The relative risk posed by certain toxic chemical releases from industrial facilities in the United States fell at about the same rate as the quantity of releases from 2001 to 2010, according to Environmental Protection Agency data.
The downward trend in both releases and risk could mean facilities that report to EPA's Toxics Release Inventory are controlling their use of higher-toxicity chemicals or curbing releases in areas that would result in higher human exposure, EPA said.
The relative risk of chemical releases scored through EPA's Risk-Screening Environmental Indicators (RSEI) model declined about 37.9 percent from 2001 to 2010, according to EPA data. During the same time period, the quantity of corresponding releases or disposal of toxic chemicals decreased 38.5 percent.
The model measures relative chronic human health risk based on the amount of chemical released, the location of the release, the chemical's toxicity, its fate and transport through the environment, the route and extent of human exposure, and other factors. The resulting scores are intended for use in screening-level activities.
Scores are calculated using data reported annually to the Toxics Release Inventory for on-site releases to air and water, transfers to publicly owned treatment works, and transfers for off-site incineration. Total releases for those pathways declined from about 2.4 billion pounds in 2001 to about 1.5 billion pounds in 2010.
The RSEI score for 2001 was 740 million, compared with about 460 million for 2010.
RSEI does not account for other release pathways, including land disposal, which typically represents the largest percentage of total releases to the environment each year.
Data also show that toxicity levels over time tend to fluctuate more than total releases. Large spikes or dips in RSEI scores can be driven by individual releases of very toxic chemicals, Lynne Blake-Hedges, who works on EPA's RSEI team, told BNA.
“Typically when you see a very large drop, it's because there was something going on in a previous year that made the score higher,” she said.
From 2003 to 2004, for example, the national RSEI score decreased by more than 200 million, largely due to a reduction in the amount of chromium and chromium compounds released.
Of the 430 chemicals included in the model, chromium and chromium compounds have consistently topped the list of chemicals with the highest RSEI scores since 2001. Chromium releases are especially common in ferrochrome production for steelmaking, as well as ore refining, chemical and refractory processing, cement production, and in other industries, EPA said on its website.
It is important to look beyond total pounds of toxic releases because chemicals in TRI vary by nine orders of magnitude in how toxic they are, Michael Ash, who is chair of the economics department at the University of Massachusetts at Amherst and has studied RSEI for about a decade, told BNA.
“If you're holding a pound [of toxic chemicals] in your hand, they're all toxic, but some are a billion times more toxic than others,” Ash said.
Risk scores for toxic releases in the United States were included in EPA's National Analysis of TRI data for the first time in 2010.
When asked why RSEI was added to the overview report, EPA told BNA in an email Jan. 28 that the agency “frequently adds new features to the TRI National Analysis to make the analysis more meaningful and interesting.”
However, to help the public interpret TRI data, EPA should feature toxicity risk scores more prominently in its National Analysis, Sean Moulton, director of federal information policy at the Center for Effective Government, told BNA.
“[RSEI] puts in place a critical component of what you need to understand toxic releases,” he said.
The report should separate risk data by industry sector as a way to “indicate which industries we want to focus on first and foremost” for reducing total pounds of toxics released, Moulton said.
“It's not always about highest quantity,” he said. “There are other industries where their toxicity is so much higher.”
EPA's methodology for RSEI has evolved since the database's public release in 1999 (23 CRR 620, 7/16/99).
The agency said RSEI data in the 2011 National Analysis included updates such as the addition of 2010 Census data and updated toxicity information for certain chemicals. EPA also recently revised the way the model took carcinogens into account, giving them greater weight than before.
Ash said there's still room for improvement in RSEI. As part of their research for the Political Economy Research Institute, Ash and fellow professor James Boyce outlined 12 potential sources of error in RSEI, ranging from incorrect or imprecise data submitted by facilities to gaps in the chemical information included in the model. Their research also suggested adding new measures, such as short-term health effects.
“Every time we update the model with new TRI data, we're always looking for ways to improve it with new data sources,” Blake-Hedges said, referring to sources like the 2010 Census.
Toxicity data are updated regularly, but RSEI researchers do not plan on broadening the model's scope in the near future, she said.
EPA's 2011 Toxics Release Inventory National Analysis is available at http://www.epa.gov/tri/tridata/tri11/nationalanalysis/overview/2011_TRI_NA_Overview.pdf.
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