Amount Of Bound Residues Research Articles

Fate characterization of bound residues of 14C-Pyraoxystrobin in soils

Formation of bound residues (BR) has generally been considered as a detoxification process for organic contaminants. BR is an indispensable component for risk assessment of pesticides. In this study, BR of 14C-pyraoxystrobin in three soils cultivated for 100 days were characterized in light fraction (LF), loosely combined humus (LCH), stably combined humus (SCH), humic acid (HA), fulvic acid (FA), and humin. Isotope labeling technique was used to detect the distribution of BR of 14C-pyraoxystrobin in the six fractions of soil organic matter (SOM). The results showed that the amount of total BR was positively correlated with the SOM content (p < 0.05). The BR of 14C-pyraoxystrobin in cambisol soil was largest at 31.26 ± 0.04% of the induced radioactivity. During the whole incubation period, the BR of pyraoxystrobin in LCH of the three soils were consistently higher than that in SCH, and the amount of BR in FA was consistently greater than that in HA. The BR of 14C-pyraoxystrobin bound with humin increased over time. In addition, a degradation product 3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-ol (M1) from the hydrolysis of pyraoxystrobin was detected in cambisol soil, indicating the bonding of M1 with the HA separated from LCH (HALCH) via ester or ether linkages. The results provide new insights into the fate of BR of pyraoxystrobin in soils and may help to develop an understanding for the risk assessment of pyraoxystrobin and other strobilurin fungicides.

Study of atrazine fate in silty loamy soils of the Paris Basin via a combination of isotopic and pyrolytic methods

The fate of organic micro-pollutants in soil largely depends on their interactions with soil organic matter (SOM). Indeed, the intensity and nature of such interactions are major factors in the control of micro-pollutant bioavailability, and hence degradation and micro-pollutant mobility in the environment [Khan and Hamilton, 1980 ; Calderbank, 1989 ; Dec et al., 1990, 1997 ; Barriuso and Koshinen, 1996]. Residual micro-pollutants, i.e. the remaining micro-pollutants and their various transformation products (metabolites), occur in soil both in the water phase and associated with the solid phase. A part of these associated molecules, termed bound residues (BRs), cannot be released via extraction with water or organic solvents like methanol. SOM plays a major role in BR formation [e.g. Loiseau et al., 2000] and different types of interaction (like covalent bonds and trapping in organo-mineral aggregates) can be implied [Hsu and Bartha, 1976 ; Schiavon et al., 1977 ; Bollag et al., 1992 ; Dec and Bollag, 1997 ; Steinberg et al., 1987; Providenti et al., 1993]. The present study is concerned with the fate of atrazine in three silty loamy soils from the Paris Basin. Atrazine is largely used (ca. 5000 T/year in France) as herbicide for maize cropping and may cause important pollution problems through transfer to water resources.