Assessment of the concentrations and human exposure to heavy metals in bathing soaps in Nigeria

Overview

Oviri, Tesi, and Emoyan measured lead (Pb), nickel (Ni), Zn, Co, cadmium (Cd), and total chromium (Cr) in 17 bathing soaps sold in Abraka, Delta State, Nigeria. The sampled categories were medicated, moisturizing, toilet, and skin-whitening soaps; the paper reports both individual anonymous sample values and category-level mean, median, and range statistics in mg/kg finished product. Across Table 2, Pb ranged 0.08-0.28 mg/kg, Cd 0.02-0.05 mg/kg, Ni 0.05-0.24 mg/kg, total Cr 0.01-0.09 mg/kg, Co 0.33-1.93 mg/kg, and Zn 0.10-6.42 mg/kg. The authors also calculated dermal systemic exposure doses and margins of safety using SCCS cosmetic-exposure defaults and concluded that all MoS values were above 100.

Key numbers

All concentration values below are from source Tables 2 and 3, in mg/kg finished soap as sold. Multiply by 1000 for ppb or ug/kg.

Individual anonymous soap samples

Category	Sample	Pb	Ni	Zn	Co	Cd	Cr
Medicated	SP1	0.10	0.19	0.40	0.56	0.03	0.07
Medicated	SP2	0.16	0.22	0.61	0.89	0.05	0.07
Medicated	SP3	0.08	0.12	1.03	1.93	0.02	0.04
Medicated	SP4	0.09	0.15	0.18	0.47	0.03	0.03
Medicated	SP5	0.11	0.20	0.22	0.33	0.03	0.03
Moisturizing	SP6	0.11	0.19	6.42	0.69	0.03	0.04
Moisturizing	SP7	0.10	0.20	0.12	0.59	0.04	0.02
Moisturizing	SP8	0.12	0.24	0.10	0.95	0.04	0.01
Moisturizing	SP9	0.12	0.18	1.05	1.01	0.05	0.01
Moisturizing	SP10	0.15	0.09	0.73	0.82	0.04	0.07
Moisturizing	SP11	0.21	0.05	0.63	0.62	0.02	0.03
Toilet	SP12	0.14	0.13	0.57	0.66	0.04	0.07
Toilet	SP13	0.18	0.21	0.61	0.73	0.05	0.07
Toilet	SP14	0.28	0.19	0.41	0.80	0.05	0.09
Skin whitening	SP15	0.12	0.11	0.32	0.42	0.02	0.04
Skin whitening	SP16	0.21	0.11	0.30	0.37	0.03	0.07
Skin whitening	SP17	0.18	0.21	0.61	0.73	0.05	0.07
All samples	Minimum	0.08	0.05	0.10	0.33	0.02	0.01
All samples	Maximum	0.28	0.24	6.42	1.93	0.05	0.09

Category summaries

Category	n	Pb mean (median), range	Ni mean (median), range	Zn mean (median), range
Medicated	5	0.108 (0.10), 0.08-0.16	0.176 (0.19), 0.12-0.22	0.488 (0.40), 0.18-1.03
Moisturizing	6	0.135 (0.12), 0.10-0.21	0.204 (0.20), 0.05-0.24	1.660 (0.61), 0.10-6.42
Toilet	3	0.200 (0.18), 0.14-0.28	0.177 (0.19), 0.13-0.21	0.530 (0.57), 0.41-0.61
Skin whitening	3	0.170 (0.18), 0.12-0.21	0.143 (0.11), 0.11-0.21	0.410 (0.32), 0.30-0.61

Category	n	Co mean (median), range	Cd mean (median), range	Cr mean (median), range
Medicated	5	0.836 (0.56), 0.33-1.93	0.032 (0.03), 0.02-0.05	0.048 (0.04), 0.03-0.07
Moisturizing	6	0.794 (0.73), 0.59-1.01	0.042 (0.04), 0.02-0.05	0.028 (0.02), 0.01-0.07
Toilet	3	0.730 (0.73), 0.66-0.80	0.047 (0.05), 0.04-0.05	0.077 (0.07), 0.07-0.09
Skin whitening	3	0.507 (0.42), 0.37-0.73	0.033 (0.03), 0.02-0.05	0.060 (0.07), 0.04-0.07

Exposure-modeling outputs

Table 4 reports systemic exposure dose (SED) under 50% and 100% bioaccessibility assumptions. At 50% bioaccessibility, maximum SED values were Cd 0.002, Pb 0.011, Cr 0.004, Co 0.075, Ni 0.007, and Zn 0.250 ug/kg bw/day. At 100% bioaccessibility, maximum SED values were Cd 0.004, Pb 0.022, Cr 0.007, Co 0.150, Ni 0.019, and Zn 0.500 ug/kg bw/day. The text states calculated MoS values for all investigated metals were greater than 100 at both bioaccessibility assumptions.

Methods (brief)

The authors purchased 17 soaps from supermarkets in Abraka, Delta State, Nigeria. They digested 1.0 g of each soap sample overnight in concentrated nitric acid, perchloric acid, and hydrochloric acid, heated the mixture to 125 C for two hours, filtered, diluted to 25 mL with 0.25 mol/L nitric acid, and analyzed Cd, Pb, Ni, Cr, Co, and Zn in triplicate by flame atomic absorption spectrophotometry using a Perkin Elmer Analyst 200. Blanks were processed in parallel; glassware was soaked in 10% nitric acid and rinsed with deionized water. Spike recoveries were 89.5-98.8%. The paper does not report LOD or LOQ values and does not speciate chromium.

The exposure model used a 60 kg adult body weight, SCCS default soap amount 18.67 g/day, exposed skin surface area 17,500 cm2, application frequency 1.43/day, retention factor 0.01, and 50% and 100% oral-bioavailability scenarios. The source treats MoS >= 100 as the no-health-risk benchmark.

Implications

Certification: This source contributes finished-product occurrence values for a provisional bathing-soaps product class and a three-sample skin-whitening soap subset. The usable concentration basis is finished product as sold; the values are not food-occurrence data and should not be routed into dietary benchmark pools.

Courses: Useful as a compact example of dermal rinse-off exposure modeling layered on finished-product heavy-metal measurements. It also illustrates why source tables should be preferred over abstract summaries when the two disagree.

App: Supports Nigeria-market personal-care context for bathing soaps and skin-lightening soaps, with concentration ranges and MoS-oriented exposure calculations. Because the source reports anonymous sample codes rather than market-share-weighted sampling, app use should frame the values as a small occurrence study, not a national distribution.

Microbiome: No microbiome data.

Update history

No substantive edit history is available in this build. The full commit record is available in git.