Thallium Pollution And Source Tracing Analysis Of Sediments In The Downstream Of A Steel-making Industry Zone,Northern Guangdong Province

Thallium(Tl)is a dispersal and rare element,it's toxicity is higher than Cd and Hg.The average content of Tl in continental and marine crusts is only 0.49 ?g/g and 0.013 ?g/g.Tl has both lithophile and sulphophile,so it can be enriched in different types of minerals such as pyrite and mica.With the development and utilization of mineral resources,different levels of Tl pollution have been found all over the world,but the existing research on Tl pollution mainly focuses on the mining and smelting areas,while fewer research paid attention to Tl pollution of steel-making plants.Previous studies of our group have shown that emissions from steel-making plant are an important potential source of Tl pollution in the environment.China is the world's largest steel producer,due to the long-term lack of supervision of Tl emissions of steel-making plant,there may be a large amount of Tl release to the environment with smelting wastewater,which poses a great threat to residents in the surrounding areas.Therefore,the research on heavy metal pollution such as Tl in the surrounding areas of steel-making plant is helpful to understand the migration and transformation of Tl in the steel smelting emissions,and provides an important theoretical basis for the prevention and treatment of Tl pollution in steel-making plant.Shaoguan City,with many large smelters and steel-making plants,is located in the upper reaches of the Beijiang River,and smelting emissions lead to the pollution of Tl and other heavy metals in the Beijiang River Basin.Three sediment profiles in the downstream,and smelting raw materials and wastes of a steel-making plant in Shaoguan City were collected in this study.The spatial distribution characteristics,pollution risk levels and sources of heavy metals pollution in sediments were studied by measuring the content of heavy metal and the Pb isotopic composition,the results show that:(1)The content of Tl and other heavy metals in sediments exceeds the background value of the crust,showing different levels of heavy metal pollution.The sources of heavy metals in the sediments of the upstream River A are complex and diverse,and the content of heavy metals is higher than that of downstream sediments;(2)The heavy metals risk assessment showed that Tl and other heavy metals in the three sediments were enriched and polluted above moderate level,and the pollution grade wasfollowed as Sb > Cd > Pb > Zn > Cu > Tl.The evaluation results of potential ecological risk index indicate that Tl and other heavy metals have different potential ecological risks to the environment and may be re-released to cause secondary pollution,which is a huge potential environmental hazard in this area;(3)The results of correlation analysis and principal component analysis show that Tl and other heavy metals in sediments are affected by human activities(4)The results of quantitative source analysis by Pb isotopes show that 77.6% – 80.9%of heavy metals in sediments are caused by human activities.The contribution rates of steel-making activities to heavy metal pollution in three sediments were 53.0%,35.7% and66.3%,respectively.Although the level of Tl pollution in the downstream of the steel-making industry zone is lower than the Pb-Zn smelter,the steel-making industry zone is also an important source of Tl pollution in the Beijiang River basin.It is necessary to strengthen the monitoring and control of Tl pollution from the steel-making plant.