8273

• UCREFRP Catalog Number: 8273
• Author: U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, U.S. Geological Survey and U.S. Bureau of Indian Affairs.
• Title: Guidelines for Interpretation of the Biological Effects of Selected Constituents in Biota, Water, and Sediment.
• USFW Year: 1998.
• USFW - Doc Type: \
• Copyright Material: NO

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( CONSTITUENTS OF" CONCERN)

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Description

Boron (B) is a metalloid, with properties
intermediate between those of carbon and
aluminum. Like aluminum, it has an
oxidation state of +3 in all of its chemical
compounds, and it is an electrical conductor in
its pure form. Like carbon, though, it can
sometimes form complex chains and rings,
and its crystalline form is nearly as hard as
diamond. Boron has an atomic number of 5
and an atomic weight of 10.81. It melts at
2,180oC. Boron is found as a hard black solid
and as an amorphous blackish-brown powder,
although the more common boron salts are
generally white or pale shades of yellow, blue,
green, or gray. (Pais and Jones 1997.)

Occurrence

Boron is widespread in the environment but
generally occurs in low concentrations; it
constitutes only 3 mg/kg of the Earth's crust
and occurs naturally only in combined form,
usually as borax (Na2B40]'lOH20), coleman-
ite (Ca2B60ll.5H20), boronatroca1cite
(CaB407NaB02'8H20), or boracite
(Mg7Cl2B]603o) (EP A 1975; NAS 1980). Areas
with the highest natural inputs of boron to
the environment are the Mojave Desert,
California, the plateau of the Alpine-
Himalayan system, and the high plateau of
the Andes (Butterwick et a1. 1989). The brines
of Borax and Mono Lakes in California are
rich in boron due to arid conditions and high
evaporative concentration (Livingstone 1963).
Boron compounds usually are degraded or
transformed to boric acid and borates, which
are the main boron compounds of ecological
significance (Sprague 1972).

In natural freshwater ecosystems, surface
water concentrations of boron rarely exceed
1 mg/L and are usually less than 0.1 mg/L;
however, in systems where boron has been
mobilized by human activities, the concen-
trations may be much higher (Maier and
Knight 1991). In a survey of 1,546 river- and
lake-water samples from throughout the
United States, the mean concentration of
boron was 0.1 mg/L, with 5.0 mg/L being the
maximum (Powell et al. 1997). Groundwater
boron concentrations are usually <0.5 mg/L
worldwide; in the United States, concentra-
tions can be as high as 5 mglL in ground-
water. Aquatic fauna can usually tolerate up
to 10 mg B/L in water for extended periods of
time without ad verse effects (Eisler 1990).
Recently, South Africa has developed a water-
quality criterion of 1 mg BIL to prote~t
aquatic ecosystems (including t~r~estnal
animals that use them). RecognLZmg that
boron sensitivity of plants is greater than that
of animals, South Africa's water-quality
criterion was based on calculation of a "final
plant value" (Roux et al. 1996).

Boron concentrations in U.s. irrigation water
typically range from <0.1 to 0.3 mg/L
(Adriano 1986). Some irrigation water
(especially pumped groundwater) ~sed ~
the western San Joaquin Valley, California,
contain far greater concentrations (Shelton
and Miller 1988); boron concentrations in the
San Luis Drain and Kesterson Reservoir were
11-18 and 13-65 mg/L, respectively (USBR
1986). Agricultural drain water contaminated
with boron is considered potentially harmful
to waterfowl and other wildlife populations
throughout areas of the Western United States
(Smith and Anders 1989).

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