Bromine [Br, 35]
49
8.3 WATERS
Mean bromine concentration in ocean water is estimated at 67.7 mg/L (Table 8.1).
In stream water, its contents are much lower, and do not exceed 4.5 mg/L. In brine and
salt lake water, its concentration may be elevated, for example, up to about 7000 mg/L in
the Dead Sea. The high solubility of bromide ions has caused its accumulation in water.
Some seaweeds absorbed Br in very high amounts, and might be a source of this
element. Organobromide compounds are needed for the metabolism of sea plants,
especially of some algae.
A great difference between Br in rainwater collected from Kola Peninsula
(<0.2 mg/L) and from the United Kingdom (15 mg/L) clearly indicates anthropogenic impact (Reimann et al. 1999).
8.4 AIR
Bromine concentration in air vary highly. In remote areas, it is within the range
0.4–20 ng/m 3 , whereas over industrialized regions it ranges from 150 to 500 ng/m 3 ,
and might increase up to about 2500 ng/m 3 . Industrial activities and decomposition
of Br pesticides are the most significant Br sources in the atmosphere. Common Br
compounds in the air are Br 2 O 3 , BrCl, BrONO 2 , and CH 3 Br.
At high temperatures, and especially under sunlight, organobromine compounds
are readily converted to free Br atoms in the atmosphere, and an unwanted side effect
of this process is ozone depletion.
8.5 PLANTS
Neither mechanisms of Br uptake by plants nor its function in plants are known.
Most probably, Br is taken up by plants with the water flow from soils and by aerial parts
from the air. Plants grown in Br-enriched soils always contain more of this element. It is
especially visible in plants grown in volcanic ash soils, containing up to 2000 mg Br/kg.
Increased levels of Br in plants cultivated in greenhouses, after a fumigation with
CH 3 Br (at the rate of 75 g/m 3 ) are a real evidence of aerial Br adsorption by plants.
Methyl bromide and other Br organic compounds used as fumigants in greenhouses
may be a serious source of Br in human diets.
Natural Br contents in crop plants do not exceed 30 mg/kg, but in forage plants, it
might be much higher, up to 120 mg/kg in grasses. Mean B contents of cereal grains
are 5.5 mg/kg in barley and 3.1 mg/kg in oats (Eriksson 2001a). Highly elevated Br
contents, up to 300 mg/kg, are reported in some food plants (Pavelka 2004).
Usually, Br is present more in shoots than in roots and tubers. Its contents in plants
do not correlate with any soil properties, but with its amounts in soils. Thus, plants
have more Br when grown in soils enriched with Br. Apparently, it might be taken
up also by the leaves from air. Especially, Br pesticides have a significant impact on
its contents in plants.
Plants differ in their tolerance to Br in soil. Some vegetables and flowers such as
potato, spinach, sugar beet, onion, carnation, and chrysanthemum are known to be
sensitive to high Br levels. Resistant to Br toxicity are carrot, tomato, celery, melon,
and tobacco. These plants may accumulate Br at about 2000 mg/kg, without showing