Shoppers buying fresh vegetables from the maze of stalls at Dar es Salaam's Kariakoo market have no idea of the risks they are taking, but food safety officials are alarmed by the chemicals and effluent in the water used on the city's urban farms.
Doreen Nkya always buys some spinach or amaranth on her way home because she considers them an important part of her family's diet. "I like vegetables because they are healthy. We don't often go without them at our dinner table," she said.
Like most other shoppers, the 33-year-old business district tailor is entirely unaware of how or where her favourite greens are grown, though urban farming is increasingly popular among poor city dwellers trying to scratch a living.
"I don't know if clean or dirty water is used to grow them, but we usually wash and boil them before eating," she told the Thomson Reuters Foundation.
Food safety authorities recently warned that Dar es Salaam residents who eat vegetables grown in the urban gardens may be exposed to health risks caused by the waste matter and industrial spills contaminating the farms' water supply.
Urban agriculture, essentially growing vegetables, is a lucrative business in Dar es Salaam employing a large number of people, officials said.
Since rapid urbanisation pushed low-income families to the margins because of inadequate housing, hunger and a shortage of clean water, vegetable growing has become a survival strategy for the urban poor who lack the skills to secure well-paid jobs.
Because of its haphazard emergence, urban farming is largely unregulated, leaving farmers free to use whatever liquids they can find - including dangerous effluents - to grow their crops, officials warned.
The Tanzania Foods and Drugs Authority (TFDA) said that vegetable farmers who use polluted water from the Msimbazi River may be endangering consumers' health.
Crops grown in an unhygienic environment where farmers use sewage or industrial spills to water their vegetables may be contaminated with pathogenic micro-organisms and chemicals likely to cause serious diseases, TFDA officials said.
"Dangerous bacteria found in vegetables can be destroyed by cooking for a long time, but chemicals including heavy metals can still find their way into people's bodies," said Candida Shirima, TFDA manager in charge of Food Risk Analysis.
Farmers in the valley beside Msimbazi Creek said they had no choice but to use whatever water was available.
Edward Merkior, a veteran vegetable grower, often taps the stream of waste water flowing from a crowded Buguruni slum to water his crops.
"I am not ashamed of using this water because we don't have access to clean piped water," Merkior told the Thomson Reuters Foundation.
The 45-year-old farmer, who grows pumpkin leaves, Chinese cabbage and fast-growing amaranth, said farmers initially used 'clean' water from the Msimbazi River, but authorities stopped them, saying that hazardous spills had tainted the water.
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"If we are forbidden to even use water from the river, how on earth can we earn a living?" he shouted angrily.
Around the country, the shortage of clean water near big towns has forced the growing number of urgan farmers to use waste water or river water tainted by chemical spills on their crops, officials said.
Anyone eating half-cooked vegetables or salads is likely to be exposed to bacteria or dangerous heavy metal that may lead to cancer, kidney failure or impaired cognitive function in children, the TFDA says.
A 2013 study by local Ardhi University, 'Heavy metals concentrations in selected areas used for urban agriculture in Dar es Salaam', suggested that the discharge of chemical byproducts into the city's creeks and valley streams had led to unacceptable levels of heavy metals such as lead, cadmium, copper and chromium.
"Our analysis showed that the soil and water samples contained substances that may be harmful to vegetable eaters," said William Mwegoha, one of the researchers.
Zawadi Herman, who has been growing vegetables in the area for 10 years, vowed to keep doing so to support her family.
"We depend on this work for our survival, if the government wants to ban it then obviously my family will suffer," she said.
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