Effect of organic carbon chemistry on sorption of atrazine and metsulfuron-methyl as determined by (13)C-NMR and IR spectroscopy.
Soil organic matter (SOM) content is the major soil component affecting pesticide sorption. However, recent studies have highlighted the fact that it is not the total carbon content of the organic matter, but its chemical structure which have a profound effect on the pesticide's sorption. In the present study, sorption of atrazine and metsulfuron-methyl herbicides was studied in four SOM fractions viz. commercial humic acid, commercial lignin, as well as humic acid and humin extracted from a compost. Sorption data was fitted to the Freundlich adsorption equation. In general, the Freundlich slope (1/n) values for both the herbicides were <1. Except for atrazine sorption on commercial humic acid, metsulfuron-methyl was more sorbed. Desorption results suggested that atrazine was more desorbed than metsulfuron-methyl. Lignin, which showed least sorption of both the herbicides, showed minimum desorption. Sorption of atrazine was best positively correlated with the alkyl carbon (adjusted R (2) = 0.748) and carbonyl carbon (adjusted R (2) = 0.498) but, their effect was statistically nonsignificant (P = 0.05). Metsulfuron-methyl sorption showed best positive correlation with carbonyl carbon (adjusted R (2) = 0.960; P = 0.05) content. Sorption of both the herbicides showed negative correlation with O/N-alkyl carbon. Correlation of herbicide's sorption with alkyl and carbonyl carbon content of SOM fractions suggested their contribution towards herbicide sorption. But, sorption of metsulfuron-methyl, relatively more polar than atrazine, was mainly governed by the polar groups in SOM. IR spectra showed that H-bonds and charge-transfer bonds between SOM fraction and herbicides probably operated as mechanisms of adsorption.
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
Anirban
A
Dutta
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
Abhishek
A
Mandal
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
Suman
S
Manna
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India.
S B
SB
Singh
Forschungszentrum Juelich GmbH, Institute of Bio- and Geosciences, Agrosphere (IBG-3), 52425, Juelich, Germany.
Anne E
AE
Berns
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India. drneerasingh@yahoo.com.
Neera
N
Singh
D000327:Adsorption; D001190:Arylsulfonates / Q000032:analysis* / Q000737:chemistry; D001280:Atrazine / Q000032:analysis* / Q000737:chemistry; D002241:Carbohydrates / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods*; D006812:Humic Substances / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D013055:Spectrophotometry, Infrared
D001190:Arylsulfonates; D002241:Carbohydrates; D006812:Humic Substances; D012987:Soil; D012989:Soil Pollutants; C050296:metsulfuron methyl; D001280:Atrazine
13C-NMR spectroscopy; Humic acid; Humin; IR spectroscopy; Lignin