Assessment of the Relationship Between Heavy Metal Content and Soil Chemical Properties in Soils of Contrasting Parent Materials in South East Nigeria

Abstract

This study investigated the influence of parent materials and soil properties on the distribution and concentration of heavy metals in soils in South East Nigeria. Three farms were sampled in each parent material at 0-20, 20-40 and 40-60 cm depths using soil auger and analyzed for selected physical and chemical properties alongside zinc, copper and lead concentrations following standard methods. The experiment was laid out as a 4×3 factorial in randomized complete block design (RCBD) with four levels of factor A (parent material) - shale, alluvium, sandstone and coastal plain sand and three levels of factor B (Soil Depth). Data collected was subjected to two-way Analysis of variance (ANOVA) using Genstat 12, significant means were separated using Fishers Least Significant Difference (F-LSD) and the relationship between heavy metal content and soil chemical properties in the parent materials was analyzed using Pearson correlation matrix plot. Soils generally showed moderate (pH = 5.6-6.0) to strongly acid (pH <5.5). Organic matter was lower in subsurface soils but moderate at 0-20cm depth (values ranged between 1.5-2.0%) and available phosphorus was seen to be moderate across all parent materials and depths studied (8-20mg/kg). Exchangeable calcium was low (<5cmol/kg), while magnesium recorded moderate to low values and potassium was generally moderate (values ranged from 0.2-0.4cmol/kg). Results also indicated clear relationships between soil properties and heavy metals in the different soil parent materials. Zn, Cu and Pb positively correlated with AP, total nitrogen and organic matter while negative correlations were observed with clay in sandstone developed soils. Zinc and lead had no observed relationship with soil properties in soils developed from shale and alluvium respectively whereas lead positively correlated with sand, calcium and magnesium in coastal plain sand. Shale derived soils exhibited the highest metal concentrations due to their fine texture and mineral rich composition while soils developed from sandstone and coastal plain sands contained significantly lower levels reflecting their lower chemical activity. The soils were generally dominated by zinc followed by lead and the least metal therein was copper. The study recommends regular monitoring of heavy metals especially those formed from metal rich parent materials, soil fertility improvement using organic amendments, adoption of soil specific management strategies and sustainable land use practices.