Sources and occurrence of trace elements in water and sediments of Darbandikhan reservoir in Iraqi Kurdistan: A human health and ecological risk assessment

Freshwater pollution is a global threat, contributing to the decline in biodiversity whilst making water unsafe for human consumption. Climate change may further aggravate water scarcity and quality. Iraq is ranked as highly vulnerable to climate change and predicted to be extremely water stressed by 2040. Iraqi population relies on surface water, yet its availability and quality face several challenges. This study reports on Darbandikhan, a major water reservoir in Iraqi Kurdistan. The occurrence, spatial/vertical distribution and associations of 50+ elements in sediments, surface and deep water in 48 sites shed light on contamination patterns and enabled identification of several geogenic and anthropogenic sources, and locally enriched areas where mitigation actions are recommended. Darbandikhan sediments revealed a distinctive geogenic signature reflecting the Zagros geological setting. The presence of mafic/ultramafic rocks and mineralisations in the catchment resulted in high levels of As, Cr and Ni in sediments, whilst no anthropogenic sources could be unequivocally discriminated. Elemental associations with a geogenic signature and higher concentrations in deep water suggested that bottom sediments act as a secondary source of potentially toxic elements into the overlying water column. By contrast, surface water composition was primarily controlled by fresh inputs from several streams draining into the reservoir. Local enrichments in As, Ba, Mo, Ni, Sb, V and Zn were traced back to specific anthropogenic discharges. Assessment of the contamination status with several indices suggested mild to moderate environmental risk and low health risk in the majority of sites, although caution in water consumption is advised.