Spatio-Temporal Trends in Heavy Metal Concentrations: Assessing Water, Sediment, and Selected Fish Species in Shiroro Lake, Niger State, Nigeria.
Abstract:
Anthropogenic activities have become the primary source of heavy metal pollution in water bodies worldwide. This study aimed to assess the spatial and temporal variations in heavy metal concentrations in sediment, water, and the muscle tissues of selected fish species in Shiroro Lake, Niger State, Nigeria. Over an eight-month period from February to September 2019, sediment and water samples were collected from three different stations within the lake. The heavy metals analyzed included chromium (Cr), cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu). The analysis encompassed three commercially important fish species: Alestes macrolepidotus, Bagrus bayad, and Clarias gariepinus.
The water quality parameters revealed the following ranges: dissolved oxygen (2.20 – 4.10 mg/L), temperature (26.60 – 30.20 oC), biological oxygen demand (1.20 – 3.00 mg/L), conductivity (49 – 120 µS/cm), alkalinity (18 – 36 mg/L), phosphate (0.16 – 2.28 mg/L), sodium (7.56 – 14.00 mg/L), pH (6.56 – 7.96), total dissolved solids (75 – 99 mg/L), total hardness (30 – 48 mg/L), and potassium (1.16 – 2.42 mg/L). The analysis of heavy metal concentrations in sediment samples from the three stations showed zinc ranging from 0.095 to 0.25 mg/L, copper from 0.015 to 0.905 mg/L, lead from 0.00 to 0.15 mg/L, chromium from 0 to 0.03 mg/L, and cadmium from 0 to 0.015 mg/L. For water samples, zinc ranged from 0.01 to 0.18 mg/L, copper from 0.01 to 0.165 mg/L, lead from 0 to 0.2 mg/L, chromium from 0.00 to 0.01 mg/L, and cadmium from 0 to 0.01 mg/L. Notably, cadmium concentrations in the water samples exceeded the toxicity threshold set by the World Health Organization (WHO) for drinking water.
In fish muscle tissues, higher levels of Zn (1.47 ± 0.50 mg/g) and Cu (0.73 ± 0.31 mg/g) were observed compared to other heavy metals analyzed. However, all heavy metal concentrations in the fish samples remained below the WHO’s maximum stipulated limits. The potential ecological risk index (PERI) mean values across all stations were as follows: Zn (0.083), Cu (0.29), Pb (2.06), Cr (0.03), and Cd (0.48). The comprehensive PERI values ranged from 0.617 to 6.902, indicating a slight ecological risk level.
The geo-accumulation index mean values reported negative values for all five heavy metals (Zn -2.42, Cu -2.06, Pb -1.56, Cr -0.92, and Cr -0.75), signifying an unpolluted state of the sampling stations. Furthermore, the enrichment factor (EF) mean values for Zn (0.08), Cu (0.05), Pb (0.41), Cr (0.02), and Cr (0.02) were all below one (<1), suggesting a crustal enrichment origin of the sampling stations.
Based on the physicochemical parameters, the water in Shiroro Lake was found to be at a low level of pollution, with all recorded water quality parameters slightly below or within WHO’s permissible limits. Nevertheless, the presence of elevated cadmium levels makes the water unsuitable for human consumption due to potential exposure risks.
Spatio-Temporal Trends in Heavy Metal Concentrations: Assessing Water, Sediment, and Selected Fish Species in Shiroro Lake, Niger State, Nigeria.