Dissolved humic substances supplied as potential enhancers of Cu, Cd, and Pb adsorption by two different mangrove sediments

Abstract

Purpose The external supply of humic substances has been recently suggested for the remediation of metal-polluted sediments; however, little is known about how to supply them and their effects on metal mobility. The study sought to investigate the sediment-metals-humic substance interaction in mangrove forest sediments. We aimed to evaluate the sediment adsorption potential in the case of large and rapid metal loads, as recently occurred in the Doce River (Brazil). Materials and methods In each mangrove forest sampling point of the Benevente River (RB) and Vitoria bay (MO), sediments were collected randomly along the river banks at a depth of 0-10 cm. Samples were characterized in terms of pH, CEC, organic carbon, texture, specific surface area, and elemental composition. The heavy metal content was measured by mass absorption spectrophotometry. Humic substances were extracted from the sediments according to the International Humic Substances Society (IHSS) method, avoiding separation of fulvic and humic acids. Original sediments were supplemented with humic substances and six Cu, Cd, or Pb concentrations. Freundlich and Langmuir equations were employed to create adsorption isotherms. Results and discussion The two sediments are significantly different, specifically with regard to organic carbon and Fe content, texture, and specific surface area. External humic substances increased the Cu adsorption capacity in both sediments but without an important change in Cu adsorption dynamics. Humic substances slightly increased the sediment adsorption capacity of Pb in RB sediment while they decreased in MO sediment, characterized by lower specific surface area, probably due to coverage of the active adsorption sites. Cd isotherms showed that the different characteristics of sediments alone do not affect Cd adsorption, but coupled with humic substances; Cd affinity for the soil surface increased five times in RB sediments confirming sediment-metalhumic substance interactions. Conclusions Humic substances affect soil metal retention mainly by altering the ion affinity for sediment surface, leading to contrasting results. The Fe concentration could be important depending on specific surface area and humic substance percentage, due to its capacity to form spheroids linked to molecules of humic substances on the clay surface. Several works have been carried out on this research area, but due to the many variables and different metal ions, we recommend further studies.

Use of Biostimulants as a New Approach for the Improvement of Phytoremediation Performance—A Review

“…HSs can also influence the fate of toxic substances by regulating their transport and stabilization in soil and, consequently, their effect on plants and soil-populating bacteria [ 78 ]. Pittarello et al [ 93 ] exploited this behavior towards mangrove sediments and found that the sediments’ absorbing capacity of copper (Cu), cadmium (Cd), and lead (Pb) was significantly increased by the addition of HSs. In another study, the same authors tested the effect of different dosages of HS PBs in mangrove ( Avicennia germinans ) seedlings grown in Cd-contaminated solutions [ 94 ].…”

Mobility and Fate of Potentially Toxic Elements in Soil Environment

“…The uptake of PTEs increases with the addition of HA because HA contains several anionic functional groups namely hydroxyl (─OH) and carboxyl (─COOH), which can act as a ligand to complex with PTE ions. [ 57,58 ] These results demonstrate that soils with high contents of OM such as mangrove ecosystems, [ 59–61 ] tend to adsorb more PTEs.…”

“…[94][95][96] The highest percentage of the OM content at pH 5.5 was ≈30% which was detected in the subtropical mangrove ecosystem. [59][60][61] In this study, PTEs adsorption experiments were conducted by varying the OM content at 0%, 10%, and 30% with changes of PTEs concentrations ranging from 0 to 500 mg L −1 for six PTEs. In 100 mL conical flasks containing the specific concentration of a PTE, 1 g of finegrained soil (i.e., 0% OM), 0.9 g of fine-size soil and 0.1 g HA (i.e., 10% OM) or 0.7 g of fine size soil and 0.3 g HA (i.e., 30% OM) were added to each flask.…”

Thinking for the future: Phytoextraction of cadmium using primed plants for sustainable soil clean‐up

“…Cd complexation with chloride ion increases with salinity unit and different Cd species can be formed depending on the Cl − concentration: CdCl + , CdCl 2 0 , CdCl 3 − , CdCl 4 2− (Kubier et al, 2019). In organic‐rich waters, sorption of Cd by humic substances plays an important role in the speciation of Cd; the more humic substances, the less Cd in water (Pittarello et al, 2019).…”