All Hazards

Boron Compounds and Their Toxicity

COLOR="#004080"> 

COLOR="#004080">SOURCES :

 

-Boric acid
(BO₃H3),

-Sodium
tetraborate, anhydrous or Anhydrous Borax (Na₂B4O7), these two
materials are mainly used in the manufacture of boron
frits.

 

- Sodium
tetraborate, decahydrate or Borax or Decahydrate Borax
(Na₂B4O7.10H₂O),

-Ulexite
(NaCaB5O9.8H₂O),

-Colemanite
(2CaO.3B₂O₃.5H₂O),

-Gerstley Borate
(North America), see our comprehensive report on this site :

-Boron
frits,

-Lead-boro
silicate.

 

COLOR="#004080">General information :

 

The natural forms
include boric acid and the borates.

 

Boric Acid,
Borates, Boron Oxide :

 

Since these
products have similar metabolism and toxicity, we will discuss
them together

 

I- Boric Acid
:

 

Boric acid
(H3BO₃, CAS # 10043-35-3) has a pH of 4 in a saturated aqueous
solution. It has antibacterial and antifongic properties, hence it
is used as a colourless disinfectant for the skin and the mucous
membranes, ocular, oto-rhino-laryngologeal and vaginal.

European
standards have set authorized concentrations of boric acid at 0.5%
for oral hygiene products and at 5% for talcs and cosmetics.

It is used in the
nuclear industry, for its capacity to absorb neutrons, for control
and emergency regulation of reactions.

 

II-Borates
:

 

Borates, among
which sodium borate or borax, are also used in :

-the glass
industry, ceramics, enamels,

-the manufacture
of cosmetics, paints, dyes,

-the treatment of
leather and wood,

as:

-fertilizers,

-weedkillers,
insecticides

-retardings of
combustion

 

III-Boron
Oxide :

 

Boron oxide, B₂O₃
CAS# 1303-86-2, formed by the thermal fusion of boric acid, is
used in the glass industry.

 

COLOR="#004080">Toxicological properties :

 

I- Absorption
:

 

A-Digestive
absorption :

Digestive
absorption is fast and almost complete; the blood peak is located
at the second hour.

 

B-Cutaneous
absorption :

These products
are little absorbed by a healthy or slightly scarified skin. Skin
absorption by a seriously injured or burned skin can be
significant and be the source of intoxication in the case of a
local treatment containing boron.

 

C-Differences
of preparation : COLOR="#004080">

There is a
significant difference of absorption between the hydrated forms
(< 1%) and the gel forms (20%).

 

COLOR="#004080">II-Distribution :

 

The distribution
in the body is ubiquitous; the concentration in body fluids is
identical to that of the plasma.

There are however
two exceptions: the bone, where it concentrates (two to three
times the plasmatic levels), and the fat tissue where one finds
only 20% of the plasmatic levels. There is no active transfer
between the blood compartment and tissues.

 

COLOR="#004080">III-Bio-transformation :

 

In the body,
borates are metabolized to boric acid which remains unchanged.

 

IV-Excretion
:

 

Whatever the
route of entry, excretion is mainly urinary (80 to 85% of the
absorbed amount) in the form of boric acid, and less in the form
of borates. Small amounts are found in the feces and perspiration.

Although not
properly evaluated, its half-life of elimination is less than 20
hours. In the case of massive ingestion, elimination is biphasic,
50% in 12 hours and 50% in 1 to 3 weeks.

 

V-Acute
Intoxication :

 

A-Oral Lethal
Dose (LD) :

In man, the oral
LD may be estimated in the following manner :

1-Newborn= 1 to 3
g.

2-Child=
5g.

3-Adult= 15 to 20
g.

 

 

B-Latency
Period :

whatever the
route of intoxication, a delay of a few hours precedes
symptomatology.

 

C-Clinical
Findings :

1-Digestive
disorders : nausea, vomiting, abdominal pains.

2-Neurological
disorders : headaches, tremors, agitation, convulsions,
hallucinations.

3-Severe
intoxication : coma, collapse, metabolic acidosis, cyanosis, fever
and respiratory depression.

4-Renal
impairment : tubular necrosis may occur (oliguria and proteinuria,
possibly anuria).

5-Cutaneous
disorders (after a few days) : extensive desquamative dermatitis
beginning with erythema involving the palms of the hands, the
soles of the feet and the buttocks, with the possibility of a
secondary generalization (formation of bubbles, massive
exfoliation), similar to Ritter's syndrome (exfoliative dermatitis
of the newborn). Alopecia may be observed.

 

Death occurs due
to infections, shock, neurological complications, the autopsy
showing renal tubular necrosis, cerebral oedema, hepatitis and
gastro-enteritis.

 

D-Laboratory
Findings :

The intoxication
is confirmed by measuring boron in blood, which is detectable
below 1µg/L. by many techniques:

 

1-In adults:

a-toxic effects
are observable from 15 to 20 mg/L. of blood boron,

b-signs of
severity are seen as low as 40 mg/L,

c-the presence of
more than 40 mg/L. suggests a serious intoxication,

d-the evolution
may be fatal for concentrations equal to 500 mg/L.

 

2-In newborns :

a-toxic effects
have been observed for blood boron levels as low as 4 mg/L.

 

E-Mortality
:

In studies dating
from the 50s, mortality is estimated at more than 50%; it relates
primarily to accidental intoxications in children.

As from the 80s,
in an American series, intoxications are generally asymptomatic
(88.3%), and never fatal. This difference may be explained by a
better way of dealing with these intoxications.

 

F-Treatment
:

Above all,
treatment is aimed at purifying (skin and mucous membranes wash,
gastric wash, hemodialysis, peritoneal dialysis ), and
symptomatic.

 

G-Skin
Irritation :

1-Borax: is a
severe eye irritant.

2-Boron and
borates: are not or only slight skin irritants.

3-Boron oxide:
causes slight irritation of the skin and mucous membranes (skin
irritation, ocular irritation, nosebleed, dryness of the mouth,
the throat and the nose, pharyngeal pain, sputum, cough),
disappearing at the end of exposure without pulmonary impairment,
nor long-term effect.

 

 

VI-Chronic
Intoxication :

In man, the
repeated inappropriate use of boric acid has caused, particularly
in children, chronic intoxications characterized primarily by
cutaneo-mucous, hair and nails disorders.

 

-dermatosis,

-conjunctivitis,

-red coloured
tongue,

-cracks of the
lips,

- loss of hair,

-digestive
disorders,

-neurological
disorders

 

These effects are
close to those observed at the time of acute intoxication and are
related to boron accumulation in the body. These disorders are
usually reversible at the cessation of its use; they are enhanced
by the presence of a pre-existing kidney insufficiency.

Workers exposed
to dust of borates or boron oxide present signs of rhinitis,
conjunctivitis or cough. In the long run, no pulmonary impairment
has been found.

In the case of
chronic intoxication, blood boron levels are frequently higher
than 30 mg/L.

 

COLOR="#004080">Effects on reproduction :

 

COLOR="#004080">A-Experimentally :

Animal
experimentation has revealed disorders of reproduction related to
boric acid and borax exposure. These were testicular and fertility
effects.

The mechanism of
this toxicity is not completely elucidated. In the female rat, an
increase in the number of spontaneous abortions and a fall in the
number of litters were observed.

A study relating
to development shows that boric acid causes birth defects in three
(3) species studied (rat, rabbit, mouse).

 

B-In Man
:

A previous study
carried out in Russia with exposure levels varying from 20 to 83
mg/m3 at 50% of the studied workstations i.e. 2 to 8 times the
currently allowed exposure limit, showed a reduction of sexual
activity and a deterioration of the quality of the sperm

In the USA, these
results were not confirmed in a study of 542 workers whose average
exposure was 19.7 mg/m3.

 

As far as birth
defects in man are concerned, there does not seem to be any case
reported in the literature.

 

COLOR="#004080">Carcinogenesis and Mutagenesis :

 

COLOR="#004080">A-Experimentally :

1-Boric acid has
not caused genetic mutations nor chromosomal abnormalities in a
series of in vitro experiments on bacteria or eucaryotic cells.

2-In the rat and
in the mouse, no carcirogenic effect due to boric acid has been
found during a 2 year experiment.

 

B-In man
:

Epidemiologic
studies have also been negative.

 

Exposure
Limits :

 

I-Gerstley Borate
:

VEMP (Quebec) : 5
mg/m3

 

II-Boron oxide
:

A-IDLH (Immediate
danger to life and health) 2,000 mg/m3

B-VEMP :
10mg/m3

 

III-Sodium
tetraborate, anhydrous or Anhydrous Borax (Na₂B4O7) :

VEMP : 1
mg/m3

 

IV-Sodium
tetraborate, decahydrate or Borax or Decahydrate Borax :

VEMP : 5 mg/m3

 

COLOR="#004080">Prevention :

 

Laws on
Occupational Health and Safety aim at the elimination of hazards
at the source.

When engineering
methods and modifications of working methods are not able to
sufficiently reduce the exposure to these substances, the wearing
of personal protective gears may become necessary. These
protective gears must be in conformity with regulation.

 

 

References
:

COLOR="#004080"> 

1-CSST-Quebec,
Repertoire Toxicologique, 2002

2-Toxicologie
Industrielle et Intoxications Professionnelles, Lauwerys R., last
edition.

COLOR="#004080">3-Potterycrafts-MSDS, United Kingdom, avril
2002.

4-Sax's
Dangerous Properties of Industrial Materials, Lewis C., last
edition.

5-Bore et ses
composés, Encyclopédie Médico-Chirurgicale,
Toxicologie-Pathologie Professionnelle, M. Falcy, mai
2002.

6-Clay and
Glazes for the Potter, Rhodes Daniel, 1973.

 

 

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By Edouard Bastarache

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