Pesticide residue monitoring in green beans from Souss-massa (Morocco) and half-life times of dithiocarbamate fungicide on green beans after field treatments by Mancozeb and Mefenoxam

Two hundred and fifteen green beans samples from an agricultural region of the Souss (Agadir, Morrocco) were analyzed for endosulfan, dithiocarbamate, bifenthrin, chlorothalonil, iprodion, procymidon and deltamethrin. Of 189 samples that contained pesticide residues, dithiocarbamates (mancozeb and mefenoxam) were detected in 43 (20 %) in the concentration range of 0.045 to 2.651 mg Kg-1. Four of them exceeded European Maximum Residue Limits (MRLs). Therefore, residue levels of mancozeb and mefenoxam were determined in green beans in an experimental greenhouse, during 17 days in which three consecutive treatments with both pesticides were applied. Sampling was carried out at 1 to 18 days after each multiple application, simulating the typical harvesting practices in greenhouse plantations. Residue levels of mancozeb and mefenoxam were determined by using a simple method consisting in a hot acid digestion of the whole sample to evolve carbon disulfide (CS2), which is further quantified by spectrophotometry. During the study, residue levels in the plantation ranged between 1.99 and 0.0012 mg/kg for mancozeb and between 1.88 and 0.001 mg/kg for mefenoxam, with median values of 0.3425 and 0.3071 mg/kg respectively. The residual concentrations after the p.i. were high than legal limits in four samples. This finding indicates the need for careful control of the spraying doses of this fungicide in the green beans.