The excessive use of hazardous pesticides for massive cotton and wheat production has deteriorated the quality of Okara district's soil. Thus, in order to sustain the production of good-quality food, it is essential to determine the residue levels of pesticides in the agricultural soil and define their possible sources. Thus, the present study focused on the determination of selected pesticides in the soil samples obtained from cotton/wheat fields by using the modified multi-residue pesticide analysis method based on GCMS and HPLC-UV. Most of soil samples were found to be highly contaminated with imidacloprid, chlorpyrifos, and α-cypermethrin residues. Selected pesticides were significantly correlated with each other at p < 0.05 except imidacloprid, which was negatively correlated with triazophos, MCPA methyl ester, selected pyrethroid pesticides, and their metabolite. Soil pH and phosphate levels were significantly positively correlated while sulfate content was negatively correlated with most of selected pesticides. The varimax normalized factor analysis divides the selected pesticides to the two major factors that explained 87.19% of the total variance which evidenced that pesticide in the same cluster shared a common source in the soil. A significant negative correlation of chlorpyrifos in the second factor pointed towards a source different from other pesticides. Factor and cluster analysis indicated that sulfate levels of soil positively affected the persistence/ mobility of imidacloprid.
Heavy metals enriched agricultural soils have been the subject of great concern because these metals have potential to be transferred to the soil solution and afterward accumulated in food chain. To study the trace metal persistence in crop soil, 90 representative soil samples were collected and analyzed for heavy metal (As, Cd, Cu, Fe, Mn, Ni, Pb, and Zn) and anions (chloride, nitrates, phosphates and sulfates). Cluster and factor analysis techniques were used for the source identification of these excessive heavy metal levels and ecological risk was determined with potential ecological risk assessment. The degree of enrichment of eight studied heavy metals in comparison with the corresponding background levels decreased in order: Cd > Pb > Fe > Ni > Mn > As > Cu ~ Zn. Arsenic and cadmium exhibited 1.30- and 1.64-fold exceeded levels than threshold limits set by National environment quality standards, respectively. Cd in cotton field's soil may lead to higher potential risk than other heavy metals. On overall basis, the cumulative mean potential ecological risk for the district (207.75) corresponded to moderate risk level with higher contributions from As and Pb especially from Cd. Cadmium formed strong positive correlation with phosphate content of soil at p < 0.01. Cluster analysis indicated that Cluster 1 (extremely polluted) probably originated from anthropogenic inputs of phosphate fertilizer and past usage of arsenical pesticides.
The influence of trace metals (Cu(2+), Zn(2+), Cd(2+) and Fe(2+)) on the photodegradation of α-cypermethrin (α-CYM) in agricultural soil was studied. The soil samples were spiked with α-cypermethrin with/without the presence of metal ions, irradiated under a UV irradiation chamber for a regular period of time and analyzed by using HPLC. The dark control sterile and unsterile soil samples spiked with α-cypermethrin and selected trace metals were incubated for the same interval of time at 25 °C. The results obtained indicated that α-cypermethrin photodegradation followed biphasic kinetics. α-cypermethrin photodegradation half-lives (t1/2) were increased to 0.71 and. 4.5 hours from 0.64 hours respectively in the presence of elevated Zn(2+) and Cu(2+) concentrations. Fe(2+) and Cd(2+) increased the photodegradation reaction kinetics from -1.078 h(-1) to -1.175 h(-1) and -1.397 h(-1) and varied the t1/2 from 0.64 ± 1.41 to 0.59 ± 2.07 and 0.49 ± 2.01 in the soil. Microbes also affected the degradation of α-cypermethrin in metal contaminated soil. The degradation rate was inhibited in unsterile soil and was found to be in the following order: Cd(2+)< Zn(2+)< Cu(2+)< Fe(2+). The degradation/persistence of α-cypermethrin was affected linearly with the increasing soil metal concentrations.
The influences of Cu(2+) and Fe(2+) on the photodegradation of soil-incorporated chlorpyrifos were investigated in the present study. The soil samples spiked with chlorpyrifos and selected metal ions were irradiated with UV light for different intervals of time and analyzed by HPLC. The unsterile and sterile control soil samples amended with pesticides and selected metals were incubated in the dark at 25 °C for the same time intervals. The results of the study evidenced that photodegradation of chlorpyrifos followed the first-order kinetics. The dissipation t0.5 of chlorpyrifos was found to decrease from 41 to 20 days under UV irradiation. The rate of chlorpyrifos photodegradation was increased in the presence of both metals, i.e., Cu(2+) and Fe(2+). Thus, initially observed t0.5 of 19.8 days was decreased to 4.39 days in the case of Cu(+2) and 19.25 days for Fe(+2). Copper was found to increase the rate of photodegradation by 4.5 orders of magnitude while the microbial degradation of chlorpyrifos was increased only twofold. The microbial degradation of chlorpyrifos was only negligibly affected by Fe(2+) amendment. The studied trace metals also affected the abiotic degradation of the pesticide in the order Cu(2+) > Fe(2+).
European Union Reference Laboratory method for Fruits and Vegetable (EURL-FV-2010-M1) for the quanti cation of pesticide residues was veri ed for the determination of multiple pesticides residues in okra. The targeted pesticides were extracted using acetonitrile with citrate buffer salts followed by cleanup with primary secondary amine (PSA) and analyzed on LC-MS/MS. The recoveries for all the targeted pesticides were within an acceptable range of 70.1 -116.6% and precision in terms of RSD was 0.3 -18.1%, respectively. The limit of quanti cation ranged from 0.002 mg/kg for carbofuran to 0.5 mg/kg for αcypermethrin. The status of pesticide residues in okra (n= 21) available to consumers in the main markets of Pakistan has been determined by using this veri ed method. Sixty-two percent of the tested samples were contaminated out of which three samples were non-compliant with European Union Maximum residue limits (EU-MRL). The pesticides violating the EU-MRL were bifenthrin, thiamethoxam, and triazophos. For all the detected pesticides, estimated daily intake (EDI) ranged between 7.39×10 −6 and 1.78×10 −4 mg/kg of body weight while the values of Health Index (HI) uctuated between 8.9×10 −5 and 1.8×10 −2 .Although, residues of some pesticides were reported to be non-compliant with EU-MRLs, yet the risk posed by these pesticides to human health was insigni cant.
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