Boron [B, 5]
41
of seawater is calculated as 380 kt (Gaillardet et al. 2003). Boron concentration in
surface water of the United States ranges from 1 to 5000  μg/L (Butterwick et  al.
1989). Fairly similar broad ranges of B in river water are given for several other
countries. Both natural and anthropogenic factors are responsible for this phenomenon. Anthropogenic sources of B in water are mainly sewage sludge, in which its
maximum concentration is in the United States, 4000 μg/L, and in Europe, 5000 μg/L
(Butterwick et al. 1989).
B concentration of groundwater is of an agricultural concern, especially in warm
and arid climatic countries. Worldwide B contents in water of these regions range
from <300 to >100,000 μg/L. The highest B concentrations in the water of the
European countries are noticed in Italy and Spain (ECETOC 1997).
The most common B species in natural water are boric acid, B(OH) 3 , and its dissociation products, such as B(OH) 4
and other borates. Soluble Al compounds react
with B in water resulting in the formation of Al–B insoluble complex. Several other
complex compounds, such as polyborates and fluoroborates, may also be formed in
water, and decrease B solubility.
Boron concentration in rainwater is relatively low (Table 7.1). Rainwater sampled
in Sweden, in 1999, contained B within the range of 1.3–2.9 μg/L, and its wet deposit
was calculated at 18 g/ha/yr (Eriksson 2001a).
Median B concentration in bottled water of the EU countries is 48 μg/L, and is
higher than those in tap water, 16 μg/L (Birke et al. 2010). Guideline value for B concentration in drinking water is established by the WHO at 2400 μg/L (WHO 2011a).
Boron is an essential micronutrient to aquatic plants, fish, and amphibians, but
may be toxic, especially borate compounds, at concentrations above 10,000 μg/L.
Some species of salmon and trout are sensitive to the increased B levels in water.
Aquatic plants of rivers with polluted water from industrial or agricultural sources
may contain B up to 170 mg/kg. However, it does not biomagnify in fish and other
aquatic food chain (Kabata-Pendias and Mukherjee 2007). Marin and Oron (2007)
suggested using duckweek (Lemna gibba) accumulating B from water up to 1900 mg/kg,
which may reduce B concentrations significantly.
7.4 AIR
B concentrations in air commonly range between 0.5 and 80 ng/m 3 . Its natural sources
are emissions from sea surface and volcanic activities. Industrial sources include various mining operation, glass, ceramic, and chemical productions. The highest amounts
of B are released from coal combustions, especially fired power plants. The global
anthropogenic B emission was estimated at 180–650  kt/yr, whereas from marine
sources at 800–4000 kt/yr (Anderson et al. 1994). According to these authors, the
total global emission of B may be up to 72,000 kt/yr. Boron from the atmosphere is
easily deposited on the Earth, with rain and dry particles.
7.5 PLANTS
Soluble species of B are easily available to plants and may be taken up passively or
actively. Properties of boric acid to complex with polysaccharides stimulate passive
sorption of B by plants. In most cases, however, B absorption follows the water flow