Monte-Carlo human health risk assessment of mercury emissions from a MSW gasification plant

Abstract

The potential impact of the atmospheric emission of mercury from a new waste gasification plant is assessed by means of a probabilistic approach based on probability density functions for the description of the input data (namely, emission rate of mercury gaseous and particulate species) and the model parameters involved in the individual risk exposure assessment through the pathways of inhalation, soil ingestion, dermal contact, and diet. The use of probability functions allowed the uncertainty in the input data and model parameters to be accounted for; the uncertainty was propagated throughout the evaluation by Monte Carlo technique, resulting in the probability distributions for the ambient air and soil concentrations nearby the plant and for the subsequent individual risk, estimated in terms of hazard index for both an adult and a child receptor. The estimated median concentration levels in air and soil are respectively in the 1.6 × 10(-3)-2.2 × 10(-2) ng m(-3) range and in the 3.5 × 10(-4)-1.7 × 10(-2) mg kg(-1) range, that is at least two orders of magnitude lower than the current background concentration in the ambient air and one order of magnitude lower than the concentration locally measured in the soil. The diet pathway is responsible for the most part (>80%) of the daily mercury intake, which, however, is at least four (median estimated values) and three orders (estimates for a reasonable maximum exposure) lower than the reference dose in the most part of the modeling domain. According to the locally measured background mercury levels in air and soil the additional contribution of the plant emissions to the environmental mercury levels appears of small significance, with an almost negligible impact on the hazard index for the population living in the neighborhood of the plant.