138
Toxic Chemicals
EFFECTIVE TOXICITY FACTOR
Table 10.1 presents the proposed ETFs for TRI chemicals. The ETFs were derived
by multiplying together each of the following factors developed in previous chapters:
• TF, toxicity factor (doses/capita-pound) (Chapter 6)
• MF, mobility factor (Chapter 7)
• PF, persistence factor (Chapter 8)
• BAF, bioconcentration adjustment factor (Chapter 9)
For those chemicals that did not have the data needed for quantifying the MF,
PF, and BAF factors, the TF was multiplied by the median value for the MF, PF, and
BAF across all the TRI chemicals, or 0.002.
TOXICITY IMPACT
Table 10.2 shows the 2007 TRI release data ranked by pounds released and includes
the calculated TUs. TU was calculated by multiplying the ETF by the amount
released in pounds and represents the estimated toxicity impact per capita of the
release of that chemical. A TU of 1 means that the pounds of a chemical released
in a given year coupled with the quantified ETF of the chemical has reached the
toxicity threshold if distributed evenly over the population of the United States. As
an example, chromium was estimated to have a TU of 70 million doses/capita based
on the quantified ETF for chromium coupled with the 2007 TRI chromium release
data. If the U.S. population were equally exposed to this amount, each person would
receive 70 million times the acceptable dose of this compound.
Table 10.3 rearranges the release data and ranks them by TU. One can see that the
top 10 chemicals on this list represent 99.98 percent of the TUs released; yet, they
represent only 17 percent of the volume of releases reported.
One distortion in this analysis is the apparent relative impact of chromium.
Undoubtedly, chromium releases are important, but the toxicity is based on a
USEPA assumption that, in general, a sixth of the chromium releases are hexavalent
chromium. All types of chromium releases are reported in the TRI together, yet
hexavalent chromium is highly toxic, trivalent chromium is only moderately toxic,
and metallic chromium is benign. As an example of a beneficial TRI modification,
it would be useful to revise the TRI such that hexavalent and trivalent chromium
were reported separately and metallic chromium eliminated from reporting. The
same logic applies for cobalt and cobalt compounds. In addition, the commercial
production of polychlorinated biphenyls (PCBs) has been banned in the United
States since 1976; the only PCB releases are due to the presence of PCBs in products
and materials produced before the ban took place and due to taking PCB-containing
equipment out of service/remediation waste.
Figures 10.1 and 10.2 present the top 2007 TRI release data ranked by releases
in pounds as compared to the top 2007 TRI chemicals ranked by TU, respectively.
The toxicity data in Figure 10.2 are shown on a logarithmic scale as the variation in
toxicity ranges widely.
Toxic Chemicals
EFFECTIVE TOXICITY FACTOR
Table 10.1 presents the proposed ETFs for TRI chemicals. The ETFs were derived
by multiplying together each of the following factors developed in previous chapters:
• TF, toxicity factor (doses/capita-pound) (Chapter 6)
• MF, mobility factor (Chapter 7)
• PF, persistence factor (Chapter 8)
• BAF, bioconcentration adjustment factor (Chapter 9)
For those chemicals that did not have the data needed for quantifying the MF,
PF, and BAF factors, the TF was multiplied by the median value for the MF, PF, and
BAF across all the TRI chemicals, or 0.002.
TOXICITY IMPACT
Table 10.2 shows the 2007 TRI release data ranked by pounds released and includes
the calculated TUs. TU was calculated by multiplying the ETF by the amount
released in pounds and represents the estimated toxicity impact per capita of the
release of that chemical. A TU of 1 means that the pounds of a chemical released
in a given year coupled with the quantified ETF of the chemical has reached the
toxicity threshold if distributed evenly over the population of the United States. As
an example, chromium was estimated to have a TU of 70 million doses/capita based
on the quantified ETF for chromium coupled with the 2007 TRI chromium release
data. If the U.S. population were equally exposed to this amount, each person would
receive 70 million times the acceptable dose of this compound.
Table 10.3 rearranges the release data and ranks them by TU. One can see that the
top 10 chemicals on this list represent 99.98 percent of the TUs released; yet, they
represent only 17 percent of the volume of releases reported.
One distortion in this analysis is the apparent relative impact of chromium.
Undoubtedly, chromium releases are important, but the toxicity is based on a
USEPA assumption that, in general, a sixth of the chromium releases are hexavalent
chromium. All types of chromium releases are reported in the TRI together, yet
hexavalent chromium is highly toxic, trivalent chromium is only moderately toxic,
and metallic chromium is benign. As an example of a beneficial TRI modification,
it would be useful to revise the TRI such that hexavalent and trivalent chromium
were reported separately and metallic chromium eliminated from reporting. The
same logic applies for cobalt and cobalt compounds. In addition, the commercial
production of polychlorinated biphenyls (PCBs) has been banned in the United
States since 1976; the only PCB releases are due to the presence of PCBs in products
and materials produced before the ban took place and due to taking PCB-containing
equipment out of service/remediation waste.
Figures 10.1 and 10.2 present the top 2007 TRI release data ranked by releases
in pounds as compared to the top 2007 TRI chemicals ranked by TU, respectively.
The toxicity data in Figure 10.2 are shown on a logarithmic scale as the variation in
toxicity ranges widely.