Fractionation and Contamination Assessment of Zn, Cu, Fe, and Mn in the Sundarbans Mangrove Soils of Bangladesh

ABSTRACT

Metals, particularly Zn, Cu, Fe, and Mn are distributed amongst several geochemical forms, influencing their solubility, mobility and toxicity in soil-water systems. In this study, Sundarbans mangrove forest soils were analyzed by sequential fractionation to understand the distribution of these metals into exchangeable (Exch), organically bound (OrgB), Mn-oxide bound (MnOB), amorphous Fe-oxide bound (AFeOB), crystalline Fe-oxide bound (CrFeOB) and residual (Res) fractions. Soil Fe was predominately present in the residual fraction (55–73%), and manganese was primarily bounded in residual (29–58%) and MnOB (5–31%) fractions. The Res, CrFeOB and AFeOB fractions of Cu account for more than 80% of the total Cu. Zinc was mostly concentrated in the residual fraction and varied between 57 to 78% of the total Zn. Principal Component Analysis (PCA) and correlation studies revealed that exchangeable and organically bound fractions of these metals were significantly correlated, and their concentrations were highly dependent on soil pH, soil texture, organic carbon and redox potential (p < 0.05). Despite low total concentration, ratio of secondary phase and primary phase (RSP) and risk assessment code (RAC) studies showed that Cu (RSP is 1–2.64 and RAC is 1–2.89) and Mn (RSP is 1–2.42 and RAC is 1–16.66) were at low to moderate contamination risk and Fe maintained no contamination (RSP and RAC < 1) in almost all the soils. In contrast, Zn showed low contamination risk in some areas. This contamination can cause adverse effects on the plants and soil-dwelling organisms of Sundarbans mangrove forest due to higher availability.

KEYWORDS:

• Sundarbans mangrove forest
• trace metals
• sequential fractionation
• Fe-Mn oxides
• environmental risk

Acknowledgments

We are thankful to the Ministry of Science and Technology, Government of Bangladesh, for supporting this MS thesis research (National Science and Technology Fellowship: 2019-2020; Merit No.: 240).

Authors’ contributions

Md Mahfuz Islam and Dr. Zakia Parveen conceived and planned this experiment. Md Mahfuz Islam and Sayada Momotaz Akther carried out the experiment, performed data analysis, and wrote the manuscript with inputs from Dr. Zakia Parveen. Md Wahiduzzaman contributed to sample preparation, laboratory analysis, and manuscript preparation. Dr. Md Faruque Hossain was involved in experimental design and manuscript preparation. Zakia Parveen supervised this research.

Consent to participate

The article does not contain any studies with human participants or animals performed by any of the authors.

Consent to publish

We declare that this manuscript is original, has not been published before, and is not currently being considered for publication elsewhere.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.