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Trace Elements in Abiotic and Biotic Environments
Median Se concentrations in bottled water of the EU countries is 0.036 μg/L, and
is lower than in tap water, estimated to be 0.115 μg/L (Birke et al. 2010). The existing guideline on Se in drinking water, last updated in 1992, established its maximum
allowable concentration (MAC) of 10 μg/L, based on an adequate and safe range of
its intake of 0.05–0.2 mg/day (EPA 2013). Previously proposed MAC, of 50 μg/L,
resulted in chronic selenosis. Provisional guideline value for Se in drinking water
established by the World Health Organization (WHO) is 40 μg/L. The guideline
value is designated as provisional because of the uncertainties inherent in the scientific database (WHO 2011a).
42.4 AIR
Concentration of Se in the atmosphere is highly variable due to its differentiated
sources: (1) evaporation from ocean and seawater surface, (2) volcanic eruptions, and
(3) industrial emissions. Their amount in air above the South Pole is about 0.06 ng/m 3 , and
in urban and industrial regions it varies within the range of 0.06–30 ng/m 3 (Table 42.1).
Its median content of air from polluted regions is estimated to be 4.0 ng/m 3 (Reimann
and de Caritat 1998). Always its higher aerial abundance is in industrial regions. The
lowest harmful Se concentration in air is estimated to be 1,000,000 ng/m 3 (ATSDR
2002b).
Enrichment of Se in marine aerosols resulted from the formation of volatile Se-organic
compounds, mainly dimethyl selenide [(CH 3 ) 2 Se]. Also dimethyl diselenide is an
easily volatile species. Increased Se levels in mosses (>1 mg/kg) and peat (>2 mg/
kg) in marine regions indicate clearly the impact of Se from the surface of seawaters
(Berg and Steinnes 1997). Substantial amounts of Se may also be volatized from
Se-contaminated soils through bacterial and phytovolatilization processes. There is
the estimation that about 45% of Se content in coal is emitted as (CH 3 ) 2 Se, which stay
relatively long, about 45 days, in air. Its global emission is estimated to be >6 kt/yr,
in both small particles and volatile compounds, which contribute to around 40% of
its aerial abundance (Schrauzer vide Kabata-Pendias 2011).
Atmospheric Se deposition is clearly shown by its high accumulation in mosses
and mushrooms. Mosses from the Scandinavian countries contain Se within the
average values of 390–2900 μg/kg (Berg and Steinnes 1997). High Se accumulation in rootless mushrooms (up to 20,000 μg/kg) indicates also its easy absorption
from the atmosphere. Several plants uptake Se from air via the leaf surface, and
then accumulate it mainly in roots, as various inorganic selenite compounds. There
is the estimation that up to about 80% of Se content in plants is from aerial sources
(Haygarth vide Kabata-Pendias 2011).
42.5 PLANTS
Selenium requirements by plants differ by species, with some plants requiring relatively large amounts, and others apparently requiring none, what is still in need of
further clarification. Most plants contain rather low Se levels, around 25 μg/kg, and
rarely exceed 100 μg/kg. However, some plants reveal a great capability to accumulate Se, up to levels about 1000 μg/kg, that may be toxic to humans and animals.