Effect Of Combined Arsenic And Lead Exposure On Their Uptake And Translocation In Indian Mustard

The problem of heavy metal pollution in soil has always been an important issue affecting the ecological environment and human health.However,there are many types of soil heavy metal pollutants brought by human activities,which have the characteristics of compound pollution.Both arsenic and lead have high biological toxicity,and are easily released into the soil environment with the mining and smelting activities of metal mines,thereby causing compound pollution of the soil and entering the human body with the food chain.Soil phytoremediation is a green and efficient method for remediation of heavy metal pollution in soil.It uses plants to selectively absorb heavy metals in the soil,thereby reducing the content of heavy metals in the soil.Super-enriched plants have better selective absorption capacity for certain specific elements,and they are usually important materials for soil phytoremediation.At present,most researches on the mechanism and application of super-enriched plants are mostly directed at single toxic elements,and relatively few reports on the mechanism of plant absorption related to compound pollution.Therefore,it is of great scientific exploration significance and application value to carry out research on the absorption and enrichment mechanism of multiple heavy metals under the compound exposure for plants with potential repair ability.In this study,Indian mustard with good enrichment ability for both Pb and As was selected as the research object.Single and joint exposure experiments of Pb and As under different concentration gradients were carried out,using techniques such as subcellular extraction and X-ray absorption spectroscopy.The characteristics and related mechanisms of Pb and As absorption and enrichment in Indian mustard under single and compound exposure were studied.The main progress has been made as follows:1)Compared with single element exposure,when Pb and As are both present,the absorption efficiency and transport coefficient of Pb and As in Indian mustard are significantly reduced.Under the combined exposure,the presence of Pb reduced the enrichment coefficient of As in Indian mustard by 91%-95%and the transport coefficient by 36%-88%;the presence of As reduced the enrichment coefficient of Pb by 13%-40%,The transshipment coefficient is reduced by 56%-84%;2)There is a negative correlation between the concentration of As and the concentration of divalent cations(such as Ca and Mg)in Indian mustard under joint exposure,indicating that there may be competitive absorption of As and these divalent cations,and this competitive absorption relationship may also be Pb There are reasons to reduce the absorption of As in Indian mustard;3)The results of the plant subcell sequential extraction experiment and X-ray absorption near-edge fine-structure spectroscopy of Indian mustard show that the mechanism of enrichment and detoxification of Indian mustard under the combined exposure of Pb and As is:Pb in Indian mustard is mostly composed of lead phosphate The form is fixed in the cell wall,and under the combined exposure,the presence of As reduces the production of lead phosphate precipitation to a certain extent;and Pb inhibits the absorption of As by Indian mustard by reducing the biological effectiveness of As;4)Competitive absorption of Pb and As and changes in element morphology and bioavailability of Pb and As at different parts of the plant and at the subcellular level are the main reasons leading to the reduction of As and Pb absorption efficiency of Indian mustard under exposure.