Sublethal Effects of Contaminants in Aquatic Food Webs—Research Challenges and Considerations for Future Studies

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U.S. Geological Survey (USGS) and academic scientists partnered to identify challenges and provide considerations for future scientific study designs to advance our understanding of the often subtle sublethal effects of contaminants on individuals, populations, communities, and entire aquatic food webs. 

Substantial progress has been made in understanding the sources, movement, and occurrence of chemical, physical, and biological contaminants in aquatic environments. Commonly used chemicals, such as pharmaceuticals, plastics, personal care products, and flame retardants often make their way into aquatic ecosystems. Some of these contaminants may be harmful if consumed at certain levels, but their presence does not necessarily indicate a health risk.  Although these contaminants are rarely lethal,  aquatic organisms often exhibit subtle and sublethal effects including changes to behavior or endocrine system function, which presents challenges to understanding contaminant exposure on individual organisms, populations, communities, or entire aquatic food webs.

Challenges associated with the effects of contaminants on aquatic food web.

Conceptual image illustrating the challenges associated with the effects of contaminants on aquatic food webs. (1) Complex contaminant mixtures; (2) sublethal effects of contaminant exposure; (3) long‐term, multigenerational exposures; (4) multiple stressors; and (5) linkages across populations and trophic levels. AFO = animal feeding operation.

Scientists on the integrated science teams supported by the USGS Toxic Substances Hydrology and Contaminant Biology combined programs partnered with scientists at several universities within and outside the United States to highlight challenges and identify considerations for future scientific study designs. Scientists identified five main challenges:  

  • compiling detailed information on the complexity of mixtures of contaminants in the aquatic environment,
  • developing information on the sublethal effects of contaminants on a wide range of aquatic organisms,
  • understanding the biological consequences of exposures of varying duration within and across generations in aquatic species,
  • integrating multiple stressors with contaminant exposure in aquatic systems, and 
  • documenting consequences of contaminant exposure on wildlife populations, communities, and entire aquatic food webs. 

The scientists provide information to show how these challenges can be addressed to fill knowledge gaps and improve future study design to advance a broader understanding of contaminants effects in aquatic systems. They emphasize the need for multidisciplinary teams to move beyond the current research focus on the effects of individual compounds on individual organisms to include a broader understanding of the effects of contaminants on populations, communities, and entire aquatic food webs. This information is valuable to scientists as they move forward with studies to understand the sublethal effects of contaminant exposure and is valuable to other stakeholders who need to prioritize and balance the risks and benefits of use of these compounds while safeguarding health.

This research was funded by the USGS Contaminant Biology and Toxic Substances Hydrology combined programs, the USGS Oregon Water Science Center, the Great Lakes Restoration Initiative through the USGS Fish and Wildlife Service Contaminants of Emerging Concern team, and from a National Science Foundation grant.


Nilsen, E., Smalling, K.L., Ahrens, L., Gros, M., Miglioranza, K.S.B., Pico, Y., and Schoenfuss, H.L., 2018, Critical review: Grand challenges in assessing the adverse effects of contaminants of emerging concern on aquatic food webs: Environmental Toxicology and Chemistry, v. 38, p. 46–60,

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