Accumulation of Pb, Cd and Ni in sediments and root of mangrove plant (Laguncularia sp) from the fringes of the Upper Bonny Estuary, Nigeria

Abstract

The accumulation of heavy metals in sediments and roots of mangrove plant (Laguncularia sp) in relation to the age of the plant root was evaluated. Composite sediment and root samples were collected from three spots per station at three different locations (St.1: Borikiri, St.2: Bundu-Ama, St3: Eagle Island) of mangrove fringes in the upper Bonny estuary. Heavy metal content of sediment and roots were analyzed using spectrophotometric methods while growth rings/bands was used to estimate age of root. There were variations in the metal content of sediments in space and time. Observed heavy metal range (μg/g) in sediments (N: 0.001 - 2.8, Pb: 0.001 - 4.5, Cd: 0.001 - 0.35) and root (N: 0.001 - 3.3, Pb: 0.001 - 7.1. Cd: 0.001 - 0.5) generally indicated higher values in roots compared to sediments. The age of the plant root examined varied between 2.3 - 5.7 years across sites. ANOVA showed significant difference (p<0.05) in metal concentration in space and time. The concentration of Pb, Cd and Ni in the root of plants fell within and slightly above standard limits of WHO/FAO Pb: 5.0 μg/g; Cd 0.2 μg/g and Ni: 1.5 μg/g).In conclusion, Pb, Cd and Ni in sediment had strong positive linear relationship with those in the plant root but the age of plant root did not give significant relationship with metal accumulation. Laguncularia roots generally accumulated more heavy metals compared to the surrounding sediments which was attributed to discrete exposure of the sites to anthropogenic impacts.

Keywords: Heavy metals, Bioaccumulation, Sediment, Mangrove plant, Niger Delta