Register      Login
Soil Research Soil Research Society
Soil, land care and environmental research
RESEARCH ARTICLE

Complexation and release isotherm of arsenic in arsenic-humic/fulvic equilibrium study

D. Mukhopadhyay A B and S. K. Sanyal A C
+ Author Affiliations
- Author Affiliations

A Department of Agricultural Chemistry and Soil Science, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal – 741 252, India.

B Current address: UBKV, Pundibari, Coochbehar, West Bengal – 736 165, India.

C Corresponding author. Email: sarojsanyal@hotmail.com

Australian Journal of Soil Research 42(7) 815-824 https://doi.org/10.1071/SR03104
Submitted: 19 July 2003  Accepted: 20 May 2004   Published: 12 November 2004

Abstract

Soil organic fractions were extracted from 2 surface soils of West Bengal, one of which was arsenic-contaminated, and were fractionated into fulvic and humic acid fractions following standard procedures. These, and one humic acid sample synthesised in the laboratory, were characterised by pH-potentiometric titrations, viscometric measurements, visible spectrophotometry, and surface tension determinations. The results have been correlated with coiling–decoiling behaviour, as well as aliphatic/aromatic balance of these acids. The stability constant (logK) of the complexes formed by these natural humic/fulvic and synthetic humic acids with arsenic in aqueous phase was evaluated by the ion-exchange method. These logK values tend to suggest that the organo-arsenic complexes were quite stable. Further, the logK values displayed an approximately inverse relationship with the viscosity-average molecular weight, excess time needed to attain a stable higher pH during the pH-potentiometric titration, and also the surface excess (in water) of the given humic/fulvic acid samples. These trends were explained in terms of the relative hydrophobic character of the acids, and their resultant tendencies to complex arsenic in the aqueous phase.

The release potential of arsenic from the arsenic–humic/fulvic complexes by soluble phophate and nitrate salts was also examined in terms of the appropriate exchange isotherms. In general, phosphate demonstrated a greater degree of exchangeability with arsenic than did nitrate, at both the lower and higher concentrations.

Additional keywords: arsenic–humic/fulvic complex, isotherms, stability constant.


Acknowledgments

The financial assistance of the Indian Council of Agricultural Research, New Delhi, India during the entire course of the study is gratefully acknowledged.


References


Abedin MJ, Cresser MS, Meharg AA, Feldmann J, Cotter-Howells J (2002) Arsenic accumulation and metabolism in rice (Oryza sativa L.). Environmental Science and Technology 36, 962–968.
Crossref | GoogleScholarGoogle Scholar | PubMed |

Young SW, Bache BW, Linehan DJ (1982) The potentiometric measurement of stability constants of soil polycarboxylate-Cu2+ - chelates. Soil Science 33, 467–475. open url image1