44
Trace Elements in Abiotic and Biotic Environments
matrix and is helpful in wound healing. It may be involved in cerebral function due
to its effects on the transport across membranes. Compounds of B have been shown
to be potent antiosteoporotic, anti-inflammatory, hypolipemic, anticoagulant, and
antineoplastic agents, both in vitro and in vivo in animals. Improvements in brain
function, bone density, immunity, cardiovascular effects, development and reproduction, and the incidence and prevalence of cancer biomarkers have been stated.
However, the cellular mechanism of B has not yet been identified.
It is stated that in areas of the world where B intakes usually were 1.0 mg B or less
a day, the estimated incidence of arthritis ranged from 20 to 70%, whereas in areas
of the world where B intakes were usually 3 to 10 mg B, the estimated incidence of
arthritis ranged from 0 to 10% (Meacham et al. 2010).
Dietary B has a low level of toxicity. A number of acute poisonings in human
from boric acid or borax have been reported following ingestion, parenteral
injection, lavage of serous cavities, and enemas and application of dressings,
powders, or ointments to large areas of burned or abraded skin. Symptoms of
acute poisoning by high doses of B include nausea, vomiting, diarrhea, headache,
desquamation, and evidence of central nervous system stimulation followed by
depression, dermatitis, lethargy, and other symptoms. In the extreme cases, kidney damage occurs, followed by circulatory collapse and death. It is not absorbed
across intact skin. However, there is evidence that B can be absorbed through
more severely damaged skin, especially from an aqueous vehicle and during
inhalation exposure.
Ingested B is rapidly taken up from the gastrointestinal tract, with possibly more
than 90% absorbed and is rapidly distributed throughout body liquids. A small
amount appears to be retained in body tissues, especially bone and spleen (Reilly
2002). Boron is mostly present in body tissues and fluids as boric acid B(OH) 3 , and
in lesser amounts as anion B OH
( ) 4
.
Due to the lack of human and the limited animal data, B is not classified as
human carcinogen (WHO 1998). For humans, B exposure occurs primarily through
the diet and drinking water. Boron is a notable contaminant or major ingredient of
many nonfood personal-care products (Hunt et al. 1991). The amount of B intake
by people is dependent on the types of food consumed. The richest sources of B are
fruits, vegetables, pulses, legumes, and nuts. Dairy products, fish, meats, and most
grains are poor sources of boron (Table 7.2). The tolerable daily intake for B is estimated at 0.17 mg/kg bw, rounded to 0.2 mg/kg bw (WHO 2011a). For the general
population, the greatest B exposure comes from the oral intake of food (65%) and
water (30%). According to the WHO, it is expected that the amounts of B taken are
0.44 μg/day through air, 0.2–0.6 mg/day through drinking water, and 1.2 mg/day
through diet (WHO 1998). Dietary intake of B in the United Kingdom ranges from
0.8 to 1.9 mg/day. However, increased consumption of specific foods, with high B
content, will increase B intake significantly; for example, one serving of wine or
avocado provides 0.42 and 1.11 mg, respectively. Other B significant sources may
be from cosmetics.
According to Meacham et al. (2010), B from dietary supplements and personalcare products is almost 100% absorbable through epithelial membranes. Some