*3.1. Concentrations of Heavy Metals in Sediment and Freshwater Snail*

The summary and some important statistics on heavy metal concentrations in sediment and freshwater mollusc from the River Kaduna used sediment quality guidelines (SQGs) to draw some important conclusions in our study which are presented in Table 1. The concentrations of the heavy metals were compared across the five sites studied both in sediment and freshwater mollusc. Site S5 which is the upstream recorded higher concentrations of heavy metals while site (S1) which the upstream recorded the least concentrations of the nine heavy metals studied.

The ranges for heavy metal concentrations in sediments were 34.54–165.32 mg/kg, 6.36–78.98 mg/kg, 1.63–59.01 mg/kg, 4.50–61.48 mg/kg, 0.96–58.84 mg/kg, 16.09–79.20 mg/kg, 39.43–96.08 mg/kg, 2.64–60.08 mg/kg and 11.42–62.61 mg/kg for Fe, Mn, Cu, Zn, Cd, Cr, Pb, Ni and Co respectively. Heavy metal concentrations in freshwater mollusc were lower than the concentrations in the sediment which ranged from Fe: 6.61–33.30, Mn: 1.34–22.75, Cu: 0.54–16.51, Zn: 1.74–18.63, Cd: 0.92–17.52, Cr: 4.26–17.24, Pb: 6.24–24.20, Ni: 0.63–14.17 and Co: 1.6–21.46.

A comparison was made between heavy metal concentrations in benthic sediment samples with TEL and PEL (Table 2). The result of the comparisons revealed that Cu, Cd, Cr, Pb, and Ni fell between TEL and PEL for 46.4, 20.8, 57.4, 100 and 61.2% of the samples respectively. However Cd again also had a value above PEL for 79.2% of the samples.
