© Benaki Phytopathological Institute
Hellenic Plant Protection Journal
8:
55-62, 2015
DOI 10.1515/hppj-2015-0008
1
Pesticide Residues and Environmental Pollution De-
partment, Central Agricultural Pesticide Laborato-
ry, Agriculture Research Center, Dokki, Giza, 12618,
Egypt
2
Tokyo University of Agricultural and Technology, 3-5-
8 Saiwaicho, Fuchu, Tokyo 183-8581, Japan
3
Packing and Packaging Materials Department, Na-
tional Research Center, Dokki, Cairo, Egypt
* Corresponding author:
residue levels trend (Malhat
et al.,
2015). Res-
idue dissipation curves can be used to esti-
mate the time required for residues to reach
levels below maximum residue limits (MRLs)
(Fong
et al.,
1999; Malhat
et al.
, 2014b). In ad-
dition, the MRL regulations require a pre-
harvest interval (PHI) to ensure that dissi-
pation of a pesticide is below the proposed
MRL at harvest time. The determination of
pesticide residues is usually accomplished
by chromatographic techniques and in-
volves many preliminary steps like extrac-
tion and clean-up for interference removal.
An adequate description of pesticide
degradation in soil is important for the risk
assessments within the pesticide registra-
tion process. The fate of the pesticides in
the soil environment in respect of pest con-
trol efficacy, non-target organism exposure
and offsite mobility has become a matter
of environmental concern (Hafez and Thie-
mann, 2003) potentially because of the ad-
verse effects of pesticidal chemicals on soil
microorganisms (Araújo
et al
., 2003), which
in turn may affect soil fertility (Schuster and
Schröder, 1990). Several factors influence
the final concentration of the pesticide in
soil including volatilization, photochemical
degradation, chemical and biological trans-
formation, leaching and sorption (Malhat
et
Degradation profile and safety evaluation of methomyl
residues in tomato and soil
F. Malhat
1,2,*
, H. Watanabe
2
and A. Youssef
3
Summary
A high performance liquid chromatography with the photodiode array detector (HPLC-
DAD) analytical method was developed to determine the residue levels and investigate the dissipation
pattern and safety use of methomyl in tomato and soil. Methomyl residues were extracted from toma-
to and soil samples with ethyl acetate. The extract was cleaned up with the QuEChERS method. The re-
sults showed that the average recoveries were in the range of 87.1–94.5%, with RSD of 6.9-11.2%. Limits
of detection (LOD) and quantification (LOQ) were 0.005 and 0.007 mg/kg, respectively. The residue lev-
els of methomyl were best described to first order rate kinetics and half-lives ranged from 1.34 to 1.8
days in tomato and soil, respectively. The theoretical maximum residue contributions for methomyl on
tomato were found to be less than the maximum permissible intake values even on zero days, there-
fore consumer health risks are minimal at the recommended dose on tomato.
Additional keywords:
Dissipation, HPLC-DAD, QuEChERS method, Risk assessment
Introduction
Tomato,
Solanum Lycopersicum L.
(Solanace-
ae), is grown throughout the globe and its
berry (fruit) constitutes an important part
of human diet (Gupta
et al.,
2011). In Egypt,
tomato is cultivated in about 221 thou-
sand hectares which represent about 34
% of the average area of vegetables, while
the fruits are basic component of the dai-
ly diet (Malhat
et al.
, 2012a). Chemical pesti-
cides are often applied for plant protection
of the crop (Singh
et al.,
1980; 1989; Awasthi,
1986). Nearly all these chemicals are readily
soluble in plant oils and waxes (Ripley and
Edgington 1983; Malhat and Hassan, 2011),
pausing an urgent need for monitoring pro-
grams of pesticide residues to properly as-
sess the relevant human exposure and envi-
ronmental risks.
Pesticide dissipation rate after applica-
tion is a useful gauge for the assessment of
