Adsorption of Herbicides on eight Agricultural Soils

A study was conducted to determine the differences in the adsorption behavior of three pesticides, nonionic atrazine [2-chloro-4-ethyl amino- 6-isopropylamino-1,3,5,-triazine], an ionic picloram [ 4- amino-3,5,6- trichloropicolinic acid] and anilide group propanil [N-3,4-dichlorophenyl) propanaamide] on eight agricultural soil samples. Data from batch equilibrium method revealed that the adsorption of herbicides on the selected soil samples followed the first order rate law. Propanil exhibited the faster rate of accumulation with 24.82% adsorption on the soil solid matrix after 0.5h as compared to that for picloram and atrazine 18.98%, 13.9% respectively. The standard error (S.E) values were from 0.034 to 1.000, 0.007 to 0.983 and from 0.691 to 0.859 for atrazine, picloram and propanil respectively. Linear, Freundlich and Langmuir models were used to describe the adsorption of the three pesticides. Values of distribution coefficient (Kd) indicated moderate to low adsorption for atrazine (mean calculated Kd: 1.1597 mlg-1) while slightly higher for picloram (mean calculated Kd: 1.5779 mlg-1) and highest for propanil adsorption (mean calculated Kd: 12.662 mlg-1) and consequently there is no considerable risk of ground water contamination. Wide variation in adsorption affinities of the soils to the pesticides was observed, Kd values for atrazine varied between 0.951 and 1.53 mlg-1 while for picloram between 0.99 and 2.309 and for propanil between 9.044 and 16.56 mlg-1.