Seasonal Variability of Organophosphate and Carbamate Pesticides in Clementines and Tomatoes in Lebanon: An ELISA based study

Abstract

Background: The intensive use of pesticides in agriculture has raised global concerns over environmental contamination and food safety, particularly in fresh produce consumed without processing. In Lebanon, pesticide residues exceeding maximum residue limits (MRLs)—including banned or unregistered compounds—have been reported in fruits and vegetables. However, no prior studies have investigated the seasonal variation of pesticide contamination using experimental detection tools like ELISA.

Objective: This study aimed to assess the seasonal variability of organophosphate and carbamate pesticide residues in clementines, with comparative data from tomatoes, using enzyme-linked immunosorbent assay (ELISA).

Methodology: A total of 116 samples were collected, including in-season and off-season clementines and locally produced and imported tomatoes sourced from different locations. Samples were subdivided by fruit part (skin vs. inside) and wash status (washed vs. unwashed). Homogenized samples were extracted with methanol, centrifuged, and tested using commercial ELISA kits. Absorbance values were measured at a wavelength of 405 nm. Data were analyzed using SPSS through univariate and ANOVA tests. Higher absorbance values indicate lower pesticide residues.

Results showed that seasonality and location had significant effects on average absorbance values (p < 0.001), indicating notable variability in pesticide residue levels. Off-season clementines exhibited significantly higher pesticide residues than in-season ones. Tomatoes, except those imported from Syria, showed no organophosphates or carbamates pesticide levels. The samples were divided into four groups: peel washes, peel unwashed, pulp washed and pulp unwashed. The differences between part and wash groups were not statistically significant.

In conclusion, this study demonstrates that off-season cultivation is associated with higher pesticide contamination in clementines, potentially due to increased pest pressure and chemical use. Residues of organophosphate and carbamate pesticides were found in imported tomatoes, while none were detected in locally grown samples.