Wastewater can add nutrients, personal-care products, and pharmaceuticals into natural water bodies, with unintended consequences to these ecosystems. For example, wastewater inputs have been linked to altered physiology and community structure of microbes, insects, mollusks, amphibians, and fish, as well as shifts in entire food webs.
One particularly disconcerting effect of wastewater on freshwater organisms is endocrine-disruption, which is when chemicals that mimic natural estrogens disrupt hormonal functions. One result is the feminization of male individuals, such as intersex (where oocytes show up in the testes) and altered sex ratios in the population (e.g., more females).
While the negative effects of wastewater are widely acknowledged (albeit not fully understood), we know little about how communities respond to improved wastewater management. A recent study by Hicks et al. in Environmental Science and Technology suggests that freshwater fish may be resilient to improvements in water quality. The study looked at rainbow darter fish before and after major improvements to a wastewater treatment plant in Ontario, Canada. Before the upgrades, 70 to 100% of the darter fish had intersex traits, which declined to <10% after upgrades were made to the plant. This study indicates that major and costly upgrades to wastewater treatment plants can help to restore our native aquatic communities. Let’s hope to see more such initiatives in the future!