10
Developing Effective
Toxicity Factors

INTRODUCTION
In the previous chapters, we derived factors for toxicity (Chapter 6), mobility
(Chapter 7), persistence (Chapter 8), and bioconcentration (Chapter 9) for the chemicals reported in the Toxics Release Inventory (TRI). This chapter develops an effective toxicity factor (ETF) in units of doses/capita-pound that can then be used to
evaluate the relative overall toxic impacts of the various TRI chemical releases.
This is an initial proposed approach; we welcome suggestions on how to
improve our analysis or use the same or additional toxicity data to relatively rank
chemicals differently. The important point to keep in mind is that the objective
of this approach was not to come up with an absolute number that we claim to
represent the actual and fixed toxic impact of a chemical. Rather, the proposed
methodology was developed solely for the purposes of coming up with a logical
means of applying published and routinely used toxicological data to then develop
chemical-specific “toxicity” factors to conduct an apples-to-apples comparison
across chemicals. This would relatively rank the potential effect among various
toxic chemicals such that reduction in the use of toxic chemicals can be targeted
and managed accordingly.
The purpose of this is to build on the emphasis of the U.S. Environmental
Protection Agency (USEPA) on persistent, bioaccumulative, and toxic (PBT) chemicals and develop an overall relative toxicity index to guide policy in reducing these
releases. In this chapter, the quantified ETF (doses/capita-pound) is then multiplied
by the 2007 TRI releases (pounds), resulting in a chemical-specific toxicity unit
(TU) in doses per capita, or a measure of the toxic impact of the release of each
chemical. Ranking the list of 2007 TRI releases by the respective TUs, in other
words, by highest overall relative toxicity, shows the trend of the top 10 chemicals on
the TRI list representing 99.98 percent of the toxic impact of the releases; yet, these
same 10 chemicals represent only 17 percent of the volume of releases reported. This
drives home the point that volume alone cannot be used to guide policy in reducing
toxic chemical use.
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