Assessment of Heavy Metals and Hydroquinone Contents of Selected Cosmetic Products Sold in Awka, Anambra State, Nigeria

This study evaluated the presence of selected heavy metals and hydroquinone in cosmetic products, specifically lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr) and nickel (Ni), together with product pH and relationships among the investigated parameters. Five cosmetic products, coded C1–C5, were selected and analysed. Hydroquinone concentrations were determined by high-performance liquid chromatography (HPLC), while heavy metal concentrations were determined by atomic absorption spectrophotometry. A calibrated digital pH meter was used to measure product pH. Heavy metal measurements were conducted in duplicate, and pH measurements were conducted in triplicate. All cosmetic samples contained lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr) and nickel (Ni). Sample C2 recorded the highest mean concentrations of Pb (1.15 mg/kg), Hg (0.09 mg/kg), Cd (0.23 mg/kg), Cr (1.47 mg/kg) and Ni (1.07 mg/kg), whereas C4 had the lowest concentrations of Pb (0.55 mg/kg), Hg (0.04 mg/kg), Cd (0.12 mg/kg), Cr (0.94 mg/kg) and Ni (0.65 mg/kg). Among the metals investigated, chromium had the highest concentrations, whereas mercury had the lowest. Hydroquinone was also detected in all samples, at concentrations ranging from 0.00409% to 0.01984% w/w in the original products. Hydroquinone concentrations were highest in C2 and lowest in C4. Sample pH ranged from 5.21 ± 0.02 to 6.38 ± 0.02, indicating mild acidity. Pearson correlations between pH and the analysed heavy metals were weakly negative (r = −0.102 to −0.201). The correlation between pH and hydroquinone concentration was negligible (r = 0.016). By contrast, correlations between the heavy metals and hydroquinone were strongly positive (r = 0.916–0.990). Hydroquinone showed the strongest correlation with Hg (r = 0.990), followed by Pb (r = 0.985), Cr (r = 0.958), Cd (r = 0.955) and Ni (r = 0.916). The calculated hazard quotients (HQ) and hazard indices (HI) were below 1 for all samples, indicating low estimated non-carcinogenic risk under the assumed exposure conditions. These findings support continued regulatory surveillance, product quality control and consumer awareness concerning cosmetic safety.