Can the hydrophobic organic contaminants in the filtrate passing through 0.45 μm filter membranes reflect the water quality?

Highlights: • The HOC concentrations passing through 0.45 μm filter membranes may not reflect the water quality. • Water quality assessment should consider the bioavailability of DOM or SPS associated HOC besides freely dissolved HOC. • Pyrene bioavailability was underestimated with traditional methods at higher SPS concentrations. • Pyrene bioavailability was overestimated with traditional methods at lower SPS concentrations. • The assessment deviation depended on concentrations and characteristics of SPS and DOM. In the traditional water quality assessment, the concentration of total dissolved hydrophobic organic compounds (HOCs) passing through 0.45 μm filter membranes is usually used to evaluate the influence of HOCs on water quality. However, the bioavailability of dissolved organic matter (DOM)-associated and particle-associated HOCs is not considered. In the present work, pyrene, fulvic acid, and natural suspended particles (SPS) were used to simulate natural water (raw water). The immobilization and pyrene content in the tissues of D. magna caused by total pyrene in the raw water and those caused by freely dissolved pyrene with the concentration equal to the total dissolved pyrene in the filtrate of raw water were compared to determine whether the total dissolved pyrene concentration can reflect the water quality. The results indicated that when the DOM concentration was 5 mg C L⁻¹ and the SPS concentration was higher than 0.2–0.4 g L⁻¹, the bioavailability of pyrene was underestimated by the traditional water quality assessment because of the SPS-associated pyrene, and it was underestimated by 23.6–63.9% when SPS concentration was higher than 0.6 g L⁻¹ due to the neglection of SPS-associated pyrene. Furthermore, the threshold value of SPS concentration was related to the SPS size and composition, and the effects of SPS and DOM on water quality were influenced by the concentration, size, and composition of SPS as well as the molecular weight of DOM. This study suggests that the traditional water quality assessment should be improved by comprehensively considering concentrations and characteristics of SPS and DOM.