Ecotoxicologists and ecologists have examined the effects of pollutants on individuals and populations largely in terms of one or only a few effects. Yet the recent trend toward a holistic approach to ecological risk assessment suggests that a rigorous paradigm should be applied to toxicants, from hazard identification to risk characterization. Recent discussions have recognized that an up-front problem formulation phase is more critical in ecological risk assessment than it is for human health risk assessment. In this article a modified environmental health risk assessment paradigm is used to examine the risk of lead to birds. This risk analysis is largely conceptual, based on laboratory and field data, and incorporates information currently available. The model expands the hazard identification phase to create a target identification phase that includes the identification of receptors, endpoints, relationships, spatial and temporal scales, and indicators. The target identification phase is unique to the particular hazard, species, population, or community being examined. Lead can cause mortality, or can indirectly affect populations through effects on the food base, avian behavior, reproductive success, and recruitment. Lead can (!) decrease the abundance and availability of prey, (2) bioaccumulate in prey causing increased lead toxicosis in predators, or (3) increase prey availability by interfering with its hiding or escape behavior. Moreover, lower abundance of prey can lead to starvation or nutrient deficiencies, which amplify the absorption and retention of lead. Lead also causes decreases in clutch and egg size, mortality of embryos and nestlings, depression of growth, and deficits in behavior that affect survival. Lead decreases migratory behavior, and increases vulnerability to cold stress, hunters, and other predators. Research needs for evaluating the risk of lead in birds include obtaining data on (!) metal dynamics within various tissues as a function of dose and time since initial exposure, (2) low-level effects on embryos, (3) effects on chicks following fledging and in the period prior to recruitment, (4) effects on adult foraging skills and reproductive behavior, and (5) the relationship between effects from exposure in the laboratory and those from exposure in the wild. This latter point is extremely important, particularly if wild birds have other means of ridding the body of lead not available or less apparent to laboratory birds.
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