Water is an essential natural resource that sustains human survival, aquatic biodiversity and ecosystem stability. Freshwater ecosystems such as rivers, streams and lakes provide numerous ecological and socio-economic benefits including domestic water supply, irrigation, fisheries, transportation, recreation and industrial utilization. Despite their importance, freshwater systems across the world are increasingly threatened by anthropogenic activities such as urbanization, industrialization, agricultural practices, indiscriminate waste disposal and population growth, all of which contribute significantly to environmental degradation and water pollution [1,2].

River ecosystems are particularly vulnerable to contamination because they serve as recipients of municipal, agricultural and industrial effluents. In developing countries such as Nigeria, rapid urban expansion and inadequate environmental management practices have intensified the deterioration of water quality in many inland water bodies. The discharge of untreated sewage, agricultural runoff containing fertilizers and pesticides, dredging activities, erosion and indiscriminate disposal of solid wastes introduce pollutants into aquatic ecosystems, thereby altering their physicochemical and biological characteristics [3,4]. These pollutants may accumulate in river sediments and subsequently pose serious environmental and public health risks.

Sediments constitute an integral component of aquatic ecosystems and act as repositories for both organic and inorganic contaminants. Sediment particles originate from weathering, erosion and transportation processes and are eventually deposited in river channels, reservoirs and other aquatic environments [5]. Apart from serving as sinks for pollutants, sediments also influence nutrient cycling, primary productivity and ecological stability within aquatic systems. However, excessive sedimentation and contaminant accumulation can negatively affect aquatic habitats, reduce water quality and impair ecosystem functioning [6].

Among the major pollutants associated with sediment contamination are heavy metals. Heavy metals such as cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn) and manganese (Mn) are of considerable environmental concern due to their toxicity, persistence and non-biodegradable nature. These metals may enter aquatic environments through industrial discharges, urban runoff, agricultural inputs, mining operations and atmospheric deposition [7]. Once introduced into aquatic systems, heavy metals tend to accumulate in sediments where they may persist for long periods and become available to aquatic organisms through bioaccumulation and biomagnification processes. Elevated concentrations of heavy metals in sediments may therefore threaten aquatic organisms and humans who depend on contaminated water resources and fish for consumption [8].

Microbial contamination of aquatic sediments also represents a major environmental and public health issue. Sediments may harbor pathogenic microorganisms, including coliform bacteria, originating from sewage discharge, animal wastes and human activities along riverbanks. The presence of high microbial loads in sediments may indicate fecal contamination and poor sanitary conditions within the aquatic environment. Such contamination can compromise water quality, affect aquatic life and increase the risk of waterborne diseases among surrounding communities.

River Benue is one of the major inland water bodies in Nigeria and serves multiple purposes including fishing, transportation, domestic activities and irrigation. However, increasing anthropogenic activities around the river have raised concerns regarding the quality of its sediments and water resources. Continuous discharge of domestic wastes, agricultural runoff and urban effluents into the river may contribute to the accumulation of chemical pollutants, heavy metals and microbial contaminants within the sediment matrix. Despite the ecological and economic importance of River Benue, information on the combined physicochemical, heavy metal and microbial characteristics of its sediments remains limited.

Therefore, this study was conducted to assess the physicochemical properties, heavy metal contamination and microbial quality of sediments collected from selected locations along River Benue, Nigeria. The findings from this study will provide baseline information on the environmental status of the river sediments and contribute to pollution monitoring, environmental management and public health protection efforts.

Study Area

The study was conducted along selected locations of River Benue, one of the major freshwater systems in Nigeria. River Benue serves several socio-economic functions including fishing, transportation, irrigation, domestic water supply and recreational activities. The river traverses densely populated and commercial areas that are exposed to various anthropogenic activities such as agricultural practices, municipal waste disposal, sand dredging and urban runoff, which may contribute to sediment contamination. Sediment samples were collected from four sampling locations namely Wadata (Site 1), Angbaye (Site 2), North Bank (Site 3) and Wukurum (Site 4). These locations were selected based on the intensity of human activities and accessibility to the river.

Sample Collection

Sediment samples were collected during the dry season between January and March 2025 using a stainless-steel sediment grab sampler. At each sampling location, triplicate sediment samples were collected at a depth of approximately 0–10 cm from the riverbed to ensure representativeness. The samples were transferred into pre-cleaned polyethylene containers, properly labeled and transported immediately to the laboratory in an ice-packed cooler for further analyses.

Sample Preparation

Sediment samples designated for physicochemical and heavy metal analyses were air-dried at room temperature for 72 hours and subsequently sieved using a 2 mm mesh sieve to remove debris, stones and other unwanted materials. The homogenized samples were stored in clean airtight containers prior to laboratory analyses. Samples intended for microbiological analysis were processed immediately after collection to avoid contamination and microbial deterioration.

Determination of Physicochemical Properties

The physicochemical properties of the sediment samples including nitrate, nitrite, fluoride, sodium and magnesium were determined using standard analytical procedures recommended by the American Public Health Association. Nitrate and nitrite concentrations were determined spectrophotometrically using a UV-visible spectrophotometer after appropriate extraction and reagent preparation. Fluoride concentration was determined using the SPADNS colorimetric method, while sodium and magnesium concentrations were analyzed using flame photometry and atomic absorption spectrophotometry respectively. All analyses were carried out in triplicates and results were expressed as mean ± standard deviation.

Heavy Metal Analysis

Heavy metal analysis of sediment samples was conducted following acid digestion procedures described by the American Public Health Association. One gram (1 g) of dried sediment sample was digested using a mixture of concentrated nitric acid (HNO?) and perchloric acid (HClO?) under controlled laboratory conditions. The digested samples were filtered and diluted with distilled water before analysis. Concentrations of copper (Cu), cadmium (Cd), lead (Pb), zinc (Zn) and manganese (Mn) were determined using an Atomic Absorption Spectrophotometer (AAS) (Buck Scientific Model 210 VGP). Heavy metal concentrations were expressed in mg/kg dry weight.

Microbiological Analysis

Microbiological analyses were conducted to determine total viable bacterial count (TVBC), total yeast count (TYC), total mould count (TMC) and total coliform count (TCC) in the sediment samples. Serial dilution techniques were employed using sterile distilled water. Appropriate aliquots of diluted samples were inoculated onto prepared culture media using the pour plate technique. Nutrient agar was used for total viable bacterial count, potato dextrose agar for yeast and mould counts, while MacConkey agar was used for total coliform determination. The inoculated plates were incubated at appropriate temperatures and durations depending on the target microorganisms. Bacterial cultures were incubated at 37°C for 24 hours, while fungal cultures were incubated at room temperature for 3–5 days. Colony counts were recorded and expressed as colony forming units per gram (CFU/g).

Quality Assurance and Quality Control

All glassware and sampling containers used during the study were thoroughly washed and sterilized prior to use. Analytical reagents employed were of analytical grade. Calibration of laboratory equipment was performed before analysis, and blank samples were included during heavy metal analysis to ensure accuracy and reliability of results.

Statistical Analysis

Data obtained from the analyses were subjected to statistical evaluation using IBM SPSS Statistics. Results were expressed as mean ± standard deviation of triplicate determinations. One-way Analysis of Variance (ANOVA) was used to determine significant differences among sampling locations, while Duncan Multiple Range Test (DMRT) was employed for mean separation at a significance level of P ≤ 0.05. Pearson correlation analysis was also performed to evaluate relationships among physicochemical properties, heavy metal concentrations and microbial parameters in sediment and water samples.

Physicochemical Properties of Sediment Samples

The physicochemical properties of sediment samples collected from different locations along River Benue are presented in Table 1. Significant variations (P ≤ 0.05) were observed among the sampling locations for all the evaluated parameters. Nitrate concentration ranged from 0.85 ± 0.07 mg/kg at Site 2 (Angbaye) to 5.02 ± 0.02 mg/kg at Site 4 (Wukurum), with a mean value of 3.50 ± 1.69 mg/kg. Nitrite concentration varied between 4.01 ± 0.01 mg/kg at Site 3 (North Bank) and 13.01 ± 0.01 mg/kg at Sites 1 and 4, with a mean concentration of 8.76 ± 4.55 mg/kg. Fluoride concentration ranged from 0.01 ± 0.01 mg/kg at Site 4 to 0.51 ± 0.01 mg/kg at Site 3, while sodium concentration varied from 7.01 ± 0.01 mg/kg at Site 2 to 69.01 ± 0.01 mg/kg at Site 1. Magnesium concentration ranged from 15.01 ± 0.01 mg/kg at Site 2 to 37.01 ± 0.01 mg/kg at Site 3. Generally, Sites 1 (Wadata) and 4 (Wukurum) exhibited relatively increased concentrations of some physicochemical parameters, suggesting possible influence of anthropogenic activities within these locations.

Table 1: Physicochemical Properties of Sediment Samples Collected from Different Locations of River Benue.

Values are presented as Mean ± Standard Deviation of triplicate determinations. Means with different superscripts across rows differ significantly at P ≤ 0.05.

Heavy Metal Concentration in Sediment Samples

The concentrations of heavy metals in sediment samples collected from different locations along River Benue are presented in Table 2. Significant differences (P ≤ 0.05) were observed among sampling sites for all evaluated heavy metals. Copper concentration ranged from 0.11 ± 0.01 mg/kg at Site 2 to 0.75 ± 0.07 mg/kg at Site 1. Cadmium concentration ranged from 2.02 ± 0.03 µg/kg at Site 2 to 13.01 ± 0.01 µg/kg at Site 1. Lead concentration showed the highest value at Site 4 (119.01 ± 0.01 µg/kg) and the lowest value at Site 2 (4.11 ± 0.01 µg/kg). Zinc concentration ranged from 1.45 ± 0.07 µg/kg at Site 2 to 9.75 ± 11.38 µg/kg at Site 3, while manganese concentration varied between 17.05 ± 0.07 mg/kg at Site 2 and 22.02 ± 0.02 mg/kg at Site 3. The elevated concentration of lead observed at Site 4 may indicate contamination arising from urban runoff, waste disposal activities and other anthropogenic inputs.

Values are presented as Mean ± Standard Deviation of triplicate determinations. Means with different superscripts across rows differ significantly at P ≤ 0.05.

Table 2: Heavy Metal Concentration of Sediment Samples Collected from Different Locations of River Benue.

Correlation Analysis between Sediment and Fish Gill Mineral Constituents

The correlation analysis between mineral constituents of sediment and fish gills from River Benue is presented in Table 3. Significant positive correlations (P ≤ 0.05 and P ≤ 0.01) were observed among several parameters. Nitrate concentration in sediment showed strong positive correlations with magnesium (r = 0.986; P ≤ 0.01) and cadmium (r = 0.740; P ≤ 0.05) levels in fish gills. Nitrite concentration in sediment exhibited strong positive correlations with sodium (r = 0.710; P ≤ 0.05), magnesium (r = 0.733; P ≤ 0.05), copper (r = 0.982; P ≤ 0.01) and zinc (r = 0.987; P ≤ 0.01) concentrations in fish gills. Fluoride concentration in sediment showed significant positive correlation with fluoride concentration in fish gills (r = 0.889; P ≤ 0.01), whereas lead concentration in sediment showed strong positive correlations with cadmium (r = 0.833; P ≤ 0.05) and lead (r = 0.984; P ≤ 0.01) levels in fish gills. These relationships suggest possible transfer and bioaccumulation of contaminants from sediments into aquatic organisms.

Table 3: Correlation Analysis of Mineral Constituent of Fish Gills and Sediments from River Benue.

* Correlation is significant at the 0.05 level (2-tailed).

** Correlation is significant at the 0.01 level (2-tailed.

Correlation Analysis between Sediment and Water Parameters

Table 4 presents the correlation analysis between sediment and water quality parameters from River Benue. Fluoride concentration in sediment exhibited significant positive correlations with nitrate (r = 0.756; P ≤ 0.05), nitrite (r = 0.974; P ≤ 0.01), fluoride (r = 0.947; P ≤ 0.01), sodium (r = 0.951; P ≤ 0.01), magnesium (r = 0.755; P ≤ 0.05), zinc (r = 0.960; P ≤ 0.01) and manganese (r = 0.841; P ≤ 0.01) concentrations in water samples. Magnesium concentration in sediment also demonstrated strong positive correlations with nitrite (r = 0.973; P ≤ 0.01), sodium (r = 0.990; P ≤ 0.01), zinc (r = 0.899; P ≤ 0.01) and manganese (r = 0.988; P ≤ 0.01) concentrations in water. Furthermore, manganese concentration in sediment showed strong positive correlations with copper (r = 0.956; P ≤ 0.01) and manganese (r = 0.902; P ≤ 0.01) concentrations in water samples. The significant correlations observed indicate strong interactions between sediment and water chemistry within the aquatic ecosystem.

Table 4: Correlation Analysis between Sediment and Water Parameters of River Benue.

* Correlation is significant at the 0.05 level (2-tailed).

** Correlation is significant at the 0.01 level (2-tailed).

Microbial Properties of Sediment Samples

The microbial properties of sediment samples collected from different locations along River Benue are presented in Table 5. Total viable bacterial count (TVBC) ranged from 2.01 ± 0.01 CFU/g at Site 4 to 3.41 ± 0.01 CFU/g at Site 3. Total yeast count (TYC) ranged from 0.81 ± 0.01 CFU/g at Site 2 to 1.46 ± 0.06 CFU/g at Site 4. Total mould count (TMC) varied between 0.81 ± 0.01 CFU/g at Site 1 and 1.61 ± 0.01 CFU/g at Site 3, while total coliform count (TCC) ranged from 11.02 ± 0.02 CFU/g at Site 1 to 17.01 ± 0.01 CFU/g at Site 4.

The elevated microbial counts recorded in some sampling locations may indicate fecal contamination and poor sanitary conditions associated with anthropogenic activities around the river environment.

Table 5: Microbial Properties of Sediment Samples Collected from Different Locations of River Benue.

Values are presented as Mean ± Standard Deviation of triplicate determinations. Means with different superscripts across rows differ significantly at P ≤ 0.05.

Key: TVBC= Total viable bacterial count, TYC= Total yeast count, TMC=Total mold count, TCC= Total coliform count, TFCC= Total fecal coliform count, CFU= Colony forming unit.

The present study evaluated the physicochemical characteristics, heavy metal concentrations and microbial quality of sediments collected from selected locations along River Benue. The findings revealed spatial variations in sediment quality across the sampling locations, indicating the influence of anthropogenic activities on the aquatic ecosystem.

The nitrate concentrations observed in the sediment samples varied significantly among the sampling locations, with the highest concentration recorded at Wukurum. Elevated nitrate levels in aquatic sediments are commonly associated with agricultural runoff, sewage discharge and organic waste decomposition [1]. The relatively high nitrate concentration recorded in the present study may therefore be attributed to increased human activities around the river, including farming activities and indiscriminate disposal of domestic wastes. Similar findings were reported by Manjare et al [9], who observed elevated nutrient concentrations in polluted freshwater systems exposed to anthropogenic inputs.

Nitrite concentrations in the sediments were also relatively high at some locations, particularly at Wadata and Wukurum. High nitrite levels in aquatic environments are often indicative of organic pollution and microbial decomposition of nitrogenous substances [10]. Excessive accumulation of nitrite may adversely affect aquatic organisms by reducing dissolved oxygen availability and altering sediment chemistry. The observed variations in nitrite concentrations among the sampling sites may reflect differences in waste discharge intensity and environmental conditions across the river locations.

Fluoride concentration in the sediment samples was generally low compared to permissible environmental limits. However, the highest fluoride concentration recorded at North Bank may suggest localized contamination from domestic and municipal activities. Fluoride contamination in aquatic sediments has been associated with industrial effluents, detergents and geological weathering processes [11]. Although the concentrations observed in this study were relatively low, continuous accumulation could pose ecological risks over time.

The sodium and magnesium concentrations recorded in the sediments varied significantly among the sampling sites. Elevated sodium concentrations, particularly at Wadata, may be associated with urban runoff and sewage contamination. Magnesium concentration was highest at North Bank, which may be linked to geological characteristics and anthropogenic inputs into the river system. Similar observations have been reported in polluted freshwater ecosystems where dissolved minerals accumulate within bottom sediments due to runoff and sedimentation processes [5].

Heavy metal analysis revealed the presence of copper, cadmium, lead, zinc and manganese in the sediment samples. The concentrations of these metals varied significantly across the sampling locations, suggesting differences in pollution sources and environmental conditions. The elevated copper concentration recorded at Wadata may be associated with urban runoff, metal wastes and domestic effluents. Copper is an essential trace element but becomes toxic at elevated concentrations due to its tendency to accumulate in aquatic organisms [8].

Cadmium concentrations observed in the sediments are of environmental concern because cadmium is a highly toxic metal with no known biological function in humans and aquatic organisms. The highest cadmium concentration recorded at Wadata may be linked to indiscriminate disposal of wastes and runoff from nearby human activities. Chronic exposure to cadmium has been associated with kidney damage, skeletal disorders and bioaccumulation in aquatic organisms [7].

Lead concentration was exceptionally high at Wukurum compared to other sampling sites. This finding suggests possible contamination from anthropogenic sources such as urban runoff, vehicular emissions, sewage disposal and commercial activities. Lead is a persistent environmental contaminant that poses serious ecological and public health risks due to its toxic and non-biodegradable nature. Similar studies have reported elevated lead concentrations in sediments from polluted rivers exposed to urban activities and industrial discharges [12]. The high lead concentration observed in this study may therefore indicate significant environmental pollution within the Wukurum axis of River Benue.

Zinc and manganese concentrations detected in the sediment samples were within moderate ranges but still reflected spatial variation among the locations. Zinc is an essential micronutrient required for biological processes, but excessive concentrations may become harmful to aquatic organisms [11]. The elevated manganese concentration observed at North Bank may have originated from natural geological sources as well as anthropogenic contributions such as erosion and waste discharge.

The correlation analysis between sediment and fish gill mineral constituents revealed several significant positive relationships among physicochemical parameters and heavy metals. The strong positive correlations observed between nitrate, magnesium, cadmium and zinc suggest possible transfer and bioaccumulation of contaminants from sediments into aquatic organisms. This observation agrees with previous findings that sediments act as reservoirs of contaminants which may subsequently enter aquatic food chains through benthic organisms and fishes [13]. The significant correlations between lead concentrations in sediments and fish gills further indicate potential ecological and public health risks associated with heavy metal accumulation in aquatic organisms consumed by humans.

Similarly, the correlation analysis between sediment and water quality parameters demonstrated strong interactions between sediment chemistry and overlying water characteristics. Significant positive correlations among fluoride, magnesium, manganese and other water quality parameters suggest active exchange processes between sediments and the aquatic environment. Sediments often function as both sinks and secondary sources of contaminants within freshwater ecosystems, thereby influencing overall water quality [2].

Microbiological analysis revealed the presence of considerable microbial loads in the sediment samples, including total viable bacteria, yeasts, moulds and coliform bacteria. The elevated total coliform counts recorded at Wukurum indicate possible fecal contamination resulting from sewage discharge and poor sanitary practices around the river environment. Coliform bacteria are widely used as indicators of fecal pollution in aquatic systems and their presence suggests contamination by pathogenic microorganisms capable of causing waterborne diseases [14].

The relatively high microbial counts observed in this study may also be attributed to the accumulation of organic matter within the sediments, which provides favorable conditions for microbial proliferation. Similar observations have been reported in freshwater systems exposed to domestic waste discharge and urban pollution [3]. The microbial contamination observed in the present study therefore highlights potential environmental and public health concerns associated with the use of River Benue for domestic and recreational purposes [15-18].

Generally, the findings of this study indicate that anthropogenic activities are contributing significantly to the deterioration of sediment quality in River Benue. Continuous discharge of untreated wastes, urban runoff and other human activities may enhance nutrient enrichment, heavy metal accumulation and microbial contamination within the river ecosystem. There is therefore a need for regular environmental monitoring, effective waste management practices and enforcement of environmental regulations to minimize further degradation of the river environment.

This study assessed the physicochemical properties, heavy metal concentrations and microbial quality of sediment samples collected from selected locations along River Benue. The findings revealed significant spatial variations in sediment quality across the sampling locations, indicating the influence of anthropogenic activities on the river ecosystem.

The physicochemical analysis showed varying concentrations of nitrate, nitrite, fluoride, sodium and magnesium within the sediment samples. Elevated concentrations of some parameters, particularly nitrate and nitrite, suggest nutrient enrichment associated with agricultural runoff, sewage discharge and indiscriminate waste disposal around the river environment.

Heavy metal analysis confirmed the presence of copper, cadmium, lead, zinc and manganese in the sediment samples. The exceptionally high lead concentration observed at Wukurum indicates substantial anthropogenic contamination, possibly resulting from urban runoff, commercial activities and improper waste management practices. The presence of cadmium and other heavy metals further demonstrates the potential ecological and public health risks associated with contamination of the river sediments.

The microbial analysis also revealed considerable microbial contamination, including high total coliform counts at several sampling locations. This indicates possible fecal pollution and poor sanitary conditions within the river environment, thereby raising concerns regarding the safety of the river for domestic and recreational use.

Overall, the study demonstrates that anthropogenic activities are contributing significantly to the deterioration of sediment quality in River Benue. Continuous environmental monitoring, effective waste management strategies and strict enforcement of environmental regulations are therefore necessary to minimize pollution and protect the ecological integrity of the river ecosystem.

Declaration of Competing Interest

Authors declare no competing interest.

Acknowledgement

The authors sincerely acknowledge the support and assistance provided by the staff of Michael Okpara University of Agriculture, Umudike during the course of this study. Appreciation is also extended to all laboratory personnel and field assistance for their technical support and cooperation throughout the research.

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