Differential Life-Stage Sensitivity to Toxicants Modeled in Three Avian Species. P. E. Woods and C. Wills, ChemRisk Division, McLaren/Hart, 1135 Atlantic Avenue, Alameda, CA 94501
Differential life stage sensitivity to toxicants is well-established for invertebrates but less so for vertebrates. Differential sensitivity may arise because of immature organ systems causing impaired clearance (i.e., detoxification of toxicants), and/or increased ingestion rates on a per-gram basis due to increased metabolic demands dictated by rapid growth or allometric (scaling) considerations. This paper models the response of the nestlings and adults of three avian species including red-winged blackbird (Agelaius phoeniceus), marsh wren (Cistothorus palustris), and wood stork (Mycteria americana) to DDT acquired from the diet. The model is based on the energetic demands of individuals at different life stages. The results indicate that differential sensitivity can be expected, and should be considered in ecological risk assessments. The standard LC50 values based on adult individuals may, in some cases, fail to protect the more sensitive nestling and juvenile birds. Ecological risk assessments are based on standard toxicity test results, therefore, may in cases where there is increased sensitivity in young birds, fail to accurately predict risks to the exposed population.