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Micro- and Nanoplastic Contamination in Surface and Groundwater

Sources of Aifam Owukpa, Ogbadibo Lga, Benue State, Nigeria: A First

Exploratory Scan

I.J. Ikwuje

, O. Ofoegbu

, G. Ikwuje

, and T. Yaro

Department of Environmental Sustainability, College of Physical Sciences, Joseph Sarwuan Tarka

University, Makurdi, Benue State, Nigeria

Department of Industrial Chemistry, College of Physical Sciences, Joseph Sarwuan Tarka University,

Makurdi, Benue State, Nigeria

Dr. John Adah College of Health Science and Technology, Otukpo, Benue State, Nigeria

DOI:

https://doi.org/10.51583/IJLTEMAS.2026.150600039

Received: 04 June 2026; Accepted: 10 June 2026; Published: 04 July 2026

ABSTRACT

The micro- and nanoplastic (MP/NP) contamination of freshwater systems has become a rapidly growing

environmental and public health concern globally, yet rural groundwater and surface water of sub-Saharan Africa

remain critically understudied. This first exploratory study in Aifam Owukpa, Ogbadibo Local Government Area

(LGA), Benue State, Nigeria, characterises MP/NP contamination across 12 purposively selected water sources

(streams, springs, and hand-dug wells) sampled during the rainy season (July–August 2025). Multi-stage

membrane filtration (5 µm and 0.45 µm), hydrogen peroxide digestion, and sodium chloride density separation

were applied for particle extraction. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR)

spectroscopy (Nicolet iS50, 4,000–400 cm⁻¹) was used for polymer identification, and Scanning Electron

Microscopy with Energy Dispersive

X-ray

Spectroscopy

(SEM-EDS;

JEOL

JSM-6610LV)

provided

morphological

and

elemental characterisation. Physicochemical parameters (pH, turbidity, electrical

conductivity, biochemical oxygen demand, and total dissolved solids) were measured and benchmarked against

WHO drinking-water quality guidelines. Microplastics were detected in 85% of sampling sites (11 of 12) at

concentrations of 45–210 particles/L (mean: 112 ± 45 particles/L), with stream sites substantially exceeding

wells and springs. Dominant polymers were polyethylene (40%), polypropylene (30%), polystyrene (15%),

polyethylene terephthalate (10%), and polyvinyl chloride (5%). Morphological analysis identified fragments

(55%), fibres (30%), and films (15%). Nanoplastic presence was inferred in 40% of samples via sub-micrometre

spectral broadening; direct quantification using Py-GC/MS or nano-FTIR is strongly recommended for future

work. Turbidity showed a strong positive correlation with MP abundance (r = 0.78, p < 0.01). SEM-EDS

confirmed high carbon content (65–75% C) and weathering-consistent morphologies indicative of local

secondary fragmentation. A GIS-based contamination hotspot map (Figure 11) spatially delineates high-,

moderate-, and low-risk zones. The single-season design and absence of contaminant adsorption data are

acknowledged limitations; future studies should incorporate comparative dry- and wet-season sampling,

quantitative nanoplastic analysis, and heavy metal/persistent organic pollutant (POP) adsorption experiments.

These findings establish a critical contamination baseline, underscoring the need for community-level plastic

waste governance and integration of MP monitoring into Benue State water quality frameworks.

Keywords: Microplastics, nanoplastics, ATR-FTIR, SEM-EDS, GIS hotspot mapping, freshwater

contamination, Nigeria, groundwater, rural water quality, polymer characterisation, seasonal variability, Benue

State.

INTRODUCTION

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Plastic pollution has received a complete overhaul to change the issue of visible, macro-scaled litter to micro-

and nanoscale, ubiquitous contamination. Microplastics (MPs) are defined as plastic particles whose longest

dimension is less than 5 mm but more than 1 µm, and nanoplastics (NPs) are less than 1 mm in diameter [1].

These particles are formed as a result of the fragmentation of larger plastic debris in the ultraviolet radiation,

mechanical abrasion, and biological degradation (secondary MPs), or due to direct emissions during production,

tire wear, washing of synthetic fabrics, and use of personal care products (primary MPs) [2]. Their hydrophobic

surfaces enable them to adsorb persistent organic pollutants (POPs), heavy metals, and pathogenic biofilms, and

convert individual particles into multifaceted chemical vectors that increase ecotoxicology risk far beyond that

of the plastic matrix itself [3].

As of 2023, the world total of plastic manufacturing was over 400 million metric tonnes per year, and it is

estimated to be doubled by 2040, unless current manufacturing and waste management trends are altered [4].

The estimates of this volume indicate that between 9% and 23% finally finds its way into the natural

environment, mainly through riverine routes [5]. No longer viewed as transitional sites to marine systems,

freshwater ecosystems are now viewed

as essential sites of accumulation and, more and more, as a literal source of human exposure via drinking water

and dietary uptake [6]. In European and Asian rivers, concentrations have been recorded at 10- 8,000 particles/L,

which is dependent on the catchment land use and urbanization [7]. The geographical conditions in the sub-

Saharan region of Africa exacerbate the plastic pollution problem; recycling rates are at the continent level, less

than 10 percent, and significant proportions of the plastic waste produced are discarded or burned [8].

The most populous country on the African continent, Nigeria, consumes more than 700,000 tonnes of plastic per

year, with a disproportionate amount of this plastic being deposited in watercourses uncontrolled [9]. Increasing

research attention has been given to urban Nigerian water bodies: boreholes in metropolitan Lagos have been

demonstrated to harbor MP concentrations 206-1,691 particles/L, with the Lagos Lagoon supporting

concentrations of 1,200-6,700 particles/m³, which has been fuelled by fragments of urban runoff and industrial

discharges [10, 11]. Nevertheless, little is known regarding the rural groundwater systems, in terms of MP/NP

contamination, in northern and central Nigeria, which is a key gap, since most rural residents use untreated

springs, hand-dug wells, and seasonal streams as the direct sources of domestic and drinking water [12].

The River Benue and tributary system of the river play a significant role in the irrigation and provision of

domestic water in Benue State, located in the Middle Belt of Nigeria, and informally known as the Food Basket

of the Nation, due to its agricultural productivity. The Ogbadibo LGA, which is situated in the southeast of the

state, is a predominantly agricultural society with a recorded history of trace metal pollution that has been

attributed to the past coal mining operations in the Owukpa area [13]. The existence of coal-based contaminants

evokes the further spectre of MP-metal co-contaminant interactions, with plastic surfaces serving as a sink to

metals like lead, cadmium, and chromium, and thus exposing humanity to increased contamination through

ingestion of contaminated water [14]. Although this represents a multi-dimensional risk profile, there has not yet

been published research that explored MP or NP contamination in the surface or groundwater of Aifam Owukpa

or of the Owukpa community, in general.

This research was planned as a pilot scan to determine baseline contamination information of Aifam Owukpa

water sources. It also tackles five objectives: (i) to identify the physicochemical quality of sampled waters within

the framework of WHO standards; (ii) to identify and measure MPs through ATR-FTIR spectroscopy; (iii) to

characterize particle morphology and elemental composition with the use of SEM-EDS; (iv) to map the spatial

distribution of MP contamination and identify potential anthropogenic sources. The research, therefore, bridges

a geographically and environmentally important gap in the fast-expanding body of research on African

freshwater MP.

Health and Ecological Aspects of Micro- and Nanoplastic Contamination.

Mechanistic evidence is increasingly becoming important in the toxicological significance of MPs and NPs in

drinking water. When ingested, particles less than 150 µm may penetrate the intestinal epithelium and enter the

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systemic circulation, and smaller NPs are able to cross the blood-brain barrier and be deposited in organ tissues

such as the liver, spleen, kidney, and testes [15]. Biological effects have been observed, such as oxidative stress,

inflammatory cytokine up-regulation, endocrine signaling pathway disruption (especially estrogen and androgen

receptors), and mitochondrial dysfunction [16]. These health risks are compounded by the chemical additives

washed out of plastics such as bisphenol A (BPA), phthalate plasticizers, and flame retardants [17].

In fresh water, MPs are taken up by organisms at various trophic levels, such as macroinvertebrates, fish, and

amphibians, ecologically. Physical ingestion decreases the efficiency of feeding, reproductive output, and

intestinal obstruction [18]. Bioaccumulation along food chains presents indirect risks to human consumers of

freshwater fish, a protein source that is of significant importance in Benue State, where artisanal fisheries on the

River Benue and its tributaries also contribute to livelihoods and food security [19]. The combination of direct

water ingestion exposure and dietary bioaccumulation pathways results in a particularly acute risk situation in

the context of Aifam Owukpa, where more than 80% of the population relies on untreated water, and subsistence

agriculture is the most important source of protein.

Technical Overview of Analytical Approaches to Micro- and Nanoplastic Detection.

A multi-step analysis workflow, involving physical isolation, chemical identification, and morphological

analysis, is necessary to detect and characterize MPs in environmental matrices with a high degree of reliability

[20]. Separating by density with saturated saline solutions (NaCl: ρ ≈ 1.2 g/cm³; NaI: ρ ≈ 1.8 g/cm³; ZnCl₂: ρ ≈

1.7 g/cm³) takes advantage of the difference in density of typical commercial plastics (PE: 0.91–0.96 g/cm³; PP:

0.85–0.92 g/cm³) relative to mineral matrices, achieving extraction efficiencies of 90–96% for these polymer

types [21]. Biogenic organic matter that otherwise would interfere with downstream spectroscopic analysis is

removed by hydrogen peroxide (H₂O₂) or by enzymatic digestion.

The most recent gold standard used in polymer identification in MP studies is ATR-FTIR spectroscopy. The

method bases measurements upon attenuated total internal reflectance to measure molecular vibrational modes,

producing absorption spectra in the 4000-400 cm⁻¹ range, which is a polymer fingerprint that can be compared

against reference libraries like the OMNIC [22] and OpenSpecy. C–H critical bands at 2920 cm⁻¹ and 2850 cm⁻¹

are diagnostic of

polyethylene, and the CH₃ rocking mode at 1376 cm⁻¹ and skeletal C-C stretch at 1168 cm⁻¹ distinguish

polypropylene. ATR-FTIR detection limits of about 10-20 µm make it inappropriate to directly characterize NPs

with

pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) or liquid chromatography-mass spectrometry

(LC-MS). In the current research, NPs were deduced using sub-micrometer spectral broadening and residue

morphologies that were in accordance with nanoscale plastic degradation, in line with resource-relevant

methodologies that should be used in research studies in low-income nations.

SEM-EDS is a complementary morphological and elemental dataset. The surface features that are resolved in

high-resolution scanning electron microscopy at acceleration voltages of 520 kV include weathering fractures,

biofouling colonization, and fibre striations to submicron resolution [24]. EDS measures elemental composition

(C, O, Cl, Si, and others), allowing polymer matrices (e.g., high Cl content PVC) to be discriminated and

inorganic contaminants adsorbed to surfaces to be identified. But EDS by its nature is restricted to elemental as

opposed to molecular characterization and thus cannot be used to establish polymer type without spectroscopic

support [25].

Nigerian and African Freshwater MP Review.

The literature on freshwater MP contamination in West Africa, despite a relative scarcity until 2022, has

increased significantly. A systematic review of the Nigerian water bodies reported MP concentrations of 86-

1,691 particles/L in borehole and well water, and fibre morphologies were predominant in locations affected by

domestic grey water and textile wash effluents [26]. Niger Delta surface water research reports of 120-850

particles/L in drinking water sources, which can be attributed to petrochemical packaging waste and oil field

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working plastics [27]. Past studies have specifically not looked into the trace metal contamination of water in

the Owukpa coal belt alone but rather the entire Benue State, a gap that the current study will directly fill [13].

South African rivers report (continent-wide) 0.3-57 particles/L, which is a relatively well-managed waste stream,

and East African studies report concentrations of 10-210 particles/L in surface waters affected by smallholder

agriculture [28]. The new agreement is that African freshwater MP levels are not as high as those in highly

urbanized European or Asian systems but are still significantly high compared to pristine backgrounds and that

rural agrarian environments are a previously underrecognized exposure route due to direct drinking of untreated

water [29].

Study Area Description

Aifam Owukpa is a sub-community within Owukpa district, Ogbadibo LGA, Benue State, Nigeria

(approximately 7°00'N, 7°40'E; elevation 200–400 m above sea level; approximate area 50 km²). The landscape

is characterized by Guinea savanna vegetation transitioning to woodland, with undulating terrain dissected by

seasonal streams draining northward towards the River Benue watershed. The population of approximately 5,000

inhabitants is predominantly engaged in subsistence and smallholder agriculture, cultivating yam, cassava, and

rice, with associated use of polyethylene mulching films, polypropylene sacks, and single-use packaging.

Proximity to the Aho market junction facilitates informal plastic waste accumulation at key hydrological nodes.

Legacy open-cast coal mining in the broader Owukpa area has historically introduced heavy metals (Pb, Cd, As)

into local drainage systems, creating a complex co-contamination context in which MP-metal interactions are

plausible and warranting investigation.

Figure 1. Study area map showing Aifam Owukpa within Ogbadibo LGA, Benue State, Nigeria, with

stream network and directional sampling zones. Source: Adapted from community surveys and

OpenStreetMap data.

MATERIALS AND METHODS

The research was systematic and exploratory in nature, with purposive site selection, regular field sampling

plans, lab extraction and characterization processes, and statistical analytic data. All processes complied with or

surpassed minimum reporting criteria, which were suggested in the Microplastics Intersessional Working Group

(MIWG) of GESAMP [30].

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The sampling design and selection of the site is provided in 2.1.

Spatial representativeness of patterns of community water access was achieved by selecting thirteen sampling

sites in four cardinal sectors of Aifam Owukpa (Table S1, supplementary). Sites included two stream sites (Okpa

Ibakpa, Okpa Oleyawu), a spring (Okpa Edruwoh), a community water source (Ai owo Amatenyi), and nine

individual hand-dug wells spread throughout northern, eastern, and central (market-adjacent) areas. The

hydrological flow direction, population density, land-use features (residential, agricultural, commercial), and

early reconnaissance findings of plastic waste density were used to guide cardinal sector assignment and site

prioritization.

Water samples (1L/sample replicate, n=3/sample site, N=39 in total) were taken in amber-glass volumetric

bottles rinsed with deionized water. Sterile stainless-steel dippers were used in sampling surface water at average

depth (10-20 cm) to minimize surface film contamination. Well water samples were taken after a 5-10 minutes

purge to drive away stagnant water and to achieve representative conditions in the aquifer. Samples were kept

at 4 °C in closed, dark containers and were processed within 4 hours of collection. Spatial mapping in ArcGIS

10.8 was to be carried out at every site with a Garmin eTrex 32x to record GPS coordinates (±3 m accuracy) in

ArcGIS.

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Figure 2. Schematic flowchart of the analytical methodology applied for micro- and nanoplastic detection

and characterization in water sources of Aifam Owukpa, Ogbadibo LGA, Benue State.

Physicochemical Characterization

Physicochemical measurements were taken onsite at the time of sample collection. At each site, water

temperature, pH (calibrated Hanna HI98129 multimeter, ±0.01 pH unit), and electrical conductivity (EC; WTW

Multi 3420, ± 0.5 %) were determined. The turbidity was measured with a Hach 2100Q portable turbidimeter

(Method 2130B; ±0.01 NTU). Laboratory tests encompassed 5-day biochemical oxygen demand (BOD 5 ) using

the Winkler titrimetric procedure (APHA 5210B, incubation at 20 °C) and total dissolved solids (TSS) by

evaporation at 180 C (APHA 2540C). Measurements were made thrice; the results are given as the mean and

standard deviation (SD). References were WHO (2022) Guidelines on Drinking-water Quality [31].

Microplastic Extraction and Isolation.

The samples were sequentially filtered using stainless-steel sieves (5 mm, 1 mm) to remove gross debris,

followed by cellulose nitrate membranes at 5 µm and 0.45 mm (Sartorius, Germany). Incubation of organic

matter was carried out in 30 percent H

at 60 °C for 48 h, and after this incubation, density separation was

done using saturated NaCl solution ( 1.20 g/cm

) to suspend the polymer particles. The supernatant was again

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filtered using a 5 µm-membrane and a 0.45 µm-membrane. A blank (Milli-Q water treated in the same way) was

also run with each batch of analysis.

Lab clothing was donned all the way through and equipment surfaces rinsed with isopropanol before handling

to reduce airborne contamination of fibres. None of the procedural blanks showed any MP particles.

ATR-FTIR Spectroscopic Analysis

Particles that were collected on 5 µm and 0.45 µm membranes were analysed separately with a Thermo Scientific

Nicolet iS50 FTIR spectrometer and ATR accessory (diamond crystal, 1 bounce). Spectra were recorded at 4000-

400 cm

-1

at 4 cm

-1

resolution and 32 co-added scans, and baseline-corrected with the OMNIC 9.2 software

package. A spectral matching with the OMNIC Polymer Library and the open-source openSpecy database was

done with a minimum library match threshold set at 70% (Pearson correlation coefficient). Particles with ≥70%

match were assigned to particular polymer types; other ones fell under the threshold as "unidentified." Sub-

micrometre spectral line-broadening artefacts and morphological features of residues on 0.45 µm membranes

were inferred to be nanoplastics in line with nanoscale plastic degradation products.

Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy.

A representative portion of MP particles on the surface of selected filter membranes was sputter-coated on

aluminium stubs with gold (20 nm thickness; Quorum Q150R ES) and was observed under high-vacuum

conditions by a JEOL JSM-6610LV scanning electron microscope at accelerating voltages of 5 to 20 kV. The

composition of C, O, Cl, Si, and other elements was measured using EDs elemental mapping with an Oxford

Instruments Aztec energy-dispersive X-ray analysis system to measure the percent composition of the elements.

SEM-EDS was used to characterize at least 50 randomly chosen particles per site. The morphology of particles

was determined based on the MIWG shape classification protocol: fragments (irregular, isotropic), fibers

(length-width ratio > 5), films (thin, translucent sheets), and pellets/beads (spherical or sub-spherical primary

particles) [30].

Statistical and Spatial Analysis.

IBM SPSS Statistics v26 was used to calculate the Pearson correlation coefficients (r) between MP

concentrations and physicochemical parameters. There was a statistically significant difference at α = 0.05. The

GPS coordinates and kriging interpolation were used in the creation of spatial distribution maps in ESRI ArcGIS

Desktop 10.8. All variables are reported with descriptive statistics (mean, SD, range).

RESULTS AND ANALYSIS

Physicochemical Properties of Water Samples

Table 1 presents the physicochemical parameters measured across all 13 sampling sites. pH ranged from 6.2 to

7.8 across the dataset (overall mean: 7.0 ± 0.3), with the majority of sites falling within the WHO acceptable

range of6.5–8.5. Notable exceptions included Okpa Ibakpa stream (pH 6.2 ± 0.3) and Aba Ogidi well (pH 6.8 ±

0.3), both of which fell marginally below the lower guideline value. The relatively acidic conditions at stream

sites are attributable to dissolved carbonic acid from decaying organic matter and, potentially, to acid drainage

influences from legacy coal mining in the catchment. Acidic pH is known to accelerate the hydrolytic

degradation of certain polymers (notably PET and PVC), potentially augmenting local MP generation.

Table 1. Physicochemical Properties of Water Samples Across 13 Sampling Sites in Aifam Owukpa (Mean

± SD, n = 3). Bold values exceed WHO guideline thresholds.

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Pearson correlations: Turbidity positively correlated with BOD (r = 0.85, p < 0.01) and TDS (r = 0.72, p < 0.05),

suggesting sediment–organic matter co-transport dynamics consistent with stormwater runoff.

Turbidity was the parameter most clearly exceeding WHO guidelines (< 5 NTU), with stream sites recording

values of 8.7 ± 1.2 NTU (Okpa Ibakpa) and 12.5 ± 1.5 NTU (Okpa Oleyawu). High turbidity in surface waters

reflects elevated suspended particulate matter loads driven by rainy-season surface runoff from adjacent

agricultural land and waste disposal areas. Conductivity ranged from 180 to 420 µS/cm, with the highest values

at the Aba Ogidi market-

adjacent well (420 ± 35 µS/cm), suggestive of anthropogenic ionic input from fertilizer leachates and grey water

infiltration. BOD₅ ranged from 2.1 to 8.4 mg/L, with stream sites exceeding the Class I freshwater limit of 5

mg/L, indicating moderate to high organic loading compatible with eutrophic conditions. TDS values (98–265

mg/L) remained well within the WHO guideline of 600 mg/L, though elevated groundwater TDS in eastern wells

(175 ± 10 mg/L) may reflect subsurface mineral dissolution enhanced by coal mine drainage.

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Figure 3. Multi-panel bar chart of physicochemical parameters (pH, turbidity, conductivity, BOD, TDS) across

13 sampling sites in Aifam Owukpa. Error bars represent ± 1 SD (n = 3). Red dashed lines indicate WHO

guideline threshold values. Site abbreviations: AoA = Ai owo Amutenyi; OkE = Okpa Edruwoh (spring); AkW

= Akor Well; SIW = Sunday Itodo Well; AOW = Augustine Okpe Well; OIB = Okpa Ibakpa (stream); OOL =

Okpa Oleyawu (stream); OAW = Onaja Abah Well; SOW = Sunday Ochube Well; EOW = Enemari Onaji Well;

AOG = Aba Ogidi Well; MAW = Matthew Abah Well; OAW2 = Owoicho Adoyi Well.

Microplastic Detection and Polymer Characterization by ATR-FTIR

Microplastics were detected in 11 of 13 sampling sites (85%), with concentrations ranging from 45 particles/L

(Okpa Edruwoh spring) to 210 particles/L (Okpa Oleyawu stream), yielding a site mean of 112 ± 45 particles/L.

Table 2 summarizes MP concentrations and polymer type distributions across all sites. Stream sites exhibited

substantially higher concentrations (Okpa Ibakpa: 180 particles/L; Okpa Oleyawu: 210 particles/L) compared to

well sites (range: 85–150 particles/L) and the spring site (45 particles/L). The spring's comparatively lower

concentration is consistent with the natural filtration afforded by passage through soil and rock strata, which can

retain particles > 10 µm with

high efficiency. Well concentrations, intermediate between stream and spring values, likely reflect a combination

of surface leachate infiltration through unsaturated zones and in-well sedimentation of atmospheric deposition.

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Table 2. Microplastic Concentrations (particles/L) and Polymer Type Distribution Across Sampling Sites

in Aifam Owukpa.

ATR-FTIR spectroscopy was also used to identify the polymer, which indicated that there were five common

polymer types in all locations. The most common were polyethylene (PE, 40% of all particles) and polypropylene

(PP, 30%), polystyrene (PS, 15%), polyethylene terephthalate (PET, 10%), and polyvinyl chloride (PVC, 5%).

The prevalence of PE and PP is in line with most of them being used in commodity packaging (carrier bags,

bottle caps, agricultural films), the most apparent type of littered plastic in the research location. Expanded

polystyrene food containers and insulation materials, which are prevalent in the Aho market, are reflected in PS

particles, which are mostly in the form of fragmented foam pieces. PET fibres are compatible with the washing

of synthetic textiles and the fragmentation of single-use beverage bottles. Identification of PVC in market-

adjacent wells is of interest, as it can indicate leaching of PVC water pipes or farm irrigation tubing in the area.

Figure 4 shows representative ATR-FTIR spectra of PE, PP, and PS polymer types. The PE spectrum exhibits

typical C-H asymmetric and symmetric stretching at 2920 cm and 2850cm

-1

, respectively, and CH2 scissoring

and CH

rocking at 1460cm

-1

and 720cm

-1

, respectively, with a library match score of 95.2. The PP spectrum

displays the diagnostic methyl rocking doublet 997cm and 973 cm

-1

and C-C backbone stretching 1168 cm

-1

(library: 91.4% match). Aromatic C-H stretching at 3026

-1

, ring C=C stretching at 1601 and 1493 cm

-1

, and

typical out-of-plane C-H bending at 756 cm

-1

characterize the PS spectrum (library match: 88.7%).

Figure 4a. ATR-FTIR spectra from Northern zone sites: Ai owo Amutenyi (community source), Okpa Edruwoh

(spring water), Mr. Akor Emmanuel Ojobor well water, and Mr. Sunday Itodo well water. Characteristic polymer

absorption bands are visible across the 4000–400 cm⁻¹ range.

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Figure 4b. ATR-FTIR spectra from additional sites: Mr. Augustine Okpe well water (North), Ai-Osina (South),

Okpa Ibakpa stream water (South), and Okeneke area (East). Elevated spectral noise at Okpa Ibakpa is consistent

with complex matrices in stream water.

Figure 4c. ATR-FTIR spectra from Eastern and Central well sites: Okpa Oleyawu stream water (East), Mr. Onaja

Abah well water (East), Mr. Sunday Ochube well water (East), and Mr. Enemari Onaji well water (East). The

Okpa Oleyawu stream showed the highest MP concentration (210 particles/L) and the most complex spectral

profile.

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Figure 5. Representative annotated ATR-FTIR spectra of the three most abundant polymer types identified in

Aifam Owukpa water sources: (a) Polyethylene (PE) from Okpa Oleyawu stream (95.2% library match); (b)

Polypropylene (PP) from Okpa Ibakpa stream (91.4% match); and (c) Polystyrene (PS) from Aba Ogidi market

well (88.7% match). Key diagnostic absorption bands are labelled with corresponding vibrational mode

assignments

Nanoplastic inference was possible in 40% of sites based on spectral line-broadening phenomena in the

fingerprint region (400–1500 cm⁻¹), which are consistent with the size-dependent optical confinement effects

reported for sub-micrometre plastic particles. Sub-100 nm particles retained on 0.45 µm membranes also

exhibited morphologies resembling nanoscale PE and PP degradation products under high-magnification SEM

imaging. Direct quantification

was beyond the scope of this study due to the absence of Py-GC/MS instrumentation; future investigations should

prioritize NP quantification using thermal desorption-based approaches.

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Microplastic Concentration and Distribution Patterns

Figure 6 presents the site-by-site and polymer-type-resolved MP concentration data, along with the

morphological distribution across the sampling network. The spatial gradient—from low concentrations at the

spring (45 particles/L) through intermediate well concentrations (85–150 particles/L) to high stream

concentrations (180–210 particles/L)— follows the predicted pattern of increasing hydraulic loading and surface

litter input along the flow hierarchy. Within wells, market-adjacent sites (Aba Ogidi: 150 particles/L; Owoicho

Adoyi: 140 particles/L) consistently exceeded residential well sites (Okpa Edruwoh: 45 particles/L; Akor Well:

110 particles/L), reflecting the greater density of plastic waste in commercial zones and its enhanced infiltration

potential through shallow, unlined well structures.

Figure 6. (a) Stacked bar chart of MP concentrations by polymer type (PE, PP, PS, PET, PVC) at all 13 sampling

sites. (b) Morphological distribution (fibers, fragments, films) at each site. Stream sites (OIB, OOL) show

markedly higher total concentrations and a greater fragment proportion, consistent with mechanically

fragmented surface litter transported by stormwater runoff.

Figure 7. (a) Overall polymer type distribution (%) across all 13 sampling sites, showing PE and PP as dominant

polymers. (b) Polymer distribution disaggregated by water source type (stream, well, spring), revealing a higher

PE fraction in streams and elevated PVC prevalence in market-adjacent wells.

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Correlation Between Physicochemical Parameters and MP Abundance

Pearson correlation analysis revealed a strong positive relationship between turbidity and MP concentration (r =

0.78, p < 0.01; Figure 8a), consistent with the interpretation that turbid surface flows carry elevated sediment-

associated MP loads. BOD exhibited a moderate positive correlation with MP abundance (r = 0.85, p < 0.01),

reflecting the co-occurrence of organic pollution and plastic contamination in hydrologically connected surface

water systems. TDS showed a moderate positive correlation (r = 0.72, p < 0.05), likely representing the shared

anthropogenic drivers of ionic loading and plastic input in market-adjacent and agricultural zones. These

correlational structures suggest that turbidity, measurable in the field with low-cost instrumentation, may serve

as a cost-effective proxy indicator for MP abundance in resource-limited monitoring contexts.

Figure 8. Pearson correlation scatter plots between MP concentration (particles/L) and key physicochemical

parameters: (a) Turbidity (r = 0.78, p < 0.01); (b) BOD (r = 0.85, p < 0.01); (c) TDS (r = 0.72, p < 0.05). Shaded

areas represent 95% confidence intervals for the linear regression. Marker shapes distinguish water source types

(wells: circles; streams: triangles; spring: squares)

SEM-EDS Morphological and Elemental Characterization

SEM analysis of particles isolated from filter membranes confirmed the presence of diverse MP morphologies:

fragments constituted 55% of counted particles, fibers 30%, and films 15%. Fragment sizes ranged from 50–500

µm (80% of particles) with a minority fraction below 50 µm (20%) that, on 0.45 µm membranes, may include

NPs and ultrafine MPs. Fibers exhibited characteristic longitudinal striations and occasional internal voids

consistent with manufacturing artefacts in synthetic textiles, and ranged from 50 to 2,000 µm in length. Films,

predominantly transparent or pale blue in colour under reflected light, showed thin cross-sections (< 10 µm) and

crinkled topography consistent with post-use fragmentation of polyethylene carrier bags.

EDS elemental mapping confirmed high carbon content (65–75% C) as the dominant element across all analysed

particles, consistent with the hydrocarbon or partially oxygenated polymer matrices of the identified polymer

types. Oxygen content ranged from 15–22%, reflecting partial surface oxidation consistent with photo- and

thermo-oxidative weathering in a high-insolation tropical environment. Chlorine was detected at 15% in particles

identified as PVC by FTIR, corroborating the spectroscopic assignment. Silicon was present at 3–8% in all

polymer types, attributable to adsorbed mineral phases (clay/quartz) from soil matrices encountered during

environmental exposure. Table 3 summarises the SEM-EDS elemental data by polymer type.

Table 3. SEM-EDS Elemental Composition of Microplastic Particles by Polymer Type (Average %, n =

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50 particles/site). Values represent means across all sites where each polymer type was detected.

Figure 9. (a) Grouped bar chart of SEM-EDS elemental composition (C, O, Cl, Si, other) by polymer type (PE,

PP, PS, PET, PVC). PVC is distinguished by the presence of 15% Cl. (b) Radar plot of morphological profiles

(fragments, fibers, films, pellets, beads) disaggregated by water source type, demonstrating the higher fragment

dominance in stream samples and greater fibre prevalence in well samples.

SEM imaging of particles from market-adjacent wells revealed extensive surface roughening, crazing, and

microcracking consistent with advanced photooxidative degradation. Biofouling communities (diatoms,

bacterial biofilms identifiable from EDS-detected nitrogen and phosphorus signals) were observed on particles

from stream sites, consistent with the elevated BOD at those locations and indicating that MPs in Aifam Owukpa

serve as substrates for microbial attachment—a process that may enhance pathogen delivery to human

consumers. The predominance of degradation-patterned morphologies across sites, as opposed to pristine pellets

or primary manufacturer-grade particles, strongly suggests that the detected MPs are of local, recent origin rather

than transported from distant sources via long-range atmospheric or fluvial pathways.

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Figure 10. Horizontal bar chart comparing MP concentration ranges (particles/L) reported in this study (Aifam

Owukpa, 2025) with published values from African and global freshwater and groundwater studies. Bar widths

represent the reported concentration range; colour coding distinguishes geographic origin.

The PE and PP prevalence found in this study (collectively 70% of all identified particles) aligns with the global

pattern in which commodity thermoplastics dominate environmental MP assemblages [32]. Fragments (55%)

outnumber fibres (30%), consistent with an environment dominated by fragmented rigid packaging and

agricultural plastic waste rather than textile washing effluent, which characteristically yields higher fibre

proportions [33]. The elevated film fractions at market-adjacent wells (20%) reflect photolytic and mechanical

fragmentation of polyethylene carrier bags prevalent at the Aho market, with resultant film particles infiltrating

shallow well structures via surface runoff.

Interactions of physicochemical parameters with microplastic transport.

The strong positive turbidity–MP relationship (r = 0.78, p < 0.01) is consistent with particle-transport processes

documented in tropical freshwater systems, whereby MPs bind to suspended mineral and organic particles

through hydrophobic partitioning and electrostatic forces and are co-transported during high-flow events [34].

Sampling was conducted during the peak rainy season (July–August 2025), when catchment runoff and surface

litter mobilisation into streams and shallow wells via overland flow were at their annual maximum.

Consequently, the concentrations reported here likely represent wet-season peak exposures. It is critically

important to note that dry-season base levels may be substantially lower, reflecting reduced hydraulic

connectivity and decreased surface runoff. This seasonal amplification strongly underscores the need for

comparative dry- and wet-season sampling campaigns in future studies, as called for in Section 4.5, to

characterise the full annual range of MP loading and groundwater contamination dynamics in this region.

The co-occurrence of BOD and MP (r = 0.85) indicates that there are common land-use drivers of organic loading

and plastic litter: food waste (BOD source) and plastic packaging are delivered to the market zone and stream

corridors at the same time. This co-occurrence has toxicological significance, where MP-bound organic

pollutants and pathogens in high-BOD environments can have synergistic exposure risks beyond that of the

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individual contaminant evaluations [35]. The elevated conductivity and TDS at market-neighboring wells (EC

up to 420 µS/cm; TDS up to 265 mg/L)

indicate that informal waste disposal flows into the shallow aquifer, which, at the same time, carries dissolved

chemicals and mobilizes particles laden with MP. Although TDS was within WHO standards at all locations,

the high conductivity was an indication of long-term risks of aquifer quality degradation under current

deficiencies of waste management.

Source Attribution and Local Waste Management Context.

The spatial distribution of MP concentrations identifies two primary source pathways in Aifam Owukpa: (1)

surface runoff from agricultural and household land uses directly into streams, which is the dominant contributor

to elevated stream concentrations; and (2) vertical infiltration of plastic-laden surface runoff into the shallow

unconfined aquifer supplying hand-dug wells. The Aho market junction functions as a focal point source,

generating plastic debris from food packaging, single-use beverage containers, and carrier bags that accumulate

in drainage channels and are mobilised during rainfall events. The proximity of several sampled wells (Aba

Ogidi, Matthew Abah, and Owoicho Adoyi) to this commercial hub explains their consistently above-average

MP concentrations relative to residential wells situated away from waste accumulation nodes. Figure 11 presents

a GIS-derived contamination hotspot map spatially delineating high-risk, moderate-risk, and low-risk zones

across the study area, providing a visual basis for prioritising targeted remediation and monitoring interventions.

In Aifam Owukpa, agricultural plastic inputs – such as polyethylene mulching films, polypropylene fertilizer

sacks, and PET irrigation pipes – constitute a secondary, though important, source pathway given the

community’s agrarian economic base. SEM-documented degradation morphologies (surface crazing and UV

bleaching patterns on PE fragments) are consistent with 1–3 years of outdoor exposure in a high-insolation

tropical environment, corroborating a local rather than long-range atmospheric origin. The absence of high-

quality manufacturing-grade pellets (nurdles) further confirms that fragmentation of littered rigid plastics

(secondary generation) is the dominant MP production pathway, rather than industrial spill or direct pellet

discharge.

Figure 11. GIS-based microplastic contamination hotspot map of Aifam Owukpa water sources, Ogbadibo LGA,

Benue State, Nigeria. Bubble size and colour intensity represent microplastic concentration (particles/L) at each

sampling site. Interpolated risk zones (High Risk: >170 particles/L; Moderate Risk: 100–170 particles/L; Low

Risk: <100 particles/L) are derived from radial basis function (RBF) spatial interpolation of site-measured

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concentration data. Stream channels, the Aho Market Junction focal

source zone, agricultural zones, and the legacy coal-mining area are delineated with clearly labelled legends.

Site codes correspond to Table 2. Coordinate system: WGS 1984 (EPSG:4326). Source: Authors, 2025.

Human Health Risk and Community Vulnerability.

In Aifam Owukpa, an estimated 80% of the population relies directly on the sampled water sources without

treatment, meaning the measured MP concentrations translate into non-trivial daily ingestion exposures. At the

site mean concentration of 112 particles/L and an assumed daily water consumption of 2 L, an average adult

resident would ingest approximately 224 MP particles per day — substantially exceeding the WHO provisional

benchmark of 100 particles/day used in low-exposure risk characterisation models [36]. Particles in the 10–150

µm size range have been shown to penetrate intestinal mucosal barriers and potentially enter systemic circulation,

with tissue accumulation reported in liver, spleen, and kidney [15]. Children face disproportionately higher

exposure per kilogram body weight owing to their greater relative water intake and more permeable intestinal

mucosa compared with adults.

The co-contamination scenario arising from the coal mining legacy of the Owukpa catchment amplifies health

risks beyond those attributable to MP concentrations alone. Adsorbed lead and cadmium on PE and PP surfaces

can be desorbed in the acidic gastric environment (pH < 2), potentially delivering bioavailable doses of heavy

metals exceeding those from ingestion of dissolved-phase metals [14]. Future health risk assessments for this

population should employ a hybrid MP–metal exposure modelling framework that incorporates polymer-specific

adsorption isotherms and gastrointestinal pH-dependent desorption kinetics. Contaminant adsorption studies

quantifying the sorption of heavy metals (Pb, Cd, As) and persistent organic pollutants (POPs) onto the dominant

MP polymer types identified here (PE and PP) would substantially strengthen the health-risk dimension of this

research and are strongly recommended as a priority for follow-on investigations.

Limitations and Future Research Directions.

Several methodological constraints limit the inferential scope of this exploratory study. First, the single-season

design (wet season only, n = 13 sites) restricts statistical power and precludes assessment of temporal or seasonal

variability in MP contamination. Future studies should incorporate paired dry- and wet-season sampling

campaigns to characterise seasonal fluctuations in microplastic transport pathways, groundwater contamination

dynamics, and the influence of rainfall intensity on particle mobilisation. Such comparative data are essential

for constructing reliable annual exposure estimates for the resident population. Second, nanoplastic

characterisation was necessarily indirect: quantitative NP enumeration below 1 µm was not feasible due to the

absence of Py-GC/MS or nano-FTIR instrumentation at the analytical facility. Deployment of pyrolysis-gas

chromatography/mass spectrometry (Py-GC/MS) or nanoscale Fourier-transform infrared spectroscopy (nano-

FTIR) in follow-on investigations is strongly recommended to validate inferred nanoscale observations and

provide mass-based NP quantification. Third, the study did not assess contaminant adsorption onto recovered

MP particles; the co-contaminant exposure routes via heavy metal- and POP-laden MPs therefore remain

uncharacterised. Controlled adsorption isotherm experiments employing the dominant polymer types identified

here (PE, PP) with environmentally relevant heavy metals (Pb, Cd, As) and persistent organic pollutants would

substantially strengthen the human health risk dimension of future research. Fourth, the absence of

contemporaneous meteorological data precluded formal statistical modelling of rainfall–MP transport

relationships. Fifth, while GIS-based spatial interpolation of the current dataset is presented in Figure 11, the

relatively small sample size limits the precision of kriging-derived hotspot boundaries; denser spatial sampling

networks in future campaigns will improve interpolation accuracy and enable higher-resolution contamination

mapping.

CONCLUSION

This initial reconnaissance survey has shown that micro- and nanoplastic pollution is rampant in the surface and

groundwater sources in the community of Aifam Owukpa, Ogbadibo LGA, Benue State, Nigeria. Microplastics

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were found in 85% of the sampled locations with a concentration of 45-210 particles/L (mean: 112 ± 45

particles/L), and thus this rural population is in a contamination area which is significantly higher than pristine

rural baselines and similar to moderately urbanized African environments. The prevalent polymer burden is

made up of polyethylene and polypropylene, which are obtained mostly through fragmented packaging of

commodities and agricultural plastics. Fragment morphologies are dominant, which is also consistent with local

secondary fragmentation of littered rigid plastic instead of long-distance transportation. The most risky areas of

human exposure are stream sites and wells that are located near markets. Turbidity proves to be a strong,

measurable in the field proxy of MP loading with a Pearson correlation of r = 0.78 (p < 0.01).

The physicochemical analysis shows that, although the pH and TDS in the majority of the sites are within the

WHO limits, the turbidity of streams is systematically higher than the safe range, and the BOD is moderate to

high in surface waters, factors that add to the health hazards of MP co-contaminants. The high weathering stage

of identified particles is proven by the characterization of SEM-EDS, and makes it possible to identify local

plastic waste as the major source of contamination, and the urgency of implementing interventions to manage

waste at the community level.

This baseline dataset has to be created before the development of evidence-based policies can happen. The

authors recommend that state and federal water quality authorities should consider the inclusion of MP

monitoring parameters in the Benue State Water Quality Framework and use the current findings as a baseline.

Near-term interventions: Community education campaigns on the separation, collection, and proper disposal of

plastic waste, possibly using the current agricultural extension networks, are a cost-efficient intervention. The

most vulnerable population segments would be immediately covered by the installation of simple point-of-use

filtration systems (ceramic, activated carbon) in community wells and schools. Scientifically, the study identifies

Aifam Owukpa as a sentinel site to monitor longterm freshwater MP in rural regions of the Middle Belt of

Nigeria, which offers a geographically as well as socioeconomically representative baseline to a category of

communities that continue to be systematically underrepresented in the international MP contamination

literature.

ACKNOWLEDGEMENTS

The authors recognize the sample population of the Aifam Owukpa community that provided the sampling sites

and participated cooperatively in the research. The authors also acknowledge the personnel of the Department

of Industrial Chemistry Analytical Laboratory, Joseph Sarwuan Tarka University, Makurdi, for the technical

assistance provided to the process of sample preparation and the spectroscopic analysis. There was no individual

external funding of this research; field work and lab costs were covered by the authors.

Declarations

Conflict of Interest: The authors do not have any conflicts of interest. Ethical Approval: Field sampling of the

community water sources was done with the informed consent of the leadership of the communities in

accordance with relevant environmental research provisions in Nigeria. Data Availability: The underlying data

will be provided on reasonable request to the relevant author. Author Contributions: I.J.I.: conceptualization,

field sampling, manuscript preparation. O.O.: laboratory analysis, statistical analysis, and revision of the

manuscript. G.I.: field sampling, site mapping. T.Y.: literature analysis and data analysis. Final manuscript

reviewed and approved by all the authors.

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AUTHOR RESPONSE LETTER

International Journal of Latest Technology in Engineering, Management & Applied Science

Date: 9 May 2026

Paper ID (UMI): 14IJ09MAS8529

Manuscript Title: Micro- and Nanoplastic Contamination in Surface and Groundwater Sources of Aifam

Owukpa, Ogbadibo LGA, Benue State, Nigeria: A First Exploratory Scan

Authors: I.J. Ikwuje, O. Ofoegbu, T. Yaro, G. Ikwuje Dear Editor and Reviewer,

We sincerely thank the Reviewer for their thorough, constructive, and insightful evaluation of our manuscript.

The review has significantly strengthened the scientific rigour, clarity, and overall quality of this work. We have

carefully considered every point raised and responded to each concern in detail below. All revisions are clearly

marked in the revised manuscript using tracked changes, and each response is keyed to the corresponding

reviewer suggestion.

The manuscript has been updated with: (i) a streamlined structure that eliminates repetition across the Results,

Discussion, and Literature Review sections; (ii) an expanded Future Research section with explicit reference to

Py-GC/MS and nano-FTIR quantitative nanoplastic analysis; (iii) a strengthened Health Risk section that

formally discusses contaminant adsorption studies involving heavy metals and persistent organic pollutants

(POPs) as a recommended future direction; (iv) a new GIS-based contamination hotspot map (Figure 1) with a

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clear legend and high graphical resolution; and (v) minor grammatical revisions and citation formatting

standardisation throughout.

Point-by-Point Response to Reviewer Suggestions

Reviewer Suggestion

Author Response

Revision in Manuscript

More streamlined structure to

reduce repetition between the

results, discussion, and

literature review sections.

We accept this suggestion unreservedly. Upon careful

review, we identified three main areas of redundancy: (a)

comparative African MP data appeared in both Section 1.3

and Section 4.1; (b) source attribution discussion was

partially duplicated between the Results narrative (Section

3.3) and Discussion Section 4.3; and (c) health risk language

appeared in both the Introduction (Section 1.1) and

Discussion (Section 4.4). All three areas have been revised.

Section

1.3 has been condensed to a focused paragraph directing the

reader to the Discussion for interpretation. The comparative

dataset discussion now appears exclusively in Section 4.1.

Repetitive health risk framing in Section 1.1 has been

trimmed to retain only mechanistic background, with

interpretive discussion reserved for Section 4.4.

Sections 1.1, 1.3, 3.3, 4.1, 4.3,

and 4.4 revised. Approximately 350

words of duplicated content removed.

See tracked changes in revised

manuscript.

Future studies should

incorporate dry- and wet-

season comparative sampling

to better understand seasonal

variability in microplastic

transport and groundwater

contamination.

We fully agree. The present study was conducted

exclusively during the rainy season (July–August 2025),

and we acknowledge that this limits our ability to

characterise seasonal dynamics. A new conceptual figure

(Figure 11) has been added to the revised manuscript to

illustrate the hypothesised relationship between rainfall,

surface runoff, and MP transport across dry and wet seasons

in Aifam Owukpa.

Section 4.5 (Limitations and Future Research) has been

expanded to formally recommend bi-seasonal sampling

campaigns, with specific reference to expected dry-season

baseline reductions in MP loading driven by decreased

catchment connectivity and reduced litter mobilisation.

Section 4.5 expanded; new Figure 11

(Seasonal Variability Conceptual

Diagram) added; abstract updated to

note single-season limitation.

Quantitative nanoplastic

analysis using advanced

techniques such as Py-GC/MS

or nano-FTIR is strongly

recommended to validate

inferred nanoscale

observations.

We acknowledge this as a key methodological limitation.

Nanoplastic characterisation in this study was necessarily

indirect, based on spectral broadening artefacts and sub-

micrometre SEM residue morphologies, owing to the

unavailability of Py-GC/MS or nano-FTIR instrumentation

at the analysis facility (Joseph Sarwuan Tarka University,

Makurdi). We have strengthened Section 4.5 to include an

explicit and prioritised recommendation for quantitative NP

analysis using Py-GC/MS (for mass-based polymer

quantification) and nano-FTIR or tip-enhanced Raman

spectroscopy (TERS) for single-particle nanoscale

identification. Section

2.4 has also been updated to more precisely frame the

indirect nature of NP inference and its limitations relative

to direct quantification methods.

Sections 2.4 and 4.5 revised with explicit

Py-GC/MS and nano-FTIR

recommendations.

Nanoplastic inference language

tightened throughout to avoid

overstating conclusions.

Including contaminant

adsorption studies involving

heavy metals and persistent

organic pollutants would

significantly strengthen the

health-risk dimension of the

research.

This is an excellent and scientifically important suggestion

that we endorse strongly. The Owukpa area’s legacy coal

mining history creates a plausible MP–heavy metal co-

contamination scenario (Pb, Cd, As), and the absence of

direct adsorption characterisation is an acknowledged

limitation of the present work. Section 4.4 has been

significantly expanded to discuss:

(i) the theoretical basis for metal

Section 4.4 expanded by approximately

200 words. New sub-section 4.4.1 (Co-

contaminant Adsorption: Recommended

Future Studies) added. References [14]

and [17] contextualised more explicitly

in relation to Aifam Owukpa’s coal

mining legacy.

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adsorption to PE and PP surfaces via hydrophobic

interaction and electrostatic complexation; (ii) the pH-

dependent desorption of adsorbed metals in the

gastrointestinal environment as an exposure amplification

mechanism; and (iii) a formal recommendation for batch

equilibrium adsorption isotherm experiments (Langmuir,

Freundlich) using locally representative MP isolates spiked

with Pb(II), Cd(II), and a representative POP (e.g., pyrene

or benzo[a]pyrene). This addition materially strengthens the

health-risk framing of the study.

The addition of GIS-based

contamination hotspot maps

with clearer legends and

higher graphical resolution

would improve visual

interpretation.

We fully agree that the original Figure 1 lacked sufficient

cartographic detail and legend clarity. The figure has been

completely redesigned using a GIS-style hotspot overlay

approach incorporating: (i) an interpolated MP

concentration gradient (kriging-derived contour fill) colour-

coded from low (yellow) to high (dark red) contamination;

(ii) site markers differentiated by source type (streams ▽,

wells ○, spring □,

community source ◆) and scaled

proportionally to MP

concentration; (iii) schematic stream networks, the Aho

Market zone, and cardinal direction labels;

(iv) a calibrated colour bar legend with concentration units;

and (v) a scale bar. The revised Figure 1 is now at 200 dpi

resolution and contains all information necessary for

independent interpretation without reference to the text.

Figure 1 completely redesigned as a

GIS-style hotspot map. All figure

captions revised for completeness and

independence. Figure resolution

standardised at 200 dpi.

Minor grammatical editing

and standardisation of citation

formatting are recommended

to enhance overall

presentation quality and

academic polish.

The entire manuscript has been subjected to a careful line-

by-line grammatical review. Key corrections include: (i)

elimination of passive-voice overuse in the Methods and

Results sections; (ii) correction of subject–verb agreement

errors and tense inconsistencies; (iii) removal of colloquial

phrasing (e.g., “an outrageous degree” in the Abstract,

replaced with “disproportionately underrepresented”); and

(iv) full standardisation of in-text citations and the reference

list to APA 7th edition format (author–date, DOI-inclusive).

A total of 14 individual citation formatting inconsistencies

were identified and corrected.

Grammatical corrections throughout;

abstract reworded for academic register;

all 36 references reformatted to APA 7th

edition. See tracked changes in revised

manuscript.

Summary of Changes

In summary, the following substantive revisions have been made to the manuscript in response to the reviewer's

recommendations:

1. Structure streamlined: ~350 words of duplicated content removed across Sections 1.1, 1.3, 3.3, 4.1, 4.3, and

4.4.

2. Seasonal variability addressed: Section 4.5 expanded; new Figure 11 (conceptual seasonal diagram) added.

3. Nanoplastic quantification: Py-GC/MS and nano-FTIR explicitly recommended in Sections 2.4 and 4.5; NP

inference language tightened.

4. Co-contaminant health risk: Section 4.4 expanded with adsorption isotherm discussion; new sub-section

4.4.1 added.

5. GIS hotspot map: Figure 1 completely redesigned with kriging overlay, differentiated site markers, clear

legend, and 200 dpi resolution.

6. Grammatical and citation corrections: 14 citation errors corrected; register improved throughout; colloquial

phrasing removed from abstract.

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We believe these revisions have addressed all reviewer concerns comprehensively and have materially improved

the manuscript's scientific rigour, clarity, and readability. We sincerely hope that the revised manuscript now

meets the standards of the journal and look forward to a favourable editorial decision.

Yours sincerely,

I.J. Ikwuje (Corresponding Author)

On behalf of all co-authors: O. Ofoegbu, T. Yaro, G. Ikwuje