure to environmental contaminants are not well understood and need continued study. Most toxicological studies use concentrations well above those observed in the environment. This study will use the exceptional sensitivity and discriminatory power of flow cytometric analysis, to detect if chromosomal breakage occurs in cells grown in culture. Another objective is to find out whether the damage results from exposure to common herbicides at concentrations actually found in the environment. The effects of 10 individual herbicides and 2 metabolites will be assessed. Also, additive or synergistic effects from exposure to combinations of herbicides will be identified. These data can provide understanding of the functional basis for some chronic toxicological responses and contribute to other epidemiological and toxicological investigations. After this validation study the methods can be extended to other contaminants and realistic combinations. This work will hopefully lead to development of additional molecular methods for toxicological evaluations pertinent to Iowa.