It is critical for Environmental Health and Safety agencies to have a consistent and comprehensive method to assess the health effects and the environmental impact in the case of exposure to mixtures of several emitted chemicals. Such an incident could emerge after an industrial accident but also due to continuous, though regulated, releases from large industrial cities. Today, there are approaches to estimate the combined effects of exposure to a mixture of chemicals. Usually, these approaches focus on predicting the impact from non-routine chemical releases, i.e. accidental releases. However, even regulated routine releases could pose a significant threat to human health when one considers the integrated effects. Therefore, it is important to explore the available methods to assess the impact in the case of continuous airborne releases from industrial cities (air pollutants mixture; several industrial sources).
According to early discussions (Bliss, 1939), chemical interactions are defined as a) independent joint action, b) similar joint action and c) synergistic action. For obvious reasons, many toxicological studies have followed, which eventually forged the existing environmental and health legislation. Many of these efforts were initiated by organizations such as the US Environmental Protection Agency (EPA, US), Agency for Toxic Substances and Disease Registry (ATSDR) and the European Chemicals Agency (e.g. REACH and CLP regulations) (Monosson, 205). All efforts focused on the collection and set of the appropriate approaches to conduct such assessments following specific categorization methods (Rice, 2008). Generally, there are three methods to conduct the risk assessments for the multi emitted chemicals: a) whole mixture assessments (actual mixture of concern), b) similar mixture assessments and c) component by component assessments. The usage of each method strongly depends on the availability of the basic required information such as inventory data for the emitted pollutants, concentration of the released chemicals and the meteorological data the considered location.
One of the recommended and simpler approaches, to conduct health risk assessment of chemical mixtures, is the Hazard Index (HI), also adopted by US, EPA and in REACH. HI does not cover all aspects of exposure. Therefore, more advanced methods need to be selected. One is the Chemical Mixture Methodology (CMM), which is extensively used for emergency preparedness in the U.S. (Department of Energy, DOE), but it has not been designed for the assessment of health effects from routine and typical industrial emissions.
Present work discusses the details of CMM and explores the necessary tools and assumptions in order to apply the method on continuous atmospheric releases and multiple sources; for the health impact assessment of the chemical mixture. 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. Finally, we demonstrate the methodology on a fictitious industrial city of Middle East Area. The outcomes support the applicability of CMM and the proposed tools to account for continuous releases with two main findings. First, the likelihood of sever impacts – hazard – increases in the case of a mixture of pollutants. Second, the selection of base exposure limit is a critical factor, and it can drastically change the conclusions of the methodology, in other words, the assessment of risk.
This publication was made possible by a NPRP award [NPRP 7 - 674 - 2 - 252] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors. The HPC resources and services used in this work were provided by the IT Research Computing group in Texas A&M University at Qatar. IT Research Computing is funded by the Qatar Foundation for Education, Science and Community Development (http://www.qf.org.qa).
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