Guidance for Groundwater
The following guidance was developed by the Health Risk Assessment Unit (HRA) of the Minnesota Department of Health (MDH) following inquiries for guidance from the Minnesota Pollution Control Agency.
Boron: Update to the 2005 Health Based Guidance for Boron in Groundwater
June 18, 2008
Chemical: Boron (B)
CAS Number: 7440-42-8
Endpoint: Developmental effects
Chronic Value: 1000 µg/L
Source: U.S. EPA Drinking Water Standards and Health Advisories, 2006
The Minnesota Department of Health (MDH) has reviewed the 2005 health based guidance1 for boron (B) and continues to recommend a water concentration of 1000 ug/L. This MDH review takes into account the U.S. Environmental Protection Agency (EPA) 2006 Drinking Water Lifetime Health Advisory2. While the value remains the same as the 2005 MDH guidance, this update reflects the availability of additional supporting information from EPA for the rationale in recommending this advice3.
The current 1993/94 MDH Health Risk Limit (HRL) for boron of 600 μg/L was derived using the 1989 EPA reference dose (RfD) of 0.09 mg/kg-day and risk assessment methodology in practice at the time of promulgation. In 2005, MDH began recommending a value of 1000 ug/L instead of this HRL value.
In 2001 the National Academy of Science evaluated the essential nature and toxicity of boron and developed a Tolerable Upper Intake Level (UL). In 2004, EPA changed the boron RfD to 0.2 mg/kg-day to reflect new toxicity data4. Both the UL and the RfD represent a daily intake level that is likely to pose little or no risk of adverse health effects. For most people food and water are considered the only significant exposure pathways for boron. The portion of daily boron intake that can be allotted to drinking water will, in part, depend on the dietary intake of boron.
Infants are considered to be a population sensitive to the toxic effects of boron. MDH continues to recommend that, as a general rule, drinking water should not contain boron at concentrations greater than 1000 μg/L. This concentration is based on infants drinking reconstituted formula in which the water is the sole source of boron intake. If drinking water is not the sole source of boron, then the corresponding “safe” water level for infants would be lower.
MDH is currently in the process of revising the HRL rules. Trace elements, such as boron, will not be part of the rules revision. Low doses of boron may be beneficial, but questions about whether it is essential remain. Within an individual, the range between beneficial and toxic quantities may be very narrow. Between individuals, beneficial and toxic quantities may overlap. Because of the difficulty in establishing a concentration value that is low enough that it will not cause toxic effects in any individual, but not so low as to deprive others of the beneficial aspects, MDH does not plan to establish an HRL for boron or other trace beneficial elements in this or future rules revision. MDH plans to develop guidance regarding recommended and toxic levels of trace beneficial elements, including boron. It is likely that the guidance will consist of a recommended range of values rather than a discrete concentration.
1 Minnesota Department of Health’s Advice for Boron (to the Minnesota Pollution Control Agency); June 2, 2005
2 US EPA, Office of Water. (2006) 2006 Edition of the Drinking Water Standards and Health Advisories
3 US EPA, Office of Water. (2006) Health Effects Support Document for Boron
4 US EPA, IRIS. (2004) Toxicological Review of Boron and Compounds (CAS No. 7440-42-8) (PDF: 876KB/144 pages)