Ecological risk assessment for xylenes and propylbenzenes in aquatic environment using a species sensitivity...

Xylenes and propylbenzenes (PBZs) are volatile aromatic hydrocarbons with high aquatic toxicity. Xylenes can be present in three isomers: o-xylene (OX), m-xylene (MX), and p-xylene (PX), while PBZs include two isomers: n-propylbenzene (n-PBZ) and isopropylbenzene (i-PBZ). Their accidental spills and improper discharges from petrochemical industries can cause severe contamination in water bodies posing potential ecological risks. In this study, the published acute toxicity data of these chemicals for aquatic species were collected to calculate hazardous concentrations protecting 95% species (HC5) using a species sensitivity distribution (SSD) approach. The acute HC5 values for OX, MX, PX, n-PBZ, and i-PBZ were estimated to be 1.73, 3.05, 1.23, 1.22, and 1.46 mg/L, respectively. The risk quotient (RQ) values calculated based on HC5 indicated their high risk (RQ: 1.23 ∼ 21.89) in groundwater, but low risk (RQ < 0.1) in natural seawater, river water, and lake water. When xylenes or PBZs leaked into the sea, they were expected to pose a high risk (RQ > 1) at the start and then a low risk (RQ < 0.1) after 10 days due to natural attenuation. These results may help to derive more reliable protection thresholds for xylenes and PBZs in aquatic environment and provide a basis for evaluating their ecological risks.