Environ. Sci. Technol. 2011, 45, 836
Response to Comment on “Role of Detection Limits in Drinking Water Regulations” We appreciate Alan Roberson’s letter to the editor regarding our recent paper “Role of Detection Limits in Drinking Water Regulations”. We agree that this is an important issue and appreciate his interest. Mr. Roberson asserts that USEPA has decided to strengthen the regulations for acrylamide, epichlorohydrin, tricholorethylene (TCE), and tetrachloroethylene (PCE), and that USEPA’s recent actions indicate a relationship between detection ability and regulatory limits. We note first that acrylamide and epichlorydrin, drinking water treatment residuals, do not have published maximum contaminant levels (MCL) or practical quantitation limits (PQL) but rather prescribed treatment technology. We find on pages 15520 (acrylamide) and 15543 (epichlorydrin) of the Federal Register that a decision to strengthen the standard is in effect a decision to mandate usage of widely available treatment chemicals with lower residual monomer levels. Detection ability does not appear to have been a consideration in this decision. Turning our attention to the pages of the Federal Register cited by Mr. Roberson for TCE (pp 15557-15558) and PCE (pp 15564-15565), we find that “EPA is not currently able to assess the potential health benefits of a revised MCL for trichloroethylene, because the revised health effects assessment is not yet available” and “EPA is not currently able to assess the potential health benefits of a revised MCL for tetrachloroethylene, because the revised health effects assessment is not yet available.” Therefore, there has been no decision to revise the MCL of either TCE or PCE. We understand that Mr. Roberson has interpreted USEPA’s conclusion to lower the PQL of TCE and PCE as naturally implying a reduction in MCL as well, because detection ability currently controls the regulation of these two contaminants. In effect, this is exactly the logic our paper investigated: whether an improvement in detection ability automatically implies a strengthening of drinking water regulations. In our paper, we assess the relationship between real improved detection ability and EPA’s decision to lower the PQL (EPA concluded it could lower the PQL for contaminants even where there was no significant improvement in detection ability since promulgation of the regulation) among contaminants controlled by detection ability (MCL ) PQL) and contaminants controlled by other factors (MCL > PQL). TCE and PCE are two out of a total of 38 contaminants that EPA decided in its 2003 and/or 2009 reviews could undergo a PQL revision. The MCLs of 18 of these contaminants are, like the MCLs of PCE and TCE, currently controlled by detection
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ability. However, we do not automatically conclude that an MCL revision is implied, although we recognize that this is possible within the current framework. Our paper explored the critical roles of cost-benefit analysis and evolving toxicological models in USEPA’s decision making process. Most importantly, we pointed out that the state of knowledge regarding health toxicology or overall cost-benefit considerations consistently overrides the tendency to lower MCLs to match detection abilities. Good examples of this process are arsenic (MCLG ) 0, but MCL > PQL, stopped by cost-benefit analysis) and chloroform (improved understanding of toxicological model reversed decision to set MCLG ) 0). Furthermore, our research indicates that detection ability has not played a significant role in actual, historical MCL revisions, and that it is not likely to dominate the regulation setting process for emerging contaminants. We recognize the potential for the MCL of PCE and TCE to be lowered to match the PQL, as for the 16 other contaminants whose MCLs are currently tied to their PQLs. If this comes to pass, it will have been because USEPA demonstrates that the potential to protect public health justifies the associated costs. However, we have not seen any additional evidence that this is likely to be the case, and we are persuaded to believe that detection abilities will continue to play a relatively minor role in determining regulatory priorities. We feel that our paper accurately represents the current state of USEPA’s decision-making apparatus and provides an informed prediction of the role of detection limits in drinking water regulation. We encourage stakeholders to remain aware of developments as they occur, perhaps most especially for decisions that imply a tighter correlation between advances in detection abilities and the strengthening of regulations. We appreciate Mr. Roberson’s interest in our paper and in ensuring a responsible and efficient regulatory apparatus and encourage stakeholders to share information that might enrich our understanding of these issues.
Ketra A. Schmitt* General Studies Unit (Centre for Technology, Innovation and Society), Faculty of Engineering and Computer Science, Concordia University
Ryan S. D. Calder Building, Civil and Environmental Engineering, Faculty of Engineering and Computer Science, Concordia University, and Conestoga-Rovers & Associates ES103766A
10.1021/es103766a
2011 American Chemical Society
Published on Web 12/15/2010
