Abstract
This study was undertaken to investigate distribution, fractionation, bioavailability and remobilization characteristics of bound soil-aged carbofuran and the effect of ageing in clay soil in a typical field of sugar beet at Loukkos in northwest Morocco. Results indicate that initially there were high levels of bound residues (BR) in the humin fraction, which decreased with incubation time and ageing of the BR. While in the fulvic and humic acid fractions, the amount of BR increased with the ageing of the BR and occurred predominantly (60%) in the fulvic acid fraction. The possibility of the mineralization and release of BR with ageing was studied using fresh soil and an incubation period of 90 days. The results indicate that the ageing of the residues have a great influence on the remobilization and mineralization rates of carbofuran BR; 9.45 to 14.90% of the total BR was released as extractable residues, and 1.95 to 4.15% was mineralized depending on the age of the residues in soil and the soil-aged carbofuran BR. The incorporation of the residues in the humin fraction is considered to be a threat to the environment. On the other hand, the clear prevalence of residues in the fulvic and humic acid fractions, may have an important effect on their bioavailability and movement in soil. Moreover, the re-extractability of BR could pose a potential environmental risk. Consequently, the BR remobilized must be taken into account when assessing for registration processes the environmental risk of pesticides persisting in soils.
Highlights
Previous investigations show that pesticides bind almost irreversibly with soil constituents, including organic compounds, resulting in the formation of non-extractable bound residues (Führ 1987; Calderbank 1989; Khan and Behki 1990; Gevao 2000; Nowak et al 2011; Liu et al 2013; Kästner et al 2014)
The result showed that initially the bound residues were mainly in the humin fraction with more than 50% of the BRs. These residues were released from the humin fraction and incorporated into humic fractions, i.e. fulvic acid (FA) and humic acid (HA), with most in the FA fraction (Fig. 1)
This study investigated the fate of carbofuran BR and the influence of ageing on the extent to which they are bound into organic matter fractions and their bioavailability
Summary
Previous investigations show that pesticides bind almost irreversibly with soil constituents, including organic compounds, resulting in the formation of non-extractable bound residues (Führ 1987; Calderbank 1989; Khan and Behki 1990; Gevao 2000; Nowak et al 2011; Liu et al 2013; Kästner et al 2014). These chemical entities are defined as pesticide residues that are not extractable using current methods. This is the result of changes in the stabilization process of the sorption phenomena from weak to strong adsorption sites and diffusion and sequestration or entrapment by sites, during which pesticides and their degradation products become increasingly more stable and less available (Bertin and Schiavon 1989; Senesi 1992; Loiseau 2001; Barriuso and Benoît 2006)
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