The occurrence of opioid compounds in wastewater treatment plants and their receiving water bodies in Gauteng province, South Africa.

The continuous influx of opioid compounds into aquatic environments has become an increasing and persistent concern, due to their extensive use. This is especially alarming as wastewater treatment plants (WWTPs) are unable to completely remove them. Despite the reported health concerns, the occurrence of opioid compounds in the environment has not received much attention. The present study investigates the occurrence of 19 opioids in four WWTPs and their respective receiving water bodies. All wastewater samples revealed opioids at concentration ranging from ng/L to μg/L with most influents having higher concentrations than effluents. WWTPs appeared to perform poorly (p > 0.05 between influents and effluents), and were unable to remove some opioids including Methadone (-27.3%) from the Leeuwkuil WWTP, Codeine (-21.7%) and Thebaine (-3.77%) from the Sandspruit WWTP, and Hydrocodone (-1.06%) from the Meyerton WWTP, respectively. Samples collected from the Leeuwkuil WWTP were the most contaminated, with eighteen out of nineteen opioid analogues exceeding 1 μg/L. Upstream surface water contained less opioids (most < LOQ) than downstream (p < 0.05), with Hydrocodone, Oxycodone, Hydromorphone, Fentanyl, Ketamine and Dihydrocodeine not detected. The occurrence of high concentrations of opioid analogues in downstream surface water (298 ng/L -10.8 μg/L for Klip River, 4.49 ng/L -13.1 μg/L for Vaal River, 70.5 ng/L -10.0 μg/L for Soutspruit River and 8.0 ng/L - 2.43 μg/L for Sun Spruit River) was directly linked to their mass loads in the respective wastewater effluent samples.