Consuming vegetables and cereals in daily meals is very important. The nutrients that are provided mostly covered all of the reactions in the human body system (Keikotlhaile and Spanoghe, 2011). However, vegetables can be toxic to humans due to pesticide usage (EL-Saeid and Selim, 2013).

Twenty three years ago at Aging City of  Anhui  Province in China, eleven people have died because of breakfast. After the case investigation, expert found that all the victim had consumed wheat spoiled by organophosphorus pesticides (Hui et al., 2003). Vegetables contamination caused by pesticide residues causes a serious problem to human health. Pesticide residues in vegetables are noxious metabolites  produced  by  usage  of  pesticide  for  long duration in vegetables planting.

The existence of pesticide residues in vegetables can lead to contamination in its nutrient and may give a concern to the consumers regarding the maximum residue limits (MRLs) of vegetables (EL-Saeid and Selim, 2013; Dasika et al., 2012). Based on Food Regulation 1985, Ministry of Health Malaysia has set particular level of MRLs for all pesticides in specific food class to all farmers.

Aly et al. (2010) mentioned that chlorpyrifos (O, O-diethyl-O-(3, 5, 6-trichloro-2-pyridyl)-phosphorothioate)  is certified as a wide spectrum pesticide  and commonly used to manage various types of pest in agriculture field and livestock (US EPA, 1986) and the structures of chlorpyrifos is as shown in Figure 1. Based on previous studies, there are several methods used to remove chlorpyrifos in vegetables and fruits. 

The methods include wash treatment using some acid (Osman et al., 2014), hydrostatic pressure process (Iizuka et al., 2013), ozonation (Kusvuran et al., 2012), and horizontal sub-surface flow constructed wetlands (SSFCW) (Agudelo et al., 2010). However, these methods were difficult to be conducted. In order to attain an effective technique in removing chlorpyrifos residues in cauliflower, five types of cleaning solutions were made to examine their effectiveness based on percentage of removal from the concentration of chlorpyrifos on samples before and after cleaning process.

Preparation of cleaning solution

Five types of cleaning solutions were prepared as follows:

Soda-salt solution: For the soda-salt solution (5%), 5 g of edible soda and 5 g of salt was added into 1 L of water. Then, the solution was stirred until completely dissolved.

Tamarind juice solution: 50 g of tamarind without its seed was weighted.   Then,   1 L  of  water  was  added  to  tamarind  and  it  was soaked for 15 min.

Flour solution: For the flour solution, 50 g of flour was weighted. Then, the flour was poured into 1 L of hot water; the solution was stirred until completely dissolved and filtered from the suspension.

Vinegar solution: For the vinegar solution, 100 ml of vinegar was measured. Then, 900 ml of water was added into vinegar, the solution was stirred lightly to dissolve the solutions. If there was residue present in the solutions, the solution was filtered and supernatant was collected.

Preparation of simulated chlorpyrifos pollution in cauliflower

Preparation of chlopyrifos mixture:  2.0 L of water was added into the 0.95 ml of chlorpyrifos. After water was added, the mixture was stirred until dissolved.

Preparation of chlorpyrifos pollution in cauliflower: A cauliflower of 1000 g was bought from the supermarket and washed with tap water and dried with absorbent paper. Then, the cauliflower was soaked in chlorpyrifos mixture for 10 min and stored at room temperature in a dark room for 24 h.

Method of cleaning samples and extraction of pesticide residues

The contaminated cauliflower was divided into five parts, of which three parts each were soaked with tap water, soda-salt solutions, tamarind juice solutions, filtered flour solutions, and vinegar solutions for 10 min separately. Then, the cauliflower was rinsed off with running tap water for 1 min. The residues cleaning process was extracted using Solid Phase Extraction (SPE).

Gas chromatography-electron capture detector (GC- ECD)

Extracted samples were injected onto GC-ECD model 7890A-Agilent (Agilent Technologies, 5301 Stevens Creek Blvd, Santa Clara, CA 95051, US) for quantitative analysis. The GC-ECD instrument is made up of two parts. The GC portion separates the chemical mixture into pulses of pure chemicals and electron capture detector was equipped with GC. The GC separates chemicals based on their volatility which they evaporate into a gas. The chemicals in the mixture separate based on their volatility. Electron capture detector converted the sample and represents it via chromatogram. Table 1 shows the instrument set up for detection of chlorpyrifos in solutions after cleaning process.

Soda-salt solution and tap water

Compared to other cleaning solutions, soda-salt solution and tap water have no removal effect on chlorpyrifos residues. Based on previous study, it is shown that soda-salt has a good removal effect on other type of pesticides. Yu-shan et al. (2013) proved that soda-salts have very good removal effect on mixed pesticide residues consisting of three types of pesticides which are dimethoate, dicofol, and cyhalothrin. The removal rates of soda-salt solutions in removing these three types of pesticide residues are very good results which are 32.5% of dimethoate, 26.9% of dicofol, and 44.4% of cyhalothrin (Yu-shan et al., 2013). However, in this project, the removing of chlorpyrifos residues cannot be detected due to the degradation of chlorpyrifos in basic medium. Besides that, soda-salt solutions have very high basic pH which is 10.82. From the previous study, the degradation of chlorpyrifos is very fast in basic medium and it was stated that in pH 8.4, the degradation of chlorpyrifos with half-life is about 16 days (Singh et al., 2003). The higher the alkalinity of solutions, the degradation of chlorpyrifos became faster. So it is difficult to detect the presence of chlorpyrifos in the sample.

In soda-salt solutions, there is a factor that had effect on the percentages of removal. After the residues cleaning process was extracted using Solid-Phase Extraction, the sample was stored for long before its analysis. So, the chlorpyrifos in the sample was degraded due to long period of time kept in basic condition.

For tap water, the removal rate is same as soda-salt solution. However, soda-salt solutions can be used as pesticides remover for other kind of pesticides. In tap water, there is no component that can contribute in removing pesticide residues. So, using tap water in removing chlorpyrifos residues in cauliflower is not good.

The authors have not declared any conflict of interests