Accumulation of heavy metals in soils and plants after long-term use of fertilizers and fungicides in Tanzania

Abstract

A study was undertaken to assess the accumulation of some heavy metals in soils and tobacco leaves from farms which received phosphate fertilizers or copper fungicides for many years. Surface soil samples were collected from various locations in the Iringa district of Tanzania, representing virgin soils, soils receiving low fertilizer inputs, those with high fertilizer inputs, and those receiving Cu fungicides. Locally occurring rock phosphate samples were also included in the study. Heavy metals in the samples were extracted using aqua regia, DTPA, or NH4NO3. Tobacco leaves were sampled to assess their heavy metal concentration. Cadmium, Zn, Mn, Cu, Ni, and Pb were determined using atomic absorption or flame emission spectrophotometry. There was a significant heavy metal enrichment of soils receiving the high fertilizer and Cu fungicide inputs relative to virgin or low input soils. This resulted in higher concentrations of the metals in the leaves of tobacco grown in these soils. Although the magnitudes were not big, therefore probably posing no immediate danger, greater risks may arise in the future due to the observed increasing trend. The phosphate rock samples contained very low concentrations of Cd but some had very high levels of Mn.