An Assessment of potential Health hazards in sweetpotatoes (ipomoea batatas) / grown and consumed in urban areas" around Nairobi

Abstract

This study was carried out to investigate the safety of urban grown food crops with respect to contamination by heavy metals. Sweetpotatoes, grown and consumed around Nairobi, were used as the reference food crop. This study involved laboratory analysis and a dietary survey. In the laboratory analysis, levels of cadmium and lead in sweetpotatoes, soils and water were determined. The survey was conducted at Kangemi location in Westlands division for the purpose of determining the amounts of sweetpotatoes eaten in a typical peri-urban low-income population, and hence postulate approximate amounts of cadmium and lead ingested by the consumers of sweetpotatoes in the population. The sweetpotato samples were collected along the banks of Nairobi River and along the roadsides of Thika-Nairobi freeway. Soil and water samples were also collected to determine whether there existed a correlation between the levels of cadmium and lead in the sweetpotato samples, soil and water. Effects of cooking, variety (White and orange fleshed) and distance from the kerb sides (5 and 10 metres) on the levels of cadmium and lead in sweetpotatoes were also investigated. In the survey, 24-hour recall was used to determine consumption levels in different age-categories. Subjects in the survey were selected purposively. The results of the study showed that; Distance from the freeway had no Significant difference (p> 0.05) in the levels of cadmium and lead. However, higher concentrations were found nearest the kerbsides. There was significant difference (p< 0.05) in the levels of lead and cadmium across the up-stream and down-stream sections of Nairobi River. There was no significant difference (p> 0.05) in the levels of lead and cadmium across the orange and white-fleshed varieties. There was no significant difference (p>0.05) in the levels of lead and cadmium in cooked and raw sweetpotato samples. Levels of both lead and cadmium in sweetpotato samples showed a positive relationship with those found in the soil and water with correlations of 0.73 and 0.74 for soil and water respectively. Generally, consumers of sweetpotatoes grown within the city consume both lead and cadmium in excess of FAO I WHO provisional tolerable intakes. The highest amounts of lead and cadmium that were ingested by the study subjects were 0.1 mg Pb I Kg b.w I week and 0.01 mg Cd I Kg b.w I week against provisional tolerable weekly intakes of 0.05 mg I Kg b.w I week and 0.007-0.008 mg I Kg b.w I week for lead and cadmium respectively.