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OAR Box 1111 

Prepped by Ryan Dugan 

Document Number: 

4£$)ll-A-1c 

Docket Number: 

A-83-22 

Printed 4/15/2008 1:25:18 PM Sheet 108 of 118 
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Preliminary Staff Conclusions and Recommendations on the 

Secondary Standard 

The available laboratory and field data indicate that at concentrations at or below those found in certain high lead environments, lead 

can: 1) affect certain plants (e.g., inhibition of photosynthesis, reduced 

growth, changes in composition), microbes (e.g., reduced abundance), and 

fish (e.g., neurological changes); and 2) alter the composition of 

microbial communities and inhibit invertebrate activity resulting in 

delayed decomposition, reduced nutrient supply, and altered soil properties 

(e.g., lower organic content). With respect to domestic animals and 

wildlife, a qualitative assessment of the available field studies and 

animal toxicological data suggests that animals may be as susceptible 

to the effects of lead as humans. 

The available data also raise concern about the continuing accumulation 

of lead in the soil reservoir that functions as a finite sink of undefined 

capacity. Due to the persistence of lead in the environment, such accumulations are expected to continue as long as inputs exceed outputs. Thus, 

even at relatively low deposition rates lead could affect the ecosystem 

over the long-term. 

The available data are limited, however, and do not permit any 

definitive findings with respect to concentration-response functions 

associated with the observed effects or provide clear quantitative relationships 

between concentrations of lead in the natural habitat and biologically 

available lead. Data are not available to determine quantitative relationships 

between ambient concentrations of lead and effects in the biota of terrestrial 

and aquatic ecosystems. These limited data do suggest, however, that 
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effects of lead on these ecosystems can be significant, although poorly 

defined, particularly with respect to their long-term implications. 

The effects of lead on ecosystems are probably more closely related 

to the deposition and long-term accumulation of lead than to current 

ambient air quality levels. This suggests that a secondary standard for 

lead in the form of a deposition rate may be more appropriate than one 

expressed as an airborne concentration level. Such a deposition standard 

is conceptually appealing because it could be a more effective method to 

provide protection against the welfare impacts of lead. Its application 

at this time is constrained, however, by practical considerations such as 

the absence of sufficient data to develop appropriate deposition targets 

and the lack of reliable methods for measuring both wet and dry deposition. 

Although quantitative relationships are not well enough developed to 

specify the most appropriate secondary standard, the key question is whether 

the range of alternative air quality levels discussed in Section VII would 

provide adequate welfare protection. While this question cannot be answered 

definitively, all but one of the air quality levels discussed in Section 

VII would likely reduce current ambient lead loading. These reductions, 

coupled with reductions achieved by the continued phase-down of lead in 

gasoline (gasoline consumption accounts for 85-90% of total airborne lead 

emissions), would likely mitigate the potential risks of lead-induced 

ecosystem effects occurring in most areas of the country. In urban centers, 

along roadsides, and in the immediate vicinity of major point sources that 

have experienced a long-term, historical accumulation of lead, and where 

the natural soil sinks for lead may be approaching or have exceeded their 

capacity to bind lead, the more sensitive components of the ecosystem 

(e.g., soil microbes) may remain at some risk that is difficult to quantify 
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at present. The level of the primary standard chosen from air quality 

ranges discussed in Section VII could, however, provide adequate protection 

from ambient-related exposures for most, if not all mammals both domestic 

and wild. Therefore, given the available data along with their major 

uncertainties, the staff recommends that consideration be given to making 

the secondary standard equivalent to the primary standard in all respects.