1. Use of Borates in Swimming Pools: Consideration of Health Effects
Kevin Cox
Senior Research Toxicologist
NSF International

2. Boric Acid and Sodium borate
Boric Acid (and Sodium Borate salts)
Active ingredients in insecticides, herbicides, algaecides, fungicides and wood and material preservatives
Used in cosmetics, pharmaceuticals, water treatment chemicals
Property
Boric Acid
Borax
Borax Pentahydrate
Anhydrous Borax
Structure
CAS#
Chemical Formula
H3BO3
Na2B4O7 10 H20
Na2B4O7  5 H20
Na2B4O7

3. Use in Swimming Pools
Boric acid is commonly used as a pH buffer in pools
Increases capacity of the water to resist changes in pH
Boric acid is a Lewis acid (acquires OH- from water)
At typical pH levels in pools, boric acid will be the primary form
Other promoted functionalities of boron
Algaecide, corrosion inhibition, protection against hypochlorite photolysis, adding tint or sparkle to water, improving water “feel”
Sodium borate salts may be used as substitutes for boric acid
Operators must be careful to add appropriate levels of boron based on the type of boron product used (e.g. boric acid v. borax)

4. Toxicity Profile of Boron
Absorption/Distribution/Metabolism/Excretion
Readily absorbed from GI tract but poorly absorbed through skin
Within the body, exists as undissociated boric acid
Limited human toxicity data exists for boron
Lethal doses range from 15 to 20 grams (adult), 5 to 6 g (child)
Animal Studies
Key toxicity findings reported in animal studies have been reproductive and developmental effects
Chronic studies did not report any increase in tumors while available genetic toxicity studies were negative
“Not likely to be carcinogenic to humans” per U.S. EPA guidelines

5. Organizational Assessments of Boron
Agency/Organization
Year
Numerical Risk Value
Basis
U.S. Environmental Protection Agency (U.S. EPA) – Integrated Risk Information System (IRIS)
2004
0.2 mg/kg-day
(oral RfD)
Used BMDL5 of 10.3 mg/kg-day based on reduced fetal weights reported from a developmental study in rats. Applied a UF of 66.
U.S. Environmental Protection Agency (U.S. EPA)
2008
5 mg/L
(lifetime health advisory for drinking water)
Used BMDL5 of 10.3 mg/kg-day based on reduced fetal weights reported from a developmental study in rats. Applied a UF of 66 and a source contribution of 80%.
World Health Organization (WHO)
2009
2.4 mg/L (drinking water limit)
Used BMDL5 of 10.3 mg/kg-day based on reduced fetal weights reported from a developmental study in rats. Applied a UF of 60 and 40% source allocation.
Agency for Toxic Substances and Disease Registry (ATSDR)
2010
0.2 mg/kg-day (intermediate MRL)
Used BMDL5 of 10.3 mg/kg-day based on reduced fetal weights reported from a developmental study in rats. Applied a UF of 66.

6. U.S. EPA FIFRA Assessment (2008)
U.S. EPA evaluated the use of boron in swimming pools as part of FIFRA regulatory requirements
U.S. EPA evaluated each specific boron use by assessing the margin of exposure (MOE)
A NOAEL of 8.8 mg/kg-day from a chronic toxicity in dogs was divided by estimated exposures to determine the MOE
The Level of Concern (LOC) was set at 100
For use of boron in swimming pools, application rates above 240 mg/L (as Borax Pentahydrate) resulted in MOE values that were below the LOC
It was recommended that end uses that exceeded 240 mg/L (as Borax Pentahydrate) be revised
Equivalent to 35 mg/L as boron

7. U.S. EPA FIFRA Assessment (2015)
In 2015, U.S. EPA re-evaluated the use of boron in swimming pools as part of requirements under FIFRA
Again, U.S. EPA evaluated each specific boron use by assessing the margin of exposure (MOE)
A NOAEL of 8.8 mg/kg-day from a chronic toxicity in dogs was divided by estimated exposures to determine the MOE
The Level of Concern (LOC) was set at 100
Using updated swimming pool exposures and a swimming pool concentration of 35 mg/L (as boron), the U.S EPA found exposures to be acceptable for children (6<11), children (11<16) and adults

8. NSF Standard 50 Assessment
As concentrations of mg/L (as boron) are commonly recommended in products, use of boron was assessed using methods of Annex R of NSF/Standard 50
NSF assessed both 35 mg/L and 50 mg/L use rates (as boron) for children and adults
U.S. EPA IRIS chronic oral reference dose of 0.2 mg/kg- day was used to assess acute and chronic exposures
Chronic exposures were assessed against the RfD adjusted to account for other sources of boron exposure
The results indicated that application rates of 35 mg/L and 50 mg/L (as boron) meet the requirements of NSF 50

9. Summary Increasing concern about exposures to chemicals in daily lives
Boron has demonstrated both reproductive and developmental toxicity in animals following oral exposure
U.S. EPA in both 2008 and 2015 has recommended a swimming pool concentration limit of 35 mg/L (as boron)
These limits were based on the toxicity observed in laboratory animals
Assessment under Annex R found mg/L application to be acceptable
As pool application rates have been established based on health effects criteria, it is important to monitor levels of boron in pools

10. Questions?