Determination of Some Physicochemical Properties, Heavy Metals and Micronutrients of Some Energy Drinks Available in Nigeria

Overview

Hamza and colleagues (Gombe State University and Yobe State University, Nigeria) quantified six heavy metals (cobalt Co, chromium Cr, cadmium Cd, arsenic As, nickel Ni, lead Pb), four essential micronutrients (copper Cu, iron Fe, manganese Mn, zinc Zn), and four physicochemical parameters (pH, turbidity, total dissolved solids TDS, conductivity) in thirty commercially available energy drinks purchased from Nigerian local markets, comprising twenty-three liquid formulations and seven powdered formulations. Liquid samples were first dried by placing a 10 mL aliquot in an oven at 105 °C to remove moisture; the residue was ground, and 1 g was digested with aqua regia (HCl:HNO₃ in a 3:1 ratio) on a Kjeldahl heater for 4–5 hours (no digestion temperature stated by the source), then diluted to 100 mL with deionized water and analysed by atomic absorption spectrophotometry (Bulk 205 AAS). Powdered samples (3 g per sample) were pressed into 25 mm pellets with an automatic hydraulic press, covered with 6 µm polypropylene X-ray foil, and analysed by energy-dispersive X-ray fluorescence (EDXRF). Statistical analyses included Pearson correlation, chi-square against WHO drinking-water comparator values, an independent-samples t-test comparing liquid versus powdered formulations, and two multiple-regression models (Mn ~ Cu + Fe + Zn; Zn ~ Cu + Fe + Mn). The authors report that 43 % of samples exceeded the WHO drinking-water TDS limit of 500 mg L⁻¹, all thirty samples exceeded the WHO conductivity limit of 400 µS cm⁻¹, and all thirty samples were below the WHO pH range of 6.5–8.5 (i.e., acidic); among the heavy metals, lead, cadmium, chromium, and cobalt exceeded the cited WHO drinking-water limits in multiple samples, with the powdered EJ and KR samples showing the highest Pb values (0.2092 and 0.1754 mg L⁻¹ respectively).

Key numbers

All concentrations are reported in the source as mg L⁻¹ on a sample-as-analysed basis. The authors used WHO drinking-water reference values as comparators throughout (Cu 2.0, Fe 0.3 [text]/2.0 [Table 5], Mn 0.4 [text]/0.4 [Table 5], Zn 3.0 [Table 5]/5.0 [text] mg L⁻¹ for micronutrients; Co 0.05, Cr 0.05, Cd 0.003, As 0.01, Ni 0.07, Pb 0.01 mg L⁻¹ for heavy metals). Note the within-paper inconsistency between the chi-square Table 5 expected values and the discussion-text WHO comparator values for Fe and Zn, recorded in Verification notes. The source does not declare an instrument limit of detection; values reported as “ND” (Not Detected) appear across multiple sample/analyte combinations and are treated here as left-censored at the unspecified instrument detection floor.

Physicochemical properties of the thirty energy drinks (Table 1, p. 216)

Per-parameter summary across the panel: pH ranged 2.92 (HS) – 5.86 (PE); all thirty samples below the WHO 6.5–8.5 lower bound. Turbidity ranged 8 (AL) – 132 (SY) NTU; all thirty samples exceeded the WHO ≤5 NTU limit. TDS ranged 293 (PW) – 1072 (PE) mg L⁻¹, with 43 % of samples exceeding the WHO ≤500 mg L⁻¹ limit (per the source’s discussion text). Conductivity ranged 347 (SD) – 2230 (PE) µS cm⁻¹; all thirty samples exceeded the WHO ≤400 µS cm⁻¹ limit.

Concentration of heavy metals in the thirty energy drinks (Table 2, p. 217–218, mg L⁻¹)

“ND” = Not Detected (left-censored at the unspecified instrument detection floor).

Per-analyte detected ranges across the panel (Table 2 as authoritative):

• Co: 0.0017 (MP) – 0.0835 (EJ powder) mg L⁻¹; cobalt exceeded the cited WHO 0.05 mg L⁻¹ comparator in three samples: EJ (0.0835 powder), PR (0.0826 liquid), and KR (0.0534 powder).
• Cr: 0.0025 (AL powder) – 0.4159 (MP liquid) mg L⁻¹; chromium exceeded the cited WHO 0.05 mg L⁻¹ comparator in multiple samples, with MP (0.4159), KR (0.3764 powder), BH (0.2563), and ES (0.2501 powder) showing the highest values. No speciation was performed; values are total chromium.
• Cd: 0.0015 (IP) – 0.0566 (MP) mg L⁻¹; cadmium exceeded the cited WHO 0.003 mg L⁻¹ comparator in essentially all samples in which it was detected, with MP (0.0566) showing the highest value.
• As: 0.0002 (HS) – 0.0451 (EJ powder) mg L⁻¹; total arsenic (no inorganic arsenic (iAs)/total arsenic (tAs) speciation) exceeded the cited WHO 0.01 mg L⁻¹ comparator in the two highest-concentration powdered samples EJ (0.0451) and KR (0.0316) and KK (0.0249).
• Ni: 0.0015 (AR) – 0.0984 (OR) mg L⁻¹; nickel exceeded the cited WHO 0.07 mg L⁻¹ comparator in several samples including OR (0.0984), FL (0.0942), WB (0.0982), and RB (0.0875).
• Pb: 0.0154 (KK powder) – 0.2092 (EJ powder) mg L⁻¹ among detected samples; lead exceeded the cited WHO 0.01 mg L⁻¹ comparator in every detected sample, with the powdered EJ (0.2092) and KR (0.1754) showing the highest concentrations.

Concentration of micronutrients in the thirty energy drinks (Table 3, p. 219–220, mg L⁻¹)

“ND” = Not Detected.

Per-analyte detected ranges across the panel:

• Cu: 0.0027 (XC) – 0.7931 (IP) mg L⁻¹; all samples below the cited WHO 2.0 mg L⁻¹ drinking-water comparator.
• Fe: 0.0096 (PH) – 5.7042 (PW) mg L⁻¹; the source’s discussion text cites the WHO Fe comparator as 0.3 mg L⁻¹ and notes that “some values exceed the WHO guideline limit of 2 mg/L,” while Table 5 lists the WHO Fe expected value as 2.0 mg L⁻¹ — a paper-internal inconsistency recorded in Verification notes. Numerous samples exceed the 0.3 mg L⁻¹ figure; PW (5.7042), SD (4.5159), OR (3.1862), BH (2.2791), ES (2.2797 powder), and BR (2.0897) exceed the 2.0 mg L⁻¹ figure.
• Mn: 0.0043 (VE) – 0.8442 (PR) mg L⁻¹; the source’s text cites a 0.4 mg L⁻¹ comparator for manganese intake-related health risk and notes that “manganese intake above 0.4 mg/L may pose health risks.” PR (0.8442), ME (0.5432), MP (0.6333), KR (0.6218 powder), PS (0.4662 powder), KK (0.4126 powder) exceed this figure.
• Zn: 0.0104 (SK) – 13.8875 (SY) mg L⁻¹; the source’s text cites a 5 mg L⁻¹ WHO drinking-water comparator while Table 5 lists the expected value as 3.0 mg L⁻¹. SY (13.8875) and HS (6.5448) exceed both figures.

Independent-samples t-test for liquid versus powdered samples (Table 4, p. 220–221, partial)

The source presents only four analytes in the Table 4 t-test panel (Co, Cr, Cu, Fe); the remaining analytes are not tabulated for the liquid-versus-powder comparison.

Chi-square test of observed mean versus WHO expected value (Table 5, p. 225)

Combined chi-square value 6.98; p = 0.0725 — not statistically significant at α = 0.05 but suggestive at α = 0.10. The source reports χ² = 6.98 and p = 0.0725 without explicitly stating degrees of freedom (df = 3 is the implied value for a four-element comparison, but the wiki page does not assert this as a source-stated figure).

Pearson correlation matrix among the four micronutrients (Fig. 6, p. 225)

Multiple-regression results for Mn ~ Cu + Fe + Zn (OLS, n=27 observations; Snapshot 1, p. 227)

R² = 0.488; adj-R² = 0.422; F(3, 23) = 7.317; p(F) = 0.00129; Durbin-Watson = 2.273; Jarque-Bera 33.082 (p = 6.55 × 10⁻⁸). Per-predictor coefficients: const 0.0927 (SE 0.061, t = 1.513, p = 0.144); Cu β = 0.6861 (SE 0.172, t = 3.994, p = 0.001, 95 % CI 0.331 – 1.041); Fe β = −0.0338 (SE 0.026, t = −1.281, p = 0.213); Zn β = −0.0088 (SE 0.028, t = −0.315, p = 0.756). The source’s prose summarises Cu as a strong, significant positive predictor of Mn (β = 0.6861, p = 0.001) and Fe and Zn as non-significant.

Multiple-regression results for Zn ~ Cu + Fe + Mn (OLS, n=27 observations; Snapshot 2, p. 228)

R² = 0.018; adj-R² = −0.110; F(3, 23) = 0.1392; p(F) = 0.936; Durbin-Watson = 2.285; Jarque-Bera 293.079 (p < 2.28 × 10⁻⁶⁴). Per-predictor coefficients: const 0.6171 (SE 0.460, t = 1.340, p = 0.193); Cu β = −0.3096 (SE 1.662, t = −0.186, p = 0.854); Fe β = 0.0056 (SE 0.203, t = 0.028, p = 0.978); Mn β = −0.4878 (SE 1.548, t = −0.315, p = 0.756). The model does not fit the Zn data.

Methods (brief)

Thirty energy drinks (twenty-three liquid and seven powdered) were purchased from local markets in Nigeria and refrigerated at 4 °C until analysis. Liquid samples were prepared for AAS by transferring a 10 mL aliquot into an oven at 105 °C to remove moisture, grinding the dried residue with a pestle and mortar, and digesting precisely 1 g of ground sample in 20 mL of aqua regia (HCl: HNO₃ 3: 1) inside a fume hood on a Kjeldahl heater for 4–5 hours with continuous addition of acid until a pale yellow solution indicated complete decomposition. After cooling, the digest was diluted with deionized water, filtered, and made up to 100 mL with deionized water. Metal concentrations were quantified using a Bulk 205 Atomic Absorption Spectrophotometer. The source does not specify whether flame-AAS or graphite-furnace-AAS was used, does not report per-analyte wavelengths, does not report instrument limits of detection or quantification, does not report certified-reference-material recoveries, and does not specify replicate structure per sample. Powdered samples (3 g each) were placed into 25 mm diameter pellet moulds, covered with a 6 µm polypropylene transparent X-ray foil, and compressed into pellets using an automatic hydraulic press; the pellets were loaded into the X-ray excitation chamber of an EDXRF spectrometer using an automated sample changer system, and a time-based irradiation program controlled by dedicated software was used to analyse both samples and standard reference materials (the reference materials are not further specified).

Physicochemical parameters were measured with: a JENWAY 3505 digital pH meter calibrated with pH 4.0/7.0/10.0 buffers; a HACH Sension 5 digital conductivity meter calibrated with a KCl standard; a HACH DR/890 digital turbidity colorimeter calibrated against turbidity standards; and a HACH Sension 5 digital TDS/conductivity meter calibrated with a standard solution.

Statistical analyses comprised Pearson correlation (output shown as a heat-mapped 4 × 4 matrix for the micronutrient analytes), chi-square comparing observed means against WHO drinking-water comparator values (χ² = 6.98, p = 0.0725; the source does not state degrees of freedom), an independent-samples t-test comparing liquid versus powder formulations on Co/Cr/Cu/Fe (none significant at α = 0.05), and two ordinary-least-squares multiple-regression models fitted on n=27 observations (Mn ~ Cu + Fe + Zn; Zn ~ Cu + Fe + Mn). No metal speciation was performed: arsenic is recorded as total arsenic (tAs), and chromium is recorded as total chromium (Cr) — no hexavalent chromium (Cr-VI) distinction is offered by the source.

Evidence Fitness

This source contributes direct primary occurrence values for ten metals (Pb, Cd, tAs, Cr, Ni, Co, Cu, Fe, Mn, Zn) plus four physicochemical parameters across thirty packaged energy drinks (twenty-three liquid and seven powdered) sold at Nigerian local markets. The principal limitations bearing on pooling eligibility and synthesis weight are:

(i) Same-dataset overlap with the companion Babayo et al. 2026 Nigerian energy-drinks paper (Contamination Factor, Metal Pollution Index and Estimated Daily Intake of Heavy Metals in Some Selected Energy Drinks in Nigeria). The thirty 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, EJ, KR, KK, PS, PE, AL, ES) and the Cd/Cr/Co/As/Ni/Pb values in Table 2 of this paper match the corresponding values in the Babayo et al. 2026 paper, where H.A. Hamza is also a co-author. The two papers report the same underlying analytical dataset but differ in downstream analysis: the present paper adds physicochemical parameters, micronutrients (Cu, Fe, Mn, Zn), and multiple-regression analyses; the Babayo paper adds Contamination Factor, Metal Pollution Index, and Estimated Daily Intake calculations. Synthesis must avoid double-counting these as two independent observations of the Nigerian energy-drinks population; read them as one dataset when combining the concentrations. The overlap is recorded with the source.

(ii) No declared analytical limit of detection or quantification. The “ND” attribution is repeated across the table without an explicit numerical floor. The lack of declared LOD/LOQ prevents pool-eligibility decisions to be made under standard censored-data treatment.

(iii) No certified reference material or recovery data reported for the AAS pathway. The XRF pathway mentions “standard reference materials” loaded into the X-ray excitation chamber but does not name the certified reference material vendor or composition.

(iv) Two distinct analytical methods used on a single dataset (AAS for liquids; EDXRF for powders). Different matrix-effects, sensitivity, and detection-limit characteristics apply to the two methods; pooling liquid and powder values within the same analyte column risks confounding analytical-method effects with sample-type effects. The source’s own t-test (Table 4) reports no significant liquid-versus-powder difference for Co/Cr/Cu/Fe but does not extend the test to Cd/As/Ni/Pb/Mn/Zn.

(v) No metal speciation. Arsenic is reported as total elemental arsenic (recorded as tAs); chromium is reported as total chromium without Cr(VI) speciation; mercury is not in the analyte panel. Among the ten HMTc/HMI analytes (Pb, tAs, Cd, methylmercury (MeHg), total mercury (tHg), iAs, Ni, aluminum (Al), Cr-VI, Sn), this source covers Pb, tAs (no iAs), Cd, Ni, and Cr (no Cr-VI) — five of ten in part, with the speciation caveats noted.

(vi) Paper-internal inconsistency in the cited WHO comparator values for Fe and Zn. The discussion text (p. 219) cites WHO Fe at 0.3 mg L⁻¹ (and also notes “some values exceed the WHO guideline limit of 2 mg/L”) and WHO Zn at 5 mg L⁻¹, while Table 5 lists Fe expected at 2.0 mg L⁻¹ and Zn expected at 3.0 mg L⁻¹. The exceedance counts in this wiki page describe both comparator versions; downstream synthesis should resolve which WHO guideline edition the authors intended.

(vii) Tables 2 and 3 list units as “mg/L” for both liquid and powdered samples. For powdered samples this implicitly assumes a reconstitution basis that the source does not state. The values are recorded here as the source presents them; downstream pooling against an as-consumed liquid basis should treat powdered values cautiously until the reconstitution dilution is verified.

(viii) Multiple-regression sample size mismatch (n=27 reported in the OLS output; n=30 stated in the methods). Snapshots 1 and 2 both report “No. Observations: 27” while the dataset contains thirty samples; the source does not state how the three missing observations were dropped (likely listwise deletion against the Mn=ND values in SY/XC/FL and the Zn=ND value in HS — but the source does not say). This caveat affects only the regression results, not the raw concentration tables.

Evidence tier set to C. The source is primary research, peer-reviewed (Communication in Physical Sciences, Vol 12, Issue 3, March 2025), but with the methodological caveats above (no declared replicate structure, no declared LOD/LOQ, no CRM recovery data for AAS, mixed-method dataset, no metal speciation, internal-numerics inconsistencies, and the powder-basis ambiguity). The raw concentration values in Tables 2 and 3 are pool-considerable for Pb, Cd, tAs, Cr, Ni, Co, Cu, Fe, Mn, and Zn at C-tier weight with explicit notation of caveats (i)–(viii), and should be co-pooled with the Babayo companion paper as a single dataset rather than as two independent observations.

Implications

• Certification: contributes direct primary occurrence values for the sports-energy-drinks HMTc category (Category 5) for the Nigerian retail market. The Pb column reports eleven detected samples ranging 0.0154–0.2092 mg L⁻¹ against the source’s cited WHO 0.01 mg L⁻¹ comparator; the Cd column reports twenty-one detected samples ranging 0.0015–0.0566 mg L⁻¹ against the cited 0.003 mg L⁻¹ comparator; the Cr column reports twenty-four detected samples ranging 0.0025–0.4159 mg L⁻¹ against the cited 0.05 mg L⁻¹ comparator; the As column reports nineteen detected total-arsenic samples ranging 0.0002–0.0451 mg L⁻¹ against the cited 0.01 mg L⁻¹ comparator. These values are co-pooled with the companion Babayo et al. 2026 paper (Contamination Factor, Metal Pollution Index and Estimated Daily Intake of Heavy Metals in Some Selected Energy Drinks in Nigeria) and complement the prior Bunu et al. 2023 Kogi-State (Atomic Absorption Spectroscopic (AAS) Analysis of Heavy Metals and Health Risks Assessment of some Common Energy Drinks) and Bayelsa-State (Heavy Metals Quantification and Correlative Carcinogenic-Risks Evaluation in Selected Energy Drinks Sold in Bayelsa State Using Atomic Absorption Spectroscopic Technique) Nigerian data, plus the Polish-market Czarnek et al. 2024 (Nutritional Risks of Heavy Metals in the Human Diet—Multi-Elemental Analysis of Energy Drinks) and Jordanian-market Al-Sayyed et al. 2024 (Screening for the Presence of Some Heavy Metals, Total Soluble Solids and Caffeine Contents in Some Energy Drinks Sold in Jordanian Market) comparators. The two Hamza/Babayo Gombe-State-University dataset publications together (n=30, 23 liquid + 7 powdered) form a single observation block for the Nigerian energy-drinks occurrence picture.
• Courses: useful as a teaching reference for (1) the importance of declared LOD/LOQ and CRM recoveries for trace-metal analysis of finished beverages; (2) the importance of separating analytical-method effects (AAS vs EDXRF) from sample-type effects (liquid vs powder) when pooling mixed-method datasets; (3) the importance of speciation (Cr vs Cr-VI; tAs vs iAs) for downstream toxicology interpretation; (4) the recurring pattern in low-resource analytical reporting where the WHO drinking-water comparator is applied to packaged beverages without addressing the as-consumed-versus-drinking-water basis; (5) the importance of declaring how dropped observations are handled in regression analyses (the n=27 vs n=30 mismatch).
• App: contributes Nigerian-market occurrence values for the packaged energy-drink product class on a single-dataset, sample-as-analysed basis. Per-sample brand identities are not disclosed by the source.
• Discovery: the source’s reference list overlaps substantially with the Babayo companion paper and includes earlier Nigerian-beverage heavy-metals surveys (Iweala et al. 2014, Izah et al. 2015, Maduabuchi et al. 2006, Onianwa et al. 1999, Salako et al. 2016, Obuzor & Ajaezi 2010); the highlighted “Jingjing L., Qianlu Q. & Yanshan C. (2020). Arsenic speciation in energy drinks and human urine by HPLC-IC-MS. Journal of Agriculture and Food Chemistry, 68, 2” and “Mehmet O., John D. R. & Jennifer L. M. (2019). Arsenic in energy drinks: A risk assessment. Journal of Food Science, 84, 5” references (highlighted in yellow in the source PDF) are potential As-speciation discovery leads.

Provenance notes

Open-access publication in Communication in Physical Sciences (CPS), Vol 12, Issue 3, March 2025, pp. 213–230. DOI: 10.4314/cps.v12i3.19. Received 18 January 2025; Accepted 02 March 2025; Published 14 March 2025. Corresponding author: Hamza Abubakar Hamza, Department of Pure and Applied Physics, Gombe State University, P.M.B. 127, Gombe, Nigeria (hamzadurbi@gsu.edu.ng; ORCID 0009-0005-9958-5508). Co-authors: Abubakar Danjuma Bajoga (Gombe State University; a.bajoga@gsu.edu.ng), Yusuf Mohammed Auwal (Yobe State University, Damaturu; auwalgamajan@ysu.edu.ng), Hankouraou Seydou (Gombe State University; seydou5k@yahoo.com). Funding: no external source of funding declared. Conflict of interest: none declared. Ethical considerations: not applicable (no human or animal subjects). Data availability: stated as “available on request.” Accessed via the Manual Fetch Discovery autopilot.

Related evidence

• Lead
• Cadmium
• Arsenic
• Chromium
• Nickel
• Cobalt
• Copper
• Iron
• Manganese
• Zinc
• Sports/Energy Drinks

Update history

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