Abstract:
Use of untreated wastewater for irrigation could have devastating effects on crop
quality. A study was conducted to determine the content of lead, cadmium and
chromium in food crops irrigated with untreated wastewater at Kibera and Maili
Saba, in Nairobi, Kenya. Crop samples were collected from farms irrigated with
untreated wastewater during the dry and wet seasons. While the safe limits of lead
and cadmium in food crops are 0.3 and 0.2 ppm, the concentration of lead and
cadmium, at Maili Saba downstream of the industrial area, in the edible crops during
the dry season was 48.4 and 26.5 ppm, respectively. Enrichment factor (EF) was used
as a measure of the risk and hazard sustained when crops are irrigated with water
that is contaminated heavy metals. Plots planted with black nightshade (BNS) and
Kales at Maili Saba, downstream of Nairobi’s industrial area, had the highest EF
values. Lead in BNS at Maili Saba during the dry season had the highest EF value of
about 2200, suggesting that irrigating BNS with contaminated sewage could be
hazardous. This study has confirmed that irrigation of food crops increases the
concentration of heavy metals such as lead and cadmium to unsafe levels.
