Abstract
Understanding the stability of chloropyromorphite (CPY) is of considerable benefit for improving risk assessment and remediation strategies in contaminated water and soil. The stability of CPY in the rhizosphere of phosphorus-deficient ryegrass was evaluated to elucidate the role of root-secreted low molecular weight organic acids (LMWOAs) on the dissolution of CPY. Results showed that CPY treatments significantly reduced the ryegrass biomass and rhizosphere pH. The presence of calcium nitrate extractable lead (Pb) and phosphorus (P) suggested that CPY in the rhizosphere could be bioavailable, because P and Pb uptake by ryegrass potentially provided a significant concentration gradient that would promote CPY dissolution. Pb accumulation and translocation in ryegrass was found to be significantly higher in P-sufficient conditions than in P-deficient conditions. CPY treatments significantly enhanced root exudation of LMWOAs irrigated with P-nutrient solution or P-free nutrient solution. Oxalic acid was the dominant species in root-secreted LMWOAs of ryegrass under P-free nutrient solution treatments, suggesting that root-secreted oxalic acid may be the driving force of root-induced dissolution of CPY. Hence, our work, provides clarifying hints on the role of LMWOAs in controlling the stability of CPY in the rhizosphere.
Highlights
The In situ immobilization of lead (Pb) in contaminated soils by phosphorus (P) -based materials including apatite minerals, nanosized hydroxyapatite, bone meal, bone char, inorganic phosphate, etc., has been considered as a promising remediation strategy, due to its low cost, high efficiency, easy-to-implement, and environmental friendly nature [1,2]
The results of this study show that the ryegrass rhizosphere pH was slightly lower than bulk pH under CPY treatments, which is in contrast to the results reported by Abbaspour and Arocena [38] even though more NO3- was supplied than NH4+
A decrease in the dry weight of ryegrass (Fig 2) induced by CPY treatments was in agreement with Abbaspour et al [37] who reported that the addition of CPY significantly decreased the dry weight production of Brassica juncea and Medicago sativa treated with P-free nutrient solution
Summary
The In situ immobilization of lead (Pb) in contaminated soils by phosphorus (P) -based materials including apatite minerals, nanosized hydroxyapatite, bone meal, bone char, inorganic phosphate, etc., has been considered as a promising remediation strategy, due to its low cost, high efficiency, easy-to-implement, and environmental friendly nature [1,2]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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