Sorption and desorption kinetics of diuron, fluometuron, prometryn and pyrithiobac sodium in soils.
The sorption and desorption characteristics of four herbicides (diuron, fluometuron, prometryn and pyrithiobac-sodium) in three different cotton growing soils of Australia was investigated. Kinetics and equilibrium sorption and desorption isotherms were determined using the batch equilibrium technique. Sorption was rapid (> 80% in 2 h) and sorption equilibrium was achieved within a short period of time (ca 4 h) for all herbicides. Sorption isotherms of the four herbicides were described by Freundlich equation with an r2 value > 0.98. The herbicide sorption as measured by the distribution coefficient (Kd) values ranged from 3.24 to 5.71 L/kg for diuron, 0.44 to 1.13 L/kg for fluometuron, 1.78 to 6.04 L/kg for prometryn and 0.22 to 0.59 L/kg for pyrithiobac-sodium. Sorption of herbicides was higher in the Moree soil than in Narrabri and Wee Waa soils. When the Kd values were normalised to organic carbon content of the soils (Koc), it suggested that the affinity of the herbicides to the organic carbon increased in the order: pyrithiobac-sodium < fluometuron < prometryn < or = diuron. The desorption isotherms were also adequately described by the Freundlich equation. For desorption, all herbicides exhibited hysteresis and the hysteresis was stronger for highly sorbed herbicides (diuron and prometryn) than the weakly sorbed herbicides (fluometuron and pyrithiobac-sodium). Hysteresis was also quantified as the percentage of sorbed herbicides which is not released during the desorption step (omega = [nad/nde - 1] x 100). Soil type and initial concentration had significant effect on omega. The effect of sorption and desorption properties of these four herbicides on the off-site transport to contaminate surface and groundwater are also discussed in this paper.
Baskaran
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Department of Agricultural Chemistry and Soil Science, University of Sydney, NSW, Australia.
Kennedy
I R
IR
D000327:Adsorption; D001565:Benzoates / Q000737:chemistry; D004237:Diuron / Q000737:chemistry; D006540:Herbicides / Q000737:chemistry*; D007700:Kinetics; D008782:Methylurea Compounds / Q000737:chemistry; D011400:Prometryne / Q000737:chemistry; D012307:Risk Factors; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical
D001565:Benzoates; D006540:Herbicides; D008782:Methylurea Compounds; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D011400:Prometryne; C005015:fluometuron; C401888:pyrithiobac sodium; D004237:Diuron