Abstract:
Sediment contamination by heavy metals resulting from anthropogenic activities is increasingly becoming a global concern
due to the risk it poses to human well-being and ecological integrity at large. The purpose of this study was to assess the heavy
metals loading in sediment along the Kawere stream. Ten sediment samples were collected, acid digested and analysed for
copper (Cu), lead (Pb), cadmium (Cd), manganese (Mn), zinc (Zn), nickel (Ni), chromium (Cr), cobalt (Co) and iron (Fe)
using a Varian AA240FS Atomic Absorption Spectrometer (AAS). The Australian and New Zealand Environment and
Conservation Council (ANZECC) guidelines for freshwater sediment quality was used as the benchmark against which the
measured metal concentrations were compared. Nemerow’s pollution and potential ecological risk indices were used to
evaluate the pollution status and ecological risk levels of the heavy metals in the stream. The results obtained indicated that,
except Cu which exceeded the ANZECC trigger value of 65 mg/kg at three sampling sites (K01=171.29 mg/kg, K05=170.83
mg/kg and K07=113.31 mg/kg), all other measured heavy metals concentrations were below their corresponding ANZECC
values. Heavy metal pollution assessment showed that three samples (K01, K05 and K07) were slightly polluted, suggesting
the likelihood of posing a health threat to the aquatic organisms and humans. Calculated Ecological Risk Index (RI) ranged
from 3.229 to 19.750 (RI < 150), representing a low ecological risk. As such, the metals, Cu, Ni, Cd, Pb, Cr, and Zn pose a
low ecological risk to the aquatic ecosystem. Although the ecological risk is low based on the current results, constant
monitoring of the stream quality is recommended due to the increasing human activities along the stream as well as the
sediments ability to accumulate and remobilise heavy metals back into the water column and possibly transferring them
through the food chain
