Assessment of legacy and emerging contaminants in sediment of an Australian deepwater ocean outfall

This study evaluated the impacts of a wastewater treatment works (WWTW) in a regional city in Australia that releases both secondary-treated wastewater and resultant biosolids into an ocean outfall (depth: 25 m). Sediments (n = 64) were collected in both nort-heast (NE) and south-west (SW) directions at 10-20, 50-100, 200-500, and 1000-2000 m distance from the diffusers. The sediments were analysed for physicochemical properties, trace metals, microplastics (MPs), estrogenicity, and estrogenic endocrine disrupting chemicals (e-EDCs). The sediments were low in clay and organic content, but were enriched in fine sands. Most of the trace metal concentrations were below the detection limit of ICP-OES. Only the concentrations of Al, Fe, Cr, and Se were reportable, but were far below sediment quality guideline values. Average MP concentrations (size: >25-5000 μm) were also low (NE: 42 particles kg^-1; SW: 54 particles kg^-1) and were composed of 68% fibres (PET and PP) and 32% fragments (PP and PE). The estrogenicity (NE: 0.89 ng EEQ g^-1; SW: 1.19 ng EEQ g^-1) of the sediments was low to medium. Estrogenic compounds most responsible for the estrogenicity were 17β-estradiol (E2) and bisphenol A (BPA). All parameters were significantly higher near the diffusers (i.e., 10-20 m) and e-EDCs, particularly E2 might pose high ecological risks to aquatic habitats at this distance. Overall, there was limited contamination in the ocean outfall sediment, which is most likely attributable to the effect of significant oceanic dilution, deficiency of clay and organic content, and high content of fine sand in sediment.