On The Chemical Mixture Methodologies for Estimation of the Integrated Health Effects
Taha, Mohamed Ahmed
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It is very worthwhile for the regulatory agencies to have an understandable method to evaluate the health effects for humans who may be exposed to several mixtures of emitted chemicals, due to continuous regulated releases from industries. Several scientific studies and approaches were developed by international environmental agencies to estimate the combined effects from exposure to a mixture of chemicals. Usually, the developed approaches focus on predicting the impact from non-routine chemical releases in the atmosphere. However, even regulated routine releases could pose significant threat to human health when one considers the integrated effects. Present study examines the available methods to estimate the impact of air pollutants mixture and in the case of continuous airborne releases from several industries (industrial cities). The Chemical Mixture Methodology (CMM) is extensively used for emergency preparedness in the U.S. (Department of Energy, DOE). CMM uses the Hazard Index (HI) method which is also one of the recommended simple approaches to conduct a health risk assessment of chemical mixtures by both the Environmental Protection Agency (EPA) and Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations. Therefore the study deals with the necessary tools in order to sustain the original CMM applicable for continuous releases in the atmosphere. These tools include: a) models to predict the emission rates of the released pollutants, b) a dispersion model (AERMOD) to predict the concentrations of the pollutants at several receptor points and c) an in-house algorithm that deploys the various realizations of the CMM. A hypothetical scenario, based on an industrial city in State of Qatar, was built using an appropriate methodology. The outcomes demonstrate the applicability of the developed CMM methodology and tools to account for continuous releases. Finally, the results for the scenario revealed two important aspects. First, that the likelihood of severe impacts ? hazard ? increase in the case of a mixture of pollutants than a single one. Secondly, the selection of the exposure limits is a critical factor that can drastically change the conclusions of the CMM method, in other words the assessment of risk.