The Uncertainty of EPA’s Human Health Risk Assessment

In the 176 pages of the EPA’s Final Site-Wide Human Health Risk Assessment, published on February 10, 2021, the EPA found that the risk we are in is, basically, uncertain.

Under section 6.3.4 Uncertainty Associated with Toxicity Values, the EPA admits it does not have a chronic inhalation reference concentration (safety level) for arsenic. The Agency for Toxic Substances and Disease Registry (ATSDR) refused to derive an inhalation minimal risk level (MRL) for arsenic, finding inhalation studies done to-date were inadequate. Therefore, due to the lack of a safety level, or toxicity value of arsenic, the analysis of arsenic levels in the HHRA studies falls under the category of Uncertainties that cannot be quantified and the direction of the effect of the uncertainty is also unknown.

Wait, WHAT???

What they don’t mention is the EPA often uses a Risk Based Specific Concentration (RSC) level to interpret chronic inhalation arsenic toxicity levels. The RSC for arsenic is 0.0023 ug/m3. Interestingly, the air monitoring data collected from the monitoring done in our area in the past (Ecology’s 1992 – 1996 air monitoring studies and Teck’s 1992-2009 air monitoring) all showed that the levels of arsenic recorded were well above the EPA’s RSC.

Under Section 6.3 Uncertainty in Risks from exposure to Non lead COPCs It is noted that the last air data collected was in 2009, at the Sheep Creek air monitoring station. Therefore, this creates a temporal uncertainty associated with the exposure to arsenic and other heavy metals of concern (lead, cadmium, mercury) because of the lack of current site-specific data. 

My biggest issue with this “uncertainty” is there should not have been a lack of data.

After concerned residents of the Northport community requested current air quality data, and the EPA announced it would not be conducting current air monitoring as part of their HHRA, in 2017 The Department of Ecology’s Air Quality Program specialists used existing air monitoring data to evaluate conditions and assess whether more air monitoring was needed.

What was the outcome of Ecology’s air quality assessment?

Previously interpreted air monitoring data suggest that current emissions from the Trail smelter continue to influence upper Columbia River valley air quality. These findings reinforce the need for current PM10 speciation monitoring in the upper Columbia River Valley near the international border and Northport area.”

– Matt Kadlec, Ecology’s Senior Toxicologist

EPA disregarding Ecology’s recommendation resulted in a lack of crucial data, creating a GREAT uncertainty. The recommendations in the HHRA could likely pose a health risk to the community, because of all the inaccurate, and uncertain findings throughout the assessment.

So I guess their statement I mentioned above sums up the findings of the HHRA perfectly:

Uncertainties that cannot be quantified and the direction of the effect of the uncertainty is also unknown.

– U.S. Environmental Agency, Region 10

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