Environmental pollution and associated ecological risk assessment of the agricultural water in the arid coastal ecosystem

Pollution of freshwater in arid regions poses a critical environmental challenge threatening water sustainability and ecosystem integrity. This study presents a comprehensive assessment of combined pollution and ecological risk from agricultural drainage water (ADW) in the Al-Qatif region, eastern Saudi Arabia. Twenty samples were collected from the agricultural drainage system in the study area and from regions with treated wastewater irrigation and groundwater irrigation. The samples were characterized for chemical and pharmaceutical pollutants using standardized laboratory methods. Then, indices of water quality and pollution, and ecological risk were computed. The study revealed that >90% of the analyzed ADW samples were extremely polluted with higher contamination of nutrients and moderate for trace elements. Three categories of pollutants (nutrients, trace and toxic elements, and pharmaceuticals) were recognized, which posed a risk to the aquatic organisms, with a hazard index exceeding the threshold value (HI>1). Moreover, pharmaceuticals showed a higher risk for algae with HI exceeding 229. The study concluded that samples from regions irrigated by treated wastewater display higher combined pollution and ecological risk than samples from fields with groundwater irrigation. This indicates that the potential sources of nutrients, trace metals, and pharmaceuticals are the treated wastewater irrigation and animal manure used to fertilize agricultural soil. Accordingly, mitigation measures, including the advancement of wastewater treatment processes, effective manure management, and constructed wetlands, can be implemented to reduce the pollution load in ADW and safeguard freshwater bodies and aquatic life. This will help enhance long-term water security and ecosystem integrity in arid environments.