Evaluation of Pesticide Residues in Saudi Arabia Ground Water

MATERIALS AND METHODS

Chemicals and reagents: Pesticide standards (DDE, DDT, Dimethoate, Toxaphen Chloroneb, Methomyl, Promoxenyl, Bendiocarb, Promoxenyl, Bendiocarb and Cypermethrin) were provided by Chem Service Inc, USA. All pesticide standards were of 98.9-99.8% purity. All the solvents (Hexan and Acetone) were residue analysis grade and stock working solutions of pesticides were prepared in acetone.

Groundwater sampling collection: Fifteen regions were selected at Central, East, North and South of Saudi Arabia scale (Tabouk, Jouf, Hail, Qasseem, Qatif, Al-Hasa, Taif, Wadi Al-Dawaser, Abha, Gazan, Dereiah, Deirab, Hardh, Kharj and Mezahmiah) to perform the survey process of pesticide residues (Fig. 1) (Al-Turki et al., 2009). Water samples were collected from three locations for each region during 2007 (one sample for each location). The Water samples were prepared and then the pesticides were extracted by MAE technique and determined with GC-MS method. The present study was carried out during the year of 2008 in Labs of the Soil Sciences Department, King Saud University, Saudi Arabia.

Preparation of spiked groundwater samples: Spiked water samples were prepared by adding an appropriate volume of spiking solution to 10 mL of water were spiked with a stock solution of the pesticides (5 mg L^-1) prepared in Acetone. The spiked samples were prepared just before analysis, waiting approximately 30 min until solvent evaporation. Water samples were extracted by MAE technique. The main purpose of this step is to calculate the average of the recovery per cent of investigated pesticides by extraction and determination techniques.

Fig. 1:	Water sampling sites in Saudi Arabia

Minimum Detection Limit (MDL): To determine the MDL and perform the GC-MS quantification using a four-point calibration curve plotting peak area versus concentration (mg L^-1) of 12 pesticides using the dilution levels ranged from 0.0001-5.00 mg L^-1.

Extraction of Pesticide Residue by MAE: EPA Method 3540C (USEPA, 1996) and CEM application note No. E003 (CEM Corporation, 1994) was modified and used during conducting of the present study (El-Saeid et al., 2010). A Microwave Assisted Extraction (MAE) system model MES-1000 (CEM Corporation, Matthews, NC, USA) with Lined Extraction Vessels (LEV) was used. Preliminary studies were performed to evaluate MAE efficiency by the effects of temperature, microwave power, extraction time and solvent volume, to extract different groups of pesticide residues from water samples. For this purpose, 10 mL of water was potted in a tetrafluoromethaxil (TFM) microwave extraction vessel with addition of 1 mL of an aqueous spiking solution containing mixture of the pesticide standard solution. Water samples were equilibrated by shaking for 1 h before microwave extraction. Finally, all samples extracted under different conditions to obtain the optimal MAE conditions with this procedure. Finally the optimum Extraction conditions with highly recovery were conducted with 10 mL water samples. Samples extraction solvent was 35 mL of Acetone and Hexane mixture in ratio of (3:2), pressure was 80 psi; microwave power was 60%, temperature was 120°C and time of extraction was 20 min. After extraction, water extracts were filtered and evaporated to dryness; the residue was re-dissolved and directly analyzed by Gas Chromatography Mass Spectrometer (GC-MS) and clean chromatograms were obtained without any additional cleanup step.

Gas Chromatography Mass Selective (GC-MS) analysis: The temperature program for the GC was as follows: isothermal for 1 min at 100°C, increased at a rate of 10°C min^-1 to 240 and isothermal for 15 min. Helium was used as a carrier gas (1.2 mL min^-1). Quantification was performed using a four-point calibration curve plotting peak area versus ppm concentration. The result was expressed in percentage recovery of pesticide (El-Saeid et al., 2010).

Quality assurance/quality control: Recoveries were determined for all samples by spiking with the mix of pesticide standards prior to extraction. Analytical method recoveries for the given set of pesticides were also determined by repeating the whole analytical procedure with the reference soil enriched by the standard mix of pesticides of the known concentration.

RESULTS AND DISCUSSION

Pesticide recovery of spiked ground water samples: The recovery percent of targeted pesticides tested in water sample ranged from 96.23 to 102.44% for all tested compounds as shown in Table 1. Reproducibility was calculated based on the replicate analyses, with relative standard deviation (RSD, %) less than 2.63%. All laboratory blanks were below the detection limit.

Pesticide residues in water samples: The pesticide residues studied are found frequently in the environment and groundwater. Microwave Solvent Extraction (MSE) with GC-MS technique was modified and developed to obtain the optimum conditions to extract and determined the pesticide residues in ground water samples collected from the mentioned 15 regions with short time, with high recovery %. MDL, extraction- determination times, averages of residues. Table 2 showing the results of mean concentration of different pesticide residues (mg L^-1) in the 15 regions. The results showed that, four pesticide residues were detected in water samples collected from Gazan (Dimethoate, pp-DDT, pp-DDE and Cypermethrin) and Taif (Dimethoate, Chloroneb, Methomyl and Promoxenyl), but 3 pesticide was detected in Al-Ahssa (Dimethoate, Chloroneb and Methomyl) and Haradh (Dimethoate, Methomyl and Toxaphen).

Table 1:	Pesticide recovery and Relative Standard Deviation (RSD) and Minimum Detection Limit (MDL) of spiked groundwater samples extracted by MAE and determined with GC-MS

Table 2:	Pesticide residues concentration and standard deviation (inside parentheses), mg L-1 of tested groundwater samples

Meanwhile, two pesticide residues were found in seven regions and only one pesticide residue was found in four regions. Many investigators reported the persistence of different pesticides left residual amounts in ground water for many areas with different levels (Matin et al., 1998; Leonard, 1990; Legrand et al., 1991; Hernandez et al., 1993; El-Kabbany et al., 2000; Shukla et al., 2006; Maloschik et al., 2007).

The most detected pesticides in water samples were Dimethoate (86.66% of total regions), Methomyl (53.3% of all regions) and Chloroneb (20% of all regions). On the other hand, the lowest detected pesticides were Toxaphen, pp-DDE and Cypermethrin (13.33% for each) and Promoxenyl, Bendiocarb and pp-DDT (6.66% for each). Dimethoate was detected at high concentration in water samples collected from Mezahemya (0.418 mg L^-1), Chloroneb (0.114 mg L^-1) in Alhassa and Bendiocarb (0.181 mg L^-1) in Abha. Therefore, residues may have been originated from earlier applications given the reported high persistence in soil and then ground water. All pesticides detected in the water samples had different concentrations of residues as reported and agreement by Kashyap et al. (2002), Sankararamakrishnan et al. (2005) and Shukla et al. (2006).

The water health standards (Drinking use) report the Minimum Concentration Level (MCL) of pesticide (0.1 mg L^-1) for the single compound, but (0.5 mg L^-1) for a group of pesticide. Four regions, Dereyah, Deirab, Haradh and Kharj registered as lower of detected pesticide than MCL. Meanwhile, the rest of regions under investigation were higher than the MCL.

The studies performed to evaluate pesticide exposure in groundwater showed that some of the monitored pesticides were present at different concentration levels. The implementation of multiresidue methods and also automated techniques such as MAE-GC/MS to improve analytical conditions would be desirable.

The pesticides, which have been detected, were higher than the qualitative target set by EPA and EU (European Union, 2004). This is due to possible transfer of pesticides from agricultural and health protection activities carried out and in near regions.

These results are alarming for the health of the human beings in the studied regions. Though, this study was done only for a short period and for some regions of Saudi Arabia, the results obtained can be used to design an Integrated Management Program to control the concentration of pesticide residues in groundwater.

CONCLUSION

The present study clearly demonstrates that agricultural practices in the agricultural area of the selected regions have degraded the quality of groundwater. The study also provides a clear example that MAE followed by GC-MS techniques can be used as a routine way for the determination of pesticide pollution in groundwater. The results of the current study suggest that contamination by pesticides in the 15 studied areas is not as severe as might be anticipated. However, this study was limited to samples collected from a small number of farms in only one phase of the growing season. At the same time, the significance of the presence of Dimethoate, carbamates and DDTs in water in close proximity to human and animal populations should not be discounted. Further residue studies in other agricultural areas of Saudi Arabia are needed in order to assess the levels of pesticide residues in ground water and living organisms in same areas.

ACKNOWLEDGMENT

Authors thank the deanship of scientific research at King Saud University for financial support through Project # DSR-AR-2-(14).