An Evaluation of the As, Cd, Mn and Hg Contamination in Soils and Plants (Amaranthus spinusis) of Kaduna Metropolis Dumpsites

Abstract

Aim: The study assesses the qualities of contaminated soils of ten municipal waste dumpsites in Kaduna metropolis, Nigeria. Study Design: Physico-chemical parameters and heavy metals were analyzed in soils and plants of ten dumpsites across wet and dry season in Kaduna metropolis. Place and Duration of Study: Department of chemistry of Ahmadu Bello University, Zaria and National Fertilizer Development Centre, Goningora, Nigeria. Within August 2011 to June 2012. Methodology: Wet acid digestion and atomic absorption spectrophotometry were used for the determination of heavy metals in both soil and the plant (Amaranthus spinusis)  while standard procedures were employed for determination of the physicochemical parameters. Results: The pH of the dumpsite soils ranged from 7.90 ± 0.02 to 9.30 ± 0.02. The organic matter contents of the dumpsite soils during the wet season were lower for most of the sites when compared to the dry season values; the control sites had organic matter contents (2.60 ± 0.01 mg/kg) which was 10% of the mean dumpsites value. Using atomic absorption spectrophotometry The range of the total metal contents of the dumpsite soils for the wet season were: As 0.013-0.054; Cd 0.22-0.29; Hg 0.133-0.624 and Mn 2.615-22.89 mg/kg. The ranges were As 0.001-0.51; Cd 0.22-0.46; Hg 0.253-0.881 and Mn 1.005-30.206 for the dry season. Amaranthus spinusis had the ranges for  the wet season being: As 0.001-0.030; Cd 0.019-0.250; Hg 0.144-0.590 and Mn 0.167-0.690 mg/kg. During the dry season A. spinusis had the ranges As 0.004-0.056; Cd 0.051-0.483; Hg 0.156-0.598 and Mn 0.228-0.700 mg/kg. Metal contamination at the dumpsites follows the ranking: Mn > Hg > Cd > As. Levels of these metals in Amaranthus spinusis and the soils did not vary significantly across the season (P < 0.05). High level of contamination of these metals was recorded at Tudun Wada (TW), Rafin Guza (RG), Angwan Dosa (AD) and Angwan Shanu (AS). The transfer ratio indicates that As and Hg were more accumulated in the plant (Amaranthus spinusis) grown on TW. Cd in the control soil (0.020 ± 0.0018 mg/kg) was 10 fold the dumpsite mean, mean As at dumpsites soil was 0.034 ± 0.0031 mg/kg but not detectable in the contro. Level of Hg in the control soil was within that obtained for the dumpsite soils( 0.502 ± 0.003mg/kg), being higher than the threshold limit. Mn in the dumpsite soils was higher than the UNEPA limit of 10.0 mg/kg; the control value was 0.690 ± 0.003 mg/kg. Conclusion: The study indicates pollution of the dumpsite soils by Hg and Mn, and this could pose health risk to man.