OIG Reports EPA’s Perchlorate RfD Is Health Protective

Dec 30: The U.S. EPA Office of Inspector General (OIG) has release a major 213-page report entitled, Office of Inspector General Scientific Analysis of Perchlorate (Assignment No. 2008-0010, December 30, 2008). In a cover letter accompanying the report, OIG indicates it is providing an opportunity to the environmental risk assessor community to review and provide scientific comment on its analysis of perchlorate. OIG notes that on February 18, 2005, EPA established a perchlorate reference dose (RfD) that corresponds to a drinking water equivalent level of 24.5 parts per billion (ppb). A U.S. EPA regulatory determination is pending on whether to issue a National Primary Drinking Water Regulation for perchlorate.

OIG says that EPA’s potential regulation of perchlorate has garnered significant interest. Of concern, according to OIG, is whether EPA’s perchlorate RfD is protective of human health at all life stages. OIG says, "We analyzed the science supporting EPA’s perchlorate RfD. Congressional interest in this public health issue is reflected in bills H.R. 1747 and S.150, which would amend the Safe Drinking Water Act to require EPA to regulate perchlorate in drinking water. We found that EPA guidance supports the use of a cumulative risk assessment when multiple stressors act through the same mode of toxicity. However, both EPA’s 2002 proposed RfD and the National Academy of Sciences Committee to Assess the Health Implications of Perchlorate Ingestion used single chemical risk assessment to derive the perchlorate RfD. By contrast, we used a cumulative risk assessment to analyze the risk from the multiple sodium iodide symporter (NIS) stressors.

"Based on our scientific analysis documented in our report, perchlorate is only one of many chemicals that stress the thyroid’s ability to uptake iodide. The other NIS stressors include thiocyanate, nitrate, and the lack of iodide. All four of these NIS stressors meet EPA’s risk assessment guidance for conducting a cumulative risk assessment using the dose addition method. Our analysis includes a cumulative risk assessment of this public health issue using all four NIS stressors. A cumulative risk assessment approach is required to better characterize the risk to the public from a low total iodide uptake (TIU) during pregnancy and lactation. Further, a cumulative risk assessment approach is required to identify potential actions that will effectively lower the risk to public health.

"For our review of the perchlorate science, we are seeking scientific comments on the use and application of a cumulative risk assessment approach to characterizing the public health risk from a low TIU during pregnancy and lactation. We are seeking scientific comments from scientists, environmental risk assessors, and related organizations. Because we are only seeking scientific comments for consideration, we are requiring responders to provide the following information: name of individual and/or organization; contact information, and scientific background or credentials. We are seeking specific, scientifically supported comments on the OIG’s use and application of a cumulative risk assessment approach to characterizing the public health risk from a low TIU during pregnancy and lactation. We are requiring any discussion or comments on scientific studies or observations to be appropriately cited and available in the public literature." Scientific comments are being requested by no later than March 10, 2009.

In summary, OIG indicates, "The OIG Analysis indicates that although EPA used a single chemical risk assessment for perchlorate, a cumulative risk assessment that assesses and characterizes the combined human health risk from all NIS stressors would better describe the nature and sources of risk affecting this public health issue. The major findings, which directly address each of seven scientific issues identified in the 'Purpose' section of this report, are as follows:

"1) NAS [National Academy of Sciences] Unconventional RfD Approach Is Conservative and Protective; 2) Increasing Uncertainty Factors Not Effective for Protecting Public Health; 3) Hypothyroxinemia Occurs Before Hypothyroidism; 4) Low Fetal TIU First Adverse Effect; 5) Perchlorate RfD Alone Does Not Protect Most Sensitive Populations; 6) Thiocyanate and Nitrate Need to be Included in Risk Assessment; and, 7) Lack of Iodide Is Dominant NIS Stressor Impacting this Public Health Issue."

OIG concludes, "The OIG Analysis of the scientific literature identified that the risk from perchlorate exposure is only part of a larger public health issue that is defined by the subtle mental deficits occurring in children born to mothers with low maternal TIU during pregnancy and nursing. The TIU results from the combined biological effect of four NIS stressors acting on the thyroid: thiocyanate, nitrate, perchlorate, and lack of iodide. The diet constantly exposes everyone to each of the four NIS stressors, and an individual’s TIU level is the result of the combined effect of all four NIS stressors, not just perchlorate exposure. The OIG Analysis concludes that a single chemical risk assessment of perchlorate is not sufficient to assess and characterize the combined human health risk from all four NIS stressors. However, both EPA’s draft perchlorate RfD from the Argus rat study and the NAS Committee’s recommended perchlorate RfD from the Greer human exposure study used a single chemical risk assessment approach. Only a cumulative risk assessment can fully characterize the nature and sources of risk affecting this public health issue. Furthermore, a cumulative risk assessment allows an informed environmental decision to be made on how to mitigate the risk effectively.

"All four NIS stressors meet EPA’s risk assessment guidance requirements for conducting a cumulative risk assessment using the dose addition method. In the OIG Analysis, we conducted a cumulative risk assessment and determined that the risk from each of the four NIS stressors is not equal. The OIG Analysis also confirmed that EPA’s perchlorate RfD is conservative and protective of human health, but limiting perchlorate exposure does not effectively address this public health issue. Potentially lowering the perchlorate drinking water limit from 24.5 ppb to 6 ppb does not provide a meaningful opportunity to lower the public’s risk. By contrast, addressing moderate and mild iodide deficiency occurring in about 29% of the U.S. pregnant and nursing population appears to be the most effective approach of increasing TIU to healthy levels during pregnancy and nursing, thereby reducing the frequency and severity of permanent mental deficits in children."

On October 3, 2008, immediately after U.S. EPA announced that it had made a preliminary determination that there is not a "meaningful opportunity for health risk reduction" through a national drinking water regulation for exposure to perchlorate [See WIMS 10/3/08], environmental advocates [Earthjustice, representing the Environmental Working Group (EWG)] announced they plan to sue the Agency. EPA said it had conducted an extensive review of scientific data related to the health effects of exposure to perchlorate from drinking water and other sources and found that in more than 99 percent of public drinking water systems, perchlorate was not at levels of public health concern [See WIMS 10/6/08].

Access the complete OIG report including the cover letter and commenting instructions (click here). Access a release from EPA (click here). Access EPA's draft regulatory determination and extensive background information (click here). Access multiple WIMS-eNewsUSA blog posts on the perchlorate issue (click here). [*Drink, *Toxics]