Occurrence and ecotoxicological risks of pharmaceuticals and illicit drugs in effluent and unsheltered homelessness-impacted river systems

Wastewater treatment plant (WWTP) effluents represent the main source of pharmaceuticals and illicit drugs (PIDs) in river systems in the U.S. Moreover, pharmaceuticals and illicit drugs (PIDs) contamination due to unsheltered homelessness, as is characterized by tents or sleeping bags along rivers and other waterways, could be another pressuring factor, but it has been studied scarcely. This study investigated the occurrence of PIDs in effluent and unsheltered homelessness-impacted sites in river systems in the U.S. In addition, potential ecological risks posed by selected pharmaceuticals to aquatic ecosystems were assessed based on risk quotients (RQs). Analyses were performed using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Several PIDs were found to be ubiquitous in the effluent-impacted sites (e.g. lidocaine, metoprolol tartrate, diclofenac acid and methamphetamine). Results also showed that PIDs contamination is ubiquitous in unsheltered homelessness-impacted sites. For example, the methamphetamine concentrations in Santa Cruz River ranged from 83.5 ng L ^− 1 to 450 ng L ^− 1 . Antibiotics (6.94 ng L ^− 1 to 626 ng L ^− 1 ) were also detected in higher concentrations in Santa Cruz River. Pharmaceuticals except sulfamethoxazole were detected at concentrations far below Predicted-no effect concentration (PNEC) values across all effluent and unsheltered homelessness-impacted river systems, indicating negligible (low) or moderate ecological risks to algae and crustaceans. However, relying solely on single-compound risk assessment might underestimate cumulative ecological risk.