TECHNICAL DETAILS ON HOW SCORES ARE DERIVED
The UTN system assigns hazard scores between 0 and 200 based on the
Total Hazard Value = (Human Health Effects + Environmental Effects)
x Exposure Potential
Human Health Effects = HVoral LD50 + HVinhalationLC50 +
HVcarcinogenicity + HVother
Environmental Effects = HVoral LD50 + HVfishLC50 + HVfishNOEL
Exposure Factor = HVBOD + HVhydrolysis + HVBCF
HVx = Hazard Value for endpoint x
Four endpoints are used as indicators of human health effects: two measures of acute toxicity to mammals (LD50 is the dose that kills 50% of organisms via ingestion; LC50 is the concentration that kills 50% of organisms via inhalation) and two measures of chronic toxicity (a carcinogenicity score based on EPA/IARC weight of evidence schemes and a multiple endpoint score based on whether a chemical possesses evidence of mutagenicity, developmental effects, reproductive effects, neurotoxicity, and/or other chronic effects.)
Three endpoints are used as indicators of environmental effects: one measure of acute toxicity to mammals (LD50 is the dose that kills 50% of organisms in a test) and two measures of toxicity to aquatic organisms (LC50 is the concentration that kills 50% of organisms in an acute test; NOEL is the no observed effect level in a chronic test).
Exposure Factors in the UTN system are based on indicators of environmental persistence and bioaccumulation in an aquatic environment. There are two indicators of environmental persistence: BOD half-life is the number of days required to reduce the biological oxygen demand from a chemical in water by half due to biodegradation by microbes. Hydrolysis half-life is the time required to reduce the amount of a chemical in water by half through reaction with water. To characterize a chemical's propensity to bioaccumulate in the environment, the UTN system uses its bioconcentration factor. BCF is the ratio of the concentration of a chemical in an organism to its concentration in the test medium or environment, typically water.
Several policy choices influence the rankings that result from use of
this algorithm. First, it is possible to give equal or different weights
to hazard values for the various endpoints within an effect category
(e.g., to give double weight to compounds that exhibit carcinogenicity).
Second, equal or different weights can be assigned to the major effect
categories (e.g., to give more weight to human health impacts than
ecological impacts). Third, some method of assigning hazard values to
parameters that lack data is required (e.g., to treat the absence of
data as indicating the absence of hazard, or to penalize data gaps). UTN
has developed several alternative chemical rankings based on different
versions of these policy choices.
EDF has selected the simplest approach for incorporating UTN scores into
the Scorecard: equal weights are assigned to endpoints and to human and
ecological impacts, and chemicals are assigned a default hazard value of
zero when required data are missing. EDF was unable to extend the UTN
system to additional chemicals because the Scorecard lacks some of data
elements that are required by this system.
UTN: Davis, G. et al.Chemical Hazard Evaluation for Management Strategies: A Method for Ranking and Scoring Chemicals by Potential Human Health and Environmental Impacts. EPA/600/R-94/177, Office of Research and Development, Cincinnati, OH. 1994. Values received in Excel file, July, 1998.