Risk assessment before and after solar photocatalytic degradation of BTEX contaminated groundwater at a gas station site in Korea

We assessed the incremental lifetime risks due to groundwater contamination with benzene, toluene, ethylbenzene, and xylene compounds (BTEX) for residents living on the site of a former gas station. Five remedial processes were applied to examine the degradation pattern of groundwater samples under similar weather conditions in winter: H₂O₂/solar light (action 1), immobilized TiO₂/solar light (action 2), TiO₂ slurry/solar light (action 3), immobilized TiO₂/solar light/H₂O ₂ (action 4), and TiO₂ slurry/solar light/H ₂O₂ (action 5). None of the remedial actions satisfied the criteria of acceptable risk (1 × 10^-6 for carcinogens) using point estimation with both central tendency exposure (CTE) and reasonable maximum exposure (RME) for all pathways via designated exposure scenarios. Regarding the total hazard index (HI) for noncarcinogens, only action 5 satisfied all the exposure scenarios, both CTE and RME, for toluene, ethylbenzene, and xylene compounds, whereas the total health risk for benzene was between 10^-5 and 10^-6 for carcinogens. Results of probabilistic estimation before and after the treatment of benzene with action 5 using a Monte Carlo simulation were 68.1% for males (95% CI: 5.0 × 10^-7 to 3.9 × 10^-6) and 74.2% for females (95% CI: 5.0 × 10^-7 to 4.6 × 10^-6), exceeding the criteria of acceptable risk (10^-6 for carcinogens). However, no adverse health risk was posed if remedial action 5 or an increased reaction time were applied. This study is a new attempt to integrate issues of groundwater contamination based on concentration and health risk assessment associated with different ex situ remedial actions.