When cows or other animals are exposed to certain chemicals, regulators need to know how much of these substances ends up in the food people eat. Because long-term feeding studies with cows are costly, scientists rely on estimation methods to determine how chemicals transfer from the environment into animals and then into milk or meat. For years, scientists have measured this "biotransfer" by relying on a formula that relates concentration of a chemical in animal tissues with daily intake, assuming how much would be distributed into fat. Now, UC Davis environmental toxicology researchers have developed a new method they say is more accurate and doesn't require measurement. The new method focuses on a chemical's structure and uses the relationship between structure and activity in a molecule to determine how biotransfer would take place, says Deanna Dowdy, a doctoral student working with professor Dennis Hsieh and research engineer and lecturer Tom McKone. Dowdy presented a paper about the new method at a recent meeting of the Society of Environmental Toxicology and Chemistry.