Metallic contamination of medicinal plants as consequences of soil pollution

Abstract

Medicinal plants used by populations are harvested in the environment subjected to contamination by pollutants including heavy metals, toxic to humans. The objective of this research is to assess contamination of 5 medicinal plants commonly used in Benin by mercury and growing sometimes in areas at risk of mercuric contamination. Material plant studied included Croton lobatus, Hemizygia bracteosa, Desmodium velutinum leaves and Cissampelos owariensis and Calyptrochilum christyanum aerial parts. These plants, as well as soils on which they are established, were collected, respectively in Abomey-Calavi, Savalou, Abomey for the 3 first plants and Avrankou for the 2 last. Direct Mercury Analyser (DMA 80 TRICELL) was used to quantify mercury in dry plant powders and dried soil grains. The results obtained reveal mercury’s presence in all plants and soils samples. Mercury concentration varies between 18.36 and 133.54μg/kg in soils and between 20.45 and 89.13μg/kg in leaves. Soil concentrations are below threshold value of 1mg/kg. Plants have been shown to accumulate mercury, or even very accumulative for Croton lobatus and Desmodium velutium. This study shows that harvesting medicinal plants on soils contaminated by heavy metal is a risk for human health.