Bioamplification as a bioaccumulation mechanism
Abstract
Persistent organic pollutant (POP) bioaccumulation models have been generally formulated to predict two main processes, bioconcentration and biomagnification. A third bioaccumulation process that can mediate chemical potential in an organism is bioamplification. Bioamplification occurs when an organism loses body weight and chemical partitioning capacity faster than it can eliminate contaminants. Bioamplification causes an increase in chemical fugacity in the animal's tissues and results in the redistribution of contaminants from inert storage sites to more toxicologically sensitive tissues. Further, bioamplification generally occurs when an organism experiences major bioenergetic bottlenecks or nutritional stress, frequently associated with critical periods in the animal's life history. The goal of this dissertation was to characterize bioamplification as a general bioaccumulation process that is additive to bioconcentration and biomagnification mechanisms of chemical exposure. Empirical studies validating bioamplification in three different animal models each undergoing a recognizable bioenergetic bottleneck during their life history were completed. Specifically, bioamplification was validated in emergent aquatic insects, fish embryos during egg development and larval fish. Bioamplification factors in the above studies ranged from 1.9-2.1 in emergent male mayflies, 1.8-5.4 in incubating yellow perch embryos and 1.5-5.3 in larval Chinook salmon (dependent on food resource availability). To complement these studies, a literature review was completed to demonstrate the wide applicability of this concept to different animal species. Examples of bioamplification were presented in invertebrates, fishes, birds and mammals corresponding to bioenergetic bottlenecks related to migration, reproduction, early life stages, metamorphosis, over wintering weight losses and disease. Bioamplification factors summarized in the literature ranged from 1.1-14 and were similar in magnitude to biomagnification factors typically reported for aquatic and terrestrial organisms. While most of the descriptions of bioamplification in the literature have treated it as a bioaccumulation curiosity, the results of this dissertation demonstrate that bioamplification is a general bioaccumulation process that contributes to enhanced chemical fugacities of POPs across the animal kingdom. Further, the results of this dissertation showed that bioamplification is producing maximum POP fugacities at critical periods over the animal's life history and as such the consequences of bioamplification may be very important to wildlife hazard and risk assessments.