Chlorothalonil in a Quartz Sand Soil:  Wetting Effects on Sorption Capacity and Bound Residue

Abstract

Chlorothalonil has been found to persist but not leach in some quartz sandy soils. For this effect to be understood, it is necessary for the numbers of occupied and empty surface sorption sites to be known. This requires that the labile surface sorption capacity θC, which is the total number of sites, be measured. Wetting effects might however, affect θC. The measurement of θC has been done only recently by very few laboratories, and the wetting effects have seldom been investigated. New analytical chemical methods are therefore required. On − line HPLC micro extraction has been used in the present work to develop a method for the titration of chlorothalonil onto the labile surface sorption sites. Two conclusions have been drawn from the measurements. The first is that θC is one to 2 orders of magnitude greater than it is for the previously reported cases. Second, the effect of wetting on bound residue formation reported by Belliveau and Langford () has been confirmed. These effects help to explain the behavior of chlorothalonil in the quartz sandy soils.

Propanil in a Manitoba soil: an interactive spreadsheet model based on conventional chemical kinetics

“…Sparks has emphasized the importance of the kinetics and mechanisms. 7 Consistent with these other reports, [6][7][8][9][10][11][12][13][14][15][16][17][18] the experimental curves in Fig. 1 show that sorption, desorption, and chemical reaction were all strongly dynamic.…”

“…7 Several authors have reported the dynamic nature of pesticide behaviour in soils. [8][9][10][11][12][13][14][15][16][17][18] They all reported that the pesticide interactions with soils changed with time during their experiments, so that equilibrium calculations would not have been valid. Because independent studies with different combinations of pesticides and soils were used, the phenomenon is evidently quite general.…”

Sorption behaviour of diuron under a mediterranean climate

“…Different authors have pointed out an increase in pesticide bioavailability and extractability with an increase in soil moisture (Gaillardon, 1996;Gaillardon and Dur, 1995;García-Valcárcel and Tadeo, 1999;Scott and Lutz, 1971) or with soil saturation (Rutherford and Chiou, 1992). On the contrary, Berglöf et al (2000) reported that sorption coefficients (Kd) of linuron slightly increased with an increasing soil water content, if less than saturated, and Gamble et al (2000) concluded that wetting of soil favoured 302 X. Louchart et al the formation of bound residues of chlorothalonil in a quartz sandy soil.…”

Studying Organic Matter Molecular Assemblage within a Whole Organic Soil by Nuclear Magnetic Resonance

“…A recent paradigm shift in the view of natural organic matter (NOM), including SOM, has taken place and stresses the importance of loose molecular assemblage of the components that make up NOM. It also exposes the major perturbations that isolating and separating SOM into humic and fulvic acid, and humin fractions has on the materials, and limits the degree to which meaningful comparison can be made between these fractions and SOM present in a whole soil In fact, the literature strongly indicates that SOM assemblage plays a major role in the behavior of in situ SOM, as it has been shown that: (i) organic matter fractions do not behave like a whole soil (Salloum et al, 2001; Todoruk et al, 2003; Borisover and Graber, 2004; Chilom et al, 2005); (ii) SOM solvation–a bulk property–affects interactions of organic compounds with SOM (Graber and Borisover, 1998; Belliveau et al, 2000; Gamble et al, 2000a,b; Borisover et al, 2001; Borisover and Graber, 2002); (iii) organic matter can be liberated from soil by perturbation of the assemblage, e.g., metal complexing agents (break cation bridges) and root exudates (break hydrophobic interactions) (Nardi et al, 2000; Yang et al, 2001), and (iv) H 2 O and dimethyl sulfoxide change the mobility of different SOM moieties (Simpson et al, 2001). Note that in situ is used here to indicate that the SOM is still in its native matrix, while ex situ indicates that the SOM has been removed from its native matrix and fractionated (thus having lost its association with other fractions).…”