A Plea for Cumulative Stressor Risk Assessments in Light of Climate Change

Abstract

Historically, environmental protection by governmental agencies has focused on controlling point-source discharges, in many cases emphasizing wastewaters laden with nutrients, pathogens, metals, and/or synthetic organics. Most non-United States countries do not focus effluent limits much beyond nutrients and dissolved oxygen and do not put limits on metals and synthetic organics. Water quality standards were established to regulate dischargers and drinking water and protect aquatic biota from impairment associated with point-source pollution. Nevertheless, widespread causes of ecosystem impairments from non-point-source (diffuse) pollution, habitat degradation, and invasive species had not been a focus of regulatory enforcement internationally. The U.S. Clean Water Act (sections 303(d), 305(b), and 314) requires each state to submit a biennial report on the quality of its water resources to the U.S. EPA. These reports identify monitored parameters causing failure of a water body to meet its “designated use”. In these reports, the overwhelming causes of impairments are single contaminants, such as chemicals, nutrients, or Escherichia coli, rather than the suite of stressors to which organisms are exposed. These stressors are certainly similar to those in other human-dominated watersheds of the world. Many international and national organizations, e.g., UNEP, WHO, IUCN, Council of Biological Diversity, JPI Oceans Knowledge Hub, Australia State of the Environment, Joint Nature Conservation Committee (UK), and U.S. EPA Office of Research & Development, and scientific authors have stated in recent years that cumulative effect assessments (CEAs) must be adopted to better protect ecosystems from physical, chemical, and biological stressors. Santos et al. (1) reviewed CEAs in terms of improving the European Water Framework Directive and highlighted the need for climate stressor inclusion. Nevertheless, most of the CEAs have failed to emphasize how climate stress and other chemical, physical, and biological stressors should be integrated (Figure 1). Figure 1. Climate-related stressors interact with traditionally managed stressors with known consequences. Cumulative stressor risk assessments are necessary for effective management. Environmental management and regulations can no longer take this overly simplistic focus. The increasing frequency and magnitude of climate change (CC)-related disasters and their interactions with these “traditional” parameters (stressors) mandate a more realistic assessment of ecosystem quality for protection, management, and restoration. Most areas of the planet have already been altered by CC, with large areas experiencing widespread devastation to ecosystems and human systems. To make matters worse, there are far more studies examining single stressors than the interaction of CC-related stressors (i.e., warming temperatures, wildfire, drought, and flooding) and stressors of traditional regulatory focus. Additionally, CC typically interacts antagonistically or synergistically with these traditional stressors, thus exacerbating adverse effects and the risk of ecosystem impairment. (2) These interactions make it challenging, if not impossible, to predict risk from single-stressor studies. Hence, we submit that (a) there is a need for more ecologically relevant experiments that rigorously consider common multiple stressors and (b) environmental science, management, restoration, and regulations advance and embrace the reality of cumulative stressor exposures. Given the above, how do U.S. EPA and other environmental regulatory agencies effectively manage for ecosystem impairments by chemical contaminants, when temperature, flooding, drought, and wildfires are increasing in scope, frequency, and magnitude? For example, low flows associated with droughts exempt wastewater dischargers from permit or water quality standards violations. In many regions, low flows are becoming the norm; therefore, wastewater is becoming a greater component of instream flows, and aquatic biota are more likely to be impacted. Conversely, flooding often overwhelms wastewater treatment plants, resulting in the release of untreated sewage. Additionally, urban and agricultural flooding also releases a wide range of potentially toxic chemicals, nutrients, and pathogens. These same streams increasingly suffer from wildfires that decimate the watershed, loading streams with eroded soils, nutrients, ash, and debris. Numerous studies have highlighted the manifold ways that a changing climate will increase both exposure to and effects of chemical contaminants (e.g., refs (3) and (4)). Will regulatory agencies continue with business as usual, adapt to manage traditional stressors in a rapidly changing environment, or throw up their arms when disasters occur and drop environmental regulations? While so many highly recognized organizations and authors have called for cumulative stressor effects and CC to be part of regulatory and management programs, there has been no apparent adoption of this call. The implementation of CEA–climate frameworks into government decision making appears unlikely given the current political environment. Consequently, academia, not-for-profit organizations, and industry must take the lead in moving the science of environmental risk assessments forward. These sectors are less encumbered by bureaucracy, tradition, and politics. Some organizations appear eager to embrace the value of explicitly considering how CC will exacerbate traditional stressors and the value of science in helping humanity navigate the impending challenges of a changing climate. To successfully move the science of CEA forward, academia, not-for-profit organizations, and industry (and government if possible) must together mobilize resources and energy to better understand, manage, and regulate the myriad ways that traditional stressors and CC interact to threaten our livelihoods. G. Allen Burton, Jr., is a Professor in both the School of Sustainability & Environment and the Department of Earth & Environmental Sciences at the University of Michigan (UM). He has an Honorary Doctorate from the University of Roskilde (Denmark) and is a Concurrent Professor at Nanjing University and an Honorary Professor at the State Key Laboratory of Environmental Criteria and Risk Assessment in Beijing. His research has taken him to all seven continents with several Visiting Scientist positions, focusing on sediment and stormwater contaminants and understanding bioavailability processes, ecological risk, and ranking stressor importance. At UM, he served as Director of the Institute for Global Change Biology, the Water Center, and the Cooperative Institute of Limnology and Ecosystems Research. He was Editor-in-Chief of Environmental Toxicology & Chemistry, was past president of the Society of Environmental Toxicology & Chemistry, and served on numerous national and international panels. He has authored 235 peer-reviewed publications. Jason R. Rohr is the Ludmilla F., Stephen J., and Robert T. Galla Professor of Biological Sciences and Chair of the Department of Biological Sciences at the University of Notre Dame. He holds B.A. degrees in biology and environmental studies, a M.A. in teaching biology, and a Ph.D. in ecology all from Binghamton University and conducted postdoctoral research at the University of Kentucky and The Pennsylvania State University. His research program emphasizes planetary health, focusing on how natural and anthropogenic environmental changes, mainly climate change, pollution, and alterations to biodiversity, affect wildlife populations, species interactions, and the spread of both wildlife and human diseases. His research makes efforts to integrate across disciplines, including ecology, the health sciences, the agricultural sciences, toxicology, conservation biology, sociology, and economics, and to address multiple Sustainable Development Goals. The primary aim of his laboratory is to understand, and develop solutions to, environmental problems to improve human health and a sustainable coexistence with the natural world. This article references 4 other publications. 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