Environmental Health Criteria, No. 204 1998, xviii + 201 pages
(English with summaries in French and Spanish), ISBN 92 4 157204 3,
CHF 42.-/USD 37.80; In developing countries: CHF 29.40. Order no.
This book evaluates the risks to human health and the environment
posed by boron, a naturally occurring element widely distributed,
in the form of various inorganic borates, in the oceans, sedimentary
rocks, coal, shale, and some soils. Boron is also used in laundry
bleach and in the manufacture of glass, glass products, fertilizers
and herbicides, antiseptics, and pharmaceuticals. Because boron is
widely detected in drinking water and occurs naturally in fruits,
nuts, and vegetables, the report gives particular attention to health
risks associated with exposure of the general population through diet
and drinking water.
A section on sources of human and environmental exposure cites evidence
that boron enters the environment mainly through volatilization from
seawater, volcanoes, geothermal steam, and natural weathering of clay-rich
sedimentary rock. Although industrial uses account for much smaller
releases, the report notes that all of the boron from the sodium perborate
contained in detergents ultimately enters the wastewater system, and
is not removed by standard water treatment procedures.
The environmental behavior of boron is covered in the next section,
which concludes that boron does not persist in the atmosphere to a
significant degree, adsorbs onto soil particles, accumulates in aquatic
and terrestrial plants, but does not magnify through the food chain.
Numerous findings indicate that boron is an essential micronutrient
for higher plants. A section on environmental levels and human exposure
cites diet and drinking water as the principal sources of exposure
for the general population. Occupational exposure to boron compounds
is judged to be potentially significant, with inhalation of dusts
singled out as the most significant route of exposure. Concerning
kinetics and metabolism in laboratory animals and humans, numerous
studies demonstrate that boric acid and borax are readily absorbed
from the gastrointestinal and respiratory tracts, widely distributed,
and rapidly excreted in urine.
The most extensive section reviews findings from toxicity studies
in laboratory mammals and test systems. General clinical signs of
exposure are described as depression, ataxia, occasional convulsions,
decreased body temperature, and violet red color of skin and mucous
membranes. The review found unequivocal evidence that the male reproductive
tract is the principal target of toxicity. The review also cites several
recent reports indicating that boron in physiological amounts is beneficial
to, if not essential for, higher animals.
An evaluation of the few human studies of toxicity concludes that
exposure is associated with short-term and reversible irritant effects
on the upper respiratory tract, nasopharynx, and eye. The most frequently
observed symptoms involve the gastrointestinal tract and include vomiting,
abdominal pain, diarrhea, and nausea. Less frequently observed symptoms
include lethargy, rash, headache, light-headedness, fever, irritability,
and muscle cramps. Data on carcinogenicity were judged inadequate
for evaluation. In line with findings from animal studies, the review
found several recent studies demonstrating that boron is a dynamic
trace element that can affect the metabolism or utilization of numerous
substances essential to life processes.
On the basis of all evidence considered, the report established a
tolerable intake for boron of 0.4 mg/ kg body weight per day.
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