Uptake and transport of Pb across the iron plaque of waterlogged dropwort (Oenanthe javanica DC.) based on micro-XRF and XANES
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Background and aim
Iron plaque at the soil-root interface is a key position for uptake of heavy metals by plants. Exploring iron plaque’s role in Pb uptake by edible vegetable roots aids understanding Pb uptake mechanisms and developing methods to reduce Pb accumulation.
Soil and plant Pb contents were determined. Micro X-ray fluorescence (micro-XRF) determined Fe and Pb distributions in waterlogged and terrestrial Oenanthe javanica DC. roots, and X-ray absorption near-edge spectroscopy (XANES) identified Pb speciation in bulk soil, rhizosphere soil and plant tissues.
Waterlogged O. javanica accumulated more Pb and exhibited a higher Pb transfer factor than terrestrial O. javanica. In waterlogged O. javanica, the iron plaque and epidermis contained the most Fe, while the root vasculature contained the most Pb. In terrestrial O. javanica roots, Fe and Pb had similar distributions. Bulk and rhizosphere soils contained different Pb species, and rhizosphere soil had Pb-humate. For iron plaque, a new Pb complex, Pb-ferrihydrite, was identified. Biologically important groups bound (-S, -COO) and precipitated (-PO4) Pb were identified in plants.
Waterlogged O. javanica root iron plaque and humic acid increase Pb uptake and accumulation. Thus, avoiding O. javanica root iron plaque formation (dry land growth) and growing in low-humic soil reduce Pb uptake and entry into the food chain.
KeywordsVegetable Oenanthe javanica DC. Iron plaque Lead (Pb) Uptake
micro X-ray fluorescence
X-ray absorption spectroscopy
X-ray absorption near-edge spectroscopy
Extended X-ray absorption fine structure spectroscopy
low-molecular-weight organic acids
Shanghai Synchrotron Radiation Facility
inductively coupled plasma mass spectrometry
inductively coupled plasma optical emission spectroscopy
Hoagland’s nutrient solution
This work was supported by the National Key Research and Development Program of China (Grant No. 2016YFC0600603), the National Natural Science Foundation of China (Grant No. 20775018, 41877505 and 41201527), the National High Technology Research and Development Program of China (Grant No. 2007AA06Z124) and the Project of China Geological Survey (Grant No. DD20160340). The Shanghai Synchrotron Radiation Facility is thanked for provision of beam time at beamlines 15 U1 and 14 W1. In addition, we thank associate Professor Yating Shen, Dr. Yuan Zeng and Dr. Xiaoyan Sun for their technical support during the experiments and data collection.
Compliance with ethical standards
Declarations of interest
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