Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2003
Publication Date: 4/1/2003
Citation: Xu, J.M., Gan, J., Papiernik, S.K., Becker, J.O., Yates, S.R. 2003. Incorporation of fumigants into soil organic matter. Environmental Science and Technology. 37(7):1288-1291.
Interpretive Summary: Halogenated fumigants are some of the most heavily used pesticides worldwide. Previous studies have shown that these pesticides are degraded more rapidly in soil with high organic matter content. Relatively little is known about the pathway and the products of fumigant transformation. In this study, we determined that the fumigants 1,3-dichloropropene and methyl bromide formed irreversibly bound residues in soil. The formation of these residues represents a detoxification mechanism, since the transformation associated with the formation of bound residues renders the fumigant inactive. Different components of soil organic matter reacted with the fumigants to a different extent. These results suggest that incorporation into soil organic matter is the predominant pathway for halogenated fumigants in soil. These results will be useful in predicting the behavior of these pesticides following soil application. In addition, these results suggest that the addition of material high in certain soil organic matter components to the soil surface may minimize environmental contamination by these pesticides.
Technical Abstract: Halogenated fumigants are some of the most heavily used pesticides worldwide. A number of studies have shown that fumigant transformation in soil is correlated with soil organic matter content. However, relatively little is known about the mechanisms of fumigant interactions with soil organic matter. In this study, we used 14C-labeled 1,3-dichloropropene (1,3-D) and methyl bromide (MeBr) to characterize their incorporation into soil organic matter and the association of bound radioactivity with the different organic matter components. The 14C activity of bound residues increased with time and reached 38-49 percent for 1,3-D and 37-42 percent for MeBr after 72 d of incubation at 25 C. More bound residues were produced for 1,3-D than for MeBr in the same soil. The distribution of 14C activity in soil humic substances followed the order of fulvic acids>>humin>humic acids. These observations suggest that incorporation into soil organic matter is the predominant pathway for transformation of halogenated fumigants in soil and that fulvic acids are likely the most significant sink of all soil organic matter fractions. It is further speculated that bound residues formed as a result of alkylation of organic matter by the fumigants through nucleophilic replacement.