Chapter 15: Emerging Toxicological Methods for Fisheries Biologists in the Twenty-first Century
Cheryl A. Murphy, Janice L. Albers, Brandon M. Armstrong, Tyler J. Firkus, and Lori N. Ivan
Ecotoxicology, the study of chemical pollutant effects on free-living flora and fauna, has been a structured discipline only since the early 1970s (Truhaut 1977). Initially distinct from human toxicology, ecotoxicology has become less so as more similarities in biological responses are observed between humans and animals—to the extent that human health and ecosystem protection are now integrated in most current risk assessments. However, one notable difference that still exists is that human toxicology focuses on the fate and impact of a chemical on a single individual while ecotoxicology focuses on the impacts on a species (particularly endangered species), populations, and/or communities.
Initially, aquatic ecotoxicology primarily focused on determining chemical doses that were lethal to the average test organism. These chemicals were introduced into the environment through anthropogenic activities, either through synthesis (e.g., pesticides) or by concentrating naturally occurring substances into areas where they are not normally found (e.g., mine tailings). Many of these contaminants resisted breakdown and had toxic effects at relatively low levels of exposure. These effects were observed and regulated by means of acute toxicity tests that measured mortality with increasing concentration. But in the early 1990s, with the recognition of widespread endocrine disruption in fish and wildlife as a result of chemical contamination, research refocused to examine grossly altered physiology or sublethal effects that impacted growth or reproduction. These new metrics were used to set water quality guidelines and criteria for freshwater and marine systems (U.S. EPA 2017). The relative sensitivity of different species could be assessed by testing multiple types of organisms and endpoints in a wide range of single chemical or chemical mixtures to determine the overall risk and consequence of exposure. However, because of the magnitude of diverse chemicals continually being added to the environment, this individual chemical–organism testing model is unsustainable if all chemicals are to be surveyed. Consequently, ecotoxicology began to move toward an approach focusing on sublethal within-organism effects by assessing and monitoring biomarkers of exposure, response, and genetic susceptibility. This change began over a decade ago, largely motivated by a National Research Council 2007 report that called for a paradigm shift in toxicity testing (NRC 2007; DiGiulio and Hinton 2008). The approach of studying the mechanistic effects of chemicals at the cellular and molecular level allows for high-throughput testing and permits lower level impacts to be translated to the population, community, and ecosystem level for ecological risk assessment (e.g., Garcia-Reyero and Murphy 2018).