Heavy Metal Levels and Potential Ecological Risks Assessed at an Agroecosystem Site in Tropical Region

Abstract

The concentrations and distribution of thirteen metals and metalloids were investigated in soils, sediments, and two biological matrices (the fish Clarias gariepisnis and the earthworm Pontoscolex corethrurus) from the CECOMAF agroecosystem, in Kinshasa, Democratic Republic of the Congo, in order to assess the impact of anthropogenic activities. The results revealed high concentrations of heavy metals, such as Cu, Zn, As, Cd, Pb, and Hg all above values recommended by sediment quality guidelines and their probable effect levels on biota. According to the calculated Enrichment Factor, soil and sediments ranked from moderately to heavily polluted by Cu, Zn, Cd, Pb and Hg. The Contamination Degree and other ecological risk indices indicated very high contamination and very high ecological risks posed by Cd and Hg, respectively. The Geoaccumulation Index indicated that current metal concentrations in the agroecosystem originated from anthropogenic activities, while the Spearman correlation matrix values indicated that Hg could originate from different sources and pathways than the other metals. It was concluded that metals from unchecked anthropogenic activities have negatively impacted agricultural activities and fish production at the CECOMAF agroecosystem. Action to reduce the contamination level and the ecological risks by remediating and preventing metal pollution in the CECOMAF agroecosystem site is recommended.