Abstract
Karst water is rich in calcium ions (Ca2+) and exhibits poor metal availability and low biodegradation efficiency. This study sought to analyze the effects and mechanisms of Ca2+ on lead (Pb) removal and absorption by Eichhornia crassipes (a floating plant common in karst areas). Moreover, the morphology and functional groups of E. crassipes in water were characterized via SEM, and FTIR. The results demonstrated that the removal rate of Pb in karst water (85.31%) was higher than that in non-karst water (77.04%); however, the Pb bioconcentration amount (BCA) in E. crassipes roots in karst water (1763 mg/kg) was lower than that in non-karst water (2143 mg/kg). With increased Ca2+ concentrations (60, 80, and 100 mg/L) in karst water, the Pb removal rate increased (85.31%, 88.87%, and 92.44%), the Pb BCA decreased (1763, 1317, and 1095 mg/kg), and the Ca BCA increased (6801, 6955, and 9368 mg/kg), which was attributed to PbCO3 and PbSO4 precipitation and competitive Ca and Pb absorption. High Ca2+ concentrations increased the strength of cation exchange, alleviated the fracture degree of fibrous roots, reduced the atrophy of vascular bundles, protected the cell wall, promoted C–O combined with Pb, enhanced the strength of O‒H, SO42−, C=O, and reduced the oxidization of alkynyl acetylene bonds.
Highlights
Karst water quality has begun to deteriorate in recent years due to increased industrial mining, agriculture, and other human activities
This study demonstrated that problem. Lead (Pb) had low toxicity on E. crassipes roots, which was attributable to the high Ca2+ concentrations in karst water
The highest bioconcentration factor and the lowest transport factor of Pb occurred in 80 mg/L Ca2+ karst water
Summary
Karst water quality has begun to deteriorate in recent years due to increased industrial mining, agriculture, and other human activities. E. crassipes has broad, thick, glossy, ovate leaves and stems, which are important for photosynthesis, food production, gas exchange, and water transpiration [7] This plant is known to adapt to a wide variety of environmental conditions and even grows well in sewage water. Concentrations in karst water may be responsible for the higher heavy metal bioaccumulation capacity of some aquatic plants in karst waters than that in other environments [19]. This study employed Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectrometry (FTIR), and other methods to investigate the Pb removal efficiency and absorption capacity of E. crassipes in karst and non-karst water at different Ca2+ concentrations. Pb-induced stress, and provides a theoretical basis for the effective application of E. crassipes for Pb remediation in polluted karst water
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