Pharmaceutical Pollution in Urban Coastal Watersheds of Eastern Saudi Arabia: Implications for Sustainable Water Resource Management

Pharmaceutical pollution in urban water poses a significant threat to coastal ecosystems, particularly in regions with rapid urbanization. This study investigates the source, occurrence, and distribution of pharmaceutical compounds (PCs) in agriculture runoff and treated wastewater (TWW) used for irrigation within urban coastal zones in eastern Saudi Arabia. Water samples were collected from TWW irrigation (2 samples) and agriculture runoff channels (10 samples) to identify and quantify the pharmaceutical pollution. The agricultural runoff samples were collected from fields irrigated with TWW and fields irrigated by groundwater (GW) for comparative study. Water samples were analyzed for 50 PCs using Liquid Chromatography-Mass Spectrometry with Direct Injection (LCMS–DI) and followed the  US EPA Method 1694. The results show that 12 PCs were detected in both water sources, including caffeine, carbamazepine, iohexol, sulfamethazine, valsartan, atenolol, diclofenac, furosemide, gabapentin, hydrochlorothiazide, naproxen, and paracetamol. Among those compounds,  caffeine, iohexol, valsartan, sulfamethazine, and gabapentin were detected with frequencies of 100%, 60%, 50%, 30%, and 20%, respectively. The remaining compounds were detected with a frequency of <20%. The results reveal that the highest concentration of PCs was observed in the main agricultural drainage channel in downstream regions. This probably reflects the cumulative input of PCs from upstream tributaries. Additionally, agricultural runoff from fields irrigated with GW contains only caffeine and sulfamethazine pollutants. However, in regions irrigated with TWW, twelve PCs were detected. The potential source for PCs in agriculture runoff from fields irrigated with GW is the manure fertilizer, which is commonly used in the study area. However, in regions irrigated with TWW, the PCs were most probably sourced from TWW irrigation. The study findings suggest enhancing wastewater treatment with advanced techniques to remove emerging pollutants and to protect the aquatic ecosystem. In addition, the study contributed to a better understanding of the urban watershed dynamics and provides insights that can inform sustainable urban water management practices, especially in urban agricultural regions where TWW is utilized for irrigation.