A Farm to Fork Risk Assessment for the Use of Wastewater in Agriculture in Accra, Ghana

Abstract

The need to minimise consumer risk, especially for food that can be consumed uncooked, is a continuing public health concern, particularly in places where safe sanitation and hygienic practices are absent. The use of wastewater in agriculture has been associated with disease risks, though its relative significance in disease transmission remains unclear. This study aimed at identifying key risk factors for produce contamination at different entry points of the food chain. Over 500 produce and ready-to-eat salad samples were collected from fields, markets, and kitchens during the dry and wet seasons in Accra, Ghana, and over 300 soil and irrigation water samples were collected. All samples were analysed for E. coli, human adenovirus and norovirus using standard microbiological procedures, and real time RT-PCR. Finally, critical exposures associated with microbial quality of produce were assessed through observations and interviews. The study found that over 80% of produce samples were contaminated with E. coli, with median concentrations ranging from 0.64 to 3.84 Log E. coli/g produce. Prepared salad from street food vendors was found to be the most contaminated (4.23 Log E. coli/g), and that consumption of salad exceeded acceptable health limits. Key risk factors identified for produce contamination were irrigation water and soil at the farm level. Storage duration and temperature of produce had a significant influence on the quality of produce sold at markets, while observations revealed that the washed water used to rinse produce before sale was dirty. The source of produce and operating with a hygiene permit were found to influence salad microbial quality at kitchens. This study argues for a need to manage produce risk factors at all domains along the food chain, though it would be more effective to prioritise at markets and kitchens due to cost, ease of implementation and public health significance.

Fig 1. E. coli concentrations in raw produce and ready-to-eat salad at different entry points along the food chain.

Solid horizontal line: limit of E. coli concentration classified as microbiologically satisfactory for consumption (% exceeding 2 Log E. coli/g—street vended salad, 90% (N = 59), farm lettuce, 88% (N = 159), market lettuce, 80% (N = 134), restaurants salad, 60% (N = 20), market cabbage, 18% (N = 129)). P-value calculated using Kruskal-Wallis test.

Fig 2. Effect of soil (A) and irrigation water (B) on farm produce quality after adjusting for seasonality.

Seasonality and soil interaction p = 0.004, 95% CI = -0.85, -0.17. Soil effect on produce contamination (point estimate for unit increase = 0.60 Log E. coli/g produce, 95% CI = 0.32, 0.87, p < 0.001). Effect of irrigation water on produce contamination (point estimate for unit increase = 0.14 Log E. coli/g produce, 95% CI = 0.02, 0.27, p = 0.027). Error bars = 95% confidence intervals (CI).