While the old adage “anything can be considered a poison depending on the dose” is true, problem contaminants in the aquatic environment typically cause adverse effects at very low concentrations (on the order of parts per million or even billion).
Aquatic pollutants originate from many everyday products: pesticides, plastics, cooling and insulating fluids in electrical capacitors and transformers, resins, paints, flame retardants, oil, coal, tar, pain relievers, birth control, and antibiotics just to name a few. Also problematic
, pollutants are mixing together in aquatic systems to make complex concoctions, and we do not know how these mixtures effect aquatic species. Some mixtures may cause adverse affects to be synergistic or additive, while others could have no effect or even cancel out the effects of another contaminant. Further complicating matters, water chemistry (e.g. pH, nutrients, and dissolved oxygen) can influence the toxicity of pollutants as well.
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Aquatic systems are particularly vulnerable to amassing pollutants because direct inputs from industry and wastewater, as well as runoff from surrounding terrestrial areas result in aquatic systems acting as contaminant repositories. Aquatic animals are also particularly vulnerable to contaminants because they are immersed and surrounded by pollutants, often for their entire lives, and are inherently sensitive to pollutants because their skin and gills are permeable.
Contaminants that fish face in today’s aquatic environment can include persistent historic contaminants like dioxin, PCBs, and DDT that Rachel Carson fought against in the 1960’s and more recent “contaminants of emerging concern”, defined by the Environmental Protection Agency (EPA) as chemicals and other substances that have been recently discovered in natural streams, and potentially cause deleterious effects in aquatic life at environmentally relevant concentrations.
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Newman MC. 2010. Fundamentals of Ecotoxicology, Third Edition. CRC Press, Boca Raton, FL, USA.
Van Aerle R, Nolan M, Joblings S, Christiansen LB, Sumpter JP, Tyler CR. 2001. Sexual distruption in a second species of wild cyprinid fish (the gudgeon, gobio gobio) in united kingdom freshwaters. Environmental Toxicology and Chemistry 20(12):2841-2847.
United States Environmental Protection Agency (USEPA). 2008. Aquatic Life Criteria for Contaminants of Emerging Concern, Part 1: General Challenges and Recommendation. White Paper, OW/ORD Emerging Contaminants Workgroup.