Dithiocarbamates and Ethylenethiourea Residue Levels In Tomato and Sweet Pepper from Kirinyaga and Nairobi Counties
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Date
2020
Authors
Karanja, Elias Kiura
Journal Title
Journal ISSN
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Publisher
Kenyatta University
Abstract
Vegetables are a major source of essential nutrients such as minerals, proteins, energy
and roughage. Some vegetables such as tomato and sweet pepper can be eaten raw or
cooked. These vegetables are affected by pests and diseases that are controlled using
pesticides among which are fungicides such as dithiocarbamates (DTCs) that are toxic
to human and animals at high concentrations. DTCs are commonly used in different
combinations in Kenya and one of their metabolites, ethylenethiourea (ETU) a
carcinogenic compound, has a long residual time of between five to ten weeks. Cooking
degrades DTCs to metabolites while proper cleaning can remove the residue
considerably. This study investigated the levels of dithiocarbamate fungicides propineb
and mancozeb, and the metabolite ETU in tomato (Lycopersicon esculentum mill) and
sweet pepper (Capsicum annum l) during wet and dry seasons and also after different
temperature and cleaning treatments. The analyte were extracted from vegetables using
acetonitrile-dichloromethane-chloroform mixture and analyzed using HPLC. The
results obtained showed residue levels of propineb and mancozeb in tomato which were
significantly higher in the wet season in three out of the four markets. The levels of
mancozeb in tomato were ranging from 2.56±0.12 mg/kg in the wet season to below
detection limit (BDL) in the dry season while in sweet pepper the levels ranged from
2.69±0.57 mg/kg in wet season to 0.16±0.00 mg/kg in dry season. Propineb levels
ranged from 3.97±0.50 mg/kg in wet season to BDL in dry season in tomato while in
sweet pepper the range was 6.54±0.72 mg/kg in wet season to BDL in dry season. The
ETU levels in tomato samples were significantly higher in dry season than wet season
and ranged from 27.94±0.39 mg/kg to BDL in wet season while in sweet pepper the
levels ranged from 8.88±1.55 mg/kg in dry season to BDL in wet season. Two out of
four markets had propineb residues in tomato above maximum residue limit (MRL) set
by WHO/FAO and EU of 3 mg/kg while there were no levels of mancozeb above MRL.
ETU mean residue levels exceeding the MRL of 0.05 mg/kg were noted in all vegetable
samples. The temperature treatment showed a significant increase of ETU residues
from a low mean of 9.43±0.03 mg/kg at 25℃ to a mean of 12.43±0.38 mg/kg at 90 ℃
showing an increase of ETU residues with cooking. Cleaning with sodium hypochlorite
(chlorine water) showed a reduction of ETU residue by 99.9% in tomato and by 100%
in sweet pepper. The mean residue levels of ETU in tomato reduced from a mean of
46±0.71 mg/kg to 0.05± 0.00 mg/kg while in sweet pepper a reduction from 2.14±0.02
mg/kg to BDL. Cleaning with water and chlorine water differed significantly in
removing the ETU residue. Mancozeb mean residue levels in tomato cleaned with
sodium hypochlorite reduced by 95.2% while propineb reduced by 80.4%. Cleaning
with sodium hypochlorite showed a significant removal of fungicides than water only.
The result from this study indicates high residue levels of mancozeb, propineb and
ethylenethiourea in fresh and cooked tomato and sweet pepper. There is therefore a
need for cleaning with chlorine water and rinsing with water before consumption and a
regular surveillance of the fungicides and metabolite.
Description
A Thesis Submitted In Partial Fulfillment of the
Requirements for the Award of the Degree of Master of
Science in Applied Analytical Chemistry in the School of
Pure and Applied Sciences, Kenyatta University
Keywords
Dithiocarbamates residue, Ethylenethiourea Residue, Sweet Pepper, Kirinyaga county, Nairobi County