Anonymous public comment

Subject: Safe Drinking Water Act regulatory determination for boron The following comments have been prepared on the Proposed Rule on May 1, 2007 (FR Vol 72 No 83, pages 24017-45058) with a determination on a set of unregulated contaminants as to whether they should be regulated with a national primary drinking water regulation. Specifically, these comments address the regulation of boron. National Primary Drinking Water Regulation Status of Boron USEPA?s determination that it was not appropriate for boron to be considered for national primary drinking water regulation, based on criteria as listed in the FR, is appropriate. Health Reference Level for Boron As noted in the FR, boron is categorized as a possible trace mineral for humans and is essential for plant growth. There is some evidence that boron deficiency in animals and humans affects cellular function and the activity of other nutrients. The primary adverse effects noted in two-year animal studies after chronic exposure to low doses of boron general involve the testes and developing fetus. The reference dose (RfD) for chronic exposure to boron is 0.2 milligrams boron per kilogram of body weight per day (mg/kg-day) and is based on developmental studies in rats. Boron is not mutagenic and USEPA determined that there is inadequate data to assess human carcinogenic potential. Therefore, no cancer slope factor has been derived. In order to evaluate the potential health effects of boron in public water systems, USEPA calculated a benchmark called a Health Reference Limit (HRL) against which to compare data from water systems. The calculated HRL is 1,400 ug/L. Although USEPA determined that an MCL for boron would not be developed, the FR notice indicates that the HRL for boron has been updated; the proposed value is 1,400 ug/L. The HRL was calculated in order to evaluate the potential health effects of boron in public water systems. For boron, the HRL was calculated as follows: HRL = [(RfD x BW)/DWI] x RSC Where: ? RfD = Reference Dose = 0.2 mg/kg-day ? BW = Body Weight = 70 kg ? DWI = Drinking Water Intake = 2 L/day ? RSC = Relative Source Contribution = 20% (this is the level of exposure assumed to be from drinking water as compared to all other sources). The resulting HRL is 1.4 mg/L (1,400 ug/L). Concentrations below the HRL would not be expected to pose significant health risk. The main comment on the HRL is that it does not incorporate the results of a preliminary chemical-specific Health Advisory Level (HAL) derived recently by USEPA?s Office of Water and presented as a poster at the March 2007 Society of Toxicology meeting (Ramasamy, et al., 2007). USEPA is in the process of developing an updated Health Advisory document to replace the previous Office of Water draft Health Advisory for boron published in 1992 to reflect more recent health and environmental effects information for boron. This document is currently being prepared for peer review. HALs establish nonregulatory concentrations of drinking water contaminants at which adverse health effects are not anticipated to occur over specific exposure durations (1-day, 10-days, several years, and a lifetime). The Office of Water developed a Life Time HAL, which is similar to the proposed Rule?s HRL, of 5,000 ug/L. The Life Time HAL is calculated using a No Observed Adverse Effects Level (NOAEL) and uncertainty factors (UF), rather than the USEPA Reference Dose on IRIS of 0.2 mg/kg-day, but the end result is essentially the same (NOAEL of 10.3 mg/kg-day divided by a UF of 66 equals 0.16 mg/kg-day). The Life Time HAL is calculated as follows: Life Time HAL = [NOAEL x BW x RSC] / [UF x DWI] Where: ? NOAEL = No Observed Adverse Effect Level = 10.3 mg/kg-day ? BW = Body Weight = 67 kg ? DWI = Drinking Water Intake = 2 L/day ? UF = Uncertainty Factor = 66 ? RSC = Relative Source Contribution = 80% (this is the level of exposure assumed to be from drinking water as compared to all other sources) Differences to note between the HRL and HAL: ? The body weight is for an adult female, as the critical effect is decreased fetal body weight, versus the 70 kg default adult body weight used in the HRL calculation. ? The RSC of 80% is based on the calculation method in the USEPA (2000) Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health. Ramasamy et al. (2007) have estimated that dietary sources correspond to 1 mg/day, which is equivalent to 0.015 mg/kg-day. When that amount is subtracted from the RfD of 0.2 mg/kg-day, 0.185 mg/kg-day is left. This represents approximately 93% of the RfD, therefore it is appropriate to default to the ?ceiling? RSC of 80%. Therefore, the use of this RSC is conservative. Based on this study by the Office of Water, the HRL should be derived in the same way as the HAL, which is 5,000 ug/L. Note that an RSC of 93% would result in an HRL of 5,800 ug/L. The HAL accounts for the mean dietary intake of boron from various food sources. For various inorganics which are commonly found from dietary sources, USEPA often attempts to account for background dietary levels when developing regulations. The RSC of 80% used in the HAL is a chemical-specific value that accounts for dietary levels of boron. References Ramasamy, S., K. Davidson and S. Kueberuwa. Development of Drinking Water Health Advisory for Boron. The Toxicologist. Abstract # 1641. 2007. USEPA. 2000. Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health. Office of Water. EPA-822-B-00-004. USEPA. 2006. Regulatory Determinations Support Document for Selected Contaminants from the Second Drinking Water Contaminant Candidate List (CCL 2). EPA Report 815-D-06-007. Draft. December 2006.