Abstract
In agricultural soils, thallium (Tl) of geogenic origin may represent a potential risk for human health, mainly via ingestion of food crops. In this work, a pot experiment was carried out to evaluate (1) the bioavailability of Tl and other potentially toxic elements (PTEs) in an agricultural soil with naturally occurring Tl; (2) the uptake and accumulation of PTEs in Lactuca sativa L. var. acephala, Diplotaxis tenuifolia L. DC and Silene latifolia Poir; (3) the health risks arising from plant and soil ingestion by different subpopulations and dermal contact of soil by farmers. In soil, only Tl and Pb pseudototal contents were above Italian screening values. Nevertheless, the promptly bioavailable contents of all PTEs were always below internationally recognized trigger values. Plants affected PTE bioavailability in soil by their rhizodepositions and accumulated PTEs in their shoots. Acceptable risks (hazard index < 1) arose from dietary intake of both L. sativa L., D. tenuifolia L. and dermal contact of soil by farmers. Significant health risks can derive from the intake of S. latifolia Poir. (accumulating high Tl concentrations), in particular by children (HI = 74). In conclusion, an adequate management and crop selection are needed to profitably exploit soils with geogenic Tl for agricultural purposes.
Highlights
Thallium (Tl) is a nonessential and highly-toxic element for living organisms, generally showing a greater acute and chronic toxicity than other harmful elements, such as As, Cd, Hg and Pb [1,2]
The soil showed a medium-low content in organic matter (OM), typical of soils exploited for agricultural purposes in Mediterranean countries
The content in total N was moderate, in a good equilibrium with the organic C content; the C/N ratio was 9.57, a value which indicated that the primary inputs of organic matter from crop residues were properly mineralised by soil microbiota
Summary
Thallium (Tl) is a nonessential and highly-toxic element for living organisms, generally showing a greater acute and chronic toxicity than other harmful elements, such as As, Cd, Hg and Pb [1,2]. Tl poisoning may lead to gastrointestinal dysfunction, ascending paralysis and mental disorders, whilst polyneuritis may occur with chronic poisoning [3,4,5]. The lethal dose of Tl for an adult human is only 8–10 mg kg−1 ; it is classified as one of the 13 priority metal pollutants by the United. The main routes of human exposure to Tl are the ingestion of contaminated food and drinking water [9]. Tl quickly reaches the principal human organs and eventually accumulates in the nervous system [10]. Tl is a rare element, ranging from 0.1 to 2.0 mg kg−1 in terrestrial environments (average content of 0.5 mg kg−1 in the continental crust) [11,12], it can occur at higher extent in various sulphide
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