Aquatic toxicity and aquatic ecological risk assessment of wastewater-derived halogenated phenolic disinfection byproducts

Increasing number of wastewater-derived aliphatic and phenolic disinfection byproducts (DBPs) were discharged into aquatic environment with the discharge of disinfected wastewater. However, the currently available aquatic toxicity data and the aquatic ecological risk information of them are limited, especially for wastewater-derived phenolic DBPs. In this study, we investigated the acute toxicity of 7 phenolic DBPs that selected from the typical five groups of phenolic DBPs (2,4,6-trihalo-phenols, 2,6-dihalo-4-nitrophenols, 3,5-dihalo-4-hydroxybenzaldehydes, 3,5-dihalo-4-hydroxybenzoic acids and halo-salicylic acids) and 4 aliphatic DBPs to Gobiocypris rarus and also assessed their potential aquatic ecological risk. Experimental results indicated that the half lethal concentration (LC50) values of 2,4,6-trihalo-phenols and 2,6-dihalo-4-nitrophenols ranged from 1 to 10 mg/L; While that of 3,5-dihalo-4-hydroxybenzaldehydes was between 10 and 100 mg/L, and 3,5-dihalo-4-hydroxybenzoic acids and halo-salicylic acids was >100 mg/L. The toxicity mode of action (MOA) identification results from three methods suggested that no clear and consistent MOA were obtained for those 11 DBPs currently. The species-specific aquatic toxicity analysis results highlighted that no aquatic species would be considered as the most sensitive species for all 11 DBPs. However, crustacean and fish were more sensitive than that of algae for most of tested compounds. Lastly, the aquatic ecological risk assessment results of those 11 DBPs revealed that all 7 phenolic and 2 aliphatic DBPs (2-bromoacetamide and bromodichloromethane) had low aquatic ecological risk, while dichloroacetic acid and dibromoacetonitrile had high aquatic ecological risk. The low environmental concentration was the main reason why high toxic phenolic DBPs (2,4,6-trihalo-phenols and 2,6-dihalo-4-nitrophenols) exhibited low ecological risk. Their ecological risk may increase with the increases of corresponding environmental concentration. Thus, more efforts should be made to determine other potential harmful effects of those high toxic phenolic DBPs and to minimize their potential ecological risk by taking appropriate measures.