Adsorption-desorption behavior of selected pesticides in some Western Australian soils

Abstract

The adsorption-desorption behaviour of four pesticides, in four Western Australian soils differing in their physico-chemical properties, has been studied using a batch technique. Sorption data for Fenamiphos, Linuron and Simazine could be fitted to a Freundlich-type equation, while that for Diquat more closely fitted the Langmuir equation. The value of the exponent in the fitted Freundlich isotherms varied from 0.70 to 1.00 for the various pesticide and soil combinations. Adsorption was found to be better correlated with organic matter than other soil properties, and decreased with increasing pH for all pesticides except Diquat. This study supports the observation of B. T. Bowman that the Freundlich equation in mole fraction form is more useful for comparing relative adsorption. Comparison of the present adsorption data with previous studies showed that the organic matter in these soils behaved differently in terms of pesticide adsorption. In particular, the octanol-water partition approach, for predicting the adsorption of non-ionic organic compounds, gave unsatisfactory predictions of Linuron and Fenamiphos adsorption in these soils. Desorption by a consecutive method showed hysteresis with all pesticide-soil combinations examined. The magnitude of the hysteresis was unaffected by changes in the soil : solution ratio. Using a dilution method, experimental procedures such as centrifugation and shaking have been shown to only slightly affect desorption hysteresis. The suggestion that hysteresis results from organic matter effectively 'locking in' the adsorbed pesticides is supported. The presence of methanol in the desorption solution results in swelling of organic polymers and facilitates the release of the adsorbed pesticides. Consequently, hysteresis was found to be essentially absent from the Linuron isotherm on removal of organic matter from the soil.

Adsorption and desorption processes of the organophosphorus pesticides, dimethoate and fenthion, onto three Greek agricultural soils

“…In any case hysteresis is dependent on the adsorption mechanism and on the chemical bonds and forces between the molecules of the adsorbate and the surface of the adsorbent [39]. According to the results contained in Tables 6 and 7, hysteresis was observed to be more evident for the soils with higher organic matter content, indicating that organic matter of the soil is the reason of hysteresis and this is in agreement with other published data [18,53]. Less obvious hysteresis occurred in the case of soils with low organic matter content implying that physical adsorption of pesticides proceed via weak interaction forces (such as London or dispersion forces) [18,54].…”

“…Furthermore experimental results of dimethoate's adsorption indicated that adsorption process of this OPP was not increased or even diminished with the increasing of soil organic matter content, which pointed the small role that OM played in dimethoate's retention, similar to other highly polar or ionisable pesticides [11,48,49]. These results and observations correspond with those of other researchers [11,49] who have reported that when organic carbon is low, there may be no relationship between adsorption of pesticides and organic matter, but other factors in the soil may play an important role, such as the inorganic matter [50][51][52], calcium concentration [53], and cation exchange capacity [53,54] and several other characteristics. Fenthion, which is a non-polar member of organophosphorus pesticides, followed the same pattern of adsorption onto the soils examined with dimethoate.…”

Sorption of Carbaryl (1-napthyl N-methyl carbamate) by Soil

“…As illustrated by the values of constants Kandl1/n,the decreasing sequence of the adsorption capacity of soils for carbaryl are Barokodali > Nalhati>Dudherkuthi> Bolpur which followed the same order as the order of organic matter content of the soils (Table 1 ).The results find support from some earlier studies (Khan et al 1987, Singh et al 1990, Adhikari et al 1991 the soils and follow the order:Dudherkuthi>Barokodali>Bolpur>Nalhati.The variable slopes of the sorption isotherms obtained for the different pesticide-soil systems studied reveal that pesticide sorption on soil is a complex phenomenon involving different types of adsorption sites with different surface energies (Felsot and Dahm 1979).…”

Kinetics and thermodynamics of adsorption of cadusafos on soils

“…Furthermore, adsorption of pesticides by soil is one of the major processes influencing their accessibility to target organisms, and their potential to reach non-target organisms. Adsorption may result in decreased biological activity, in enhanced rates of degradation, and in retardation in movement with leaching solutions [8]. While it has been recognized that laboratory studies may give different estimates of partitioning in comparison with field conditions [9], standard batch sorption procedures are still of value for initial estimation of sorption behavior, and in some cases have been shown to provide values comparable to field studies [10].…”