POLLUTION LOCATOR|Risk Scoring Systems Similar to Toxicity Equivalence Potentials

The Toxicity Equivalence Potential risk scoring system was developed because there is a growing need for comparing releases of toxic chemicals into different environmental media. The public wants information about the potential health impacts of pollutant releases companies report to regulatory agencies, engineers need to compare the environmental impacts of alternatives when they practice design-for-environment, and companies and consumers would like to compare the environmental impacts of different goods and services by accounting for the effects of pollutants released during production, use and disposal.

This website's risk scoring system has been developed after careful review of several similar scoring systems that also attempt to meet these needs. These systems all share a risk assessment framework: they utilize environmental fate and exposure models to predict the dose organisms receive after a toxic chemical is released into an environmental compartment, and then compare this dose with indicators of chemical toxicity to produce a risk index. The systems vary in the extent to which they focus on specific types of releases, address ecological as well as human health impacts, and rely on different sources of data.

One similar system has been developed to index chemical releases that are reported to regulatory agencies:

Minnesota Toxicity Index

The Minnesota Pollution Control Agency has developed an indexing system for toxic air pollutants that is very similar to this website's method in that it takes both toxicity and exposure potential into account. The purpose of the system is to compare chemicals released to air in terms of their propensity to be environmental hazards. Minneapolis Environmental Management has recently applied this risk indexing system to rank TRI facilities by relative toxicity to humans and ecosystems, and proposes to assess higher emissions fees on facilities with higher risk scores. The Minnesota Pollution Control Agency has applied the indexing system to over 183 substances.

In the Minnesota Toxicity Index, a fugacity model is used to estimate chemical concentrations in different environmental media, taking into account environmental fate and transport processes. A multi-pathway exposure model is then used to estimate the cumulative dose of a chemical that humans receive after a standardized amount of the chemical is released to air. Doses are compared with toxicity benchmarks (reference concentrations, or cancer risk levels) to derive an index for human health risk.

There are several differences between the Minnesota Toxicity Index and this website's risk scoring system. The MTI also generates ecological toxicity indicators for aquatic and terrestrial organisms. It is focused on ranking air releases and does not develop indices for water or land releases. The system's human health index produces a single combined measure of cancer and noncancer health effects, based on the assumption that exceedance of a noncancer reference dose is equivalent to exceedance of a 1-in-100,000 cancer risk level. In some cases, the human health index utilizes toxicity values (threshold limit values) that this website's system does not consider reliable.

Pratt, G.C., P.E. Gerbec, S.K. Livingston, R. Oliaei, G.L. Bollweg, S. Paterson and D. Mackay. An indexing system for comparing toxic air pollutants based upon their potential environmental impacts. Chemosphere 27(8): 1359-1379. 1993.

Minneapolis Environmental Management. Minneapolis Air Toxics Brief and Emissions Fee Proposal for Point Source Air Emissions (Draft 5/12/97). Minneapolis Air Quality Management Authority, MN. 1997.

This website's risk scoring system has been explicitly designed to be consistent with the emerging framework for Life Cycle Analysis (LCA) being developed by the Society of Environmental Toxicology and Chemistry. The impact evaluation component of LCA utilizes a set of equivalency potentials to address different environmental impacts. Human toxic equivalency potentials (TEPs) express the release of a chemical in terms of an equivalent (equally toxic) mass release of a reference chemical. TEPs are attractive in the policy arena because they follow the example of well-established equivalents that have been developed for global warming and ozone depletion (CO2- and CFC11-equivalents, respectively).

Two similar systems have been developed to provide summary measures of the environmental health impacts of chemical releases for life cycle analysis:

ICI Environmental Burden Methodology

ICI, one of the largest multinational chemical manufacturers, has developed a method for evaluating its environmental performance based on the estimated "Environmental Burden" created by company activities. ICI uses its EB methodology to rank the potential environmental impact of its different emissions and to improve its environmental management and reporting. ICI believes the EB method provides a more meaningful picture of the potential impact of emissions compared with the customary practice of merely reporting the weights of substances discharged. ICI advertises the method as a way to give the public a better understanding of the potential problems associated with its emissions.

The EB methodology is based on a set of recognized global environmental impact categories which may be affected by various emissions to air or water. Currently, the system accounts for acidity, global warming, human health effects, ozone depletion, photochemical ozone (smog) creation, aquatic oxygen demand and ecotoxicity to aquatic life. Factors are assigned to each individual emission which reflects the potency of its possible impact (substances may have different potencies for different impacts). The environmental burden for each impact category is calculated by multiplying the weight of each substance emitted by its potency factor and summing across all substances capable of adversely affecting that category.

Like this website's risk scoring system, ICI's EB method uses the carcinogen benzene as a reference chemical for measuring human health effects. All chemical releases are converted into benzene-equivalents using a potency factor based on the occupational exposure standard for this chemical in the United Kingdom. ICI's method only addresses the potential human health impacts of carcinogens released to air: it does not address noncancer health effects or the human health impacts of chemical releases to water. ICI's benzene-equivalents differ from this site's TEPs in two important respects: this website's benzene-equivalents include consideration of exposure potential and not just toxicity, and compare the toxicity of other chemicals to benzene using cancer potency factors and not less reliable occupational standards.

Michael Wright, David Allen, Roland Clift and Hein Sas. Measuring the Corporate Environmental Performance: The ICI Environmental Burden System. Journal of Industrial Ecology 1:4, Fall 1997.

European Union System for the Evaluation of Substances (EUSES)

The European Union System for the Evaluation of Substances has been developed to quantitatively assess the risks posed by new and existing chemicals to human health and the environment. EUSES is a software system that can make use of newly standardized international data sets on chemical characteristics and uses for both screening-level and detailed risk assessments. It can characterize health risks to specific human populations (workers, consumers, and general public) as well as various ecological systems (aquatic and terrestrial).

EUSES has six modules that combine information about the physico- chemical properties of a substance with data on use and emissions to model environmental distribution and fate and then estimate the exposures experienced by humans and wildlife. Using toxicological benchmarks for both human and ecological effects, EUSES produces "risk characterization ratios" that indicate when chemical releases are likely to result in toxic doses that exceed acceptable levels.

EUSES can produce localized risk assessments if provided with sufficient data. It can also be run at a regional level with more generic input data and the results can be used to develop equivalency factors for placing chemical impacts on a common scale. The Dutch National Institute of Public Health and Environmental Protection developed human toxicity equivalency potentials for about 100 substances using an early version of EUSES, normalizing all chemicals to 1,4-dichlorobenzene.

This website's risk scoring system is very similar to EUSES in its approach to environmental fate and transport modeling (both systems use a Mackay- type level III multi-media fugacity model). The systems differ in that CalTOX includes more pathways in its total exposure modeling and relies on risk assessment values (not predicted no effect levels) to indicate variations in toxic potency across chemicals.

European Union. EUSES, the European Union System for the Evaluation of Substances. National Institute of Public Health and the Environment (RIVM), the Netherlands. Available from the European Chemicals Bureau (ECB/JRC), Ispra, Italy.

Guinee, J., R. Heijungs, L. van Oers, D. van de Meent, T. Vermeire and M. Rikken. LCA Impact Assessment of Toxic Releases: Generic modeling of fate, exposure and effect for ecosystems and human beings with data for about 100 chemicals. Ministry of Housing, Spatial Planning and Environment, The Hague, Netherlands. 1996.