Assessment of Bacteria and Heavy Metals Contamination in Lettuce at Farm Gate and Market in the Accra Metropolis

Abstract

The bacteria and heavy metals contamination of lettuce from two vegetable growing farms irrigated with either stored municipal, stream or polluted drain water were assessed on farm and in the market. A total of 120 irrigated lettuce samples consisting of sixty samples from each farm and the market were collected. All samples were analysed using standard methods. The total coliform levels of lettuce from the farm ranged from 5.63 to 9.38 log MPN/100 g, 5.32 to 10.38 log MPN/100 g, and 6.38 to 10.38 log MPN/100 g when irrigated with stored municipal water, stream water and drain water, respectively. Irrespective of the irrigation water used on the lettuce, the total and faecal coliform levels were above the ICMSF recommended levels of 1x103 100 g-1. Significant difference (p=0.05) was observed between the lettuce irrigated with municipal water and drain water. Thirteen gram-negative bacteria species were identified for irrigated lettuce both on farm and at the market. One bacterium of pathologenic concern, Klebsiella pneumoniae occurred to a lesser extent, on both farm and market-derived lettuce depending on the source of irrigation water. The heavy metals concentration in all lettuce samples examined were far below FAO/WHO recommended levels for safe vegetables consumption. It is therefore recommended that lettuce bought from farm gates or markets be washed properly to reduce the bacteria contamination before it is consumed.