Research status and development trend of causes of thallium pollution in surface water and soil environment
Thallium(Tl)is considered one of the most toxic heavy metal elements,more toxic to humans than Hg,Cd,Pb,Zn and Cu.This paper summarized the elemental characteristics of Tl and its geochemical behavior,the global distribution of Tl deposits and metallogenic epoch,compared and analyzed the differences in the distribution of Tl in rocks,and systematically reviewed the toxicology and pathogenic mechanism of Tl,Tl pollution source analysis and tracing,and Tl migration and transformation in the hypergene environment.It is found that Tl is distributed in the three major types of rocks,but Tl in magmatic rocks shows regular distribution.Tl is strongly associated with hydrothermal deposits and is mainly enriched in Pb,Zn,Sb,Hg,As and other deposits associated with low-temperature hydrothermal deposits,and it is preferred to enter sulfide melts,resulting in higher Tl concentrations in sulfide-bearing deposits.In general,the distribution of soil Tl pollution and Tl minerals in China has the characteristics of"high in the south and low in the north",indicating that Tl pollution is significantly related to the mining and smelting of Tl deposits.Tl in water mainly migrates as Tl+,which can replace K+into clay minerals or oxidize into Tl3+through microbial action.After Tl enters the plant through the plant root system from the soil,it will be unevenly distributed in the plant.203Tl is more likely to diffuse dynamically to the cell membrane surface.Plant roots preferentially absorb lighter Tl isotopes(203Tl),and heavier Tl isotopes(205Tl)remain in the growth layer.By comparing the Pb isotope and Tl isotope tracer techniques,it is found that the Tl isotope method has the advantages of fast response and strong sensitivity for the source and migration process of tracer materials,but the improvement of Tl isotope technology needs to be further improved by the Tl isotope database.Spatio-temporal simulation of Tl pollution formation and evolution is an important means to reveal pollution sources,pollution processes and development trends,and to carry out regional risk assessment.However,data acquisition,model selection and verification,uncertainty analysis,system integration and decision support need to be further studied.
thalliumoccurrence stategeochemical behaviormigration and transformationsource analysis
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