Biogeochemical survey of the Allchar (North Macedonia) arsenic-thallium ore body: a focus on hyperaccumulator plants

Abstract Background and aims The Allchar site in North Macedonia has a unique geology exceptionally enriched in arsenic and thallium, making the local soils extremely toxic to plant life. Surprisingly, the mineralized soils at Allchar host a diverse flora, with unknown metal(loid) accumulation potential for most of these plant species. The main aim of this study was to determine the elemental profiles ('elementomes') of plant species growing naturally in the Allchar area and to assess their elemental accumulation in relationship to concentrations in the soil in which the plants grow. Methods Samples of in total 23 plant species (with at least 4 replicates per species) and their associated rhizospheric soils were collected in the field at the Allchar site in North Macedonia and analysed with monochromatic X-ray fluorescence analysis for total and DTPA-extractable metal and metalloid concentrations. Results High foliar concentrations of thallium were found in some plant species, being the most extreme in Silene latifolia , at 79,200 µg g −1 thallium, whilst arsenic concentrations are generally low in most of the plant species analysed. Thallium hyperaccumulation (> 100 µg g −1 ) was found in the families Violaceae, Lamiaceae and Caryophyllaceae. Particularly high foliar thallium concentrations were found in Viola arsenica and V . tricolor subsp. macedonica , reaching up to 31,600 and 11,700 μg g −1 thallium, respectively. The elemental concentrations in soil and plant samples reflect that of the local mineralogy of the three different areas investigated at the Allchar site, with the highest mean values for thallium and arsenic in the Crven Dol area, and 249 and 3970 μg g −1 , respectively, in the plants that were analysed. Conclusion The present study led to the discovery of several new thallium hyperaccumulating plant species, such as Clinopodium alpinum , Anthyllis vulneraria and Linum hirsutum , whereas the thallium concentrations found in Silene latifolia are the highest thus far recorded in nature highlighting the potential of this species for thallium phytomining applications.