TRI toxicity changes Dear Editor: Your article "Power Plants' TRI Reports Spur Relative Risk Debate" {ES&T 1999, 33 (13), 268A) highlights the significance of reporting toxic emissions. We believe that extending the reporting requirements to more industries will be beneficial in the long run, despite the current concerns of electric utilities and methodological issues such as reporting thresholds. Your article speculated that industries have been substituting emissions of more toxic materials for less toxic materials as the overall mass of emissions has declined. As shown in the table, the overall Toxics Release Inventory air emissions (for substances reportable in both years) declined by approximately 39% from 1988 to 1997. The subset of TRI chemicals with occupational exposure standards (Threshold Limit Values) declined by 56% and represented 71% of the total emissions in 1997. If the TLV is used as an indicator of toxicity {ES&T 1995, 29 (3), 86A-90A), the toxicity-
weighted air releases normalized to sulfuric acid-equivalent emissions can be calculated. The toxicityweighted emissions declined by 36% over this period. However, the average toxicity of TRI chemicals released to air has increased by 46% from 1988 to 1997. Therefore, al-
Year
1988
Total TRI air emissions (million lbs) TRI air emissions with TLV Standards (million lbs) Toxicity-Weighted TRI air emissions— CMU-ET (million lbs of sulfuric acid equivalent) Ratio of CMU-ET to total TRI air emissions
2177
2119
though average toxicity of air emissions appears to have increased, the overall "environmental burden" expressed by TLV-weighted air emissions decreased from 1988 to 1997. CHRIS HENDRICKSON ARPAD HORVATH Department of Civil and Environmental Engineering Carnegie Mellon University Pittsburgh, PA 15213 Tel.: (412) 268-2941 Fax: (412) 268-7813 E-mail:
[email protected] [email protected] 1997 a
1332
940
Erratum 519
332
.24
0.35
In the figure "Megacity growth trends," which is part of the feature article "Megacities: Sweet Dreams or Environmental Nightmares?" (ES&T 1999, 33 (11), 228A-240A), the labels for London and Mexico City were inadvertendy transposed before printing the issue. The error is ours, not that of the author.
'Approximate number; some chemicals were reportable in 1997 but not in 1988.
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