Potentially toxic metal contamination, pollution, and ecological risk assessment in volcanic soils of Njombe-Penja Banana Plain, Cameroon Volcanic Line

Abstract

This study is aimed at assessing the contamination levels, ecological risk, and mitigation strategies of potentially toxic metals in volcanic soils of Njombe-Penja Banana Plain. Soil samples were collected and analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Results show that the concentrations of Cd (0.05–2.80 mg/kg), Co (12.30–78.90 mg/kg), Cr (44–142 mg/kg), Cu (22.20–251 mg/kg), Hg (0.06–0.19 mg/kg), Ni (35.20–139 mg/kg), Pb (5.80–48.70 mg/kg), Ba (199–469.17 mg/kg), Sr (25.30–509 mg/kg), V (91–284 mg/kg), and Zn (54.80–1010 mg/kg) exceed the geochemical threshold values. Pollution indices such as contamination degree (C_d 11.62–79.97) and pollution load index (PLI 0.56–2.80) indicate soil contamination. Nemerow integrated pollution index (NIPI 0.17–20.67), enrichment factor (EF 0.04–9.43), geo-accumulation index (Igeo − 3.39–4.84), and modified degree of contamination (mC_d 0.78–5.32) suggest moderate to very high pollution levels in soil ecosystem. Potential ecological risk index (Er 0.77–857.14; RI 117.41–1095.39) and modified hazard quotient (mHQ 0.10–4.11) show low to very high ecological risk of potentially toxic metals with probably toxic and biological effects on humans and biota. Natural and anthropogenic activities are major sources of soil contamination and toxic metallic pollution of volcanic soils. This study suggests that proper focus should be placed on monitoring the point and non-point sources of toxic metals entering soils from domestic and agricultural practices. This research work serves as a warning to companies and farmers about potentially toxic metal pollution of volcanic soils in Njombe-Penja Banana Plain.