Physiological and Biochemical Mechanisms That Regulate the Accumulation and Toxicity of Environmental Chemicals in Fish

Abstract

The field of environmental toxicology is complex and multidisciplinary in its approach, and must involve physical, chemical, and biological understanding in order to resolve the present and future environmental perturbations caused by toxic chemicals. The latest Pellston Workshop on bioavailability and chemical interactions was concerned primarily with understanding the relationships between toxic chemicals and the physical-chemical and biological processes inherent to the aquatic environment In order to link these important environmental interactions to animal responses, a transition had to be made from environmental availability to accumulation and toxicity. This involved knowledge of the important exchange surfaces and the mechanisms that control the flux of chemicals across such surfaces. Figure 1 presents this transition in the context of ecological risk assessment inputs such as hazard, exposure, and biological receptors. This description further summarizes the processes that control the movement of chemicals through the environment; the source of contamination, transport through the system, transformation from one form to another by either biotic (i.e., biodegradation by microorganisms and/or biotransformation by higher organisms) or abiotic (i.e., photooxidation, hydrolysis) processes, and the fate as determined by bioaccumulation, sorption to sediment, or evaporation. These natural processes ultimately determine a chemical’s bioavailability to aquatic organisms. The animals exposed to concentrations of specific chemicals represent the receptor. The impact of chemical exposure on the receptor organism depends on a number of major ecological variables such as species, lifestage, habitat, and trophic level. The environmental exposure of the animal to the chemical provides both a total dose received (in milligrams per kilogram per day) and an accumulated dose [body burden (in milligrams per kilogram)]. Modifying factors (physiological and biochemical mechanisms) in the animal control the magnitude of chemical uptake and accumulation and, thus, the toxic response of the animal. Toxic response is tied to a specific internal dose (in milligrams per kilogram) or exposure concentration (waterborne, food) and describes the hazard. Toxic responses (acute and chronic) are measured in single-species toxicity tests to determine potential hazard and to establish dose-response relationships. The proper collection and synthesis of these data inputs (Figure 1) will provide aquatic toxicologists with a better mechanistic approach to understanding the impacts of chemical toxicants on the environment. Figure 1 The major environmental and toxicological factors impacting the toxic response of animals to environmental toxicants. https://www.w3.org/1999/xlink" xlink:href="https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003578895/0174d1ec-4831-4e37-848c-d19e409e478d/content/fig20_1.tif"/>

Topics & Concepts