When municipal wastewater treatment plants clean up sewage, they never fully remove some types of contaminants. The plants don’t track or treat some chemicals, such as pharmaceuticals, so these compounds remain in the water1, or effluent, that plants release into the environment. Now Canadian researchers report that effluent can cause metabolic stress in rainbow trout, which could harm the long-term health of fish populations (Environ. Sci. Technol., DOI: 10.1021/es103122g2).

Sewage treatment primarily reduces or removes trash, debris, organic matter, and disease-causing organisms from wastewater. Scientists worry about the impacts of the remaining compounds on aquatic organisms. Previous studies have investigated how individual chemicals or classes of these chemicals affect animals, particularly through their endocrine systems. Jennifer Ings, a graduate student at the University of Waterloo3, and her colleagues wanted to understand how animals responded to a realistic mix of the substances that linger in treated municipal wastewater.

The researchers placed cages containing eight to16 juvenile trout (Oncorhynchus mykiss) at five locations in the Speed River in Guelph, Ontario. Three of the sites were downstream of a municipal wastewater treatment plant. The water at these spots consisted of 100%, 50%, and 10% effluent. The final two sites were upstream of the plant and […]