Pesticides Residues and Microbial Contamination of Tomatoes Produced and Consumed in Kenya

Abstract

Tomato is one of the most cultivated and consumed vegetables in the world. The main production in Kenya is by small scale farmers who may not comply with the prescribed pesticides practices. Similarly, the environment or postharvest handling may be the source of bacterial contamination. Freshly consumed tomatoes are thus likely to contain high pesticide residues levels and bacterial loads. This study was designed to determine on-farm pesticide practices, pesticide residue levels, bacterial load and consumers’ awareness on potential presence of pesticide residues and bacteria on fresh tomatoes sold in markets. A cross-sectional survey with tomato farmers using a semi-structured questionnaire was randomly administered to 52 participants in Mwea. A number of 240 tomatoes samples were collected twice a month from three open-air markets and two supermarkets from January to June 2017 in Nairobi for pesticide residues and bacterial analyses. For further studies, sampling of freshly prepared tomato for salad from three restaurants and three hotels of the four stars levels and above randomly selected in Nairobi was also conducted. A total of six samples was collected for pesticide levels and bacteria load analyses. Lastly, consumers’ awareness of pesticide residues and bacteria on fresh tomato was assessed using a semi-structured questionnaire administered to 101 households in Kangemi in Nairobi. E. coli and Salmonella presence on tomato were detected using pour and spread plate’s methods respectively followed by enumeration and biochemical characterization. QuECHERS followed by GCMS tandem LCMS/MS were used for detections. Data from surveys (farmers and consumers) were analyzed using SPSS and tested at 95% level of confidence. About 90 % farmers were males, 46% were 36 to 49 years old and 4% had never attended any school. Around 93% spray pesticides once a week on-farms, 77% observe at least 7 days pre- harvest period, 6% spray at postharvest and education had a negative correlation (p= -0.003) on on-farms pesticide use. About 48.5% of tomatoes analyzed had pesticide residues of which 27.27% were single, 21.21% multiple and 6.06% and 1.51% had levels above EU and Codex MRLs respectively. Tomatoes had 96% of E. coli load and the same samples had 20% of non-typed Salmonella spp. About 50% of E. coli had levels above recommended load (log10cfu.ml-1 > 2). Freshly prepared tomatoes for salad were free of Salmonella. Single and multiple pesticide residues were detected of which, omethoate (0.08 mg.kg-1; LOQ 0.02 mg.kg-1; MRL 0.01 mg.kg-1) and dimethoate (0.04 mg.kg-1; LOQ 0.02 mg.kg-1; MRL 0.01 mg.kg-1) had levels above EU MRLs. Consumers’ awareness on enteric bacteria load had no significant difference (p= 0.083) between males and females. However, the sociodemographic characteristics significantly influenced consumers’ awareness (p< 0.05) on pesticides presence on tomato. About 86% and 74% of consumers knew pesticide and bacteria can be found on tomato (p= 0.000) respectively. The study concludes that, farmers in Mwea were conversant with pesticides, and most of them observe good practices. Single and multiple residues were detected in samples and very few were above EU and Codex MRLs. Most fresh tomatoes sold in open air markets and supermarkets in Nairobi contain E. coli above acceptable load and some samples contain Salmonella. Consumers were slightly more aware of health effects of bacteria than with pesticide residues. The level of education influences the awareness of consumers on pesticide health effects thus, information, education and communication are necessary.