ACCUMULATION OF HEAVY-METALS IN SOILS AND PLANTS AFTER LONG-TERM USE OF FERTILIZERS AND FUNGICIDES IN TANZANIA

A study was undertaken to assess the accumulation of some heavy metals in soils and tobacco leaves from farms which received phosphate ferti lizers or copper fungicides for;many years. Surface soil samples were collected from various locations in the Iringa district of Tanzania, r epresenting virgin soils, soils receiving low fertilizer inputs, those with high fertilizer inputs, and those receiving Cu fungicides. Local ly occurring rock phosphate samples were also included in the study. H eavy metals in the samples were extracted using aqua regia, DTPA, or N H4NO3. Tobacco leaves were sampled to assess their heavy metal concent ration. Cadmium,Zn, Mn, Cu, Ni, and Pb were determined using atomic ab sorption or flame emission spectrophotometry. There was a significant heavy metal enrichment of soils receiving the high fertilizer and Cu f ungicide inputs relative to virgin or low input soils. This resulted i n higher concentrations of the metals in the leaves of tobacco grown i n these soils. Although the magnitudes were not big, therefore probabl y posing no immediate danger, greater risks may arise in the future du e to the observed increasing trend. The phosphate rock samples contain ed very low concentrations of Cd but some had very high levels of Mn.