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ESTIMATION OF THE CONCENTRATION OF HEAVY METALS IN FORAGES HARVESTED AROUND DIBETE AREA, BOTSWANA

Abstract

This study was carried out to determine the levels of five heavy metals:lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn) in roadside forages harvested along a major highway (A1) in Dibete. The selected site was based on the forage harvesting activities within the area. Forage samples were collected at distances of 0, 15, 30, and 1000 m from the road. Atomic Absorption Spectrophotometer was used to analyse heavy metal concentration levels. Data were subjected to ANOVA at probability of 5% using the General Linear Models (GLM) procedure of SAS. Heavy metal concentrations were recorded in mg/kgwith Pb being highest at 3.6897±0.431 followed by Cr at 0.2085±0.084, Cd; 0.1297±0.056, Cu; 0.0867±0.060 and Zn the least at 0.0520±0.019. There were significant differences (P<0.05) in the concentrations of the five heavy metals at various distances. Heavy metal contents in forages at different distances from the road decreased with increasing distances from the road. The results showed that road side forages are contaminated with heavy metals. The high concentrations of heavy metals at 0 – 15 m from the roadside edge suggest that forages close to the roadside are a potential health hazard to both humans and livestock.Higher concentrations of heavy metals were recorded during the dry season relative to the wet season. The concentration of Cu was found to be independent of seasonal variation at P<0.05. These results suggest that forages harvested within road reserves should be used with extreme caution to feed livestock. It appears that forages harvested ≥30 m from the road have acceptable concentrations of heavy metals and could be used for livestock feeding.

Dr.John Cassius Moreki, Tshoganetso Owen Woods and Patrick G. Nthoiwa

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