Risks of urban agriculture: lead and cadmium intake by Kigali residents from locally grown produce

摘要

This study determined the concentrations of lead and cadmium in edible parts ofudColocasia esculenta, Amaranthus spp.and Ipomoea batata cultivated on farms inudindustrially polluted sections of Nyabugogo Marsh in Kigali, Rwanda. Theudconcentrations in all three crops exceeded European Union (EU) standards for metaludconcentration in food crops. C. esculenta roots (Taro) contained the highestudconcentration of lead (1.02 mg kg-1) and cadmium (0.56 mg kg-1), approximately tenudand six times over the EU limits, respectively. Even though I. batata (sweet potato)udcontained the lowest concentrations of lead (0.75 mg kg-1), this is almost eight timesudthe upper limit. The highest bioaccumulation factors (the ratio of plant metaludconcentration to that of the soil in which it is found growing) for both metals wereudobserved in amaranth plants. The concentrations of lead and cadmium in the farmudsoils were all acceptable based on EU standards (300mg kg-1 for lead and 3mg kg-1 respectively.udThe average daily consumption by an adult in the community living around the Marshudand where some of the produce is sold is 50g of amaranth, 120g of taro and 180g ofudsweet potato. Based on the metal concentration and these rates of consumption, theuddaily dietary intake of lead by an adult in the community from amaranth, taro andudsweet potato is 1 x 10-4, 3 x 10-4 and 4 x 10-4 mg kg-1 respectively. The daily intake ofudcadmium is 4 x 10-4, 1.7 x 10-4 and 1.2 x 10-4 mg kg-1 for amaranth, taro and sweetudpotato respectively. These metal intakes are well within the recommendations setudforth by the World Health Organisation.udThe community also has access to multiple sources of dietary and non dietary zincudsuch as beans, milk and rain water collected from zinc coated roofing sheets, whichudserves to ameliorate the effects of cadmium. It is however worth noting that surveyuddata may have yielded overestimates of these zinc sources, due to the conditionsudunder which the surveys were conducted i.e. in the hearing of neighbors due to theudcramped nature of housing, which may have prompted respondents to inflateudconsumption quantities of expensive food items.udThe calculated maximum recommended quantities for daily intake of the crops areudvery large and are unlikely to be consumed by the population i.e. >2kg of amaranth,ud>2 kg of taro and 3 kg of sweet potato per day for an adult. Additionally, because this is a poor community, access to such quantities of food on a daily basis is not likely.udThe community is therefore not exposed to health risks from consuming metaludcontaminated crops, largely because of the small quantities consumed. The localudpopulation is therefore at no immediate risk to exceeding metal consumption limits byudconsuming vegetables grown in the Nyabugogo Marsh, but the threats will likelyudincrease if the pollution of the Marsh is not addressed.