Comparative Study of Pyrethroid Residues in Fruit Peels and Flesh Using Solid-Liquid Extraction Combined with Magnetic Solid Phase Extraction

Introduction:  Many fruits show high amount of nutrients in their peels as compared to flesh. Thus, nutrition specialists recommend consuming the whole fruit rather than the peeled. However, the majority also assumes that peels are more susceptible to pesticide residues, if the fruits are not properly cleaned. To achieve the maximum benefits of fruit consumption, it would be helpful to e able to make comparisons between the pyrethroid levels in peels versus flesh.

Purpose:  This study aimed to develop a fast and convenient detection method for pyrethroid residues in fruit peels and flesh and to compare the pyrethroid residues in fruit samples.

Methods:  The application of a laboratory prepared polystyrene magnetic nanoparticles (PSt@MNPs) based magnetic solid phase extraction technique combined with liquid-solid extraction helped clean the sample and preconcentrate the targeted analytes prior to HPLC quantification. Optimization of the parameters affecting extraction efficiency was carried out.

Results:  Analytical performances were evaluated by carrying out experiments at optimum conditions. Results showed that the LODs and LOQs were below 0.1445 and 0.5116 ng g^-1, respectively, for the six pyrethroids tested. The recovery rates were within the range of 73.6 – 123.1% with intra-day and inter-day RSD being less than 16.5 and 15.4%, respectively; suggesting satisfactory reproducibility of the proposed method. Real sample analysis was performed using six commonly consumed fruits, obtained from local supermarkets in Singapore; including apples, pears, oranges, peaches, and nectarines. Peels and flesh were tested separately to study the difference of pyrethroid residues in different parts of fruits. Permethrin residue was detected on the grape peel sample. No violation was reported, since the residue amount detected was far below the maximum residue limit set by the government.

Significance:  The results suggest that the proposed method is a promising, rapid, and convenient way to analyse pyrethroid residues in fruit peels and flesh.