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 overall scores indicate how a chemical compares
with others in terms of its potential to pose risk to both human health and ecosystems. The graphic shows where a chemical's overall 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 10% 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 human and ecological toxicity, persistence in the environment and bioaccumulation potential. The system has important limitations because it does not actually estimate human exposures to toxic chemicals, but relies on more readily available surrogate measures of exposure potential. These surrogate measures focus on chemical persistence and bioaccumulation in an aquatic environment.
The WMPT scoring system assigns twice as much importance to a chemical's
exposure potential as it does to its toxicity characteristics. 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 overall risk screening score.
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