EPA Draft Science Supplement Bolsters Case For Tougher PM Standards

Source: By Stuart Parker, InsideEPA • Posted: Sunday, October 3, 2021

EPA’s just-released draft supplemental science assessment of particulate matter (PM) health and visibility impacts reinforces earlier evidence supporting tougher federal air standards, bolstering agency efforts to tighten the limits in its ongoing reconsideration of a Trump-era decision that left them unchanged from 2012 levels.

In its supplement to the 2019 integrated science assessment (ISA) that served as the basis for the Trump EPA’s decision, EPA staff finds that new science gathered since the 2018 cutoff for studies included in the ISA supports and builds on the original conclusions, such as findings that there is no safe level of exposure to fine PM (PM2.5).

“Recent studies published in the U.S. and Canada provide additional support for the conclusions of the 2019 PM ISA,” staff says. The “recent studies support, and in some instances strengthen, the evidence presented in the 2019 PM ISA,” and “many of the recent epidemiologic studies evaluated report positive associations in areas with annual average or mean 24-hour avg PM2.5 concentrations similar to, or in many cases lower, than those studies evaluated in the 2019 PM ISA,” the draft concludes.

In the last review of PM national ambient air quality standards (NAAQS) concluded in December, staff recommended tightening a key annual health limit from 12 micrograms per cubic meter (ug/m3) down to a level between 8ug/m3 and 12 ug/m3. Trump EPA Administrator Andrew Wheeler, however, overrode that advice, with the majority backing of the agency’s Clean Air Scientific Advisory Committee (CASAC), retaining the full suite of PM standards dating from 2012.

The staff recommendation, made in a policy assessment (PA) document, relied in large part on positive associations found in epidemiological studies between exposure to PM2.5 and mortality at levels of exposure below the current NAAQS.

Now, staff says new science if anything boosts evidence of PM2.5 causing premature death, specifically from cardiovascular problems. Staff must submit their draft conclusions for review to a reconstituted CASAC, and a special PM expert panel, prior to finalizing the supplemental ISA and issuing another PA document that would then form the basis of proposed and final EPA rules.

EPA aims to complete reconsideration of the Trump NAAQS rule in 2023, and has lined up a series of meetings of the CASAC PM panel this fall to consider the supplemental science.

“Recent studies of cardiovascular mortality and morbidity also indicate that associations are relatively unchanged in copollutant models and that most assessments indicate a linear, no-threshold concentration-response (C-R) relationship with initial evidence of non-linearity at lower concentrations for some outcomes,” the supplement says.

This reinforces the earlier staff conclusion that there is no discernible safe threshold for PM2.5 exposure. However, confidence in the linear nature of the exposure-risk relationship is lower at very low levels of exposure, the document says.

For long-term PM2.5 exposure and mortality, “The assessment of the C-R relationship continues to generally support a linear, no-threshold relationship with certainty down to 4 μg/m3. However, some uncertainties remain about the shape of the C-R curve at relatively low PM2.5 concentrations (<8 μg/m3).”

Epidemiological Studies

In addition, new science aims to bolster epidemiological studies that some critics say are prone to bias and “confounding” by non-air pollution factors such as income, preexisting health conditions and climate.

The supplement says, “recent epidemiologic studies that conducted accountability analyses or employed causal modeling methods also report positive associations across a number of statistical approaches, which further supports a relationship between short-term PM2.5 exposure and cardiovascular effects.” Similarly, studies on long-term exposure and effects have sought to reduce such uncertainty.

Further, the supplement adds to the body of evidence of PM2.5’s disproportionate impact on minority and low-income communities. The supplement says, “recent studies support, and in some instances extend, the evidence base indicating that non-White populations, specifically Black individuals, and low [socio-economic status] individuals, experience disparities in both PM2.5-related health risks and exposures compared to non-Hispanic White populations.”

Although the ISA and supplement do not attempt a full assessment of all ecosystem impacts of PM, the supplement finds that recent studies support the earlier finding that PM causes visibility impairment.

John Bachmann, a former longtime EPA air office official and member of the Environmental Protection Network of EPA alumni, said, “We are pleased EPA has decided to conduct a supplemental review of the National Ambient Air Quality Standards (NAAQS) for particulate matter (PM). This will allow inclusion and reconsideration of a number of important new scientific studies that were ignored in the previous administration’s review. The inclusion of these studies will build an even stronger case for strengthening standards for harmful particulate pollution to be more protective of public health.”

In addition, “EPA’s reinstatement of the Clean Air Scientific Advisory Committee’s PM panel will ensure a far more balanced and informed review of available scientific information and policy options,” Bachmann said.

Narrow Scope

However, EPA staff says the supplement has “narrow scope,” and does not attempt the full weight-of-evidence review of a full ISA. “Therefore, this Supplement critically evaluates and provides key study specific information for those recent studies deemed to be of greatest significance for impending regulatory decisions regarding the PM NAAQS in the context of the body of evidence and scientific conclusions presented in the 2019 PM ISA.”

Critics of EPA’s NAAQS review process may question the study selection process for the supplement, which is one aspect of a broad review of the NAAQS process now being undertaken by a National Academy of Sciences (NAS) panel. The panel is examining the agency’s “causality framework” that ranks the likelihood of a pollutant “causing” various adverse health and environmental effects, but will not conclude its findings in time to influence the outcome of the PM reconsideration.

In an early working session, one member of the NAS panel described EPA’s study selection process as something of a “black box,” because it is unclear how EPA selects the “policy-relevant” studies it relies on to form regulatory conclusions. — Stuart Parker (sparker@iwpnews.com)

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