How safe are crops grown in wetlands?

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John Kasozi

Kampala, Oct 02, 2006 (New Vision/All Africa Global Media via COMTEX) --MOST food crops grown in urban wetlands absorb a number of pollutants. This is especially so with sweet potatoes and cocoyams.
Recent research undertaken by leading East African scientists under the Lake Victoria Research Initiative of the Inter-university Council of East Africa raises the need for serious attention to possible effects of lead and cadmium on human health.
"The sweet potato is a source of carbohydrates for poor urban dwellers in East Africa. If it is grown in wetlands, there is a possibility for it to take up lead from burning leaded petrol and flaking leaded house paints," says James Nsumba, an agronomist. According to the research, cocoyam was found to be three times more resilience than sweet potato, surviving even at 800 particles per million (lead). All sweet potato varieties experimented had succumbed.
Cocoyam is well known for its tolerance to heavy metals and was included in the study for comparison purpose.
Nsumba, Finster Grey et al, in their 2003 Field Survey Science Total Environmental journal reported that metals pose greater risks to children since they absorb between 30 and 75% of the metal in what they eat, whereas adults absorb only about 11%. Lead, even ingested at low concentrations, is associated with impaired brain development, balance problems, heightened risk of tooth decay, hearing loss and shortened stature among children.
In adults it leads to tiredness, loss of appetite, reduced libido in men and the risk of high blood pressure.
In December 2003, a story by the Nairobi-based Daily Nation newspaper about high concentrations of lead in the sukumawiki (kale) sold in Nairobi sparked mixed reactions from the public.
The story from the 2003 United Nations Environment Programme report, stated that the Nairobi sukumawiki contained 5,000 microgrammes of lead per kilo, which is above the World Health Organisation recommended standard of 300.