Chemicals and solvents
Sigma-Aldrich and Dr. Ehrenstorfer, Germany, provided certified reference materials of fenoxaprop-p-ethyl (94.85 % pure) purity, as well as twenty other pesticides (>97 % pure) of various classes. Bayer, USA, provided the formulation (Whip-Super 9% EC). J.T. Baker, Avantor, USA provided high performance liquid chromatography (HPLC) grade acetonitrile, acetone, ethyl acetate (EA), dichloromethane (DCM), and water. Rankem, India, supplied analytical grade anhydrous magnesium sulphate (MgSO4), sodium chloride (NaCl), and sodium sulphate (Na2SO4). To eliminate undesired phthalets, anhydrous magnesium sulphate was heated for 5 hours at 500oC. PSA was received from Agilent Technologies, United States.
Equipment
Sample preparation equipment included a vortex mixer (Spinix, Tarson, India), rotospin (Tarson, Kolkata, India), silent crusher (Heidolph, Schwabach, Germany), separating funnel shaker (Yamato Scientific, Japan), centrifuge (Superspin, Plasto-Craft), rotary vacuum evaporator with temperature controlled water bath (HS 2001 NS, Germany), and mechanical shaker (Scientech Technologies, India). For weighing, an electronic analytical balance, Sartorius GD603 (Sartorius, Germany), with a readability of 0.001ct/0.2 mg, was utilised. In the filtration procedure, membrane filter paper, Nylon 6,6, Ultipor N66 membrane, 13 mm (Pall Life Sciences, USA), and syringe filter (SGE Analytical Science, Australia) were employed.
Standard preparation
In a 100 mL volumetric flask, a stock solution (1000 mgL-1) of fenoxaprop-p-ethyl was prepared and diluted with acetonitrile. Using serial dilution procedures, additional working standards of various concentrations (10, 5, 2.5, 1, 0.5, 0.1, and 0.05 mgL-1) were prepared. The additional twenty CRM (certified reference material) pesticide solutions (targeted for water sample analysis) were prepared in the same way, using serial dilution processes. All of the standard solutions were kept refrigerated (-18oC) and out of direct sunlight.
Field studies
For three years, field trials with jute (variety Basudev) were conducted in Madanpur, West Bengal, India (23.0089° N, 88.4912° E) in accordance with good agricultural practice (GAP). A warm and wet climate, such as that provided by the monsoon climate during the fall season (March-August), followed by summer, was selected for growing jute. The jute field was adjacent to a pond where jute retting took place. Figure 1 shows the schematic diagram of the total jute cultivation area.
Sampling and storage
Fenoxaprop-p-ethyl (Whip-Super 9 % EC) was sprayed with a high volume Knap-sack sprayer at 67.5 g a.i. ha-1 (750 mLha-1). On day 0 (2 h), 1, 3, 5, 7, 14, and 21 days following the herbicide spray, 100 g representative samples were obtained from the replication plot. Water samples were obtained during harvest (110 days) from the jute field area and from the nearby pond, which was used for jute retting. Amber glass bottles (2 litres) with stopper tops were used and kept in an ice box at 4°C.
Sample preparation
Jute samples (Leaves and fiber)
After quartering, a representative chopped sample of jute leaves (100 g) was obtained from each replicate and treatment for extraction. After homogenising the material, 10 g was put in a 50 mL centrifuge tube with 10 mL of acetonitrile and vortexed for 1 minute. The mixture was homogenised once again in a quiet crusher at 12500 rpm. 4 g of anhydrous MgSO4 and 1 g of NaCl were added to the mixture and vortexed for 1 minute before being rotospined for 5 minutes and centrifuged for 10 minutes at 5000 rpm (RCF-3354). After centrifugation, 1 mL of supernatant was transferred to a 2 mL micro-centrifuge tube and cleaned using dispersive solid-phase extraction with primary secondary amine (PSA) sorbent (50 mg) and anhydrous MgSO4 (150 mg), followed by centrifugation for 10 minutes at 5000 rpm. HPLC with a UV-VIS detector was used to evaluate the residue level of the supernatant extract.
Soil samples
A representative air-dried soil sample (50 g) was shaken in a mechanical shaker at 175 rpm for 30 minutes with 100 mL of acetone. A similar procedure was used two more times. The filtrate was evaporated to dryness by a rotary vacuum evaporator (RVE) at 40oC after filtration through the buchner funnel. The concentrated remainder was diluted in 2 mL of ethyl acetate and chromatographed on a silica gel column. The column was packed with an activated silica gel/charcoal (20:1) combination sandwiched between two layers of anhydrous sodium sulphate and eluted with 100 mL of ethyl acetate. RVE was used to evaporate the final elute to dryness, and the final volume was made up with acetonitrile (1 mL) for residue quantification.
Water samples
The standard, established liquid-liquid extraction (LLE) model was used to analyse multi-pesticide residues in water samples. Water samples collected in the field and pond were filtered using a Whitman glass-fiber filter (GF/C, 0.45 mm). Then, in a 1 liter separatory funnel containing 150 g of NaCl, 750 mL of filtrate water was extracted three times with 70, 40, and 40 mL of solvent mixture in a separating funnel shaker at 220 rpm. EA: DCM was the solvent combination (8:2). A total of 150 mL of organic solvent layer was collected in a 250 mL conical flask after passing through anhydrous Na2SO4. The solvent was then evaporated to dryness in a 40oC rotary vacuum evaporator. The dried residues were reconstituted in a tube with 5 mL of hexane for evaporation to dryness over Turbo-Vap at 35oC, and the remainder were reconstituted in 1 mL of acetone. The sample was syringe filtered and transferred to a 2 mL vial for HPLC and Gas Chromatography-Mass Spectrometric (GC-MS) analysis after 3 minutes of sonication.
Fish Samples
Fish samples were collected from the pond which was used for jute retting at the time of harvesting and retting. Ten samples were collected from each season. This sample material was homogenised for 10 minutes in a Robot Coupe Blixer at 16990 x g. This sample (15 g) was placed in a 50 mL centrifuge tube, along with 15 mL of acetonitrile, and shaken for 1 minute on a vortex mixer. The mixture was then homogenised for 1 minute in a Silent Crusher at 525 x g. It was mixed with sodium chloride (1.5 g) and anhydrous MgSO4 (4 g). A vortex mixer (1 minute) and rotospin (5 minutes) were used to completely mix the chemicals, which were subsequently centrifuged for 5 minutes. The supernatant (5 mL) was added to each of three 15 mL centrifuge tubes containing 250 mg PSA sorbent + 750 mg anhydrous MgSO4, to improve the dispersive solid-phase extraction (dSPE) cleanup stage. The tube was sealed, stirred for 30 seconds on a vortex mixer, and centrifuged for 5 minutes at 8495 g speed. Under a moderate stream of nitrogen, the supernatant (1 mL) was evaporated to dryness at 40°C. Before the instrumental analysis, the residue was reconstituted in 1 mL acetone and filtered through 0.2 m ultipore nylon 6,6 membranes.
Instrumental analysis
Fenoxaprop-p-ethyl has previously been determined using LC in conjunction with various detectors such as mass spectrometry (Chen et al. 2011) or UV-VIS detectors (Singh et al. 2013). In the current investigation, fenoxaprop-p-ethyl was measured for the first time in a jute crop using an Agilent 1200-HPLC fitted with a UV-VIS detector and a perfect chrome 250 4.6 mm (RP C-18) column across three years. The pump was self-contained (quaternary), and the injection capacity was 10 L. The mobile phase was acetonitrile:water (8:2) at a flow rate of 0.5 mLmin-1. The wavelength was determined to be 240 nanometers. Fenoxaprop-p-ethyl had a retention time of 10.732 minutes. Agillent Chem Station Software was used to collect and process the data.
Water samples were evaluated using a mass selective detector (MSD) on a GC-MS, QP 2010 Plus (Shimadzu Corp., Kyoto, Japan). The initial temperature was raised from 40°C to 250°C, and the injector temperature was set at that level. Helium was employed as a carrier gas (purity 99.999%). The temperature of the ion source was set to 250°C, while the temperature of the contact was set to 280°C. The instrument was set to spit mode with a split ratio of 1:10 and a sample injection volume of 2 L. GC-MS Lab Solution Software was used to collect and process the data (version 4.45).For identification, confirmation, and quantification, pesticide-specific retention durations, molecular mass, and m/z ions were employed. The approach was validated in accordance with the SANTE/12682/2019 requirements. The LOD and LOQ were computed using S/N ratios of 3:1 and 10:1, respectively. For assessing the linearity and regression coefficients, a six-point (0.01–1.0 mg kg-1) calibration curve was created (R2). In a five-repetition recovery experiment, the water sample was fortified with the standard solution at LOQ, five times LOQ, and ten times LOQ levels.
Matrix effects
In pesticide residue analysis, a matrix effect is defined as an unexpected suppression or increase in analyte response produced by co-eluting matrix components. HPLC analysis was used to examine matrix effects caused by jute leaves, soil, fiber, and field water by matching the peak area of the chromatogram produced using solvent and matrix matched standards. The influence of matrixes (%ME) on pesticide chromatographic interactions was studied using the equation below (Savini et al. 2019).
ME (%) = (S-1) ×100
Where S = (Tmax∕Tstd), Tmax denotes the peak area of the fortified extract and Tstd represents the peak area of the pure standard. A positive value of %ME denotes a matrix enhancement, and a negative value will be a matrix suppression. %ME value less than 20 indicates that it is not significant (Ferrer et al. 2011).
Data and statistical analysis
The first-order kinetic equations were used to determine the dissipation dynamics and half-life of fenoxaprop-p-ethyl. Dt =D0 e-kt and t1/2= (0.693/k), Where, Dt is the concentration of fenoxaprop-p-ethyl at time t, D0 is the initial concentration, and t1/2 is the half-life. The half-life was calculated using equation t1/2 = (0.693/k), where k is rate constant in days (Li and Wu. 2008).
Risk assessment of fenoxaprop-p-ethyl in jute leaves
In both rural and urban India, a jute leaf is regarded as a green leafy vegetable. As a result, risk assessment is critical for food safety. TMRC (theoretical maximum residue contribution), MPI (maximum permissible intake), and ADI were used to assess the danger of fenoxaprop-p-ethyl in jute leaves (acceptable daily intake). TMRC (mg person−1 day−1) = [residue amount (mgkg-1) × the consumption of leafy vegetable (jute leaves) in an average Indian diet (g person−1 day−1)] (Kumari et al. 2013). ADI = (NOAEL) non-observed adverse effect level of fenoxaprop-p-ethyl / safety factor (100).The ADI of fenoxaprop-p-ethyl was found to be 0.01 mg kg-1 body weight−1 day−1 (EFSA, 2012). MPI = acceptable daily intake (ADI) × average body weight of an Indian adult (Loutfy et al. 2015) MPI = 0.01× 65 =0.65 mg person−1 day−1 Where average body weight of an Indian adult (65 kg) and consumption of leafy vegetable (jute leaves) in India is 50 g day−1 per capita (Sachdeva et al. 2013).
Risk assessment of water
Following the EPA's Level of Concern (LOC) for aquatic creatures (e.g., fish) in pond water next to the jute field, the safety index or risk quotient (RQ) was reviewed and curtained, assuming the potential dangers connected with the presence of pesticide residues (USEPA 2017a). The RQ ratio reflects the high and low–risk states of aquatic ecosystems and was calculated by dividing a point estimate of exposure by a point estimate of effects, with fish serving as an example of an aquatic species. The following formula was used to determine RQ:
RQ = EEC/LC50 or EEC/EC50 or EEC/NOAEC (Bhattacharyya et al. 2021)
Where EEC = Estimated Environmental Concentration (i.e. detected pesticide level in pond water); LC50 and EC50 = Median Lethal and Effective Concentration, respectively (for estimation of acute toxicity); and NOAEC = No Observed Adverse Effect Concentration (for estimation of chronic toxicity). The pesticide properties data base (PPDB 2020) was used for the collection of all eco-toxicological (EC50 or LC50 or NOAEC) data.