Effect of Seasonal Variation on the Persistence and Dissipation Behaviour of the Herbicide Mixture of Fomesafen + Quizalofop-Ethyl in Tropical Soybean Agroecosystem and Safety Risk Assessment

10 Weeds are the major limiting factor for optimum soybean production in India. The herbicide mixture of fomesafen 11 and quizalofop-ethyl provides effective control of a broad spectrum of weeds, but its fate in the tropical soybean 12 ecosystem is unknown and also the risks involved to the consumer and the environment are still unexplored. Hence, 13 a supervised field trial was conducted following the post-emergence application of fomesafen 12% + quizalofop- 14 ethyl 3% in two consecutive seasons. The dissipation of fomesafen followed biphasic double first order in parallel 15 kinetics, whereas quizalofop-ethyl dissipation followed first order kinetics. A significant difference in the 16 persistence of fomesafen was observed due to seasonal variation of meteorological parameters. However, the 17 variation was significant only in plant, but non-significant in soil, in case of quizalofop-ethyl. The overall shorter 18 persistence of both fomesafen and quizalofop-ethyl was recorded in warmer climatic conditions of Season I than 19 Season II. The results thus indicated that care must be taken during application of this herbicide mixture in cold 20 climatic regions, since both the herbicides may exhibit higher stability. The absence of end-point residues at harvest 21 concluded that the formulation is safe for application in tropical agroclimate. The low chronic dietary toxicity and 22 low soil ecological toxicity indicated that the herbicide mixture will offer no threat against consumer health and soil 23 ecosystem. However, there was a concern about the toxicity against soil algal population which needs to be reconfirmed by further studies.

application (Noyes et al. 2009). Therefore, conducting dissipation experiments under varying climatic conditions is 72 necessary to predict the fate of pesticides accurately. This is extremely important especially for herbicides, since 73 unlike other agrochemicals they are intended to persist longer in environment and change in climate thus tends to 74 aggravate not only the risk of environmental contamination but also the detrimental effect induced by the herbicides 75 on soil dwelling organisms. Again, the post-emergence herbicides may also contaminate the existing crop in field, 76 making it unfit for domestic consumption as well as for export. Therefore, assessing the risk involved due to field 77 application of herbicides is necessary to ensure the food and environmental safety. However, no information is 78 available regarding the fate of the aforesaid herbicide mixture in soybean and its impact on dietary as well as soil 79 ecological risk.

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Therefore, the objectives of the current research are to assess the dissipation dynamics of the herbicide 81 mixture (fomesafen 12%+quizalofop-ethyl 3%) in soybean and the impact of seasonal variation on its persistence.

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Besides, the risks involved towards soil ecological environment and consumer health are also evaluated.   Table S1. Soybean seeds (variety: Pusa 16) were sown in 5m×4m plots at a spacing of 30 cm×10     The deoiled cake sample (2 g) was taken in a 50 mL centrifuge tube and 10 mL 5 % aqueous sodium chloride 128 solution was added. The mixture was vortexed for one minute. Then 10 mL acetonitrile was added and vortexed 129 again for 2 minutes, followed by rotospin for 15 minutes at 50 rpm. The sample was centrifuged at 10,000 rpm for 5 130 minutes. Then 6 mL supernatant was evaporated to dryness and reconstituted separately with acetonitrile (1.      The predicted no effect concentration (PNEC) was obtained by dividing the toxicity value of respective target 187 organism by corresponding assessment factor which was 50 for both the cases. The risk factor is considered high if  all the substrates proved that the methods were accurate and repeatable (Table S2). The matrix effect of both 195 fomesafen and quizalofop-ethyl was within ±20% (Table S2) and the specificity of the method was also found to be 196 acceptable as the responses of both the compounds were <30% of the matrix matched standard at the desired 197 retention time in control samples. The limit of quantification (LOQ) of both the molecules was 0.01 mg kg -1 .

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The dissipation of fomesafen in soil and soybean plant followed the biphasic DFOP kinetics ( Fig. 2; Table 1). The

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Unlike fomesafen, the dissipation of quizalofop-ethyl followed SFO kinetics in both soil and soybean plant 209 ( Fig. 3

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The average initial concentration of quizalofop-ethyl in soil ranged between 0.034-0.055 mg kg -1 in Season I and 236 0.035-0.053 mg kg -1 in Season II (Fig. 3a). The half-life of quizalofop-ethyl in field soil was 1.63-1.70 days in 237 Season I and 1.66-1.83 days in Season II (Table 1). The variation in the persistence of quizalofop-ethyl in soil 238 between two consecutive seasons was found to be non-significant (Table S3). The reason underlying the fact is that

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Besides, Das et al. (2020) described that the rate of deesterification of quizalofop-ethyl reduces at lower pH. The pH 243 of the soil in our experiment was acidic i.e. 6.4 (Table S1). Hence, quizalofop-ethyl showed an overall higher 244 persistence in our experiment with half-life of 1.63-1.83 days in soil (Table 1)

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The persistence of quizalofop-ethyl in soybean plant varied significantly between two consecutive seasons 247 (

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The dissipation of quizalofop-ethyl in soybean plant is represented in Fig. 3b. It has already been reported that the

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Availability of data and materials

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The datasets used and/or analyzed during the current study are available from the corresponding author on 302 reasonable request.

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Competing interest

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The authors declare that they have no competing interests.

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No funding was received for conducting this study.  The temporal patterns of maximum, minimum and soil temperature; maximum and minimum relative humidity (RH I and RH II); cloud octa; bright sunshine hours; UV index and total solar intensity in Season I (a) and Season II (b) Figure 2 Dissipation of fomesafen in soil (a) and soybean plant (b) applied at two treatment doses (T1 and T2) in Season I and Season II