Contamination Factor, Metal Pollution Index and Estimated Daily Intake of Heavy Metals in Some Selected Energy Drinks in Nigeria

Overview

Babayo and colleagues (Gombe State University; Abubakar Tafawa Balewa University, Bauchi; Yobe State University, Damaturu) quantified cobalt (Co), chromium (Cr), cadmium (Cd), arsenic (As), nickel (Ni), and lead (Pb) in thirty commercially available energy-drink samples purchased from Nigerian retail outlets, comprising twenty-three liquid formulations and seven powdered formulations. Liquid samples were digested with aqua regia (HCl:HNO₃ 3:1) on a Kjeldahl heater for 4–5 hours and analysed by atomic absorption spectrophotometry (AAS; Bulk 205 instrument). Powdered samples were pressed into 25 mm pellets with a hydraulic press, covered with a 6 µm polypropylene film, and analysed by X-ray fluorescence (XRF). Contamination Factor (CF), Metal Pollution Index (MPI), and Estimated Daily Intake (EDI) were computed for both adults (60 kg body weight; 0.6 L/day intake) and children (20 kg body weight; 0.3 L/day intake). The authors report that cadmium, nickel, and lead were the most critical contaminants, with several powdered formulations (EJ, KR) and isolated liquid formulations (SY, MP, PR) exceeding the manuscript-defined reference values. Powdered formulations generally exhibited relatively higher concentrations than liquid formulations for several metals.

Key numbers

All concentrations are reported in the source as mg L⁻¹ for both liquid and powdered formulations (Tables 1, 2, and 4). The authors used WHO drinking-water reference values as the comparator baseline (last row of Table 1): Co 0.05 mg L⁻¹, Cr 0.05 mg L⁻¹, Cd 0.003 mg L⁻¹, As 0.01 mg L⁻¹, Ni 0.02 mg L⁻¹, Pb 0.01 mg L⁻¹. Liquid values were measured by AAS; powdered values were measured by XRF (see paper-internal unit-basis caveat in Verification notes).

Concentration of heavy metals in liquid energy drinks (Table 1, p. 5–6, mg L⁻¹, n=23)

Sample-code legends are not expanded by the source. Dash (–) indicates not detected.

Concentration of heavy metals in powdered energy drinks (Table 1, p. 5–6, mg L⁻¹, n=7)

Contamination factor (CF) (Table 2, p. 6–7)

Contamination Factor was computed as CF = C(metal) / C(background), where the background was the reference value used by the source. The same WHO drinking-water reference values listed above were used as the CF denominator. CF < 1 = low contamination; CF = 1 = at the permissible threshold; CF > 1 = above the acceptable limit.

Highest CF values among liquid samples (selected, all metals above the reference):

Highest CF values among powdered samples:

Metal Pollution Index (MPI) (Table 3, p. 7–8)

MPI was computed as the arithmetic mean of CF values across the six metals for each sample: MPI = Σ(Cᵢ/Rᵢ) / n. MPI < 1 = relatively low overall pollution; MPI > 1 = elevated cumulative metal burden. The source describes the index as a “geometrical mean” in Section 2.3.2 but presents the arithmetic-mean form in Equation 2 and reports values consistent with the arithmetic mean of CF/n.

MPI ranged from 0.12 (VE, liquid) to 4.06 (EJ, powder). Powdered formulations EJ (4.06) and KR (3.66) recorded the highest cumulative metal burden.

Estimated Daily Intake (EDI) (Table 4, p. 8–10)

EDI was computed as EDI (mg kg⁻¹ d⁻¹) = (C_metal × D_food intake) / B_average body weight. The authors used 0.6 L/day (adults; 60 kg body weight) and 0.3 L/day (children; 20 kg body weight) as intake volumes, anchored to a stated requirement of “300–600 ml/day which is equivalent to 0.3–0.6 L/day based on Calcium requirement in human body” (Section 2.3.3, p. 3). The WHO reference EDI row at the bottom of Table 4 lists Co 5×10⁻⁴ (adult) / 8×10⁻⁴ (child), Cr 5×10⁻⁴ / 8×10⁻⁴, Cd 3×10⁻⁵ / 5×10⁻⁵, As 1×10⁻⁴ / 2×10⁻⁴, Ni 2×10⁻⁴ / 3×10⁻⁴, Pb 1×10⁻⁴ / 2×10⁻⁴ mg kg⁻¹ d⁻¹.

Notable EDI exceedances called out by the source (Section 3.4, p. 10–11):

Children’s EDI values were consistently higher than adults’ for the same metal across most samples, driven by the lower assumed body weight (20 kg vs 60 kg) despite the lower assumed intake volume (0.3 L vs 0.6 L).

Methods (brief)

Thirty commercially available energy-drink samples (23 liquid + 7 powdered) were purchased from supermarkets, retail stores, and street vendors across Nigerian markets to ensure representative sampling. Different brands, batch numbers, and production dates were considered. Samples were transported to the laboratory in their original packaging and stored under recommended conditions prior to analysis.

Liquid samples (n=23): 10 mL of each energy drink was measured using an analytical balance and transferred into a digestion flask. A mixture of concentrated hydrochloric acid (HCl) and nitric acid (HNO₃) in a 3:1 ratio (aqua regia) was added to each sample. Digestion was performed in a fume hood on a Kjeldahl heater for 4–5 hours until the solution became pale yellow. After cooling, the digested samples were diluted with deionised water and filtered to remove particulates. The final volume was adjusted to 100 mL for analysis. Samples were analysed using a Bulk 205 Atomic Absorption Spectrophotometer (AAS) according to the manufacturer’s instructions.

Powdered samples (n=7): 3 g of each powdered energy-drink sample was pressed into pellets of 25 mm diameter using a hydraulic pellet press. Each pellet was covered with a 6 µm polypropylene film to prevent contamination and placed in the X-ray Fluorescence (XRF) excitation chamber. Quantitative elemental analysis was conducted using a time-controlled irradiation program, and the generated spectra were used to construct calibration curves for the determination of metal concentrations in the samples. The XRF instrument model and manufacturer are not specified in the source.

Data analysis used Contamination Factor (CF) per Ureso et al. 1997 (Equation 1), Metal Pollution Index (MPI) per Ureso et al. 1997 (Equation 2; described as a “geometrical mean” in prose but presented as an arithmetic-mean form in the equation and consistent with the arithmetic-mean values in Table 3), and Estimated Daily Intake (EDI) (Equation 4, miscaptioned as “(4)” in the source despite being the third numbered equation; standard formulation EDI = C × D / B). Statistical software is not specified.

The source does not report instrument-method limits of detection or limits of quantification, certified-reference-material recovery percentages, blank-correction details, or replicate analyses per sample. The arsenic measurement (AAS for liquids, XRF for powders) is total arsenic and is not speciated into inorganic and organic forms. The chromium measurement is total chromium and is not speciated into hexavalent chromium (Cr-VI) and Cr-III. Mercury, inorganic tin, and uranium were not measured. Among the ten HMTc/HMI analytes, this source covers Pb, Cd, total arsenic (tAs), Cr, Ni, and Co (six of ten); methylmercury (MeHg)/total mercury (tHg), tin (Sn), uranium (U), and aluminum (Al) are not addressed; inorganic arsenic (iAs) is not addressed at speciation level (the tAs measurement is recorded with the caveat above).

Evidence Fitness

This source is direct primary occurrence evidence for finished energy drinks measured in Nigeria in 2026. The analytical methodology — aqua-regia digestion followed by AAS for liquids, and hydraulic-press pelletisation followed by XRF for powders — is method-appropriate for the matrices analysed, but the source has several quality-control gaps and one significant unit-basis caveat that bear on pooling eligibility and synthesis weight:

(i) No analytical quality control reported. The source does not report limits of detection (LOD), limits of quantification (LOQ), certified-reference-material (CRM) recovery, blank correction, or replicate-sample structure for either AAS or XRF measurements. Analytical reproducibility cannot be independently verified from the published article.

(ii) Unit-basis inconsistency between liquid and powder measurements. Liquid samples were analysed by AAS after aqua-regia digestion, with concentrations correctly reported in mg L⁻¹ of the original beverage. Powdered samples were analysed by XRF on solid pellets, which natively yields concentrations in mass fraction (mg kg⁻¹ of solid powder), not mg L⁻¹ of a reconstituted beverage. The source reports all powder values in mg L⁻¹ alongside the liquid values without describing a reconstitution factor or per-serving conversion, and the CF, MPI, and EDI calculations apply the same WHO drinking-water reference values to both basis types. This is a paper-internal unit-basis inconsistency that limits direct comparability of liquid and powder values and that bears on any downstream pooling. For HMI ingestion, the powdered-formulation values are treated as reported but routed to a separate energy-drink-powder matrix string to keep the basis difference visible.

(iii) Sample identity is opaque. Sample codes (SY, RB, PH, PW, XC, HS, 3H, WB, BR, HD, BH, OR, SD, BS, ME, VE, FL, PR, SK, IP, MP, AR, CX for liquid; EJ, KR, KK, PS, PE, AL, ES for powder) are not expanded into product types, brand identifiers, or formulation classes. The per-sample category-level signal (liquid vs powder, Nigeria-market) is preserved; per-sample formulation-class signal is not recoverable from the source.

(iv) Reference-value framework. The CF, MPI, and EDI calculations all use WHO drinking-water guideline values as the reference baseline rather than an energy-drink-specific contaminants limit (which does not exist for Nigeria at the time of the source’s writing). This is the same comparator framework Czarnek et al. 2024 used for Polish energy drinks and is appropriate where no matrix-specific cap exists, but it means the “exceedance” findings are exceedances of a drinking-water cap applied to a non-drinking-water matrix, not of a regulatorily binding energy-drink limit.

(v) EDI consumption anchor is biologically incongruous. The 300–600 mL/day intake anchor is described in Section 2.3.3 as derived from “calcium requirement in human body,” which is not a recognised anchor for energy-drink consumption modelling. The EDI numbers themselves are correctly computed from the stated inputs, but the choice of intake rate is not supported by a population-level consumption survey of Nigerian energy-drink consumers.

(vi) Publication venue is lower-tier. IRE Journals (Iconic Research and Engineering Journals) is a broad-scope open-access engineering venue without a high-impact-factor reputation; its peer-review rigor is not equivalent to journals such as Food Chemistry or Nutrients. The source content is methodologically structured and quantitatively concrete, but the venue places an upper bound on evidence weight.

Reported public evidence label: Direct evidence — primary occurrence data for the energy-drinks and energy-drink-powder matrices in Nigeria.

Evidence tier set to C. This is primary research with peer-review structure and concrete quantitative measurements, which puts it above narrative-review tier-C floor, but the absence of LOD/LOQ/CRM-recovery reporting, the unit-basis inconsistency in powder reporting, the lower-tier venue, and the opaque sample-code identities together prevent a tier-B promotion. Tier-A would require larger sample sizes, full analytical-QC reporting, As/Cr speciation, multi-region sampling, and a higher-impact peer-reviewed venue, none of which this study provides.

Implications

• Certification: contributes Nigeria-market primary occurrence values for the sports-energy-drinks HMTc category (Category 5 row 9). Per-sample Pb values in liquid formulations range from non-detect to 0.1393 mg L⁻¹ (SY); in powdered formulations from 0.0154 mg L⁻¹ (KK) to 0.2092 mg L⁻¹ (EJ). Per-sample Cd values range from non-detect to 0.0566 mg L⁻¹ (MP, liquid) and 0.0183 mg L⁻¹ (ES, powder). Per-sample tAs values range from non-detect to 0.0056 mg L⁻¹ (MP, liquid) and 0.0451 mg L⁻¹ (EJ, powder). All values are tier-C and should not be used in isolation to set or revise an HMTc threshold; they contribute as one Nigeria-market input to the broader category-level distribution alongside higher-tier evidence such as Czarnek 2024 (Poland), Izah 2016 (Nigeria, general beverages), and Koga 2021 (regional soft drinks).
• Courses: useful as a teaching reference for (1) the methodological hazard of comparing liquid (AAS, mg L⁻¹) and powder (XRF, native mg kg⁻¹ reported as mg L⁻¹) measurements within a single CF / MPI / EDI framework without an explicit reconstitution factor; (2) the application of WHO drinking-water reference values as a comparator baseline where no matrix-specific contaminant cap exists for a beverage class; (3) the worked example of CF and MPI computation from raw concentration data; (4) the practical structure of an EDI calculation across adult vs child populations using assumed body-weight and intake-volume inputs.
• App: contributes per-sample percentile-eligible values for the sports/energy-drinks product class in the Nigerian market, with liquid and powdered formulations routed to distinct matrix strings. Per-sample identities are coded (SY, RB, etc.) in the source and remain coded here; the contribution is to the Nigeria-market category-level distribution.
• Discovery: useful comparator studies referenced for downstream ingestion include Hamza et al. 2025 (physicochemical properties, heavy metals, and micronutrients of Nigerian energy drinks, Communication in Physical Sciences 12(3):933–950) and Hamza et al. 2026 (analysis of heavy metals and health risk assessment of selected energy drinks in Nigeria, Journal of Science, Engineering and Technology 14:2 1–11). Both are author-self-citations from the same research group and may share sample sets with the present study; if ingested, the overlap question should be checked explicitly.

Provenance notes

Open-access article published in IRE Journals (Iconic Research and Engineering Journals), Volume 9, Issue 9, March 2026, ISSN 2456-8880, DOI 10.64388/IREV9I9-1715689, pages 3050–3061. Citation: Babayo, I.I.; Hamza, H.A.; Bakura, U.M.; Aliyu, A.M.; Auwal, Y.M. Contamination Factor, Metal Pollution Index and Estimated Daily Intake of Heavy Metals in Some Selected Energy Drinks in Nigeria. IRE Journals 2026, 9(9), 3050–3061. Affiliations: Department of Pure and Applied Physics, Gombe State University, Gombe, Nigeria (Babayo, Hamza, Auwal); Department of Science Education (Physics), Abubakar Tafawa Balewa University, Ningi/Kano Road, Gubi Campus, ATBU, Bauchi, Nigeria (Bakura); Department of Physics, Yobe State University, Damaturu, Nigeria (Aliyu). No funding statement, ethics statement, or conflict-of-interest declaration appears in the published article. Accessed via the Manual Fetch Discovery autopilot; the file was initially saved as unknown2026-heavy-metals-energy-drinks-nigeria.pdf because first-author identification deferred to ingest-time PDF inspection.

Related evidence

• Lead
• Cadmium
• Arsenic, Total
• Chromium
• Nickel
• Cobalt
• Sports/Energy Drinks

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