Behavior of methamidophos residues in peppers, cucumbers, and cherry tomatoes grown in a greenhouse: evaluation by decline curves.

Residue levels of methamidophos were determined in peppers, cucumbers, and cherry tomatoes grown in commercial greenhouses, up to 6 weeks after being sprayed with Monitor (methamidophos 60%). Mathematically defined decline curves were established by determining optimal relationships between methamidophos residues and time, using different models. Model functions that best fit experimental data were 1st-order function for cucumber, 1.5th-order function for pepper, and 1st-order root function for tomato. However, in all cases, the 1st-order function was legitimized statistically. Half-life times determined from the optimal functions were 8.68 days (cucumber), 13.28 days (pepper), and 2.77 days (tomato), whereas half-life times determined from the 1st-order reaction function were 8.68 days (cucumber), 17.04 days (pepper), and 7.47 days (tomato). In this work, some experiments to determine residue levels of methamidophos in these vegetables after multiple applications were also carried out. The unexpected high residue levels found in all cases after five successive applications seem to indicate that methamidophos presents certain long-term accumulative effects in the three studied vegetables.