Dithiocarbamates and Ethylenethiourea Residue Levels In Tomato and Sweet Pepper from Kirinyaga and Nairobi Counties

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.