Fulvic acids from Amazonian anthropogenic soils: Insight into the molecular composition and copper binding properties using fluorescence techniques

Three-year field experiments revealed the immobilization effect of natural aging biochar on typical heavy metals (Pb, Cu, Cd)

Biochar has been widely used for the remediation of heavy metal contaminated soil, while the long-term field aging on its properties and the performance in the ability of metal immobilization must not be overlooked. In this study, the stability of immobilized heavy metals (Cd, Cu, Pb) on biochar during a 3-year remediation for soil in the field was investigated through desorption experiments. The results indicated that the application of biochar and its aging in the field both remarkably increased the immobilization of the 3 metal ions in the field under 3-year remediation. The cumulative desorption of the 3 metals decreased with biochar aging, and the desorption rate of Pb2+, Cu2+ and Cd2+ in T3 (Application of 30 t·hm-2 of biochar) for the third year was 0.08 %, 0.20 % and 13.15 %. Meanwhile, both the desorption rates and extents exhibited significant difference with the order of Pb2+ < Cu2+ < Cd2+. The increased soil pH, the enhancement of O/C ratio (Increase from 0.30 for fresh BC to 0.61 for aged BC(S3)) and oxygen-containing functional groups in biochar, and the accretion of organo-mineral micro-agglomerates on biochar surfaces and in pores during field aging process jointly contributed the immobilization of metals in soils mainly through co-precipitation and complexation. Our results provide new insights into the practical application of biochar in soils contaminated with multiple heavy metals from the perspective of long-term effects, which suggests that the potential release risk of metals become slighter over time.

Applying fulvic acid for sediment metals remediation: Mechanism, factors, and prospect

Fulvic acid (FA) has been shown to play a decisive role in controlling the environmental geochemical behavior of metals. As a green and natural microbial metabolite, FA is widely used in environmental remediation because of its good adsorption complexation and redox ability. This paper introduces the reaction mechanism and properties of FA with metals, and reviews the progress of research on the remediation of metal pollutant by FA through physicochemical remediation and bioremediation. FA can control the biotoxicity and migration ability of some metals, such as Pb, Cr, Hg, Cd, and As, through adsorption complexation and redox reactions. The concentration, molecular weight, and source are the main factors that determine the remediation ability of FA. In addition, the ambient pH, temperature, metal ion concentrations, and competing components in sediment environments have significant effects on the extent and rate of a reaction between metals and FA during the remediation process. Finally, we summarize the challenges that this promising environmental remediation tool may face. The research directions of FA in the field of metals ecological remediation are also prospected. This review can provide new ideas and directions for the research of remediation of metals contaminants in sediments.

Field-scale fluorescence fingerprints of biochar-derived dissolved organic matter (DOM) provide an effective way to trace biochar migration and the downward co-migration of Pb, Cu and As in soil

Although the benefits of biochar amendment for heavy metal(loid) immobilization in soil have been widely recognized, its migration in soil and the resultant effects on the risk of downward migration of metal(loid)s are still poorly understood. In this study, based on biochar derived dissolved organic matter (DOM), excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) technique was employed to trace biochar migration within one year in 0-100 cm soil profiles in the field. The vertical co-migration of Pb, Cu and As was also analyzed. With biochar amended, DOM, humification index (HIX) and biological index (BIX) in 0-60 cm soil profiles increased significantly, while pH only increased in the topsoil. The identified water-extracted DOM components showed that biochar could enhance the content of fulvic acids and humic acids in soil DOM and biochar might migrate downward to 60 cm soil profiles. Furthermore, toluene/methanol-extracted DOM also confirmed the migration extent of biochar, which was more suitable to trace biochar migration because of its high resistance to the long-term ageing in the field. Moreover, we found that biochar reduced the content of Cu in 0-60 cm soil profiles, but increased the available Pb and As in the 20-40 cm soil layers. The Pearson's correlation study confirmed a strong correlation (0.568**≤R ≤ 0.803**) between the content of heavy metal(loid)s and humic-like components of soil DOM, which suggested that biochar co-migrated with Pb, Cu and As, and the potential environmental risks of biochar should be fully evaluated while it was applied for soil metal(loid) remediation.

Process and mechanism between water-extracted organic matter and trace metallic ions in sediments of Yangtze River estuary

In order to better understand the bioavailability, toxicity, migration and transformation behaviors of trace metals in river estuary, this study deeply investigated the interactions between organic matters in sediments and trace metals. The results suggested that both protein-like molecules and marine humic acids could react with trace metals (Cu²⁺ and Cd²⁺). These two fluorescent substances fixed trace metals through carboxyl group, hydroxyl group, and phenol hydroxyl group, and protein-like molecules were more sensitive than marine humic acids. Moreover, Cu²⁺ possessed stronger binding ability and more active sites with both protein-like molecules and marine humic acids. Hence, Cd²⁺ exhibited higher environmental risks due to the higher migration and transformation. The thermodynamic results revealed that the reaction between WEOM and trace metals was spontaneous and exothermic, and low temperature was favorable for immobilization of Cu²⁺ or Cd²⁺.This study could help to understand environmental behaviors and impact of trace metals on the sediments of Yangtze River estuary.