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Boron

4. What are the effects of boron on humans and mammals?

  • 4.1 How does boron act in humans and mammals?
  • 4.2 What are the effects of boron on laboratory animals?
  • 4.3 What are the effects of boron on humans?

4.1 How does boron act in humans and mammals?

The source document for this Digest states:

Kinetics and biological monitoring

The pharmacokinetics of boron appear to be quite similar across species in the following respects:

a) Absorption of borates is essentially complete (approximately 95% in humans and rats), and boron appears rapidly in the blood and body tissues of several mammalian species following ingestion.

b) Distribution of boron in mammals appears to occur by passive diffusion throughout the body fluids. In contrast to soft tissues and blood, bone shows selective uptake of boron (>4 times higher than serum) and significantly longer retention times.

c) Metabolism of boric acid is thermodynamically unfavourable in biological systems. Thus, the ionic species in systemic circulation are expected to be equivalent across mammals. This eliminates a major source of potential uncertainty for risk extrapolation, as interspecies differences in enzymatic pathways and/or metabolic rates do not need to be taken into consideration.

d) Elimination kinetics (especially route of elimination and terminal half-life) also appear to be similar for humans and rats.

The similarities in pharmacokinetic parameters between humans and rats, the species defining the no-observed-adverse-effect level (NOAEL) for laboratory studies, reduce the uncertainty for risk extrapolation between these two species.

Source & ©: IPCS "Environmental Health Criteria (EHC) 204 ",
Summary of the Report, Chapter 1.1.3
For more information, see the full IPCS document
Kinetics and Metabolism in Laboratory Animals and Humans , Chapter 6

For details on: See the full IPCS assessment:
Absorption Chapter 6, section 6.1 
Distribution Chapter 6, section 6.2 
Metabolism Chapter 6, section 6.3 
Elimination and Excretion Chapter 6, section 6.4 

4.2 What are the effects of boron on laboratory animals?

The source document for this Digest states:

Effects on experimental animals and humans

The data regarding developmental and reproductive toxicity show that lower fetal body weight in rats is the critical effect. The NOAEL for lower fetal body weight is 9.6 mg boron/kg body weight per day. The lowest-observed-adverse-effect level (LOAEL), at which rats show slight (approx. 5%) fetal body weight differences and rib anomalies, is about 13 mg boron/kg body weight per day. As dose level increases, the effects that are seen (and the doses at which they are seen) are:

a) further rib effects and testicular pathology in the rat (approx. 25 mg boron/kg body weight per day);

b) decreased fetal body weight and increased fetal cardiovascular malformations in the rabbit, and severe testicular pathology in the rat (approx. 40 mg boron/kg body weight per day);

c) testicular atrophy and sterility in the rat (approx. 55 mg boron/kg body weight per day); and

d) reduced fetal body weight in the mouse (approx. 80 mg boron/kg body weight per day).

Animal studies on mice and rats showed no evidence of carcinogenicity of boric acid.

Source & ©: IPCS "Environmental Health Criteria (EHC) 204 ",
Summary of the Report, Chapter 1.1.4
For more information, see the full IPCS document
Effects on Laboratory Mammals and In Vitro Test Systems , Chapter 7

4.3 What are the effects of boron on humans?

The source document for this Digest states:

Based on the lack of human data and the limited animal data, boron is"
not classifiable as to its human carcinogenicity".

Only a few human studies have been conducted to assess health effects associated with exposure to boron compounds. The available data show that exposure is associated with short-term irritant effects on the upper respiratory tract, nasopharynx, and eye. These effects, however, appear to be short-term and reversible. The sole long-term (7-year) follow-up study failed to identify any long-term health effects, although a healthy worker effect cannot be entirely ruled out given the rate of attrition (47%). Two descriptive studies assessed fertility and secondary sex ratios in relation to exposure. Neither study reported a detrimental effect on demonstrated fertility for its select sample. Although an excess percentage of female births has been suggested, the absence of statistical significance and attention to other co-variates known to affect sex ratios warrants careful interpretation of this finding. No studies have been identified that assess the spectrum of reproductive outcomes, such as time-to-pregnancy, conception delays, spontaneous abortions, and sperm analyses in males. The role of other lifestyle or behavioural factors in relation to health and fertility requires further study to identify potentially sensitive populations and to evaluate reproductive effects more fully.

Source & ©: IPCS "Environmental Health Criteria (EHC) 204 ",
Summary of the Report, Chapter 1.1.4
For more information, see the full IPCS document
Effects on Humans , Chapter 8


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