Investigation of lead sources in manioc flour from riparian communities in the Tapajos Region, Brazilian Amazon

摘要

From a previous pilot study, the Tapajos River basin riparian population was found to have elevated blood lead (PbB) levels, ranging from 0.59 to 48.3 mu g/dL. Preliminary analyses of these results initially pointed to the metallic plates used in the production of manioc flour as a possible source. The main objective of this study was to investigate the potential environmental sources of Pb in the manioc flour in this region. The study was carried out in eight communities on the Tapajos River, where samples of manioc flour, metal plates and soil from manioc plantations were collected. In addition, samples of deposited sediments from the Tapajos River and its tributaries and riverbank sediments were collected. The metal composition was analyzed by SEM, XRF and GFAAS. The results show that the concentrations of Pb in manioc flour ranges from 0.08 to 0.31 mg/kg and the manioc paste from 0.004 to 0.037 mg/kg. The metallic plates used in the manioc-roasting process are made of carbon steel without Pb in the bulk alloy. Pb concentrations in soils where manioc roots were cultivated range from 8.9 to 26.1 mg/kg and Zn concentrations range from 12.7 to 59.1 mg/kg, indicating a contribution of polymetallic geological deposits. The clay-rich samples have high metal contents (including Pb, Zn and Cu). The Pb content of the clay samples ranges from 10.6 to 25.1 mg/kg. These results suggest that it is unlikely that the Pb found in the manioc flour originates from the metal plates used in its roasting process, rather, it seems to be associated to environmental factors determined by the local geology and soil composition.