Metal and metalloid speciation and pollution assessment across a small-scale mining creek system tributary

The degree of toxic metal and metalloid [metal(loid)] pollution in a tributary creek, which flows along a small-scale gold mining area, was assessed using modeled speciation profile and various environmental pollution indicators. Sediment and water samples were collected from five different locations representing the creek’s upstream, midstream, and downstream areas. Concentration of As, Cd, Cu, and Pb in the sediment and aqueous samples were determined. Chemical speciation of the target analytes in the creek system was performed using geochemical software PHREEQC utilizing elemental concentration in sediment and aqueous phase, temperature, pH, dissolved oxygen, and identified minerals as input values. The concentrations of the metal(loids) in the sediments of midstream and downstream were higher compared to the average shale value (ASV) and toxicological reference values (TRV). Similarly, the total concentrations of As and Cu in creek water exceeded the local guidelines for effluent waters. Speciation results identified HAsO 4 2− , Cd 2+ , CuOH + , and PbOH + as the major species of the target analytes. Supersaturation of elements in sediment and low solubility in the aqueous matrix point out to resuspension and transport of metals as colloidal suspensions. The enrichment factor (EF) and geoaccumulation index ( I geo ) values indicate significant levels of enrichment and pollution in the midstream and downstream areas. The increasing pollution load index (PLI) suggested the progressive deterioration from the upstream (0.8 to 1.7) down toward the midstream (PLI = 2.0 to 18.0) and downstream (PLI = 2.4 to 17.5). Speciation and environmental index results confirmed that anthropogenic sources in the midstream were transported to the downstream catchment.