Assessment of selected pharmaceuticals in Riyadh wastewater treatment plants, Saudi Arabia: Mass loadings, seasonal variations, removal efficiency and environmental risk

Despite increasing interest in pharmaceutical emissions worldwide, studies of environmental contamination with pharmaceuticals arising from wastewater discharges in Saudi Arabia are scarce. Therefore, this study examined occur-rence, mass loads and removal efficiency for 15 pharmaceuticals and one metabolite (oxypurinol) from different ther-apeutic classes in three wastewater treatment plants (WWTPs), in Riyadh city in Saudi Arabia. A total of 144 samples were collected from the influents and effluents between March 2018 and July 2019 and analyzed using Solid Phase Extraction followed by triple quadrupole LC-MS/MS. The average concentrations in the influents and effluents were generally higher than their corresponding concentrations found either in previous Saudi Arabian or global studies. The four most dominant compounds in the influent were acetaminophen, ciprofloxacin, caffeine, and diclofenac, with caffeine and acetaminophen having the highest concentrations ranging between 943 and 2282 mu g/L. Metformin and ciprofloxacin were the most frequently detected compounds in the effluents at concentrations as high as 33.2 mu g/L. Ciprofloxacin had the highest mass load in the effluents of all three WWTPs, ranging between 0.20 and 20.7 mg/day/ 1000 inhabitants for different WWTPs. The overall average removal efficiency was estimated high (>= 80), with no significant different (p > 0.05) between the treatment technology applied. Acetaminophen and caffeine were almost completely eliminated in all three WWTPs. The samples collected in the cold season generally had higher levels of detected compounds than those from the warm seasons, particularly for NSAID and antibiotic compounds. The esti-mated environmental risk from pharmaceutical compounds in the studied effluents was mostly low, except for antibi-otic compounds. Thus, antibiotics should be considered for future monitoring programmes of the aquatic environment in Saudi Arabia.

Automated summary

Despite limited studies on pharmaceutical wastewater contamination in Saudi Arabia, this study investigated the occurrence, mass loads, and removal efficiency of pharmaceuticals in three wastewater treatment plants (WWTPs) in Riyadh city. The concentrations of pharmaceuticals in the influents and effluents were generally higher than previous studies. Acetaminophen, ciprofloxacin, caffeine, and diclofenac were the most dominant compounds in the influent, while metformin and ciprofloxacin were frequently detected in the effluents. The overall removal efficiency was high, and acetaminophen and caffeine were almost completely eliminated. Antibiotic compounds posed a higher environmental risk and should be monitored in Saudi Arabia's aquatic environment.