Deriving Trigger Values For, and Assessing Hazard Posed By, Volatile Chlorinated Hydrocarbons in a Sydney Estuary

The hazard of adverse effects to aquatic organisms arising from groundwater contaminated with a complex mixture of volatile chlorinated hydrocarbons (CHCs) discharging to Penrhyn Estuary, Sydney, Australia was determined using the hazard quotient (HQ) method. The hazard posed by 14 volatile CHCs acting individually and collectively as a mixture was assessed. The hazard was determined using measured aqueous concentrations of the volatile CHCs (at high and low tide and an average of the two) and the corresponding trigger values from the Australian and New Zealand water quality guidelines. Low reliability trigger values were derived in this study for fi ve volatile CHCs, in accordance with the methodology in Australian and New Zealand water quality guidelines. High ecological hazard was posed by some individual CHCs at sites close to the contaminant source in the upper and inner estuary, while the corresponding hazard in the outer estuary was low. The hazard was always greater at low tide than high tide in the inner and outer estuary, presumably due to the infl ow of tidal water and subsequent dilution of contaminants. The chemicals that posed the greatest hazard were 1,2-dichloroethane, tetrachloroethene and vinyl chloride. Six of the nine sites received a high hazard for at least one volatile CHC. Assessing the hazard posed by the mixture always increased the HQ values compared to that for individual chemicals but it did not increase the number of sites which received a high hazard (i.e. 6 of 9 sites). The hazard assessment indicates that more detailed assessment in the form of a probabilistic risk assessment and direct toxicity assessment is warranted. Limitations identifi ed in this hazard assessment include the use of low reliability trigger values for individual chemicals, additivity of toxicants and highly variable (spatially and temporally) concentrations.