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.
SYSTEMS FOR WEIGHTING RELEASES BY TOXICITY AND EXPOSURE POTENTIAL
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.
SYSTEMS PRODUCING EQUIVALENCY POTENTIALS FOR USE IN LIFE CYCLE ANALYSIS
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
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.