Accessory Minerals and Potentially Toxic Elements in Tanzanian Vermiculites with Respect to Agricultural Applications

Abstract

The study assessed accessory minerals and metals in Tanzanian vermiculites with respect to their potential suitability for agricultural applications. Mineral and chemical analyses were involved. Pot experiments were also conducted to assess plant uptake of metals from soil with vermiculites. Fibrous sepiolite and amphiboles were minerals of health concern found in some samples. The sepiolite fibers had aspect ratios similar to those of asbestos minerals, which cause respiratory disorders and lung cancer when inhaled and thus pose a potential health risk to animals and humans. The amphibole fibers were thicker than 10 μm and are unlikely to be inhaled. Chromium (Cr) and nickel (Ni) concentrations in some samples were greater than the limits permitted in agricultural soils, but the elements are not highly plant available and do not inhibit the uptake of essential macronutrients. Heating vermiculites at 400–600 °C enhanced extractability of Cr and Ni and should preferably be avoided.

Keywords:

• Amphiboles
• metals
• sepiolite
• Tanzania
• vermiculite

Acknowledgments

The first author is much indebted to the Commonwealth Commission in the United Kingdom for supporting this research as part of his PhD studies at the University of Aberdeen.