Thallium [Tl, 81]
325
Most of aquatic phyto- and zoo-species are capable to concentrate Tl within the
range of 0.02–0.5 mg/kg. However, there are limited data on its toxicity (Lin and
Nriagu vide Kabata-Pendias and Mukherjee 2007).
The median Tl concentration in bottled water of the EU countries is 7.98 ng/L,
and it is slightly lower than in tap water, estimated to be 9.98 ng/L (Birke et al. 2010).
49.4 AIR
The mean Tl concentrations in air vary from 0.06 to 0.22 ng/m 3 (ATSDR 2002b).
It enters into the atmosphere mainly from industries, such as cement plants, metallurgical plants, coal combustion, and burning solid waste. Due to physicochemical
properties (volatilization), it cannot be easily precipitated from emitted gases.
49.5 PLANTS
Thallium contents of plants seem to be a function of its concentrations in soils,
especially its mobile fractions. Its reference content is estimated to be 0.05 mg/kg,
and it is higher in herbage and woody plants than in other plant species (Nolan
et al. 2004). The common ranges of Tl amounts are given for various plants as
follows (in mg/kg): herbages, 0.02–1.0; vegetables, 0.02–0.13; clover, 0.008–0.01;
and meadow grass, 0.002–0.0025. Grass from Zn–Pb industrial areas contains Tl
within the range of 0.98–3.46 mg/kg (Adamiec and Helios-Rybicka 2004). In industrial
regions, Tl may be easily absorbed by plants, especially herbages and mushrooms,
from aerial deposits.
Some plants, mainly of the Cruciferae and Gramineae families, may serve as
hyperaccumulators for phytoremediation of Tl-contaminated soils. The hyperaccumulator, Iberis intermedia, contain Tl up to 4000 mg/kg, even when grown in soil
with Tl content only 16 mg/kg (Nolan et al. 2004). Cruciferae species, grown near
cement plants, accumulated Tl up to about 450 mg/kg (Kabata-Pendias 2011). Also
plants grown in soils over Tl enrichment rocks contain its highly elevated amounts.
Thallium, especially of anthropogenic origin, is easily mobile in soils, and thus
easily available to plants. The depletion in the rhizosphere under elevated Tl concentration, without any effect on Tl uptake by plants, indicates that its transport to roots
is mainly diffusion driven (Al-Najar et al. 2002).
Increased Tl levels in plant tissues are highly toxic to all plants. Its content in
roots, at about 2 mg/kg, may inhibit germination, plant growth, and chlorophyll content. Concentration of Tl in nutrient solution, at about 5 mg/L, decreases the length
of roots of some plants, without any other symptoms. Especially sensitive plants to
increased Tl levels are Leguminosae species, cereals, buckwheat, and tobacco.
49.6 HUMANS
Thallium content in the human body is no more than 0.5 mg, and the level in the
blood is 0.5 μg/L (Emsley 2006). The average content of Tl in the human body, measured in the U.S. population, was approximately 0.1 mg, and the blood concentration
of 3 μg/L (Lansdown 2013). There is no biological role for Tl. It accumulates in the