Study: Urban farm vegetables high in mercury, faecal content

An analysis of heavy metals and pathogen levels in vegetables grown using water from selected urban areas of the Greater Accra Metropolis has revealed that consumers face health risks linked to mercury (a heavy metal) and faecal coliforms.

The study, titled ‘Analysis of Heavy Metals and Pathogen Levels in Vegetables Cultivated Using Selected Water Bodies in Urban Areas of the Greater Accra Metropolitan Area (GAMA)’, was published in April 2024.

It examines the levels of heavy metals and faecal coliform in two vegetables, lettuce and bell pepper, cultivated using open-surface wastewater from drains and constructed reservoirs at various locations within GAMA.

Using concurrent mixed methods, questionnaires were administered to 67 vegetable farmers, followed by the collection of vegetable samples from three urban farm sites – Haatso, Dzorwulu, and the Weija Irrigation Scheme site (WISS) – for laboratory analysis.

The concentrations of lead (Pb), mercury (Hg) and cadmium (Cd) were determined using atomic absorption spectroscopy after microwave digestion of the vegetables, while total faecal coliform was quantified using the MacConkey-Endo broth method.

Results from all three sites showed that the concentrations of Cd (≤0.001 μg/mg) and Pb (≤0.005 μg/mg) in lettuce were within the World Health Organization’s (WHO) permissible levels.

However, the levels of Hg (≥0.309 μg/mg) and faecal coliform (>5 count/100 ml) in the vegetables from all three sites exceeded the WHO permissible limits.

The study concludes that consumers of vegetables from such urban farms are exposed to health risks associated with Hg and faecal coliforms.

When contacted, a team member of the study, Alan Gbeasor, told the B&FT that the phenomenon is a significant issue. The study indicates the need to intensify education on the health risks of consuming vegetables produced from open-surface water sources in the observed sites. I

t also suggests the enforcement of existing phytosanitary standards to enhance food safety and the quality of urban vegetables.

Conventional practice

Open-surface water sources have, indeed, been utilised for irrigating vegetable farms in cities and many urban centers. These open-surface waters often contain unmonitored concentrations of health-threatening contaminants, posing risks to human health, especially when used to produce vegetables for consumption.

However, information on the levels of heavy metals and faecal coliform bacteria in such vegetables at selected sites, particularly in the Greater Accra Metropolitan Area (GAMA) of Ghana, is scarce.

Urbanisation causing water scarcity

The rapid rate of urbanisation (56.7 percent) in the country and unpredictable rainfall patterns, leading to freshwater scarcity, have compelled many small-scale farmers to resort to using polluted or contaminated wastewater sources for urban vegetable farming.

This practice not only raises concerns about the quality of agricultural produce, but also gives rise to potential food safety and health risks for urban families who rely on these vegetables in the Greater Accra Metropolitan Area.

According to the Mordor Intelligence Report in 2024, the country’s vegetable market share is estimated at US$0.95billion and is projected to reach US$1.2billion by 2029.

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