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. Key words: Heavy metals, Mangifera indica, BAF, gold mining, Nigeria.  
Highlights
Mining for gold in Nigeria has been a prolong practice since the early 20th century
This study aimed at determining the concentration of heavy metals (Pb, Cd, As, Ni, Cu, Cr, Mn, Zn, Co, Al, Fe, Au) in mango plant parts from the gold mining areas of Zamfara State, Nigeria
At Kadauri, the control site, heavy metals in mango roots were in the order: Pb > Fe > Au > Al > Zn > Cu > Mn > As > Cd > Co > Cr > Ni with the highest 19.80 ± 19.59 mg/kg and lowest 0.44 ± 0.65 mg/kg as average values for Pb and Ni respectively
Summary
Mining for gold in Nigeria has been a prolong practice since the early 20th century. The genesis of gold mining dates back to 1913 when gold was discovered in Northern Nigeria (present Zamfara and Kogi States) and reached its peak in the 1930s before the Second WorldWar when the mines were abandoned by the colonial masters. Mining for gold in Nigeria has been a prolong practice since the early 20th century. The genesis of gold mining dates back to 1913 when gold was discovered in Northern Nigeria (present Zamfara and Kogi States) and reached its peak in the 1930s before the Second World. War when the mines were abandoned by the colonial masters.
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