Imagine living near a dumpsite where everyday wastes hide dangerous secrets that could threaten your health and the environment—sounds alarming, right? That's exactly what this study uncovers in Benue State, Nigeria, where industrial and domestic garbage might be silently polluting the soil and endangering both people and nature.
Ecological and Human Health Risk Assessment of Soil Samples from Vicinities of Dumpsites in Residential and Selected Industrial Layouts in Benue State, Nigeria
Ecological and Human Health Risk Assessment of Soil Samples from Vicinities of Dumpsites in Residential and Selected Industrial Layouts in Benue State, Nigeria ()
- Introduction
Environmental pollution is a pressing global challenge that deeply affects the well-being of people and communities everywhere. The rapid increase in fossil fuel consumption, improper sewage management, and widespread misuse of agricultural chemicals all contribute to the widespread issue of pollution across our planet [1].
Over time, the waste generated from industrial expansion, often discarded carelessly, has become a significant problem in developing nations. Many of these wastes include hazardous substances that can seep into the ground, build up in soil and riverbeds, and spread to the entire ecosystem [2].
Industrial byproducts can disrupt hydrological systems and ecosystems, while also posing serious dangers to people and wildlife. The buildup of toxic pollutants in soil, water, and air leads to health concerns and environmental damage [3] [4].
Hazardous wastes are known for their flammable, reactive, explosive, and poisonous traits. Examples include wastes from fertilizer plants, paint factories, dye manufacturers, pharmaceuticals, products with heavy metals, auto repair shops, infectious biological materials, and battery recycling. These are commonly thrown away as regular trash [5].
Battery waste, for instance, is often discarded carelessly, allowing its toxins to leach into the earth, contaminating soil and waterways [6]. And here's where it gets controversial—some argue that such pollution is unavoidable in growing economies, but others insist it's a preventable crisis through better waste management.
The textile sector produces a wide range of environmental issues [7]. Solid wastes mainly consist of fabric scraps, yarns, and packaging, while the sludge contains high levels of organic substances, nutrients, heavy metals, and harmful microorganisms [8].
Fertilizer production is a source of natural radioactive elements and heavy metals like mercury (Hg), cadmium (Cd), arsenic (As), lead (Pb), copper (Cu), nickel (Ni), and uranium (238U), thorium (232Th), and polonium (210Po). This results in pollution of soil, water, and air, and when fertilizers are applied incorrectly, they can introduce toxic heavy metals into farmland, turning agricultural soils into pollution hotspots [10].
The chemicals in paints lead to high levels of organic acids, suspended solids, colored compounds, and dangerous pollutants such as heavy metals in the waste [11].
Dumpsites serve as the primary repositories for household and industrial trash. Abandoned sites are often repurposed for farming, parks, or homes without checking for hidden risks. The soil might even be used as fertilizer elsewhere, rich in minerals and organics, but potentially loaded with toxins that harm living things. Plus, these sites release unpleasant odors and smoke, causing sickness in nearby residents.
To study this, researchers used Scanning Electron Microscopy (SEM) to examine soil surface structures, X-ray Fluorescence (XRF) to identify elements and their percentages, and X-ray Diffraction (XRD) to detect minerals and calculate crystal sizes with the Debye-Scherrer formula:
β(2θ) = kλ / (L cos θ) (1)
where k is 0.94.
Despite the importance of dumpsites in the country, they've been understudied, especially for their mineral and toxic content. Most research has focused on large landfills [12], light industrial areas [13], and e-waste sites [14].
This research aims to evaluate the ecological and health risks from soil and water near dumpsites in residential and industrial areas of Makurdi, Benue State, Nigeria.
- Materials and Methods
Certified reagents like nitric acid, hydrochloric acid, sulfuric acid, and sodium hydroxide were sourced. Equipment included Energy Dispersive X-ray Fluorescence, X-ray Diffractometer (XRD), Scanning Electron Microscope, and Atomic Absorption Spectrophotometer (AAS) (see Table 1).
2.1. Sampling
Topsoil samples (0-20 cm deep) were gathered from various dumpsites using an auger, including those near paint factories, dye plants, auto battery shops, and fertilizer producers in Makurdi. Three samples per site were collected. A control sample came from a residential area without industrial or dump history, located upwind and over 2 km away to avoid contamination from air or runoff. This site features low-density housing, no traffic, and no farming, providing a baseline for local soil.
Locations
Codes
Latitude (°) Longitude (°)
Fertilizer Dumpsite Soil Sample
FDSS
1) 7.748280 8.531422
2) 7.745808 8.525397
3) 7.745982 8.525323
Dye Dumpsite Soil Sample
DDSS
1) 7.745705 8.514172
2) 7.745695 8.514149
3) 7.745697 8.514419
Battery Dumpsite Soil Sample
BDSS
1) 7.744887 8.513710
2) 7.744868 8.513618
3) 7.744871 8.513741
Paint Dumpsite Soil Sample
PDSS
1) 7.742112 8.513122
2) 7.731222 8.517217
3) 7.736231 8.517281
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.
After collection, samples were air-dried, ground with a mortar and pestle, and sieved to 2 mm. They were stored in sealed plastic bags at room temperature for 24 hours before transport to the lab at Joseph Sarwuan Tarka University.
Sample Preparation
A 1.0 g portion of dried, sieved soil was mixed with aqua regia (HCl:HNO3 in 1:3 ratio) in a 250 mL flask. Heated for 1 hour, cooled, and filtered with Whatman paper. Diluted to 50 mL with distilled water.
2.2. Physicochemical Analysis
pH, electrical conductivity, organic matter, phosphate (PO4³⁻), and nitrate (NO3⁻) were tested per standard procedures [15]. For beginners, pH measures acidity—lower numbers mean more acidic, which can affect soil health and plant growth.
2.3. Sample Characterization
Heavy metal levels were measured via Atomic Absorption Spectrophotometry (AAS).
X-ray Fluorescence Spectroscopy (XRF) quantified major oxides and elements.
X-ray Diffraction (XRD) analyzed mineral phases and crystal sizes using the Debye-Scherrer formula:
β(2θ) = kλ / (L cos θ) (1)
with k at 0.94.
Scanning Electron Microscopy (SEM) examined surface textures.
2.4. Ecological Assessment
Soil contamination and risks were assessed through various indices.
2.4.1. Geoaccumulation Index (Igeo)
This index compares metal levels in soil to natural backgrounds, adjusted for natural variations. Calculated as:
Igeo = log₂ Cn / (1.5 Bn)
Where Cn is the sample concentration, Bn is the background level, and 1.5 corrects for geological factors. Background values came from the control sample, representing pre-human levels in Makurdi soils.
2.4.2. Contamination Factor (CF)
CF shows how much a site exceeds background levels:
CF = C₀ / Cn (3)
Where Cn is the metal concentration, C₀ is the average background.
2.4.3. Ecological Risk Assessment
Risks were evaluated using:
ERI = TR × CF (4)
Where CF is the contamination factor, ER the risk per element, RI the total sum. TR indicates toxicity—higher for more dangerous metals.
2.4.4. Enrichment Factor
EF distinguishes human-induced pollution from natural sources:
EF = (Cxmetal / Fesample) / (Crefmetal / Febackground) (5)
Iron (Fe) was chosen as the reference due to its abundance and stability in soils.
2.5. Human Health Risk Assessment
Risks come from three pathways: ingestion (eating soil), inhalation (breathing dust), and dermal contact (skin exposure). Doses calculated for children and adults.
Ingestion dose:
D_Ing = C × IngR × EF × ED / (BW × AT) × 10⁻⁶ (6)
Where IngR is 200 mg/day for children, 100 for adults; EF (exposure frequency) = 300 days/year; ED = 6 years for children, 24 for adults; BW = 15 kg children, 70 kg adults; AT = ED × 365 days.
Inhalation dose:
D_Inh = C × InhR × EF × ED / (BEF) (7)
InhR = 7.6 m³/day children, 20 m³/day adults.
Dermal dose:
D_der = C × SA × kp × ET × EF × ED × ABS / (BW × AT) × 10⁻⁶ (8)
SA = 2800 cm² children, 5700 cm² adults; ABS = 0.001 for all metals.
2.5.1. Hazard Quotient (HQ)
HQ for non-cancer risks:
HQ = CDI / RfD (9)
CDI is daily intake, RfD is safe dose [USEPA, 1999]. HQ > 1 means risk; <1 is safe.
2.5.2. Hazard Index
Sums HQs for overall risk:
HI = Σ HQ_i (10)
HI > 1 indicates potential harm.
2.5.3. Carcinogenic Risk
Cancer risk from lifetime exposure:
ILCR = CDI × CSF (11)
ILCR is incremental lifetime risk; CSF is slope factor.
- Results and Discussion
3.1. Physicochemical Parameters
See Table 2 for pH, conductivity, organic matter, nitrates, and phosphates.
pH ranged from 2.81 (acidic) to 7.80 (alkaline), average 6.04. Acidic soils near BDSS and PDSS make metals more available for plants [17][18], while alkaline near FDSS, DDSS aligns with other studies [19]. pH influences metal mobility—acidity can release toxins.
Conductivity: 259-4757 µS/cm, highest at BDSS from salts [20]. High conductivity indicates soluble ions, potentially harmful.
Organic matter: 2.54-3.91%, highest at BDSS, possibly lowering pH [21]. Organic matter binds toxins but can decompose unpredictably.
Phosphates (PO4³⁻): 12.8-38.8 mg/L, linked to fertilizers. High at FDSS from production; others from farming runoff.
Nitrates (NO3⁻): 2.11-7.25 mg/L, low overall, suggesting no excess nitrogen pollution. Matches paint site data [22].
Table 2. Physicochemical parameters of soil samples from selected vicinities of dumpsites around residentials/industrial areas.
Location pH Electrical Conductivity (µS/cm) Organic Matter NO3⁻ (mg/L) PO4³⁻ (mg/L)
FDSS 7.80 ± 0.04 363 ± 0.68 3.49 ± 0.05 2.11 ± 0.01 38.8 ± 0.35
DDSS 7.60 ± 0.04 318 ± 0.79 2.54 ± 0.02 2.93 ± 0.01 12.8 ± 0.68
BDSS 2.81 ± 0.00 4757 ± 0.81 3.91 ± 0.03 7.25 ± 0.03 18.1 ± 0.19
PDSS 5.94 ± 0.11 259 ± 0.59 2.56 ± 0.06 3.14 ± 0.04 26.2 ± 0.18
Control 6.20 ± 0.00 123 ± 0.53 3.82 ± 0.03 8.56 ± 0.03 46.0 ± 0.03
FDSS: Fertilizer Dumpsite Soil Sample, DDSS: Dye Dumpsite Soil Sample, BDSS: Battery Dumpsite Soil Sample, PDSS: Paint Dumpsite Soil Sample.
3.2. Concentrations of Heavy Metals
See Table 3 for Fe, Pb, Cr, Cd, Zn, Mn, Cu.
Fe: 0.471-4.06 mg/kg, below some limits [23]. Iron is essential but can indicate other pollutants.
Pb: 0.337-2.47 mg/kg, exceeds WHO 0.01 mg/kg, from paints, batteries, fuel [24]. Higher than other studies [25], especially near batteries [26]. Lead causes brain damage, especially in kids.
Cr: 2.05-2.37 mg/kg, causes skin issues, mutations [27]. Lower than some sites [28][29]. Chromium can build up dangerously.
Cd: 0.094-0.143 mg/kg, within limits, from tires, paints [30]. Lower than other dumps [31]. Cadmium harms kidneys and bones.
Zn: 0.023-0.228 mg/kg, from batteries, electronics [32]. Excess causes stomach issues and disrupts ecosystems.
Mn: 0.094-1.03 mg/kg, below WHO 100 mg/kg, from alloys, fertilizers. High doses mimic Parkinson's [27].
Cu: 0.026-0.883 mg/kg, from wires, fertilizers. Causes vomiting, liver damage [33][34].
Table 3. Mean concentration (mg/Kg) of selected heavy metals in soil samples.
Heavy Metals FDSS DDSS BDSS PDSS Control WHO (mg/Kg)
Fe 4.06 ± 0.002 1.72 ± 0.002 0.471 ± 0.004 3.31 ± 0.002 1.54 ± 0.001 0.5 - 50
Pb 0.337 ± 0.003 1.81 ± 0.003 1.48 ± 0.002 2.47 ± 0.002 0.289 ± 0.001 0.01
Cr 2.30 ± 0.002 2.37 ± 0.001 2.12 ± 0.001 2.05 ± 0.002 0.025 ± 0.001 0.05
Cd 0.094 ± 0.001 0.143 ± 0.001 0.110 ± 0.000 0.136 ± 0.001 0.012 ± 0.001 1 - 3
Zn 0.044 ± 0.006 0.166 ± 0.003 0.023 ± 0.004 0.228 ± 0.005 1.76 ± 0.002 95
Mn 0.483 ± 0.001 1.03 ± 0.001 0.317 ± 0.001 0.094 ± 0.001 0.148 ± 0.001 100
Cu 0.057 ± 0.001 0.083 ± 0.001 0.026 ± 0.001 0.883 ± 0.007 0.005 ± 0.001 100 - 200
FDSS: Fertilizer Dumpsite Soil Sample, DDSS: Dye Dumpsite Soil Sample, BDSS: Battery Dumpsite Soil Sample, PDSS: Paint Dumpsite Soil Sample.
3.3. Assessment of Ecological Risk Indices
Geoaccumulation Index: See Table 4. FDSS shows unpolluted to polluted levels; DDSS highly polluted; BDSS moderate; PDSS extreme for some. And this is the part most people miss—pollution indices reveal hidden threats that build over time, potentially harming wildlife and soil life [35].
Contamination Factor: Table 5. High for Cr, Cd; low for Zn, Mn. Matches other studies [36].
Enrichment Factor: Table 6. Shows human sources, e.g., severe enrichment near dyes [37].
Ecological Risk Index: Table 7. Very high for some metals, total risk considerate to very high. Anthropogenic activities drive this [36], risking ecosystem collapse.
Table 4. Geoaccumulation Index (Igeo) of heavy metals in soil samples.
Heavy Metals FDSS DDSS BDSS PDSS
Fe 0.816 −0.425 −2.29 0.516
Pb −0.366 2.06 1.77 2.51
Cr 5.92 5.96 5.80 5.75
Cd 2.38 2.99 2.61 2.92
Zn −5.88 −3.99 −6.97 −3.54
Mn 1.12 2.21 0.516 −1.24
Cu 2.83 3.38 1.70 6.78
Contamination factor: The contamination factor of the metals is tabulated in Table 5.
Table 5. Contamination Factor (Cf) of heavy metals in soil samples.
Heavy Metals FDSS DDSS BDSS PDSS
Fe 2.64 1.12 0.306 2.15
Pb 1.17 6.26 5.12 8.55
Cr 92.0 94.8 84.8 82.0
Cd 7.83 11.9 9.17 11.3
Zn 0.025 0.066 0.013 0.129
Mn 3.26 6.96 2.14 0.635
Cu 11.4 16.6 5.20 177
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.
Heavy Metals FDSS DDSS BDSS PDSS
Pb 0.441 5.59 16.7 3.97
Cr 35.4 86.3 281 38.7
Cd 3.29 11.9 33.4 5.86
Zn 0.009 0.085 0.043 0.061
Mn 1.24 6.24 7.01 0.292
Cu 4.67 16.0 18.3 89.0
Table 7. Ecological Risk Index (ERI) of heavy metals in soil samples.
Heavy Metals FDSS DDSS BDSS PDSS
Fe 2.64 1.12 0.306 2.15
Pb 5.85 31.3 25.6 42.8
Cr 184 190 170 164
Cd 235 357 275 339
Zn 0.025 0.066 0.013 0.129
Mn 3.26 6.96 2.14 0.635
Cu 57.0 83.0 26.0 585
RI 488 669 499 1134
3.4. Human Health Risk Assessment
Chronic Daily Intake (CDI): See Tables 8-9. Ingestion highest, but all <1, meaning low risk [38]. Children more vulnerable due to size and habits.
Hazard Quotient and Index: All <1, no non-cancer risks [39][40], though some studies find higher [41][42][43].
Carcinogenic Risk: Table 10. All low (<10⁻⁶), safe [44][45], within limits [46][47], unlike others [48].
Table 8. Chronic Daily Intake (CDI) of selected heavy metals in soil samples.
(Full table data as in original, but abbreviated for space.)
Table 9. Hazard Quotient (HQ) and Hazard Index (HI) of selected heavy metals in soil samples.
(Full table data as in original.)
Table 10. Carcinogenic risk assessment of selected heavy metals in soil samples.
(Full table data as in original.)
3.5. Reconciliation of Ecological and Human Health Risk Assessments
High ecological risk (RI 488-1134) contrasts with low human risk because ecology considers total pollution impact, while health focuses on current exposures. But here's the controversy—is this acceptable, or does high ecological damage signal impending human threats through food chains or land changes? We need ongoing monitoring to prevent future issues.
- Chemical Characterization
SEM: Figure 1 shows fragmented grains at some sites, indicating leaching risk, vs. compact elsewhere.
XRD: Figure 2, Table 11. Minerals like quartz, kaolinite vary by site.
XRF: Figure 3. Major elements: Ca, Fe, K, etc.; minors include toxic Pb, Cu, Zn.
- Conclusion
This study examined risks from dumpsites in Benue State. Soil showed varying contamination, high ecological risks but low human health ones currently. Monitoring is key.
What do you think—should stricter regulations force better waste disposal, even if it slows economic growth? Agree or disagree in the comments!
