1 Introduction

Europeans soils showed 80% pesticide residues in tested samples. Literature showed that 317 soil samples were tested for 76 different residues of pesticides while 43 pesticide residues were noticed in tested soil samples (Silva et al., 2019).

The pesticide used as crop protection agents is directly related to the increase in agricultural activity across the world. Although these chemicals are useful in disease control, it persists the degradation and could stay in marine systems aimed at centuries after application. Usually, soil pollution with residues of pesticides has developed an abundant problem and responsibility for the deterioration of food chain quality and sustainable agriculture (Gill and Garg, 2014). The concentration of 16 investigated pesticides was ranged from 0.096 to 3.12 μg g−1, with an average value of 1.17 μg g−1 in all soil samples. In the area under investigation, cypermethrin was encountered most frequently, while hexachlorobenzene was the least detected pesticide. The study showed that mitigation measures concerning pesticide application to the land should be taken to decrease organochlorine (OCP) and other pesticide residues in order to improve the soil quality in the Jordan valley (Batarseh and Rakan 2013). The extractability of 13 organochlorine pesticides aged in six different soil types was investigated. Acceptable recoveries were achieved for most of the analytes spiked into five of the soil types. No apparent correlation was perceptible between the soil characteristics and extractability of the aged analytes, signifying exhaustiveness of the extraction (Hussen et al. 2017).

The residues of organophosphates (OPPs) observed in the samples of soils remained chlorpyrifos (10–40 μg kg−1), profenofos (20–40 μg kg−1), and pirimiphos-methyl (10–40 μg kg−1). The absorptions of O.P. endurance in samples of soils analyzed from the numerous spaces were usually beneath and inside US MRLs for croplands, though pirimiphos-methyl and chlorpyrifos mean concentrations noted were initiated to overhead their own agricultural soil US MRLs at Nkrankwanta (Benedicta et al. 2016). The distribution and transfer of OCPs in the land of different forest types in Mt. Shergyla, southeast T.P., under identical ecological and climatological circumstances were studied (Luo et al. 2019).

The sixteen OCPs were detected to examine the properties of wetland reclamation and reclamation antiquity on OCP levels. Their outcomes presented that average ∑DDTs, HCB, MXC, and ∑OCPs were maximum in surface soils. The occurrence of dominant DDT isomers (p,p’-DDE and p,p’-DDD) designated the historical input of DDT and significant aerobic degradation of the compound (Junhong Bai et al. 2015).

Pesticide residue analyses were conducted after extraction via an adapted QuEChERS method for tropical soils; extracts were screened for more than 500 pesticides using HPLC-MS/MS and GC-MS/MS. Glyphosate and metabolite residues were found in each of the tested fields. EU-banned pesticides like DDT and other POPs were found in both systems. Intensive cropping fields show between 13 and 25 different pesticide residues (Sanchez et al. 2019).

A validated new method was established to know the quantification of 74 trace pesticides associated with different chemical groups in soil samples of Al-Jouf Province of Saudi Arabia. The extraction was done rapidly, reliably, inexpensively, operatively, and safely and was investigated by gas chromatography-mass spectrometry triple quadrupole. Pesticide residues were observed by putting them on the altered QuEChERS and GC-MS/MS method; the levels remained extended from 0.043 to 0.02 mg kg−1 for 18 diverse pesticides, 1.99 to 1.00 μg kg−1 for 16 different pesticides, 0.99 to 0.50 μg kg−1 for 12 diverse pesticides, and lesser than 0.50 μg kg−1 for 28 dissimilar residues of pesticides (EL-Saeid et al. 2019).

In the terrains of Saudi Arabia, under crop production, usage takes augmentation from 1.25 million hectares (m ha) in 1988 to 1.59 million hectares by 1994 (Hussain and A1-Saati 1999). From the most extreme current standard evaluation of agrarian zone, the Tabuk locale, the only significant area in Saudi Arabia which adjusts nation territory (7%) alone, has perceived an expansion of 10% in uncovered soil change to rural soils somewhere in the range of 1988 and 2008 (Al-Harbi 2010) even though the tendency in horticultural land utilization is irretrievable owing to the foreseen ascending in crop generation; Saudi Arabia faces a natural hazard due to the consistent cert in amplified usage of pesticides. Saudi Arabia, in the past, in relation to the pesticide imports signposted an estimated of around 5000 tons in 1976 to 20,000 tons in 1990 (Al-Saleh et al. 1999 and Al-Saleh et al. 2012). Despite being barred, this chemical is widely consumed for the controlling of disease born via vector and is identified to persevere in the environment for years afterward suggestion (Al-Saleh et al. 1998). Also, the existence of pesticides in edible vegetables and grain food was found in Riyadh and Al-Qassim (Osman et al. 2010). With respect to the groundwater contamination, conflicting to collective confidence that the desert kingdom of Saudi Arabia has subterranean aquifers, there are reports that display that 50% of wells are shallow having 50- to 200-m depth, making the risk of pesticide contamination more conceivable (Sheta et al. 2000 and Alabdula’aly et al. 2010).

Previously, soils of many regions of Saudi Arabia have been studied and a risk assessment along with presence of pesticide residues revealed the presence of DDT (dichlorodiphenyltrichloroethane) besides its metabolite HCH (hexachlorocyclohexane), in soils and groundwater (Al-Wabel et al. 2011 and El-Saeid et al. 2011). However, comprehensive modeling on a large-scale, small-scale, or catchment-level studies is not reported. Soils with less amount of soil organic carbon (SOC) are shown to dissipate pesticides mainly by volatilization due to weaker adsorption of pesticide molecules to the organic content (Burkhard and Guth 1981). There have been studies investigating the volatile losses of pesticides with pesticide vapor pressures ranging between 8.7 × 10−10 and 30,000 Pa (American Society for Testing and Materials 1987, Guth et al. 2004, Woodrow et al. 1997, and Woodrow et al. 2001). The volatilization has been shown to correlate with the rates of evaporation losses and can be used as a source function for dissipations due to soil–air exchange (Wesenbeeck et al. 2008). It has been shown that vapor pressure is the best predictor of evaporation losses as compared to Henry’s law constant, water/air, and soil/air distribution coefficients with good correlation for 80 different chemicals 71 and 123 crop surface and soil studies, respectively, carried out under the controlled environment of laboratory and greenhouse (Reichman et al. 2000a). While vapor pressure can account for the evaporation losses, a comprehensive model including the entire range of factors affecting the dissipations of pesticides necessarily includes the octanol-water partition coefficient (Kow) (Reichman et al. 2000b). More precisely, the partitioning of pesticide molecules into the soil and then sorption into the deeper layers and groundwater is estimated by the partition coefficient of the organic content available in the soil Koc (Goss and Schwarzenbach 2001). An exact correlation between logKow and logKoc is assumed; however, this assumption of single parameter linearity is not valid for soils with more complex organic matter, giving the necessity to characterize the organic matter or include more parameters which can describe the chemical interaction between the pesticide molecule and the surrounding soil organic content (Bronner and Gos 2011, and Ahmed et al. 2001). A hypothesis worth testing in soils with low organic carbon is to correlate the percentage loss of pesticide quantities against the simpler octanol-water partition coefficient (Kow) with an assumption that there exists a good correlation owing to less complicated nature of the organic matter available for interaction with the pesticide molecule in the soils. In fate assessment modeling of pesticide residues, Kow is widely used as a measure of hydrophobic character of a compound in a two-phase system consisting of two largely immiscible solvents, n-octanol and water. The Saudi Middle Eastern soils are portrayed by low measures of SOC inferable from sparse precipitation and bone-dry condition. In such a scenario, the extrapolation of physicochemical properties against the percentage loss over time can provide an estimation of the amount of residual material remaining in the soil for assessing risk towards human and non-target species. The aim of the present research is to (i) report the pesticidal residue existence in agricultural soils of Al-Kharj and (ii) to know the correlation among the major physiochemical pesticide properties against the loss of pesticide from the soils. This methodology is relied upon to yield significant discoveries which can additionally help to understand the destiny and display the development of pesticide in croplands where the natural soil carbon is low.

2 Materials and Methods

2.1 Soil Samples Collection

The soil samples were collected from the Al-Kharj governorate, situated southeast of Riyadh in Saudi Arabia. The weather in this zone is arid, with a yearly rainfall of 132 mm. Al-Kharj is measured to be coastal with alluvium testimony. The category of soil is aridisol and entisol along with saline and calcareous.

2.2 Pesticide Standards

Pesticide standards of spinosad, chlorpyrifos methyl, dimethoate, chlorpyrifos, lindane (γ-HCH), methidathion, heptachlor, α-B-endosulfan, o,p-DDT, p,p-DDT, bifenthrin, permethrin, β-cyfluthrin, and methomyl with purity of 98–99.8% were provided by AccuStandard, 153 Inc., New Haven, CT, USA, as individual (50 mg) or combination values at a concentration of 100 μg mL−1. All solvents (methanol, dichloromethane, hexane, acetone, and acetonitrile) used for the extraction and analysis were residue-analysis grade and purity about 99.9%, purchased from Fisher Scientific (Fair Lawn, New Jersey, USA). QuEChERS kits and SPE tubes were purchased from Phenomenex, Madrid Avenue, Torrance, CA, USA.

2.3 Soil Sampling Collection and Preparation

Ten sites were selected in the Al-Kharj region to accomplish the survey procedure of pesticide residues in soil. Three soil samples were placid from different locations for a separate section. For individual sites, three areas were thoroughly picked to assemble the soil samples from the outside layer (0–30-cm depth) and subsurface layer (30–60-cm depth). The samples of soils were located in a clean plastic sheet and concerned judiciously on the place with a small spade. Around 1-kg portion of every replicate sample was collected. The collected samples of soils were subjected to drying (air) and after that passed through a sieve (2.0 mm). Spiked soil samples were arranged by the addition of proper measurements of spiking solution (5 mg L−1 of pesticides in acetone) to 05 g of soil. The spiked soil samples were settled impartially formerly to analysis, waiting about 30 min until the evaporation of the solvent. Entirely, soil samples were extracted by means of QuEChERS and analyzed by GC-MS/MSTQD.

2.4 Extraction and Cleanup of Multipesticide Residue by QuEChERS

To extract the targeted pesticides, 10 g of soil sample was placed into a centrifuge tube (50 mL), then deionized water was added (7 mL), mixture was vortexed and permitted to hydrate for 25–30 min, and acetonitrile (10 mL) was added to respective samples, shaken well for 5–6 min to extract pesticide residues. The contents of citrate salts Mylar pouch were added to a portion of soil sample in the centrifuge tube. Samples were instantly vortexed for at least 120 s and centrifuged (≥ 3500 rcf) for 5–6 min. 1.5 mL aliquot of supernatant was transferred to a 2-mL C-18 SPE tube. Samples were vortexed for 2 min and centrifuged for 2 min at high rcf (e.g., ≥ 5000). Finally, pesticides in the extracted soil samples were analyzed by GC-MS/MSTQD (EL-Saeid et al. 2019).

2.5 Analysis by GC-MS/MS

Whole determinations have been passed out by means of the conventional Thermo Scientific™ TSQ 8000™ triple quadrupole GC-MS/MS system connected with the Thermo Scientific™ TRACE™ 1310 GC with SSL Instant Connect™ SSL module and Thermo Scientific™ TriPlus™ RSH autosampler. Splitless time 1.0 min G.C. Column T.R. ™ 5 MS, 30 m × 0.25 mm × 0.25 μm, carrier gas He (99.999%), flow rate 1.4 mL/min, constant flow, temperature program 100 °C, 1 min; 10 °C min−1 to 160 °C, 4 min and 10 °C/min to 260 °C, 2 min, transfer line temperature 280 °C, total analysis time 19.2 min, TriPlus RSH autosampler injection volume 1 μL. Ionization mode E.I., 70 eV, ion source temperature 250 °C, scan mode t-SRM by means of timed acquisition t-SRM transitions setup inevitably buildup by AutoSRM software. Transitions of operation conditions are shown in (Table 1).

Table 1 GCMSMSTQD 8000 SRM instrumental conditions
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2.6 Quality Control/Assurance

All the chemicals and solvents used in this study were 99.99% pure and residue analytical grade. By using pesticide standard mixture, the recoveries were detected in entire samples. The recoveries were extended from 98 to 102% for all detected pesticide residues in soil samples. The analysis was done to keep reproducibility and repeatability under acceptable range. All the blank samples were in limit of detection (LOD) and limit of quantification (LOQ).

2.7 Statistical Analysis

Paired t test for determining the significance levels and single parameter least squares regression equations (sp-LSRE) among the parameters were attained by means of SAS statistical software (SAS Institute, 1998).

3 Results and Discussion

3.1 Organochlorine Pesticide Identification, OCPs

The studied soil samples were loamy sand, and sandy loam, and their content of organic matter are low with values of 0.28–1.03% for surface layers and of 0.03–0.76% for subsurface layers. Organochlorine pesticides included in this experiment were p,p-DDT, o,p-DDT, heptachlor, lindane, and endosulfan. The maximum concentrations detected for these residues in the investigation were 0.025 mg kg−1, 0.025 mg kg−1, 0.190 mg kg−1, 0.149 mg kg−1, and 0.115 mg kg−1. Average pesticide residue concentrations of the OCP residues in each of the surface and subsurface layers during winter (season 1, 01/2010) and summer (season 2, 06/2010) seasons are given in Table 2. The frequency of occurrence of the p,p isomer of DDT (n = 3) is higher than that of the associated o,p compounds (n = 1) in all the sampling sites of the Al-Kharj region. The high detection frequencies and residue values of p,p-DDT compared to its isomer o,p-DDT are in accordance with the previous finding related to the isomers of DDT and its metabolites and indicate the presence of degradation products as compared to the newly added DDT (Wang et al. 2008, Ssebugere et al. 2010, Gonzalez et al. 2010, and Kodeˇsovaa et al. 2011). α-B-Endosulfan, a cyclodiene pesticide, was found to be at concentrations as high as 0.115 mg kg−1 in soil samples; the frequency of occurrence was observed as 100% for this residue, suggesting a widespread of endosulfan in Al-Kharj region. Heptachlor levels were recorded at the highest levels amounting to 43%, 37%, 43%, and 38% of the total OCPs detected in the study in the surface and subsurface layers of summer and winter respectively as indicated in Fig. 1. The levels of lindane were recorded as 0.103 mg kg−1, 0.135 mg kg−1, 0.105 mg kg−1, and 0.149 mg kg−1 in soil layers (surface and subsurface) in summer and winter respectively. Figure 1 shows the relative abundance of the five types of pesticides studied namely OCP, OPP, pyrethroids, carbamates, and spinosad and the comparative change in the residue levels between the surface layer during winter and summer, subsurface layers during the winter and summer, between the surface and subsurface layers during the winter, and surface and subsurface layers during the summer seasons. It was found that residue levels were in the following order: OCP > OPP > pyrethroids > carbamates. This finding calls for the need to adjust pesticide usage, especially the OCPs and OPPs, which are banned in many parts of the world due to their potentially hazardous environmental effects.

Table 2 Mean of pesticide residues in Al-Kharj agricultural soil samples indicating the four datasets used in the study
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Fig. 1
figure 1

a Pesticide residue (OCPs, OPPs, carbamates, pyrethroids, and spinosads) levels (mg/kg) in summer surface soil samples, b pesticide residue levels (mg/kg) in summer subsurface soil samples, c pesticide residues levels (mg/kg) in winter surface soil samples, and d pesticide residue levels (mg/kg) in winter subsurface soil samples

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3.2 Organophosphate Pesticide Identification and Other Pesticide Groups

The range for the organophosphorus pesticides studied was chlorpyrifos-methyl (0.089–0.009 mg kg−1), dimethoate (0.367–0. 021 mg kg−1), chlorpyrifos (0.233–0.019 mg kg−1), bifenthion (ND), and methidathion (ND) in the surface layer during the winter. Among the OPPs, the dimethoate was found to be in maximum quantity in all the four datasets for surface layer, and subsurface layer in summer and winter, representing the amounts as 0.180 mg kg−1, 0.208 mg kg−1, 0.189 mg kg−1, and 0.207 mg kg−1, thus giving the indication of excessive usage of this OPP in the studied region. The pyrethroid studies in the region were permethrin and β-cyfluthrin, while permethrin was detected with a maximum level at 0.119 mg kg−1 in the subsurface layer during winter; the β-cyfluthrin levels were non-detectable or below the quantitation levels throughout the study. An interesting observation with regard to the usage of pyrethroids is that the studied region has measured pyrethroid levels next to OCPs and OPPs and carbamates (Fig. 2), suggesting fourth place in terms of usage, despite the fact that pyrethroids, owing to their relatively lesser environmental toxicity to non-target organisms, are ghastly replacing the OCPs and OPPs in their use as insecticides. The carbamate studied was methomyl, which was found to be in 0.255 mg kg−1, 0.281 mg kg−1, 0.263 mg kg−1, and 0.309 mg kg−1 in the surface and subsurface layers during the summer and winter seasons. Biopesticide spinosad was found in all the samples and was recorded at 0.013 mg kg−1, 0.002 mg kg−1, 0.011 mg kg−1, and 0.002 mg kg−1 in surface and subsurface layers for summer and winter seasons.

Fig. 2
figure 2

Regression plots of vapor pressure and n-octanol/water partition coefficients against the residue levels from Al-Kharj soils

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3.3 Statistical and Correlation Analysis

Statistical investigations were performed between assembled methods for soil layers present on surface and subsurface for winter and summer seasons independently; similarly, gathered methods for winter and summer were thought about for surface and subsurface soil layers independently. Two followed matched t tests for means correlation were applied to investigate at 5% probability level or at 95% certainty interim. Significant outcomes were acquired as abridged in Table 3. The levels for pesticide buildup were similarly more in the surface layers as compared to the subsurface layer in both the winter and summer seasons; this means that extensively there are more measures of natural carbon in the soil to hold the buildup in the surface layer without a probability of filtering totally to the subsurface layers. All the pesticide levels decreased from winter to summer season except the dimethoate which has the least vapor pressure among all the pesticide residues with a significant change in the concentrations; the dimethoate has a vapor pressure of 3.2 × 10−8Pa. Based on Student’s t probability distribution, the residues of dimethoate, chlorpyrifos, lindane, heptachlor, endosulfan, and methomyl were found to have a significant change in the concentrations between the seasons. The vapor pressure ranged between 3.2 × 10−8 Pa and 5.3 × 10−2 Pa, and Kow ranged between 0.69 and 54.6. The negative change in the dimethoate concentrations is a possible indication of the existence of soil–air exchange phenomenon in the region.

Table 3 Two-tailed paired t test at 95% CI for pesticide residue level variation
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The correlation coefficients found for various comparisons of the data are given in Table 4, and the physiochemical properties (chemical structure, molecular weight, vapor pressure (Vp) Pa at 25 °C, n-octanol/water partition coefficients (logKow), and water solubility (Sw) mg/L at 25 °C) and pesticide identification are given in Table 5; the vapor pressure single parameter least squares regression equations (sp-LSRE) yielded a coefficient of 0.015 and 0.030 for surface and subsurface comparisons for winter and summer seasons respectively. Likewise, the octanol/water partition coefficient single parameter least squares regression equations (sp-LSRE) yielded a coefficient of 0.12 and 0.05 for surface and subsurface comparisons for winter and summer seasons respectively. The regression plots are indicated in Fig. 2 which showed the hypothesis of the experiment to correlate the vapor pressure and the octanol/water partition coefficients against the residue levels from Al-Kharj soils is significant to allow the participation of the microbial or other kinds of decay process that may hinder the direct correlation of residue levels to the physiochemical properties (Ghafoor et al. 2011, Scholtz and Bidleman 2007, and Mackay et al. 1997).

Table 4 The single parameter least squares regression equations (sp-LSRE) for Vp and Kow against residue level variation for pesticides with significant change in concentration (p < 0.05)
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Table 5 Physiochemical properties of residues
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4 Conclusion

Assessment of Al-Kharj agricultural area for 14 pesticide residues belonging to OCPs, OPPs, pyrethroids, carbamates, and biopesticides was performed to obtain the residue level profiles. The soil was found to be contaminated with spinosad, chlorpyrifos methyl, dimethoate, chlorpyrifos, lindane (γ-HCH), heptachlor, α-B-endosulfan, o,p-DDT, p,p-DDT, permethrin, and methomyl. The profiles were investigated for potential dissipation into the air and groundwater by direct comparison of essential physicochemical properties and it has been inferred that the region required a more detailed study involving modeling of pesticide transport into the soils to evaluate the risk of air and groundwater contamination primarily.