What Is Boron and Where Does It Come From?

Boron is a naturally occurring element found in rocks, soil, and water. It enters water supplies primarily through the weathering of boron-containing minerals such as borax, kernite, and tourmaline. Seawater contains approximately 4.5 mg/L of boron, and coastal groundwater can be influenced by saltwater intrusion.

Natural boron concentrations in freshwater typically range from 0.01 to 1.5 mg/L, but can exceed 5 mg/L in regions with boron-rich geology, including parts of Turkey, Chile, the western United States, and the Middle East. Volcanic and geothermal areas often have elevated boron in surface and groundwater.

Anthropogenic sources include industrial wastewater from glass and ceramics manufacturing, detergent production (sodium perborate was historically used as a bleaching agent), coal combustion, and boron-containing fertilizers and pesticides. Desalinated seawater, if not specifically treated for boron, can contain boron above guidelines for drinking water and irrigation.

Health and Agricultural Effects of Boron

Boron is an essential micronutrient for plants and may have nutritional functions in humans. However, excessive boron exposure has adverse effects on both human health and agriculture.

In animal studies, high boron intake has been associated with reproductive toxicity, including reduced fertility and developmental effects on offspring. The WHO used the no-observed-adverse-effect level (NOAEL) for reproductive effects in rats to derive the drinking water guideline value of 2.4 mg/L, applying an uncertainty factor for interspecies and intraspecies variability.

The agricultural impact of boron in irrigation water is a major concern. Boron has a narrow range between deficiency and toxicity in plants. Sensitive crops including citrus, stone fruits, grapes, and beans can show leaf tip necrosis, reduced yield, and other phytotoxicity symptoms at boron concentrations as low as 0.5-1.0 mg/L. This makes boron control critical for agricultural irrigation, particularly in arid regions where boron concentrates through evapotranspiration.

In desalination, boron treatment is a key design consideration. Seawater RO permeate typically requires additional treatment to meet both drinking water and irrigation standards for boron.

Regulatory Limits for Boron in Water

The EPA has not established an MCL for boron. Several U.S. states, including California, have notification levels or public health goals for boron in drinking water (California's notification level is 1.0 mg/L).

How to Test for Boron in Water

Boron is measured by laboratory analysis using ICP-OES (EPA Method 200.7) or ICP-MS (EPA Method 200.8). The carmine and azomethine-H colorimetric methods are also used. Samples should be collected in plastic (not glass) containers, as boron can leach from borosilicate glass.

For agricultural applications, soil boron levels should also be assessed alongside irrigation water analysis to determine the cumulative boron load on crops.

Treatment Methods for Boron Removal

Boron-Selective Ion Exchange Resin

Boron-selective resins containing N-methylglucamine functional groups form stable complexes with boric acid and are the most effective technology for achieving low boron concentrations. These specialized ion exchange systems can reduce boron to below 0.3 mg/L and operate effectively across a wide pH range. The resin is regenerated with acid (typically sulfuric or hydrochloric acid) followed by caustic rinse.

Multi-Pass Reverse Osmosis with pH Adjustment

Standard single-pass reverse osmosis at neutral pH achieves only 60-80% boron rejection because boric acid is uncharged at neutral pH. By raising the pH above 9.2 between first and second pass, boric acid converts to the charged borate ion (B(OH)4-), enabling rejection rates above 95% in the second pass. This multi-pass approach is standard in seawater desalination for boron compliance.

High-Rejection RO Membranes

Membrane manufacturers have developed boron-rejecting RO elements that achieve higher boron rejection at neutral pH compared to standard membranes. While these specialty membranes do not eliminate the need for pH adjustment or multi-pass design in stringent applications, they can reduce the overall system complexity and cost.

Electrocoagulation

Electrocoagulation using aluminum electrodes can co-precipitate boron with aluminum hydroxide flocs. This technology is used as pre-treatment or polishing for boron reduction in industrial wastewater applications.

Frequently Asked Questions

Why is boron difficult to remove with reverse osmosis?

At neutral pH, boron exists primarily as undissociated boric acid (B(OH)3), a small uncharged molecule that passes through RO membranes more readily than charged ions. Standard single-pass RO achieves only 60-80% boron rejection at pH 7. Raising the pH above 9.2 converts boric acid to the charged borate ion (B(OH)4-), which is rejected at rates above 95%. Multi-pass RO with inter-stage pH adjustment is the standard approach for achieving low boron in RO permeate.

What is the boron limit for irrigation water?

Boron tolerance varies widely among plant species. Sensitive crops such as citrus, avocado, and beans can show toxicity symptoms at boron concentrations as low as 0.5 mg/L. Moderately tolerant crops like wheat and corn tolerate up to 1.0-2.0 mg/L. The FAO recommends a maximum of 0.7 mg/L for sensitive crops and notes that concentrations above 3.0 mg/L may damage most crops.

What are the health effects of boron in drinking water?

Animal studies have shown that high boron intake can affect reproductive and developmental health. Based on these studies, the WHO established a guideline value of 2.4 mg/L for boron in drinking water. The EPA has not set an MCL for boron but has established a health advisory of 6.0 mg/L for long-term exposure. Some countries, particularly in the EU, apply more stringent limits of 1.0-1.5 mg/L.

Need to Remove Boron from Your Water?

ForeverPure specializes in boron removal systems for desalination, agricultural irrigation, and industrial process water. Our solutions include boron-selective ion exchange systems, multi-pass RO with pH adjustment, and integrated treatment trains. Our engineering team designs systems to meet your specific boron target and application requirements.

Contact ForeverPure for a customized boron removal solution.