Soil samples (waste effluents) of topsoil (0 - 20 cm) were collected with auger

Table 1. Coordinate of sample locations.

Key:FDWS: Fertilizer Dumpsite Water Sample, DDWS: Dye Dumpsite Water Sample, BDWS: Battery Dumpsite Water Sample, PDWS: Paint Dumpsite Water Sample, FDSS: Fertilizer Dumpsite Soil Sample, DDSS: Dye Dumpsite Soil Sample, BDSS: Battery Dumpsite Soil Sample, PDSS: Paint Dumpsite Soil Sample.

from dumpsites of paint industry: dye factory, Automobile battery repair shop and fertilizer plant industry all within Makurdi metropolis. Three (3) soil samples were collected from each site. A control soil sample was collected from a residential area within Makurdi metropolis that has no history of industrial activity or use as a dumpsite. The specific location was selected to be upwind and at a significant distance (>2 km) from the investigated dumpsites to minimize the potential for contamination via atmospheric deposition or leachate. The land use is characterized by low-density housing with minimal traffic, and the site is not used for agriculture, ensuring it represents a background baseline for the local soil conditions against which the dumpsite samples could be compared. The collected soil samples were air dried, crushed with mortar and pestle and pass through 2 mm sieve and stored in the sealed plastic bags at room temperature for 24 hrs. The soils were placed in polyethylene bags and labeled accordantly and taken to the Department of Chemistry Laboratory Joseph Sarwuan Tarka University Makurdi for preparation and analysis.

Sample Preparation

Exactly 1.0 g of the dried and sieved soil sample was weighed into 250 mL conical flask. A known amount of freshly prepared aqua-ragia (HCl:HNO₃) in a ratio of 1:3 was added. The beaker was covered with a filter paper; the solution was heated for 1 hour using a hot plate. The mixture was allowed to cool and filter with whatman filter paper into a 50 mL standard volumetric flask, the filtrate was diluted to 50 mL with de-ionised distilled water.

pH, Electrical conductivity, Organic matter, Phosphate ion ( PO 4 3 − ) and Nitrate ion ( NO 3 − ) f the samples were carried out following documented procedures [15].

Atomic Absorption Spectrophotometer (AAS): Heavy metals concentration were determined by Atomic Absorption Spectrophotometry.

X-ray Fluorescence Analysis (XRF): Quantitative analysis of the major oxides and elements within the ore was determined by X-ray Fluorescence Spectroscopy.

X-ray Diffraction Analysis (XRD): XRD analysis was conducted for the qualitative (phase identification) and quantitative analyses of the minerals in the soil samples. Diffraction pattern was presented and crystalline sizes was computed using the Debye-Scherrer equation given as:

with k as 0.94.

Scanning Electron Microscopy Analysis: Surface morphology of soil samples was determine by Scanning Electron Microscopy.

The soil heavy metals contamination levels and ecological risk were evaluated using the various indices.

2.4.1. Geoaccumulation Index (I_geo)

The following equation was used to calculate the geoaccumulation index (I_geo):

where; C_n represents heavy metal (n) concentration in the sample, Bn represents heavy metal (n) concentration in the geochemical background, 1.5 represents the background matrix correction due to lithogenic effects.

The geochemical background concentrations (Bn) used for the I_geo and Contamination Factor (CF) calculations were derived from the control sample collected in this study. This sample, taken from an uncontaminated residential area, provides a local baseline for pre-anthropogenic metal concentrations in the soils of the Makurdi metropolis.

2.4.2. Contamination Factor (CF)

The contamination factor (CF) was used to evaluate heavy metal contamination.

where; C_n represents the concentration of each element;C₀ is the average concentration of each element.

2.4.3. Ecological Risk Assessment

In this study, the following relationships was used to assess the ecological risk and environmental risk potential (RI) of soils.

where; CF is the pollution factor, ER indicates the ecological risk of each element studied, RI represents the sum of the elements. The high value of TR indicates the toxicity of heavy metals.

2.4.4. Enrichment Factor

The determination of the EF indicates the level of contamination of metals in the soil, which is a useful index for separating the natural and human sources of metals from each The EF for each metal was calculated based on the ratio between the normalized element and the background value of the elements.

where; Cref is the concentration of the reference element in the sample, Cx is the concentration of the element considered in the sample.

Iron (Fe) was selected as the normalizing element due to its abundance as a major constituent of the Earth’s crust, its generally low mobility in soil environments, and its minimal variation from anthropogenic inputs in the study area compared to other major elements.

There are three common pathways for exposure to heavy metals related to soil including ingestion (Ing), inhalation (Inh) and dermal contact (Der). Equations below were used to calculate dose received via each of these exposure pathways:

where; D Ing and C are the dose contacted through ingestion of soil (mg/kg/day) and exposure point content (mg/kg) of the analyzed elements, respectively, IngR (mg/day) is the ingestion rate (200) for children and 100 for adults, EF (days/year), ED (years), BW (kg) and AT are the exposure relative frequency (300), exposure duration (six for children and 24 for adults), average body weight (15.0 for children and 70 for adults) and averaging time (exposure duration 365 days for non-carcinogens), respectively.

where; D_Inh (mg/kg/day) is the dose contacted through inhalation of soil sample, lnhR (m³/day) is the inhalation rate (7.60 for children and 20.00 for adults)

where,

D_der (mg/kg/day) is the dose absorbed via dermal contact.

SA (cm²) are the exposed skin area (2800 for children and 5700 for adults), ABS dermal absorption factor (0.001) for all analyzed elements, respectively.

2.5.1. Hazard Quotient (HQ)

The HQ for non-carcinogenic risk was calculated using the equation by USEPA (1999)

USEPA (1999). Guidance for performing aggregate exposure and risk assessments. Office of Pesticide Programs, Washington, DC.

where,

CDI is the daily dose of heavy metals (mg/l) to which consumers might be exposed.

RfD is the reference dose which is the daily dosage that enable individual to sustain this level of exposure over a long period of time without experiencing any harmful effects.

If HQ > 1, it represents adverse non-carcinogenic effects of concern, while HQ < 1 represents acceptable level.

2.5.2. Hazard Index

The toxic risks due to potentially hazardous substances present in the sample are assumed to be additive.

The HQs may be summed to arrive at the overall toxic risk.

where,

HI is the hazard index for the overall toxic risk.

n is the total number of metals under consideration.

HI < 1 indicates no adverse health effects, whereas HI > 1 indicates the possible health effects.

2.5.3. Carcinogenic Risk

Cancer risk is the hazard from a lifetime average dose exposure to 1 mg/kg body weight/day of a pollutant. Cancer risk is expressed in terms of incremental lifetime cancer risk (ILCR), which is the probability that one may develop cancer over a 70-year lifetime due to a 24-hour exposure to a potential carcinogen [16]. Cancer risk is calculated as the product of CDI (mg/kg/day) and cancer slope factor (CSF) measured in (mg/kg/day)

where:

ILCR is the incremental life cancer risk.

CDI is the chronic intake (mg/kg/BW/day).

CSF is the cancer slope factor.

The results of the physicochemical parameters of the soil samples; pH, Electrical conductivity, Organic matter, Phosphate ion ( PO 4 3 − ) and Nitrate ion ( NO 3 − ) were presented in Table 2.

pH: The pH of the soil samples ranges from 2.81 to 7.80 across the sampling sites withthe highest pH value recorded in FDSS and lowest in BDSS. The mean value of Ph⁻ in this study was 6.04 ± 0.05 and it was within the acceptable limit. The result shows that, samples from BDSS and PDSS were acidic to slightly acidic, this indicate that metals may be available in their ionic species or in soluble organometallic forms therefore readily available for plant uptake as acidity decreases as also reported by [17][18]. While samples from FDSS, DDSS and the control indicate that, the soils from the two dumpsites are alkaline which is in agreement with research reported by [19]. Soil pH is among the factors that affect the distribution and availability of heavy metals in the soil.

Electrical conductivity: The EC values of soil samples obtained in this study ranges from 259 to 4757 µS/cm with the lowest value observed in PDSS and the highest value in BDSS. The high value observed in BDSS could be attributed to the presence of soluble salts that might have leached out from the waste in the study site [20].

Organic matter: The concentrations of organic matter in the soil sample of the dumpsites range from 2.54 to 3.91 with the lowest value recorded in DDSS and the highest value observed in BDSS. That of the control sample was 3.82 ± 0.03 mg/L. The presence of the high content of organic matter in the soil can be another possible reason for the low pH observed in BDSS [21].

Phosphate ion ( PO 4 3 − ): The concentrations of phosphates in the dumbsites range from 12.8 to 38.8 mg/L with DDSS recording the least value and FDSS recording the highest value. The control sample reported 46.0 ± 0.03 mg/L. The high level of phosphates in these locations especially that of FDWS is attributed to the production of synthetic fertilizers while that of DDWS, BDWS, PDWS and the control sample may also be related to the run-off from farmlands from inhabitants who engage in agricultural activities using both natural and synthetic fertilizers.

Nitrate ion ( NO 3 − ): The concentration of nitrates across the sampling points range from 2.11 to 7.25 mg/L with FDSS observed to be the lowest value and BDSS recorded the highest value. The control sample reported 8.56 ± 0.03 mg/L. These results suggest that, there is no high amount of macro-nutrients of Nitrogen, Phosphorus from the dumpsites. The value of nitrate obtained in the soil of paint dumbsite (2.56) correspond with the work of [22].

The results of the mean concentrations of the heavy metals (Fe, Pb, Cr, Cd, Zn, Mn and Cu) in soil samples were presented in Table 3.

Table 2. Physicochemical parameters of soil samples from selected vicinities of dumpsites around residentials/industrial areas.

FDSS: Fertilizer Dumpsite Soil Sample, DDSS: Dye Dumpsite Soil Sample, BDSS: Battery Dumpsite Soil Sample, PDSS: Paint Dumpsite Soil Sample.

Fe: The mean concentrations of Fe in the soil sample of the dumpsites range from 0.471 to 4.06 mg/kg with the lowest value in BDSS and the highest value recorded in PDSS respectively. The control sample was observed to be 1.54 ± 0.001 mg/kg. The result of Fe in dumbsites is lower than that of [23].

Pb: The mean concentration of Pb in the soil samples collected around the different dumpsites range from 0.337 to 2.47 mg/kg with the lowest and highest values recorded in FDSS and PDSS respectively. There was a slight difference between the levels of Pb in the dumpsites soil and the control sample which was reported to be 0.289 ± 0.001 mg/kg. The concentrations of Pb in the various dumbsites were higher than the value found in the control site, indicating the impact of anthropogenic activities in and around the dumpsites. The results obtained from the analysis exceed the WHO permissible limit of 0.01 mg/kg. The presence of lead in the soil beyond the permissible level may be due to the disposal of wastes material such as paint, textiles, lead acid batteries waste or spillage of leaded fuel, food packaging materials and Polyvinylchloride materials (PVC), scrap metals, oil from mechanic workshop and other automobile part deposited on the dumpsites [24]. The mean concentrations of Pb in this study were higher when compared with that of Awotan dumpsite in Ibadan (0.49 mg/kg and 0.10 mg/kg respectively). [25] who worked on the heavy metal contents in soils at dumpsites. This result on Pb concentration around the battery dumpsite agreed with previous reports on similar environments [26].

Cr: The mean concentrations of Cr across the various dumpsites range from 2.05 to 2.37 mg/Kg with the lowest value in PDSS and the highest value recorded in DDSS respectively. The value of the control sample was observed to be 0.025 ± 0.001 mg/Kg. Exposure to Cr is associated with allergic dermatitis in humans, it also causes mutagenic, carcinogenic and teratogenic effects on humans [27]. The values of Cr obtained in this study were lower than 16.33 ± 3.51 to 66 ± 14.11 mgkg reported by [28] in selected dumpsites in Nasarawa, Kogi and Niger States. Similarly, low levels of chromium have been observed in surface soils under waste dumps in Onitsha, Nigeria [29].

Cd: Cadmium mean concentrations ranged from 0.094 to 0.143 with the lowest and highest concentrations recorded in FDSS and DDSS respectively. The value of the control sample was observed to be 0.012 ± 0.001 mg/kg. The mean value of Cd was 0.121 ± 0.001 mg/kg and this was within the acceptable limit. The Concentrations of Cd may be attributed to various sources, some of which include automobile tire dust, burning of oil and tyre, plastic wrappings, paints, dyes, and especially, refuse dumps and commercial activities [30]. The result observed in this study was lower than that of [31] on the study on selected dumpsites.

Zn: The mean concentration of Zn in the soil samples range from 0.023 to 0.228 mg/Kg with the lowest and highest concentrations recorded in BDWS and PDWS respectively. The control sample recorded 1.76 ± 0.002 mg/Kg. The presence of Zn in the soil at the different dumpsites could be credited to the disposal of dry cells in the municipal waste, the burning of electronic waste materials containing alloys of brass and bronze, empty cans of fungicides, pigments and pesticides as well as the disposal of metallic objects containing galvanizing steel and iron in the dumpsites. With regard to the paint-industry contaminated site, the value reported here was higher than that of [32] and this may be due to different geological locations. Long term exposure to Zn can result in gastrointestinal irritation and interference of physiological processes. In adversely affects plant health, extreme intake by humans aggravates Cu deficiency. It can also interrupt microbial activity in soils, as it harmfully influences the activity of microorganisms and earthworms and as a result, retards the breakdown of organic matter [27].

Mn: The mean concentrations of Mn range from 0.094 to 1.03 mg/Kg with the lowest value in PDSS and the highest value recorded in DDSS respectively. The value of the control sample was observed to be 0.148 ± 0.001 mg/Kg. The results obtained from this analysis are below the WHO permissible limit of 100 mg/Kg. The presence of Mn in the various dumbsites could be due to the composition of metal alloys and other manganese compounds in batteries; Potassium permanganate as oxidant for cleaning, bleaching and disinfection purposes, other manganese compounds are also used in fertilizer. Manganese is equally essential for plants and animals but poisonous at high concentrations. The harmful effect in humans is always related with severe psychiatric disorder resembling schizophrenia, followed by permanently crippling neurological disorder clinically similar to Parkinson’s disease [27].

Cu: The mean concentrations of Cu across the various dumpsites range from 0.026 to 0.883 mg/Kg with the lowest value in BDSS and the highest value recorded in PDSS respectively. The value of the control sample was observed to be 0.005 ± 0.001 mg/Kg. The presence of copper in the soils can be linked to anthropogenic activities such dumping of copper containing wastes like electrical wires, fertilizers, textile, plumbing materials and migration of leachate rich in copper into the nearby soils. Excessive dietary copper intake in mammals causes nausea, vomiting and diarrhea. It also causes pathological changes in brain tissue. Copper accumulates in the liver, kidney, cornea, and brain [33]. The accumulation of Cu in the brain leads to trauma and eventual death. The results obtained for Cu in this study from paint dumpsite were also similar to that of [34].

Table 3. Mean concentration (mg/Kg) of selected heavy metals in soil samples.

FDSS: Fertilizer Dumpsite Soil Sample, DDSS: Dye Dumpsite Soil Sample, BDSS: Battery Dumpsite Soil Sample, PDSS: Paint Dumpsite Soil Sample.

Geo-accumulation index: The geo-accumulation index of the soil samples was presented in Table 4 FDSS shows that, Pb and Zn were unpolluted, that of Fe fell within unpolluted to moderately polluted; Mn were moderately polluted, Cd and Cu were moderately to strongly polluted while Cr fell within the extremely polluted of the geo-accumulation index interpretation scale. That of DDSS shows that, Fe and Zn were unpolluted; Pb, Cd and Mn were moderately to strongly polluted; Cu was strongly polluted and Cr extremely polluted. The I_geo values for BDSS indicated that, the dumpsite soil was not polluted by Fe and Zn meaning that these two metals did not cause contamination, unpolluted to moderately polluted was observed by Mn, moderately polluted was observed by Pb and Cu, moderately to strongly polluted was noticed by Cd and extremely polluted observed by Cr. The I_geo values for PDSS shows that, dumpsite soil was not polluted by Zn and Mn, unpolluted to moderately polluted was noticed by Fe and strongly polluted was observed by Pb and Cd while extremely polluted was observed by Cr and Cu. Increasing anthropogenic activities cause increased geo- accumulation of these metals in the soil that are known carcinogenic and mutagenic to flora and faunas, when in extreme concentrations thereby impacting the natural manageable level that is assimilated to prevent adverse ecological impact [35].

Contamination factor: The contamination factor of the metals is tabulated in Table 4. The result shows that, CF of Cr and Cd in all the dumpsites were greater than 6 (CF > 6) and were considered highly contaminated. The CF of Zn in all the dumpsites was within the classification; CF < 1 signifying low contamination. Moderate CF was observed by Fe in all the studied sites excerpt BDSS (0.306) which report Low CF. Low CF was observed by Mn in PDSS, Moderate contamination in FDSS and BDSS respectively. The high metal contamination of Cr, Cd, Pb, Cu and Mn in the different dumpsite could be due to presence of these elements from anthropogenic activities. These results are similar to the work reported by [36].

Enricment factor (EF): The values of the enrichment factor (EF) of the analysed metals with respect to natural background concentrations are presented in Table 5. The result shows, no enrichment in FDSS, moderate enrichment in PDSS, moderately severe enrichment in DDSS and severe enrichment in BDSS for Pb. The result observed for Pb in DDSS and BDSS were similar to that reported by [37]. In the case of Cr, dumpsites FDSS and PDSS shows very severe enrichment while that of DDSS and BDSS were observed to be extremely severe enrichment. The enrichment of Cd was observed to be; moderate enrichment in FDSS; moderately severe enrichment in PDSS; severe enrichment in DDSS and very severe enrichment reported in BDSS. Zn recorded no enrichment in all the studied dumpsites indicating that there was no enrichment with this metals in the study sites. The enrichment factor of Mn was observed to be; no enrichment in FDSS and PDSS, moderately severe enrichment in DDSS and BDSS. While that of Cu reported moderate enrichment in FDSS, severe enrichment in DDSS and BDSS and extremely severe enrichment in PDSS, this observation was for Cu was similar to that of [37].

Ecological risk index (ERI): Table 6 present the Eri assessment of the analyzed heavy metals from dumpsites. Soil samples from studied dumpsites indicated low Eri for the heavy metals (Fe, Zn and Mn) except for Cd which reported very high potential ecological risk in DDSS and PDSS and high potentical ecological risk in FDSS and BDSS, Cr recorded high potentical ecological risk in all the sampled sites. The results of the Er revealed that Fe, Zn and Mn were less than 40 (Er <40) across the study sites indicating low ecological risk. While Cr, Cd and Cu were more than 320 and therefore pose a very high ecological risk. These results disagree with that of [36]. Furthermore, the ecological risk showed considerate ecological risk (300 ≤ Eri < 600) in FDSS and BDSS and very high ecological risk (≥600) in DDSS and PDSS respectively. This could be due to anthropogenic activities around the dumpsites. Furthermore, the ecological risk showed considerate ecological risk (300 ≤ Eri < 600) in FDSS and BDSS and very high ecological risk (≥600) in DDSS and PDSS respectively. This could be due to anthropogenic activities around the dumpsites. The comprehensive potential ecological risk index (RI) shows that FDSS and BDSS have considerate ecological risk while DDSS and PDSS have very high ecological risk therefore exhibit high risk of pollution (669 and 1134). This indicates that, considering the soils studied and other matters (both living and non-living), the environment are at high risk of various degrees of pollution which will cause serious health problem to the habitants and other living things in the dumpsite.

Table 4. Geoaccumulation Index (I_geo) of heavy metals in soil samples.

Contamination factor: The contamination factor of the metals is tabulated in Table 5.

Table 5. Contamination Factor (Cf) of heavy metals in soil samples.

Enrichment factor (EF): The values of the enrichment factor (EF) of the analysed metals with respect to natural background concentrations are presented in Table 6.

Table 6. Enrichment Factor (EF) of heavy metals in soil samples.

Table 7. Ecological Risk Index (ERI) of heavy metals in soil samples.

Chronic Daily Intake (CDI): The results of assessment of human exposure to the heavy metals through calculating the Chronic Daily Intake (CDI), Hazard quotient (HQ) and Hazard index (HI) through ingestion, dermal contact and inhalation pathways are presented in Tables 7-9 respectively.

Table 8. Chronic Daily Intake (CDI) of selected heavy metals in soil samples.

The Chronic Daily Intake (CDI) of the heavy metals in Table 8 shows that, ingestion, dermal and inhalation values for children and adults were also less than 1 indicating low contamination. This shows that, there were no-non carcinogenic risks after the selected metals in both adults and children; this assertion was similar to that reported by [38]. Although, it is observed that, the magnitude of risks of the heavy metals toxicity for children were higher than for adults for almost all heavy metals in this study. The reason could be the lower body weight of children, differences in physiological factors, contact frequency and dietary habits.

Table 9. Hazard Quotient (HQ) and Hazard Index (HI) of selected heavy metals in soil samples.

The result of the HQ and HI tabulated in Table 9 revealed that the highest individual target Hazard Quotient (HQ) of the dumpsites was contributed by Pb while the least was Zn. However, the hazard quotients of all the heavy metals measured in both water and soil samples across the dumpsites were less than one (<1), the related standard limit by USEPA. This indicates less non-carcinogenic risks present in the samples or acceptable levels of non-carcinogenic health risks. It was observed that, higher HQ values were revealed for children compared to adults, similar observation was also reported by [39]. Similarly, hazard index (HI) of the analyzed heavy metals in the soil sample from the dumbsites were below the acceptable safe level of one (<1) as set by USEPA. This indicated that there is no likelihood of non-carcinogenic health risks effects [40]. [41] also reported Hazard Index of less than one (< 1) in the soil samples but [42][43] reported an elevated hazard index estimate above the acceptable safe level.

Table 10. Carcinogenic risk assessment of selected heavy metals in soil samples.

Table 10 present Carcinogenic Risk Assessment (CRA) of the soil sample showed that, carcinogenic risk assessment of the heavy metals in the dumpsites across the age groups and entry routes ranged from 2.71 × 10⁻⁶ to 7.54 × 10⁻¹¹; 2.59 × 10⁻⁶ to 9.87 × 10⁻¹¹ and 1.57 × 10⁻⁷ to 8.19 × 10⁻¹² for Pb, Cr and Cd respectively. All the values reported in this study were low risk (CR < 1) and below the [39]. This may be due to low activities of the heavy metals assessed at the dumpsite. Therefore, soils around the dumbsites are safe from cancer for both adults and children. A related outcome was stated by [44] and [45] who specified cancer risk to be of low value. The carcinogenic risk levels for children and adult generally fell within the acceptable range for carcinogens, which typically ranges from 10^–6 to 10^–4 according to [46] Li etal., (2017). This finding is similar with the work previously reported by [47] but contradict the work of [48].

The apparent discrepancy between high ecological risk (RI = 488 – 1134) and low human health risk stems from their distinct assessment frameworks. Ecological risk reflects the total metal concentration and its inherent toxicity to soil ecosystems, indicating significant degradation and potential for biodiversity loss. In contrast, human health risk is based on specific, current exposure pathways (ingestion, dermal, inhalation), which presently result in a daily intake below harmful thresholds.

However, the low human health risk is conditional. The high ecological contamination represents a latent public health threat. Persistent metals like Pb, Cd, and Cr can bioaccumulate in crops and livestock, potentially entering the food chain at concentrations far exceeding direct soil exposure. Furthermore, changes in land use—such as agricultural expansion, residential development, or groundwater use—could create new exposure pathways.

Thus, while current exposure levels are low, the degraded soil ecosystem poses a clear future risk. Preventive measures, such as restricting agriculture and settlement on these sites, are urgently needed to mitigate potential health impacts from bioaccumulation or altered land use. Continuous monitoring is recommended.