Study warns of highly contaminated fruits,vegetables in open markets and supermarkets

The vegetables and fruits you eat at home or at your favourite lunch-time joint may be poisoning you and your children, according to a shocking new study.

The joint research by the University of Nairobi and Strathmore University has established that most fruits and vegetables sold in Kenya contain a cocktail of harmful pesticides and heavy metals that exceed safe levels.

Testing of numerous samples of common vegetables and fruits drawn from open-air markets and supermarkets in Nairobi, Nakuru and Machakos found that kales (sukuma wiki), amaranth, tomatoes, and mangoes contained the chemical residues at levels not regarded as safe by the World Health Organisation (WHO).

In particular, high levels of lead were detected in samples collected from farmers in Machakos.

The researchers say laboratory studies have showed that pesticides can cause health problems including birth defects, nerve damage and cancer over a long period.

“There is a heavy use of pesticides in tomatoes, kale and amaranth sold in the towns under study as indicated by the high level of residues. Some of these pesticide residues found in the samples were above the recommended maximum levels,” states the report titled, Evaluation of the safety of selected fruits and vegetables sold in the domestic markets in Kenya.

The results also show that due to poor production and handling practices disease-causing viruses, bacteria and fungi contaminate most raw fruits and vegetables.


“Contamination with pathogens could be due to poor handling of manure by farmers and poor adherence to the instructions that come with the pesticides. Generally, pesticides are denatured (worn out) within certain periods and this may cause problems if the period stipulated is not strictly adhered to,” said Kenneth Wameyo, a veterinary surgeon.

He said most retailers sprinkle or moisten vegetables and fruits with unclean and sometimes contaminated water in bid to keep them fresh and appealing.

“Contamination from manure could be due to poor usage and application of manure. Animal waste should only be used as manure once it has been dried and treated, but most farmers apply it when it is still wet and contagious, which is a sure source of disease,” Dr Wameyo said.

The study also suggested possible contamination during transportation of the commodities. Most traders transport vegetables and fruits using open trucks. 

Although the researchers did not establish at what point the food is most vulnerable, they pointed out that fresh produce maybe contaminated at any point from the farm to the table. The major source of contamination is animal or human faeces.

“Vegetables and fruits with thinner skins such as strawberries, peaches, peppers, spinach and lettuces, kales, cabbage, traditional vegetables and apples can have highest levels of pesticide residue. The vegetables and fruits with the lowest residue include avocados, mangoes and bananas,” states the report.

The study also revealed a new phenomenon where vegetables and fruits grown in separate towns sometimes have different nutritional values. This means that a person eating vegetables grown in Machakos, for instance, might not get the same nutrients as another consuming the same fruit in Nakuru.

“The nitrate content in the leafy vegetables (kales and amaranth), tomatoes and mangoes varied greatly ranging from above 200mg/100g fwb in mangoes sold in the supermarkets in Machakos town to 50mg/100g fwb in tomatoes sold in open air market in Nairobi,” adds the study.

The researchers say there is need to carefully regulate the use of pesticides on fruits and vegetables to ensure they do not pose unreasonable risks to human health or the environment.

The findings, according to the lead researchers, mean a big population of Kenyans are exposing themselves to a myriad of health problems ranging from those whose causes might be difficult to trace like birth defects and nerve damage, to cancer and other diseases that might occur over a long period of time.

The study, which was conducted between July and August last year, was led by Dr Cecilia Onyango, a lecturer at the Department of Plant Science and Crop Protection at the University of Nairobi and Dr Catherine Kunyanga, lecturer at the Department of Food Science, Nutrition and Technology at the same institution.

It was commissioned by a multi-stakeholder forum Agri Profocus and Dutch NGO, Hivos and funded by the Dutch government.

Doctors have been recommending more consumption of vegetables and fruits as a way of fighting lifestyle diseases like high blood pressure, obesity and some forms of cancer. 

However, reliance on pesticides and associated risks has seen the emergence of organic markets and restaurants that only sell naturally grown vegetables and fruits.


Currently, the horticulture industry is the fastest growing agricultural subsector in the country, and is ranked third in terms of foreign exchange earnings from exports after tourism and tea.

Fruits, vegetables and cut flowers dominate horticulture in Kenya where agriculture accounts for about 24 per cent of the country’s Gross Domestic Product. An estimated 75 per cent of the population depends on farming either directly or indirectly.

Kenya imports approximately 7,000 metric tones of pesticides worth Sh4.3 billion every year, an indication that the problem could persist if urgent measures are not taken to address it.

“The leafy vegetables (kales and amaranth), tomatoes and mangoes sold in both open-air and supermarket chains in the towns under study were contaminated by pathogenic microbes, had pesticide residues some of which were beyond the allowed limits and these included Dimethoate, Bifenthrin, Metribuzin, Cyromazine, Metalaxyl and Pyrimethamil and contained heavy metals,” states the report.

While the effect of the pesticides and heavy metals present in vegetables and fruits could be ruining lives slowly, one of the worst cases of widespread calamity caused by food happened in 2004.

The presence of high levels of aflatoxin in maize in January to June 2004 in Eastern Kenya resulted in a total of 317 reported cases of direct poisoning with 125 deaths.

 Maize sampled from the affected areas had aflatoxin B1 concentrations that were 220 times greater than the level allowed by food safety standards.

The findings pose a great challenge to the Government and the various agencies charged with setting standards for food and agricultural products.

In Kenya, 30 technical committees whose secretariat is at the Kenya Bureau of Standards, develop the standards.

Food standards give specifications for the compositional requirements, microbial requirements, the tolerance limits for contaminants, packaging, labelling and the hygiene conditions necessary for products to be passed on as consumable.