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Scientists warn Nairobi fish have chemicals that could cause cancer

July 3rd, 2016 4 min read

Some of the fish consumed in Nairobi, Kiambu and Machakos counties are contaminated with chemicals, including those known to cause cancer, a research has shown.

While most of fish eaten in Nairobi comes from Lake Victoria, a significant percentage of farmed tilapia in neighbouring Kiambu and Machakos Counties is sold and consumed in the city.

The fish is sold in restaurants, open markets, kiosks, roadside eateries and some at the famous Gikomba market in Nairobi.


An investigation by researchers from the University of Nairobi tested 213 fish samples from 60 ponds in Kiambu and Machakos and found them to be contaminated with banned agricultural chemicals.

The findings, published in February in the journal Cogent Environmental Science confirmed residues of DDT, Lindane, Heptachlor and Dieldrin, Endrin in almost all the samples.

Human poisoning from Aldrin and Dieldrin is characterised by major body convulsions. Heptachlor is highly toxic to humans and can be absorbed through the skin, lungs and the food tract.

These chemicals are banned in most countries and in Kenya by the Pest Control Products Board. The study led by Dr Isaac Omwenga, showed Lindane and DDT as the most prevalent in all the samples analysed.

“While the contamination did not breach international health safety standards, it is an extremely worrying trend,” Dr Laetitia W. Kanja of the University of Nairobi and one of the study authors told the Nation.

More samples from Kiambu were found to be contaminated compared to those from Machakos, possibly because of the heavy use of agriculture chemicals in central Kenya.

Kiambu was also found to have more earth ponds which easily allow for leaching of the agricultural chemicals into the fish farming environment.


Kiambu County recently announced a Sh2.6 million fish-farming expansion programme with Nairobi and locals as the principal markets. Experts say it is important to factor in the health concerns.

“The issue of chemical residues must first be addressed maybe through non-leaching ponds and caveat on dangerous chemicals or both,” says Dr Kenneth Wameyo a consulting veterinary surgeon in Nairobi.
DDT residue was found in all tested fish body parts including muscle and liver with the highest concentration found in the brains. The head usually reserved for those with best fish eating skills is considered most nutritious.

“Our evidence suggests recent use of DDT in the study area hence more strict control measures against the use of this chemical need to be put in place,” wrote Dr Omwenga and his team.

Last June, the World Health Organisation (WHO) classified the chemical Lindane as carcinogenic to humans and DDT as possibly carcinogenic. This week the WHO is meeting to review the caveats against a number of harmful agricultural products including Lindane.

DDT has been linked to a cancer which attacks the body’s immune system, testicular and liver.


A check at the Pest Control Products Board shows Lindane to have been banned for use as an insecticide in Kenya in 2011 and DDT in 1986 for use in agriculture. But the board at the same time has registered several agricultural products such as Acarin, Dicofol and Kelthane, which contain DDT.

The use of DDT was, however, brought back in 2006 for malaria control through residual indoor spraying especially in western Kenya. But recent studies show this strategy to have failed hence putting the lives of Kenyans and the environment at risk.

A recent Dispatch (Volume 21, Number 12—December 2015) by the US Centres for Disease Control and Prevention in Nairobi, showed the malaria mosquito to have developed high levels of resistance against DDT. Separate studies in Western Kenya have found extensive soil poisoning by various chemicals.

In January, Dr Elijah Ngumba of the University of Jyvaskyla, Finland, published a landmark study showing the whole of the Nairobi River basin to be extensively contaminated with residues from HIV and Aids drugs.

Residues of three first line HIV and Aids medicines were found in all rivers in Nairobi including at Athi River’s Fourteen Falls, a popular fishing and recreation site.

Dr Ngumba in the study published in Science of the Total Environment demonstrated that the waters of Nairobi rivers had high concentration of the antiretrovirals Lamivudine, Nevirapine and Zidovudine and other antibiotics.


The chemicals, he said were not just affecting fish in some of the rivers but the waters are also used to raise crops and livestock whose products are consumed in the city and nearby counties.

A policy brief by the Ministry of Agriculture estimates about 50,000 bags of maize and 15,000 bags of beans are produced in Nairobi annually.

The ministry estimates that up to a quarter million chicken are reared within Nairobi and about 45,000 goats and sheep.

Environmentalist Isaac Kalua, who also chairs the Kenya Water Towers Agency, says there is inadequate waste water treatment systems for removing chemical component before the water is returned for use into the environment.

Even where waste water works exists, a recent Sino-Africa study indicates they were never designed for the removal of pharmaceutical waste.

Dr Omwenga and his team argue that, some of the chemicals found in the fish though banned are bound to linger in the atmosphere for some time hence remaining a matter of serious concern.

“But these are not excuses for allowing people to consume chemicals no matter the level of concentrations, the same fish are also eaten by birds and other life forms which have a lower tolerance levels,” says Dr Kalua.