Potential ecological risk assessment of heavy metals associated

Overview

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Key numbers

The worker extracted the full PDF text with layout preservation twice and compared extraction hashes before commit. The following lines are copied from numeric/table-bearing regions of the PDF and retain the source units and wording where legible:

The moderators accounted for R2* of 95.73% of the total explanatory capacity of the model. The
The meat processing industry uses over 62 × 106 m3 of water annually, representing over 29% of all freshwater used in agriculture
on the animal and the technique used in each business. The water usage ranges from 1.0 to 8.3 m3, with about 0.4–3.1 m3 lost as
According to the FAO’s agricultural outlook for the next decade (2020–2029) (4), meat consumption is expected to increase by 12%
as fats, greases, hairs, feathers, meats, dung, grits, undigested feed, blood, and about 80% freshwater (8).
Most organic load in abattoir liquid waste originates from blood and lipids (11). Blood from the abattoirs comprises about 18%
pollutant in abattoir liquid waste, with the highest COD value (375,000 mg/L) (1,27). Blood also contributes significant N to liquid
Several studies have also reported the presence of heavy metals in abattoir liquid waste (1,8,9,28). Due to the extensive range of
waste compiled from different literature are summarized in Table 1.
metals with particular reference to human health, highlighted in Table 2.
and muscle, requiring 1–100 mg/day by an adult (36). Bone and muscle account for more than 50% of the metal in the body. Cu is
Zn, Cd, and Hg occur naturally and belong to Group 12 of the periodic table. Compared to Cd and Hg and several other metal ions
milk. Other human health impacts associated with exposure to Zn are summarized in Table 2.
Fe is the most abundant metal in the earth’s crust (42) and belongs to Group 8 of the periodic table. The biological properties of Fe
Mn is a trace element that all animals require in their diet. It is located in Group 7 of the periodic table. While it can be inhaled from
vegetables (45). Mn aids bone development, controls metabolic activities such as protein and energy metabolism, and protects cells
and associated human health risks (Table 2) have been documented (46).
Cr is a chemical element belonging to Group 6 of the periodic table. It is an essential nutrient for human health, but too much can be
The chemical element, Ni, is a trace metal that belongs to Group 10 of the periodic table. It is required for animal nutrition.
Physically and chemically, Cd is a soft, silvery-white metal akin to Zn and Hg of Group 12 of the periodic table. It is a highly
liquid waste (9,13,39). The human health effects of Cd are highlighted in Table 2.
contribute to about 80% of the aggregate, with volcanoes and forest fires accounting for the rest (53). Many countries have designated
Pb is a chemical element located in Group 14 of the periodic table. It is one of the most environmentally hazardous heavy metals. It
where Tri is the individual heavy metal toxicity response coefficient (Cd = 30, Cr = 2, Pb = 5, Ni = 5, As = 30, Cu = 10, Zn = 1, Hg = 40,
concentration of Cd, Cr, Pb, Cu, Zn, and Hg in freshwater are 0.008, 0.00018, 0.005, 0.01, 0.01 and 0.00008 (69), respectively. Table 3
than 40, in the ranges of 40 < Er ≤ 80, 80 < Er ≤ 160, 160 < Er ≤ 320, and greater than 320, are assigned low, moderate, appreciable,
high, and serious risks, respectively. Similarly, when RI values are less than 150, in ranges of 150─300, 300─600, and 600 and above,
research has been conducted to evaluate heavy metal levels in abattoir liquid waste (a few results are summarized in Table 6). Un
sample size by one (i.e., n = 15), as depicted in Tables 4, 5, 6, and 7. Therefore, we regard the RIs, which are surrogates of the abattoirs,
The abattoirs are all found in Nigeria, and their respective geographic point coordinates are displayed in Table 4. Their spatial
the literature (Table 6); the rest ((iii)-(v)) were non-existent. It was envisaged that the three moderators ((i), (ii), and (vi)) could
Equations (1)–(3) were applied to the metal levels, compiled from the eight articles (Table 6), to compute the Ers and RIs (Table 7).
in Table 5, all the meta-regression data were standardized to achieve zero means, unit standard deviations (SDs), and unit variances
Ers and RIs computed from metal concentrations in Table 6.
where s is the sample SD, x is the observation, x is the mean, and n is the number of samples. The square root of the τ2 is also an
The heavy metal concentrations reported in abattoir liquid waste from the various literature are presented in Table 6. The authors
Across the abattoirs, the mean metal concentrations ranged from 0.07± 0.06 (SD)/0.02 (SE) for Cr to 8.13 ± 25.08 (SD)/7.92(SE)
liquid wastes, with the highest concentration of 79.5 mg/L, detected at Minna Central abattoir. The following interesting observations
L), Cd (0.74 mg/L), Mn (0.38 mg/L), and Zn (0.25 mg/L) dropped to 0.10, 0.12, 0.13, and 0.18 mg/L (9,13), respectively, after a
decade. These correspond to 54.5, 83.8, 65.8, and 28.0% differences; (ii) Only Ni’s concentration increased from 0.41 to 1.5 mg/L,
representing 72.7% difference, with Fe maintaining a fairly constant value (0.10 mg/L vs. 0.11 mg/L) over the same timeframe (9,13);
0.13 mg/L detected in 2020 (9); (iv) Cu and Pb were not investigated in this abattoir (9); and (v) Among the metals, Cr had the lowest

Methods (brief)

sample size by one (i.e., n = 15), as depicted in Tables 4, 5, 6, and 7. Therefore, we regard the RIs, which are surrogates of the abattoirs,
used in many statistics settings. In a meta-analysis, heterogeneity can point to variations across samples, within individual samples,
where s is the sample SD, x is the observation, x is the mean, and n is the number of samples. The square root of the τ2 is also an
estimators, possibly due to its appropriateness for smaller sample size. Hence, this section used it to interpret meta-regression analysis
findings of several studies are comparable (17–19), this approach has some limitations. For instance, when the sample size is small,
(12) F.O. Owagboriaye, G.A. Dedeke, K.O. Ademolu, O.A. Adebambo, Bioaccumulation of heavy metals in earthworms collected from abattoir soils in Abeokuta,
(13) J.C. Akan, F.I. Abdulrahman, E. Yusuf, Physical and chemical parameters in abattoir wastewater sample, Maiduguri Metropolis, Nigeria, Pac. J. Sci. Technol. 11
(41) L.M. Plum, L. Rink, H. Haase, The essential toxin: impact of zinc on human health, Int. J. Environ. Res. Publ. Health 7 (4) (2010) 1342–1365, https://doi.org/
(82) R.B. Agbor, S.P. Antai, Physicochemical and microbial properties of water samples around abattoirs in calabar, Int. J. Sci. Eng. Res. 10 (6) (2019) 1317–1335.
(87) J. Frost, Heterogeneity in Data and Samples for Statistics, Statistics By Jim, 2021. https://statisticsbyjim.com/basics/heterogeneity/.
(96) G.K. Kinuthia, V. Ngure, D. Beti, R. Lugalia, A. Wangila, L. Kamau, Levels of heavy metals in wastewater and soil samples from open drainage channels in

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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
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised