Safety concerns over Mwea rice in Kenya

Food experts including at the National Irrigation Board have warned of widespread contamination of rice from Mwea Irrigation Scheme in Kirinyaga County.

The experts say a most comprehensive analysis of rice from the scheme shows widespread contamination with toxins of public health concern.

The team has tested rice from Mwea for nine types of poisons called mycotoxins, including aflatoxins and confirmed contamination though at low levels.

“Our study provides evidence of potential food safety concerns and calls for an urgent policy on safe rice production,” says Dr Samuel Mutiga of the Nairobi based International Livestock Research Institute (ILRI) and the lead investigator.

Great Concern

This, the team from the National Irrigation Board, ILRI, University of Nairobi and the International Rice Research Institute says is of great concern since the scheme provides about 80 per cent of rice consumed in Kenya.

“Though generally we found the toxins at low levels this should in no way suggest the rice is safe for human consumption.  Rather it confirms long term consumption of toxins known to compromise human health,” said Dr Mutiga.

A long-term, exposure to small amounts of carcinogenic substances, the experts warn could cause different types of cancer.  

“We hope this report will create awareness for rice growers, traders, consumers, extension staff, and policymakers to stop further exposure of consumers to these toxic and carcinogenic substances in Kenya,” Dr Mutiga told the Standard in an interview on Tuesday.


Of concern he said is the fact that some of the rice was infected with multiple types of mycotoxins, some carcinogenic and others known to suppress human immunity.

Probable cancers from the identified toxins, the team says may include throat, lung and liver tumors and kidney problems as well.

The team had tested white milled rice from Wang’uru, Kagio, Kandongu, Kimbimbi, and Mutithi suburbs of Mwea Irrigation Scheme for nine types of mycotoxins and confirmed their presence.

“This is the first study to report multiple mycotoxins in rice produced in Kenya an indication of chronic consumer exposure from local rice,” says the study published last month (11th March 2021) in the journal Toxins.


Mycotoxins are naturally occurring toxins or poisons produced by certain fungi or mould  that grow on a variety of foods including cereals, nuts, spices and dried fruits.

Long-term or chronic exposure to the mycotoxins, including aflatoxin, the World Health Organisation warns, can lead to liver or kidney cancers, birth defects in children and compromised body immunity.

The new study proposes immediate measures be put in place to protect consumers which should include adequate drying of rice before storage  while farmers are educated to stop heaping damp paddy during transportation or storage.

“The breakage of kernels should be avoided during milling, while milled rice should be stored in hermetic (air-tight) bags and under ventilated sheds.”

Additionally, Dr Mutiga suggests farmers should be educated to adequately dry the grain to below 14 per cent moisture content before delivering to the mill.


This is the second time in as many years experts are raising safety concerns over rice consumed in Kenya.  Data presented at the last annual scientific conference of the Kenya Medical Research Institute in 2019 showed rice sold in Nairobi, Mwea, and Thika to be highly contaminated with aflatoxins.

 “We have established that a lot of locally-produced and imported rice contains aflatoxin-causing agents and maybe a threat to human health,” said Youmma Douksouna, the lead study author.

He attributed the presence of aflatoxin in rice to poor handling and packaging, sale of expired grains, and long periods of storage and transportation of imports.

Rice is the third most consumed food in Kenya after maize and wheat with consumption estimated to be increasing at a rate of 12 per cent annually.


The annual national rice consumption is estimated at 538,000 metric tonnes compared to an annual production of 112,800 tonnes.

With a projected population growth rate of about 2.7 per cent per year, the estimated annual national requirement may reach up to 570,490 tons by 2030.

Apart from the mycotoxins, rice production in Mwea is also threatened by one of the world’s 100 most invasive species.

Two weeks ago the irrigation board, Kenya Plant Health Inspectorate Service (Kephis) and the Centre for Agriculture and Biosciences International, confirmed   that a pest that has devastated rice at the scheme since last year is among the most dreaded in the world.

Samples sent to the UK for genetic identification, the team reported had confirmed the pest as Apple snail or Pomacea canaliculata, which has caused massive rice damage in Asia.


“This is the first documented record of P. canaliculata in Kenya, and the first confirmed record of an established population in continental Africa,” wrote the team in the journal CABI Agriculture and Biosciences.

The pest first reported in  the scheme in February last year has infested over 1,500 hectares of rice  mainly in Ndekia and Tebere  areas  of Mwea destroying almost 50 per cent of the crop.

To control the pest Kephis boss Theophilus Mutui has called for strict quarantine measures to curb the spread of the snail into other rice-producing risk areas in the country. 

By Gatonye Gathura

About Gatonye Gathura 142 Articles
Science Journalist

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