Effects of tea tree oils on removing pesticide residue in cowpea

Abstract: Pesticides are widely used as an insurance policy against devastating crop losses from pests and diseases. Excessive usage of pesticides may lead to contamination of the crop and the environment, eventually posing a risk of pesticide-related illnesses to humans. Previous literature has shown that water washing is only partially effective in removing pesticides, and in the case of liposoluble pesticides, a cosolvent must be used as an adjuvant. Recently, naturally occurring adjuvants are gaining prominence over synthetic chemical compounds. Tea tree oil (TTO, the oil of Melaleuca alternifolia), a natural, volatile essential oil, is mainly extracted by steam distillation from the fresh leaves and terminal branchlets of the plant. It has attracted significant interest due to its antifungal, antiviral, and antibacterial bioactivities. However, to the best of our knowledge, there are fewer experimental data evaluating its efficacy in the removal of pesticide residues. In this study, the effects of TTO on removing pesticide residue were carried out in the cowpea. Volume:volume (v:v) concentrations of 0.05%, 0.1%, 0.2%, 0.4% and 0.8% of TTO and water soluble tea tree oil (WTTO) in water were used to remove a standardized pesticide mixture (organophosphorus, pyrethroid, and carbamate compounds) from cowpeas. Sample pretreatment (pesticide application to cowpeas) was performed according to agricultural industry standards. The objective pesticide residues in cowpeas were assayed by gas chromatography (GC) and chromatography-mass spectrometry detection (GC-MS), and then the clearance rate was calculated. The results showed that TTO was able to remove the three kinds of pesticides from cowpeas. Moreover, the removal efficiency increased with increasing concentration of TTO. The effect of clearing organophosphate was much more obvious than that of either pyrethroid or carbamate. It was suggested that small liposoluble molecules of TTO rapidly infiltrate the cowpea surface to dissolve the organophosphate pesticides depending on the compatibility principle. For carbamate pesticides, such as carbofuran, owing to its high polarity, TTO could not infiltrate into the internal of cowpeas to dissolve the residuals, resulting in the lower clearing efficiency. In conclusion, to remove pesticide residues, the commercially available extract TTO was more effective than deionized water in removing pesticide residues from fruits and vegetables. In comparison, WTTO was even more effective in removing pesticide residues than the same concentration of TTO. Among all treatments, 0.8% WTTO showed the greatest removal efficiency. The removal rates achieved by WTTO were as follows: 80.48% for isocarbophos, 94.54% for malathion, 82.79% for triazophos, 84.58% for chlorpyrifos, 72.20% for omethoate, 80.51% for cypermethrin, and 72.21% for meta-tolyl-N-methylcarbamate (MTMC). Therefore, TTO is expected to be useful as a fruit and vegetable cleaning adjuvant.