Although detected at low concentrations, pharmaceuticals are specifically designed to be biologically active even in small quantities and can have significant impacts on aquatic organisms including bacteria, algae, invertebrates, and fish. There is an ever-growing body of research that demonstrates the negative impacts of pharmaceutical compounds to the environment at even low-level concentrations.

• One study showed that common pharmaceuticals like ibuprofen are taken up and negatively affect the physiology of mussel species at levels of two to three orders of magnitudes higher than found in the wastewater treatment plant effluent that these mussels were exposed to. (Ericson et al. 2010).
• Amphetamines and antidepressants in stream water can disrupt the timing of emergence of aquatic insects and fish behavior can be altered when consuming prey contaminated with antidepressants (Richmond et al. 2018).
• Antidepressants can alter the reproduction, behavior, and development of a wide suite of aquatic organisms (Moreira et al. 2022).
• Researchers found similar concentrations of pharmaceutical compounds in aquatic invertebrate larvae and their land-based predators, indicating that there is transfer to higher levels in the food web. This study also indicated that aquatic and riparian organisms are exposed to some drugs at levels comparable to human dosages (Richmond et al. 2018).

Perhaps the most well-studied negative impact from medicine in the environment is that posed by antibiotics and antimicrobial substances. Triclosan is an antimicrobial that was historically found in a wide variety of personal care products, and as a result t is estimated that 75% of Americans are exposed to it and it has been detected in aquatic environments and animals (Weatherly and Gosse 2017). While antibiotics are essential for treating bacterial infections, the improper use and disposal of antimicrobial substances can lead to changes in normal bacterial communities in ecosystems, potentially leading to the emergence of antibiotic-resistant bacteria (Endale et al. 2023).