Bioaccumulation of heavy metals in mangoes (Mangifera indica L.) found in the vicinity of gold mining sites of Zamfara State, Nigeria

Abstract

The impact of gold mining on mango (Mangifera indica L.) grown in the vicinity of gold mining sites in Zamfara State, Nigeria have been assessed over the dry and wet seasons. Samples of mango plant parts were collected from 3 impacted sites and a control site monthly between March and August 2014, and analysed for selected heavy metals using Atomic Absorption Spectrophotometer. The results obtained indicate that Pb was the most abundant heavy metal in the mango roots (95.17 ± 68.49 mg/kg), stems (87.89 ± 64.11 mg/kg) and leaves (67.11 ± 57.11 mg/kg) found in Kwali and the least abundant metal was Ni (0.30 ± 0.44 mg/kg) in Kadauri (control site). The mean values of these metals were found to be above the WHO (1996) and Nigerian FMEnv maximum permissible limits indicating high level of contamination from gold mining activities. The abundances of the metals followed an unsequential pattern in the order Pb > Fe > Au > Al, depending on the location, and differed significantly (P<0.05) across sampling stations. Remarkably higher values of the contaminants were observed in the dry than the wet season. The sequence of heavy metal accumulation in the mango plants were Roots > Stems > Leaves > Fruits which revealed that the roots bio-accumulated the heavy metals more than the fruits. Bio-accumulation factor (BAF) values determined varied with specific heavy metals, location and the season. Most BAF values were higher than 1 indicating that Mangifera indica is a hyperaccumulator and could be used as bioindicator for pollution studies.