Ecological Risk and Bioaccumulation of Heavy Metals in Soil–Vegetable

Overview

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Key numbers

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Journal of Agriculture Sustainability and Environment ISSN: 2997-271X
https://doi.org/10.56556/jase.v4i2.1385
Abubakar Mohd Habu1*, Ali Sanusi Hassan1, Adeniyi Olarewaju Adeleye2, Michael Edet Nkereuwem3,
concentrations reaching 23.0 mg/kg in carrot shoots and Fe at 1046.5 mg/kg in onion leaves, whereas Cu and Zn
remained within safe limits. The soils were slightly alkaline with pH 7.76 and a sandy-loam texture which,
exceeding 1 corroborated the presence of cumulative pollution at several sites. Overall, the results underscore
sustaining agricultural production in many developing countries (Singh 2021; Nowwar et al., 2023). In arid and
nutrient-rich composition (Qadir et al., 2022; Chen et al., 2023). Wastewater is known to contain essential plant
Global Scientific Research 21
et al., 2021; Woldetsadik et al., 2023). Despite these agronomic benefits, wastewater often contains substances
soils and pose long-term ecological and health risks (Abbas et al., 2023). Metals such as lead (Pb), cadmium
sources (Abdullahi et al., 2025; Ugya et al., 2019). These metals are non-biodegradable and can persist in the
(Bellanthudawa et al., 2023; Zhou et al., 2020).
pH, soil texture, organic matter content, redox potential, and irrigation practices (Wu et al., 2022). In many urban
facilitates their uptake by plants (Golia, 2023; Lucija et al., 2025). Consequently, high concentrations of metals
damage, neurological disorders, and cancer (Boahen et al., 2024; Mawari et al., 2022). In Africa, wastewater
commercial, and industrial wastewaters are used for year-round vegetable production (Tayo, 2021). In Kano
for irrigation (Abdulsalam et., 2023). In such regions, monitoring programs are often absent or poorly managed,
(Bellanthudawa et al., 2023; Oladipo et al., 2022). Heavy metal pollution not only threatens human health but
nitrogen fixation and nutrient cycling (Rashid et al., 2023). These ecological disruptions impair soil fertility,
contaminated with industrial effluents (Abdullahi et al., 2025; Shawai et al., 2019). Crops such as lettuce,
et al., 2025; Shawai et al., 2019). Previous studies have reported elevated levels of lead and cadmium in
ecological risks remain scarce (Zhang et al., 2023). The long-term accumulation of heavy metals in soil can
risks—undermining efforts to promote sustainable urban agriculture (Bellanthudawa et al., 2023; Zhou et al.,
severity of contamination relative to background levels (Hakanson, 1980; Müller, 1969; Tomlinson et al., 1980).
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The research was conducted in Tamburawa, located approximately 25 km southeast of Kano metropolis, Nigeria
(Figure 1). The area lies within the Sudan savanna ecological zone, characterized by distinct wet and dry seasons.
standard protocols for trace metal studies in crops (Anirban et al., 2023; Ene et al., 2024). At each sampling plot,
randomly selected healthy plants, pooled to form one replicate (n = 3 per species). This sampling design ensured
(Sultana et al., 2022).
2023). The cleaned plant materials were then cut into small pieces, air-dried under shade for 5–7 days, and stored
Global Scientific Research 23
Figure 1. Study Area; Tamburawa, Kumbotso Local Government Area, Kano State, Nigeria
approximately 200 g of root-adhered soil was collected from a 0–20 cm depth at three points per plant, pooled,
air-dried, and sieved through a 2 mm mesh (Asamoah et al., 2025; Carrera et al, 2025). Thus, each vegetable
species had three rhizosphere composite replicates (n = 3).
Global Scientific Research 24
disaggregate clods, and sieved through a 2 mm mesh to remove stones and coarse debris (Asamoah et al.,2025;
Carrera et al, 2025). The processed samples were stored in clean polyethylene zip-lock bags and kept in a
Heavy metals in soil and plant samples were extracted using the wet digestion method following APHA (2012)
and USEPA (1996) protocols. Approximately 1.0 g of the sieved sample was weighed into a digestion flask,

Methods (brief)

rhizosphere soil and edible parts of vegetables (cabbage, carrot, lettuce, onion, and spinach) multiple samples of
which were analyzed using Atomic Absorption Spectrophotometry (AAS). Key physicochemical soil parameters
three composite replicate samples were collected per vegetable species. Each composite comprised five
Immediately after collection, samples were thoroughly washed with tap water to remove visible soil and dust
in labeled paper envelopes pending laboratory digestion and heavy metal analysis.
Rhizosphere soil samples were collected simultaneously with the vegetable samples. The rhizosphere was
approximately 200 g of root-adhered soil was collected from a 0–20 cm depth at three points per plant, pooled,
samples were taken across the root zone and combined to form one representative sample. The rhizosphere soils
Following standard soil preparation procedures, samples were air-dried at ambient temperature, crushed to
disaggregate clods, and sieved through a 2 mm mesh to remove stones and coarse debris (Asamoah et al.,2025;
Carrera et al, 2025). The processed samples were stored in clean polyethylene zip-lock bags and kept in a
Sample digestion and heavy metal analysis
Heavy metals in soil and plant samples were extracted using the wet digestion method following APHA (2012)
and USEPA (1996) protocols. Approximately 1.0 g of the sieved sample was weighed into a digestion flask,
complete digestion. After cooling, each digest was filtered through Whatman No. 42 filter paper into a 50 mL
as the stock digest for heavy metal determination. Samples with concentrations exceeding the calibration range
of the Atomic Absorption Spectrophotometer (AAS) were appropriately diluted (1:2, 1:5, or 1:10) with
AAS following the APHA (2012) standard procedure. To ensure quality assurance and quality control (QA/QC),

Implications

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Verification notes

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
3171d06	2026-08-02	major	1 section added
bc84bfc	2026-08-02	major	6 sections added; narrative text revised