EPA recently released the second draft of an Integrated Science Assessment (ISA) for “ecological effects” from NOx, SOx and PM, which include effects on flora, fauna and water resources. The ISA will be used to determine the need for revising the current secondary national ambient air quality standards (NAAQS) for these pollutants. Other welfare effects that could be caused by these substances, such as effects on visibility, climate or building materials, will be addressed in the ISAs for the primary (health-based) standards for the substances.
The NOx and SOx ecological effects previously were addressed in a 2008 ISA. The specific effects considered are too numerous to discuss here, but they are listed in a table in the new draft ISA that compares the 2008 conclusions with those presented in the new draft. All of the effects analyzed in the 2008 ISA were determined to be “causal” pursuant to EPA’s classification scheme (meaning that they are caused by the pollutants at issue). However, those determinations did not result in a change in the secondary standards, owing to the uncertainties involved in identifying ambient concentrations necessary to alleviate the effects. EPA took the position that the existing suite of primary and secondary standards also would provide adequate protection against these ecological effects.
In the new draft, all the effects determined to be causal in 2008 retain that classification. However, the new draft addresses the following five effects not classified in 2008:
- N deposition and the alteration of the physiology and growth of terrestrial organisms and the productivity of terrestrial ecosystems;
- Acidifying N and S deposition and the alteration of the physiology and growth of terrestrial organisms and the productivity of terrestrial ecosystems;
- N deposition and increased nutrient-enhanced coastal acidification;
- N deposition and changes in biota, including altered physiology, species richness, community composition, and biodiversity due to nutrient-enhanced coastal acidification;
- S deposition and changes in biota due to sulfide phytotoxicity, including alteration of growth and productivity, species physiology, species richness, community composition, and biodiversity in wetland and freshwater ecosystems.
All these effects, most of which were discussed in the 2008 ISA but not classified, would now be classified in the new ISA as causal on the basis of more recent information. The general conclusion is that new evidence supports the prior classifications and improves quantification of dose-response relationships. However, there is no clear statement that quantification has improved sufficiently to allow use of ecological effects as a basis for revising the standards, and in many cases the draft ISA finds that quantification remains subject to significant uncertainty.
Unlike the 2008 ISA, the new draft includes ecological effects from ambient PM. EPA’s last discussion of this issue, in the 2009 PM ISA, concluded that there is likely a causal relationship between PM deposition and various ecological effects, but that the specific relationships cannot be quantified as a result of a number of uncertainties. As a result, the PM secondary standards were not revised at the conclusion of the last review. The new draft ISA draws the same conclusions on the basis of the more recent studies.
The Clean Air Scientific Advisory Committee (CASAC) will review this new draft of the Eco ISA, after which EPA is likely to finalize the ISA and prepare a draft Policy Assessment (PA) that makes recommendations for retaining or revising the current secondary standards based on the science presented in the ISA.