What are USEPA’s New PCE Toxicity Values About?

It has been a year since the USEPA issued its new toxicological profile for tetrachloroethylene (PCE).  The new profile resulted in the revision of PCE’s toxicity values in EPA’s Integrated Risk Information System (IRIS).  Despite their obscurity, IRIS toxicity values carry great importance because they are at the heart of the risk assessment process and thus play a central role in determining the extent of waste site cleanups.

What was unusual about the PCE toxicity value change is that the new values indicate PCE is less toxic than previously thought; this is a rare occurrence because most IRIS values changes have gone the other way.  EPA did not come up with the idea of lowering its estimate of PCE toxicity by itself; it received “encouragement” from a National Research Council (NRC) expert advisory committee.  To EPA’s credit, they solicited the input from NRC, even if not all at the agency were happy with the recommendations they received.  It turned out that NRC placed greater emphasis on higher quality scientific studies (those with more controls and less ambiguous toxicity endpoints) and urged EPA to discount studies of lesser scientific quality.  The higher quality studies indicated that PCE was in fact less toxic than previously thought

Very Interesting, but why is this Important?

EPA’s old PCE toxicity values suggested that PCE was so toxic that even concentrations in air that were too low to measure could pose a serious health risk.  As a result, PCE became a significant driver of cleanup actions at many waste sites where vapor intrusion was a pathway of concern.

As you likely know, vapor intrusion is an exposure pathway whose significance many environmental scientists and regulators consider to have been underestimated in the past. Remedial actions to address vapor intrusion have thus become more common, even in situations previously thought to have been satisfactorily closed-out.  In many of these vapor intrusion situations it has been the presence of PCE in air that drives remedial actions.  With PCE now recognized as being less toxic, some of these remedial actions may not be necessary.

Have State Agencies Adopted the New PCE Toxicity Values?

Much of the waste site cleanup work in the US takes place at the direction of state governments.  Most states and political bodies with waste site cleanup laws specifically cite EPA’s IRIS database as the first choice for all risk assessment toxicity values.  However, some states take an à la carte approach with IRIS; reserving their right to use their own toxicity values when they see fit.  Massachusetts is just such a state and its PCE toxicity values date back to the early 1980s (and have evolved since then), a time when there were no federal standards for PCE in drinking water.  MassDEP (then DEQE for the nostalgic) was responding to a big PCE problem in drinking water pipes and in the absence of federal criteria, it took a commendable DIY approach.

What about New Jersey?

But, this post is not about Massachusetts, it’s about New Jersey and its January, 2013 adoption of EPA’s new toxicity values for PCE. Like Connecticut, New Jersey tried to adopt a semi-privatized waste site cleanup law (modeled on the Massachusetts Contingency Plan), but neither state had the much success with their program..  Some place the blame for this lack of success on the inflexibility of NJ DEP and CT DEEP; I am not quite close enough to either situation to comment.

Now the New Jersey DEP seems intent on getting its privatized waste site cleanup program back on track.  It is breathing new life into its LRSP program and in January of this year it issued final guidance to address vapor intrusion sites.   As part of its vapor intrusion guidance, NJDEP has adopted the new EPA IRIS toxicity values for PCE.  By adopting the EPA values, New Jersey raises the threshold at which remedial action is required at sites with PCE.

Among the states, New Jersey is generally perceived to err on the side of environmental cautiousness and its adoption of the new EPA PCE toxicity factors can only add to the momentum in favor of  nation-wide adoption.   New Jersey is off to a good fresh start with its privatized cleanup program.