Dithiocarbamate Fungicides and Ethylenethiourea Residue Levels in Tomato and Sweet Pepper from Markets: Kirinyaga and Nairobi Counties, Kenya

Abstract

Vegetables are a major source of essential nutrients such as minerals, proteins, energy and also a source of 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 ethylenthiourea (ETU) a carcinogenic compound has a long residual time of between five to ten weeks. This study determined the residue levels of propineb, mancozeb and its metabolite ETU on tomato (Lycopersicon esculentum Mill) and sweet pepper (Capsicum annum L) during wet and dry seasons. The analyte was extracted from the vegetable using acetonitrile-dichloromethane-chloroform mixture and analyzed using HPLC together with method validation. The method of analysis had R2 values (0.948-0.999) and recoveries ranging from 91.26-95.89 %. 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 results from this study indicates high residue levels of mancozeb, propineb and ethylenethiourea with significantly higher levels of dithiocarbamates in wet season and significantly higher levels of ETU in dry season.