Fractionation and bioaccumulation of copper and zinc in wetland soils of the Niger Delta determined by the oil palm

Abstract

The concentration, mobility, bioavailability, distribution and associations of two essential micronutrient elements (copper and zinc) to the oil palm in wetland soils of the Niger delta region of Nigeria was assessed by means of chemical fractionation analysis. The water soluble and plant available fractions were introduced into the sequential extraction scheme. Also assessed were the bioaccumulation (concentration and distribution) of these metals in the leaves and fruits of the oil palm of various ages found around the soil profiles. Copper was obtained more in the amorphous Fe-oxide fraction (151.05 mg kg−1), but evenly distributed in the exchangeable component (16.16%) with a maximum value of 126.6 mg kg−1. The water soluble and plant available fractions had 16.15 and 7.54% distribution of Cu respectively. Zinc had 2.35 and 30.42% distribution in the water soluble and plant available fractions respectively. The lowest mean amount of Cu (1.33 mg kg−1) was determined in the leaves of palms of ages 15–32 years. Palms greater than 60 years had the highest mean concentration of copper (3.91 mg kg−1) in the leaves while the endosperm (kernel) of palms between 2 and 10 years had concentration of 9.07 mg kg−1. The fibrous oily mesocarp had the highest amount (16.78 mg kg−1) of copper in the older palms (>60 years). Similarly, Zn was dominant in the older palms with a mean concentration of 187.14mg kg−1 obtained in the endosperm (kernel). The bioaccumulation pattern of both metals by the palms irrespective of age and the fractionation analysis revealed sufficient bioavailable and reserved amounts of Zn and Cu in the wetland soils.