Guidelines for Canadian drinking water quality boron: Overview

The main source for Canadians' exposure to boron is through food, although consumer products can also contribute significantly to exposure. Exposure through drinking water can contribute up to 16% of total dietary boron exposure. In most Canadian drinking water supplies, boron is below 0.1 mg/L. Higher concentrations of boron (1 to 8 mg/L) can be found in certain areas of Canada, particularly in groundwater supplies in areas with naturally occurring boron. However, elevated concentrations of boron are likely to occur only in a limited number of drinking water systems in Canada. Intake of boron from drinking water through skin contact or inhalation during showering or bathing is expected to be negligible.

Health effects

Boron is not an essential element, but some studies indicate it may be beneficial to human health. Studies in humans have found possible associations between boron and effects on reproduction and development. However, these studies have a number of design limitations and cannot be used for risk assessment. Studies in animals have consistently observed adverse effects to the male reproductive system following ingestion of high levels of boron, which supports effects seen in human studies. Testicular effects observed in dogs were the most sensitive endpoint and are used to establish the health-based value (HBV) of 0.1 mg/L. The HBV is derived using a conservative approach, intended to be protective against potential reproductive effects.

Treatment and analytical considerations

The guideline development process considers the ability to both measure (quantify) and remove (treat) a contaminant in drinking water. There are several methods available for the analysis of total boron in drinking water at concentrations well below the HBV. therefore, measurement is not a limitation in the establishment of a MAC. Measurement should be for total boron, which includes both the dissolved and particulate forms of boron in a water sample.

Treatment technologies that are available to remove boron from drinking water supplies include reverse osmosis (RO) and ion exchange (IX). However, data from municipal-scale treatment plants indicate that a treated water concentration of 0.1 mg/L is not achievable for most systems. Assessment of the data indicates that a treated water concentration of less than 5 mg/L is achievable using RO or IX (with boron selective resin (BSR)) treatment systems of varying complexity that are designed and operated for boron removal. This offers drinking water treatment providers flexibility in the type of RO or IX processes that can be used to achieve the MAC including systems with higher boron concentrations (≥ 5 mg/L) in their source water. A concentration of 5 mg/L in treated water is also achievable for small drinking water systems using less complex technologies (single-pass RO system designed for boron removal) that may be more practical where resources are limited.

Although options for residential-scale treatment technologies that are effective for the removal of boron are limited, RO and distillation treatment units are expected to be capable of removing boron to 5 mg/L or less in treated water.

Since treatment technology achievability is a limiting factor in establishing a guideline for boron in drinking water, Health Canada and the Federal-Provincial-Territorial Committee on Drinking Water will continue to monitor new developments in treatment technologies to revise and update the guideline and the guideline technical document as required.

Distribution system

Where boron is present in source water, utilities should determine if boron needs to be included in their distribution system management plan. Although information on the presence of boron in distribution systems has not been reported in the literature, utilities that have aluminium or iron oxide deposits in the distribution system may need to confirm that the accumulation and release of boron (along with other metals such as manganese, arsenic and uranium) is not occurring.

Application of the guideline

Note specific guidance related to the implementation of drinking water guidelines should be obtained from the appropriate drinking water authority.

All water utilities should implement a risk management approach such as the source-to-tap or water safety plan approach to ensure water safety. These approaches require a system assessment to characterize the source water; describe the treatment barriers that prevent or reduce contamination; identify the conditions that can result in contamination; and implement control measures. Operational monitoring is then established, and operational/management protocols are instituted (for example, standard operating procedures, corrective actions and incident responses). Compliance monitoring is determined and other protocols to validate the water safety plan are implemented (for example, record keeping, consumer satisfaction). Operator training is also required to ensure the effectiveness of the water safety plan at all times.

The HBV is derived using a conservative approach, intended to be protective against potential reproductive effects. The guideline is risk managed to take into consideration the treatment challenges of achieving a lower MAC, in particular the limited resources and options available to small drinking water systems and private well owners.

Efforts should be made to reduce boron in drinking water to levels lower than 5 mg/L where possible. Lower concentrations can be achieved by some drinking water treatment systems depending on the source water quality, the type of treatment technology in place and the operational conditions of the treatment plant.

An exceedance of the MAC should be investigated and followed by the appropriate corrective actions, if required. For exceedances in source water where there is no treatment in place, additional monitoring to confirm the exceedance should be conducted. If it is confirmed that source water boron concentrations are above the MAC, then an investigation to determine the most appropriate way to reduce exposure to boron should be conducted. This may include use of an alternate water supply or installation of treatment. Where treatment is already in place and an exceedance occurs, an investigation should be conducted to verify treatment and determine if adjustments are needed to lower the treated water concentration below the MAC.