U.S. EPA developed the Waste Minimization Prioritization Tool (WMPT) to
help guide the national effort to reduce the quantity and toxicity of
hazardous wastes. WMPT is a software system that provides relative
rankings of more than 1,300 chemicals according to their environmental
persistence, bioaccumulation potential, and human and ecological
toxicity. The WMPT ranks chemicals separately according to
their human health risks, their ecological health risks, and
their overall environmental health risk.
WHAT DO THE SCORES MEAN?
WMPT ecological scores indicate how a chemical compares
with others in terms of its toxicity to aquatic ecosystems and its
exposure potential. The graphic shows where a chemical's ecological
score falls relative to all chemicals that have been ranked using the
WMPT system, and indicates whether a chemical is more or less toxic than
most chemicals. Chemicals that score at the far right end of the scale
are significantly more hazardous(in the worst 11% according to this
scoring system).
All chemicals scored by a system are placed in "bins" defined by
percentiles (e.g., a chemical's score is in the least toxic
25% of chemicals scored by a system). The graphic illustrates
which bin a chemical falls in according to each scoring system in
Scorecard. Looking across these different systems, it is possible to
identify chemicals that consistently score as high or low hazards, as
well as chemicals that score high on some measures (such as human health
hazards) but low on others (such as ecological hazards).
STRENGTHS AND WEAKNESSES OF THIS TYPE OF SCORING SYSTEM?
WMPT scores are based on measures of toxicity, persistence in the
environment and bioaccumulation potential. The system has important limitations
because it does not actually estimate environmental exposures, but
relies on more readily available surrogate measures of exposure
potential. Because of the need to
include many data-poor chemicals, the system is also based on a
relatively small set of toxicity indicators. Only data on acute and
chronic aquatic toxicity are used to assign a general ecological
toxicity score. If aquatic organisms are not the most susceptible
wildlife affected by a toxicant, WMPT scores may understate the
potential risk to ecosystems.
The WMPT scoring system assigns twice as much importance to a chemical's
exposure potential as it does to its inherent ecological toxicity. A
chemical's rank is driven by the scores assigned to its persistence and
bioaccumulation potential, and substantial variations in toxicity
potential may not be reflected in a chemical's ecological risk screening
score.
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