Accumulation of some metals in Morinda lucida from Nigeria

Abstract

Transfer coefficients of the four metals As, Cd, Hg, and Pb were determined in the leaves and barks of Morinda lucida collected in Nigeria, with the view to quantify relative differences in the bioavailability of the metals to these parts of the plant. Samples were acid digested and the levels of the metals in the digestates were determined using an atomic absorption spectrophotometer. Certain properties of the soils, i.e., pH, clay fraction, electrical conductivity, cation exchange capacity, and organic matter, were also determined. The latter influence the bioavailability of the metals. All parameters correlated with the concentrations of the metals in soils. Transfer coefficient values recorded for Cd and Pb in various tissues of M. lucida Benth were within the expected ranges, while those of As and Hg showed elevated topsoil concentrations of metals. The order of bioavailability of the metals and their bioaccumulation in the tissues of M. lucida Benth was Hg > Cd > As > Pb. Stem barks of the plant showed the least bioaccumulation of all four metals and hence are most suitable for therapeutic purposes. Vegetative parts of M. lucida Benth used for therapeutic purposes should be sourced at sites that will give low transfer coefficient in order to reduce human exposure to toxicity associated with ingestion of heavy metals.

Keywords:

• M. lucida Benth
• toxicity
• bioaccumulation
• heavy metals
• therapeutic purposes
• Ado-Ekiti

Acknowledgments

The contributions of Miss Kemi Falusi of the Department of Nursing, Faculty of Health Sciences, Obafemi Awolowo University, Ile Ife (Nigeria) and Mr Salami B.A. of the Federal Science and Technical College, Usi Ekiti (Nigeria) toward the success of this work were greatly appreciated.