Persistence of fenitrothion in oranges and clementines after treatment with emulsifiable concentrate and microencapsulate formulations

The rate of decline of fenitrothion residues was investigated in oranges and clementines after treatment with two different kinds of commercial formulations: emulsifiable concentrate (Afidina M) and microencapsulate (Fenitrocap and IPM 400). The study was performed on the fruit and leaves over 131 and 161 days for oranges, and over 78 and 86 days for clementines, respectively. In fruit, the experimental data showed a similar behaviour of the active ingredient for both kinds of commercial formulations. High mean levels of fenitrothion (between about 0.4 and 0.8 mg kg(-1)) were persistent for at least 75 days after treatment in oranges and 50 days in clementines, with statistically significant declines observed only at days 110 and 78, respectively. A rapid decline of fenitrothion levels was observed in orange and clementine leaves during the starting phase followed by a slower decrease during the later stage; the decline was more pronounced with the treatment of emulsifiable concentrates. These findings are indicative of a poor degradability of fenitrothion in citrus fruits, and suggest that repeated or uneven applications of the pesticide should be avoided in order to exclude the risk of exceeding the maximum residue level permitted by the current regulations.