Fate Of A Novel Strobilurin Fungicide Pyraoxystrobin In Flooded Soil

Pyraoxystrobin, ((E)-2-(2-((3-(4-chlorophenyl)-1-methyl-1H-pyrazole-5-yloxy) methyl)) phenyl)-3-methoxyacrylate) is a novel strobilurin fungicide with excellent and broad spectrum antifungal efficiency. Environmental behaviors of the new fungicide must be assessed to understand its potential risks to environment. However, the study about the behavior of pyraoxystrobin in the flooded soil has not reported. In this study, the. extractable residues, bound residues and mineralization, as well as the dissipation rates of pyraoxystrobin were investigated in three flooded soils using 14C tracing technique. Flotation followed by sequentially extraction was applied to the soils containing BR of pyraoxystrobin to study the distribution of BR in soil light fractions (LF), loosely combined humus (HI), stably combined humus (H2) and refractory soils (H3). Acid precipitation was performed for the separation of humic acid (HA) and fulvic acid (FA) in each extracts. The total organic carbon content of HA and FA and the radioactivity associated with the separated organic matter were also measured. This study aims to give a deep insight into the environmental behavior of pyraoxystrobin and may be beneficial to the risk assessment for other analogous fungicides.Results showed that pyraoxystrobin didn’t undergo appreciable dissipation during the 100-d incubation in some tested soils, with the amount of 70.01%,28.58% and 83.85% parent compound remaining in the solonchak (soil A), cambisol (soil B), and acrisol soil (soil C) at the end of the incubation, respectively.Almost no 14C-pyraoxystrobin was mineralized to 14CO2 (< 0.5%) over the experimental period.Less than 9% of the radioactivity was distributed to aqueous phase, while the majority of extractable residues (> 65.39%) were recovered in the organic extracts. Organic matter had a dominating influence on the bound residues formation and the fractions of bound residues increased as the soil organic matter content increased. Almost no radioactivity was determined in the LF in all the tested soils over the incubation period. The distribution of BR in H1, H2 and H3 was increased with the incubation time and the level of BR associated with H1 was greater compared to H3 and H2 in the three soils. The radioactivity associated with FA was consistently higher than that in HA. For example, at the end of incubation, about 4.21% and 1.65% of applied 14C-pyraoxystrobin associated with NaOH extractable FA and NaOH/Na4P2O7 extractable FA in soil A, respectively, which was much greater than that associated with NaOH extractable HA (1.10%) and NaOH/Na4P2O7 extractable HA (0.94%) in the same soil. The H2 was more efficient than H1 for the formation of BR in soil A. The enrichment capacity of HA extracted by NaOH in soil B was much higher than that of HA in other soils. The low enrichment values in soil C may partly account for the low proportion of BR in this soil.