Mercury presence in cassava farming, Manihot esculenta Crantz, in the vicinity of artisanal gold exploration areas in Southern Amazonia

Abstract

Cassava, Manihot esculenta Crantz (Euphorbiaceae), a native plant to Brazil, is one of the main sources of carbohydrate in the diet of Brazilians. In gold-mining regions, such as the south of the Amazon, it is inevitable that crops will come closer to Artisanal and Small-scale Gold Mines (ASGM), creating risks of production contamination by mercury (Hg). Due to the importance of cassava in the population’s diet, the present study aimed to evaluate the effect of the proximity of ASGM on Hg concentrations in soil and cassava samples and to assess the risk of human exposure to Hg through consumption of this food. Samples were collected in two areas along the BR-163 highway, in the State of Mato Grosso, Brazil. Forty-two samples of cassava (roots, stems and leaves) and soil were collected. It seems there is no effect of ASGM on Hg soil concentrations. The highest concentrations of Hg in the leaves were observed in the area close to ASGM, indicating higher atmospheric deposition. In the mining area, the higher bioconcentration factor indicates the outcome of Hg from the atmosphere also on the concentrations in the roots. Daily intake and health risk quotient estimation were performed for cassava and cassava flour, with the highest values observed in the vicinity of ASGM, however, all below the established limits, indicating that, currently, the consumption of these foods by the population is safe. The cassava crop can be used as a bioindicator of atmospheric pollution by Hg caused by ASGM.