A pediatric health risk assessment of children's toys imported from China into Nigeria

Abstract

Trade liberalization led to the flooding of the Nigerian markets with ‘‘made in China’’ children's toys. Information about metal contamination in toys is vital to ensure the safety of children's product. This is a pediatric health risk assessment of three toxic metals (Pb, Cd and As) in children toys purchased from Nigerian market. Thirty cheap ‘‘made in China’’ toys were purchased from stores in Port Harcourt, Nigeria. Three toxic metals (Pb, Cd and As) in the thirty toys samples were determined by absorption spectrophotometry. Pb, Cd and As were present in all the toys at levels below the limits set by EU. The oral and dermal exposure risk assessment showed no significant non-carcinogenic and carcinogen health risks of public health concern. Some ‘‘made in China’’ toys imported into Nigeria may not add to the body burden of these metals in children.

Environmental Science; Biological Sciences; Health Sciences; Potential toxic metals; Health risk assessments; Chronic exposure; Children; Public health

1. Introduction

Trace metals have been detected in toys and baby products (Levin et al., 2008). Lead and cadmium are used as stabilizers in certain plastics, paint color enhancers, or anti-corrosion agents in children's toys (Kumar and Pastore, 2007; Greenway and Gerstenberger, 2010; Al-Qutob et al., 2014). The restrictions on the use of lead has justified substitution with cadmium since it also prevents formation of hydrochloric which can degrade the polymer (Kumar and Pastore, 2007) but the justification for the use of arsenic in toys remain unclear although some suggest it may be due to certain color dyes. Metals may be released from toys through saliva during mouthing, sweat during dermal contact, or gastric fluids after partial ingestion (i.e., scraped coatings, fibers or textile, or broken sections) (Guney and Zagury, 2012).

Mouthing in children is one important behavior that has been identified to expose them to environment chemicals. Babies and young children frequently mouth objects, including toys, resulting in saliva mobilization and oral exposure to toxic chemicals (Moya et al., 2004). Children and particularly infants are more vulnerable to heavy metal toxicity with compromised renal function, bone deformities, neurological disorders, gastrointestinal complications, cancer etc associated with exposure to these metals (Jarup, 2003; Habeler, 2008; MFMER, 2011). A ‘‘risk triangle’’ with metal-tainted children's toys, accessibility of the toys to children, and their vulnerability to exposure has been identified (IFCS, 2006).

Young children and the developing fetus are especially vulnerable to the neurotoxic effects of Pb, and subtle effects on intelligence and attention occur even at very low exposure levels (Attina and Trasande, 2013). Fatal acute poisoning in a child was reported following ingestion of a charm with very high lead content (Levin et al., 2008). Even with the regulation of Pb and Cd contamination in children's products, recent research still showed ongoing contamination in toys (Guney and Zagury, 2013; Hillyer et al., 2014).

Inorganic As is a carcinogen implicated in several cancers of the skin, lungs, liver, and bladder. Lower level of exposure can cause nausea and vomit, decreased production of red and white blood cells, abnormal heart rhythm, and damage to blood vessels. Chronic exposure to As can cause skin darkening and the appearance of small warts on the palms, soles, and torso (Ismail et al., 2017).

The information about metal contamination in toys is vital to ensure the safety of children's product. Trade liberalization in Nigeria led to the flooding of the markets with all and sundry items including cheap children's toys from China. There have been earlier reports of high lead and cadmium levels in children's toys from China in the Nigerian market (Omolaoye et al., 2010; Oyeyeola et al., 2017). There were recalls of low-cost toys and jewelries by US. Consumer Protection Safety Commission (USCPSC) in 2007 and strict regulation for Pb in children products. This is pediatric health risk assessment of the levels of Pb, Cd and As in some ‘‘made in China’’ children's toys sold in Nigeria.

2. Materials and method

2.1. Sample collection

Using a market-basket method, thirty ‘made in China’ low cost toys were purchased from supermarket and street vendors in Port Harcourt, Nigeria from January–February 2018. The plastic toys included teethers, balloon, toy cars/planes, and rattles. The brittle/pliable toys consisted of playdough, crayon, and watercolor pen. The paint coating was scrapped from plastic toy car and building blocks.

2.2. Heavy metal assay

Toy's surface paint was removed by scraping with clean razor blades. In all sample mass ranged from 15–25mg. To avoid cross-contamination of samples, fresh razor blades were used for scraping of each toy new gloves and underlying paper on the lab bench to prevent contamination.

Samples were placed in test tubes and 5 mL trace metal grade nitric acid was added, along with two small boiling chips. After initial heating at 90–100 °C until fuming stopped, samples were placed in an oil bath or heating block for vigorous digestion at more than 120 °C for 3 h (Weidenhamer, 2009). Samples were cooled and diluted to 25 mL in volumetric flasks, rinsing 4 times with 4 mL portions of water, transferring as much residue as possible. After dilution to volume, samples settled at least 0.5 h before analysis. If needed, samples were diluted further with 5% trace metal grade nitric acid. The concentrations of Pb, Cd and As in toy samples were analyzed in triplicates using an Atomic Absorption Spectrophotometer (Perkin Elmer AAS-700).

2.3. Quality control

The range of the calibration curve was used to calculate the range of application. Samples were also diluted and reanalysed when necessary to fit within the range of the calibration curve. The accuracy of the method was determined by analysis of a soil Certified Reference Material (CRM) (TraceCERT® 16595 for Pb, 51994 for Cd and 39436 for As). The results of this CRM analysis are required to be within the 95% confidence interval of the corresponding certified values. Furthermore, the relative standard deviation (RSD) was measured in triplicate analyses of the CRM under repeatability conditions. The CRM was also used as quality control sample in each series of measurements. The RSD between replicate analyses was less than 4%.

2.4. Human health risk assessment

Human Health Risk Assessment was undertaken using methodologies proposed by the United States environmental protection (U.S. EPA, 1991). This USEPA model as described in the Risk Assessment Information System (RAIS), 2007 (http://rais.ornl.gov/), supported by the Toxicological profiles developed by the USEPA Integrated Risk Information System (IRIS) (http://cfpub.epa.gov/ncea/iris/index.cfm) and by the US Agency for Toxic Substances and Disease Registry – Toxicological profiles (ATSDR) (http://www.atsdr.cdc.gov/toxfaq.html) were all employed in the pediatric health risk assessment Table 1.

Table 1.

Description of the variables in Health Risk Assessment.

Parameters	Description	Value	Unit	Source
THQ	Target Hazard Quotient	-	-	-
TTHQ	Total Target Hazard Quotient	-	-	-
ADI	Average Daily Intake	-	-	-
CS	Concentration of Metal	-	$\mathit{mg}/\mathit{kg}$	From this study
ing	Ingestion Rate (Child)	0.0002	$\mathit{kg}/\mathit{day}$
EDnc	Exposure Duration for Non-Carcinogenic	6	$\mathit{years}$	RAIS 2013
EDc	Exposure Duration for Carcinogenic	70	$\mathit{years}$	USEPA (2007)
EF	Exposure Frequency	365	$\mathit{Days}/\mathit{years}$	USEPA (2007)
ATnc	Average Time of Exposure for Non-Carcinogenic Element	EDnc $\times 365=2190$	days	RAIS 2013
ATc	Average Time of Exposure for Carcinogenic Element	EDc $\times 365$= 25550	days	RAIS 2013
BW	Body Weight	15	$\mathit{kg}$	RAIS 2013
SA	Surface Area	2100	$\mathit{c}{\mathit{m}}^2$
ABS	Absorption Factor	0.001,0.03	$\mathit{mg}/\mathit{c}{\mathit{m}}^2$	USEPA (2004)
CF	Conversion Factor	$1\times {10}^{-0}$	$\mathit{kg}/\mathit{mg}$	USEPA (2004)
AF	Adherence Factor	0.2	$\mathit{mg}{\mathit{m}}^{-1}$	-
RFD	Reference Dose	-	$\mathit{mg}/\mathit{kg}-\mathit{day}$	RAIS 2013
CSF	Cancer Slope Factor	-	$\mathit{mg}/\mathit{kg}-\mathit{day}$	RAIS 2013

2.5. Oral exposure to heavy metal in toys

$${\text{ADI}}_{\text{ing}}=\frac{\text{C×IR×EF×ED×CF}}{\text{BW×AT}}$$ (1)

2.6. Dermal exposure to heavy metal in toys

$${\text{ADI}}_{\text{dermal}}=\frac{\text{C×SA×SL×ABS×EF×ED×CF}}{\text{BW×AT}}$$ (2)

2.7. Non-carcinogenic risk assessment

Non-carcinogenic hazards are characterized by a term called hazard quotient (HQ). HQ is a unitless number that is expressed as the probability of an individual suffering an adverse effect. It is defined as the quotient of ADI or dose divided by the toxicity threshold value, which is referred to as the chronic reference dose (RfD) in mg/kg-day of a specific heavy metal as shown in Eq. (3) (U.S. EPA, 2004).

$$\text{THQ}=\frac{\text{ADI}}{\text{RfD}}$$ (3)

The non-carcinogenic effect to the population is as a result of the summation of all the THQs due to individual heavy metals or Hazard Index (HI) as described by USEPA document (U.S. EPA, 2004). Eq. (4) shows the mathematical representation of this parameter:

$$\text{HI}=\sum _{k=1}^n\text{HQI}$$ (4)

2.8. Carcinogenic risk assessment

The lifetime cancer risk was calculated using:

$$\text{Riskpathway}=\sum _{k=1}^n\text{ADIkCSFk}$$ (5)

Where Risk is a unitless probability of an individual developing cancer over a lifetime. ADIk (mg/kg/day) and CSFk (mg/kg/day) are the average daily intake and the cancer slope factor, respectively for the k heavy metal, for n number of heavy metals. The slope factor converts the estimated daily intake of the heavy metal averaged over a lifetime of exposure directly to incremental risk of an individual developing cancer (U.S. EPA, 2004).

The total excess lifetime cancer risk for an individual is finally calculated from the average contribution of the individual heavy metals for all the pathways using the following equation:

$$\text{Risk}(\text{total})=\text{Risk}(\text{ing})+\text{Risk}(\text{dermal})$$ (6)

where Risk (ing) and Risk (dermal) are risks contributions through ingestion and dermal pathways. Both non-carcinogenic and carcinogenic risk assessment of heavy metals are calculated using RfD and CSF values derived are shown in Table 2.

Table 2.

Oral and Dermal Reference dose (Rfd) for no-carcinogenic and cancer slope factor (CSF).

Metal	Oral Rfd	Dermal Rfd	CSF oral	CSF dermal
Pb	${0.0035}^{(c)}$	${0.0005}^{(a)}$	${0.0085}^{(a)}$	-
Cd	${0.001}^{(c)}$	${0.00005}^{(c)}$	${0.38}^{(b)}$	-
As	${0.0003}^{(c)}$	${0.00012}^{(c)}$	${1.5}^{(a)}$	${1.5}^{(a)}$

$(a)$ = RAIS (2013) Risk assessment information system.

$(b)$ = Walkes and Rehm (1994).

$(c)$ = AERIS Software Inc., 1991.

3. Results

Metal levels in the toys sample are shown in Table 3. All the 30 toy samples analyzed were found to contain Pb (4.16–9.747), Cd (1.942–6.50) and As (1.459–6.318 mg/kg). The highest Pb, Cd and As levels were found in samples $A_{11}$(Donkey -9.747 mg/kg), $A_3$ (Balls -6.50 mg/kg) and $A_{19}$ (Toy rabbit -6.318 mg/kg) respectively. Whereas the lowest levels of Pb, Cd and As were detected in $A_{12}$ (Teddy bear - 4.16 mg/kg), $A_9$(Bird - 1.942 mg/kg) and $A_{21}$ (Fischerpince rattle - 1.459 mg/kg) respectively.

Table 3.

Pb, Cd and As levels (mg/kg) in children's toys.

Sample	Description	Pb	Cd	As
EU Regulation		90 mg/kg	23 mg/kg	47 mg/kg
A1	Toy ant	6.435	4.246	2.184
A2	Ball 1	7.127	4.196	3.659
A3	Ball 2	5.618	6.5	3.527
A4	Toy duck	5.152	4.276	2.572
A5	Aircraft	6.398	3.513	1.723
A6	Jelly fish toy	4.556	2.264	4.252
A7	Dolphin toy	7.822	5.183	2.764
A8	Toy feeding bottle	6.496	4.397	2.492
A9	Bird	5.383	1.942	3.205
A10	Bat man	4.692	3.282	4.365
A11	Donkey	9.747	6.257	3.175
A12	Teddy bear	4.16	2.482	1.586
A13	Baby rattle	8.505	2.218	4.642
A14	Baby 1	7.213	5.354	4.294
A15	Baby 2	8.762	3.827	5.108
A16	Toy frog	9.218	5.342	4.361
A17	Power rangers	8.184	6.287	3.813
A18	Toy sheep	7.643	4.1	2.642
A19	Toy rabbit	8.161	5.082	6.318
A20	Pacifier	8.374	4.735	4.273
A21	Fischerpince rattle	6.453	3.517	1.459
A22	Mask 1	6.218	2.178	5.111
A23	Mask 2	7.832	3.66	2.253
A24	Toy cat	6.249	2.835	3.643
A25	Toy spider	8.177	4.799	5.432
A26	Toy bee	5.659	5.255	3.182
A27	Robot	7.272	3.723	1.499
A28	4 hand reptile	6.149	3.538	4.386
A29	Policeman	4.592	4.592	2.178
A30	Pig head	5.353	5.353	2.947

The oral and dermal Chronic Daily Intake CDI target hazard Quotient (THQ) and total target hazard Quotient (TTHQ) of Pb, Cd and As are shown in Table 4. The THQ and TTHQ of Pb, Cd and As were less than 1 with the highest oral and dermal THQ seen in Toy $A_{19}$ (Toy rabbit with value 0.364 and 0.045) respectively suggesting no significant health risk from heavy metal exposure in toys.

Table 4.

Oral and dermal Chronic Daily Intake CDI (mg/kg/bw/dy), Target Hazard Quotient (THQ) and Total Target Hazard Quotient (TTHQ) of Pb, Cd and As in children toys.

Sample	Oral							Dermal
	CDI			THQ			TTHQ	CDI			THQ			TTHQ
	Pb	Cd	As	Pb	Cd	As		Pb	Cd	As	Pb	Cd	As
A1	8.2E-05	5.4E-05	2.8E-05	0.0235	0.0543	0.0931	0.171	1.7E-07	1.1E-07	1.8E-06	0.00033	0.0023	0.0143	0.017
A2	9.1E-05	5.4E-05	4.7E-05	0.026	0.0537	0.156	0.236	1.9E-07	1.1E-07	2.9E-06	0.00037	0.0023	0.024	0.027
A3	7.2E-05	8.3E-05	4.5E-05	0.0205	0.0831	0.1503	0.254	1.5E-07	1.7E-07	2.8E-06	0.00029	0.0035	0.0231	0.027
A4	6.6E-05	5.5E-05	3.3E-05	0.0188	0.0547	0.1096	0.183	1.4E-07	1.1E-07	2.1E-06	0.00027	0.0023	0.0168	0.019
A5	8.2E-05	4.5E-05	2.2E-05	0.0234	0.0449	0.0734	0.142	1.7E-07	9.4E-08	1.4E-06	0.00033	0.0019	0.0113	0.014
A6	5.8E-05	2.9E-05	5.4E-05	0.0166	0.0289	0.1812	0.227	1.2E-07	6.1E-08	3.4E-06	0.00024	0.0012	0.0278	0.029
A7	0.0001	6.6E-05	3.5E-05	0.0286	0.0663	0.1178	0.213	2.1E-07	1.4E-07	2.2E-06	0.0004	0.0028	0.0181	0.021
A8	8.3E-05	5.6E-05	3.2E-05	0.0237	0.0562	0.1062	0.186	1.7E-07	1.2E-07	2E-06	0.00034	0.0024	0.0163	0.019
A9	6.9E-05	2.5E-05	4.1E-05	0.0197	0.0248	0.1366	0.181	1.4E-07	5.2E-08	2.6E-06	0.00028	0.001	0.021	0.022
A10	6E-05	4.2E-05	5.6E-05	0.0171	0.042	0.186	0.245	1.3E-07	8.8E-08	3.5E-06	0.00024	0.0018	0.0286	0.031
A11	0.00012	8E-05	4.1E-05	0.0356	0.08	0.1353	0.251	2.6E-07	1.7E-07	2.6E-06	0.0005	0.0034	0.0208	0.025
A12	5.3E-05	3.2E-05	2E-05	0.0152	0.0317	0.0676	0.115	1.1E-07	6.7E-08	1.3E-06	0.00021	0.0013	0.0104	0.012
A13	0.00011	2.8E-05	5.9E-05	0.0311	0.0284	0.1978	0.257	2.3E-07	6E-08	3.7E-06	0.00044	0.0012	0.0304	0.032
A14	9.2E-05	6.8E-05	5.5E-05	0.0264	0.0684	0.183	0.278	1.9E-07	1.4E-07	3.5E-06	0.00037	0.0029	0.0281	0.031
A15	0.00011	4.9E-05	6.5E-05	0.032	0.0489	0.2177	0.299	2.4E-07	1E-07	4.1E-06	0.00045	0.0021	0.0334	0.036
A16	0.00012	6.8E-05	5.6E-05	0.0337	0.0683	0.1859	0.288	2.5E-07	1.4E-07	3.5E-06	0.00048	0.0029	0.0286	0.032
A17	0.0001	8E-05	4.9E-05	0.0299	0.0804	0.1625	0.273	2.2E-07	1.7E-07	3.1E-06	0.00042	0.0034	0.025	0.029
A18	9.8E-05	5.2E-05	3.4E-05	0.0279	0.0524	0.1126	0.193	2.1E-07	1.1E-07	2.1E-06	0.00039	0.0022	0.0173	0.02
A19	0.0001	6.5E-05	8.1E-05	0.0298	0.065	0.2693	0.364	2.2E-07	1.4E-07	5.1E-06	0.00042	0.0027	0.0414	0.045
A20	0.00011	6.1E-05	5.5E-05	0.0306	0.0605	0.1821	0.273	2.2E-07	1.3E-07	3.4E-06	0.00043	0.0025	0.028	0.031
A21	8.3E-05	4.5E-05	1.9E-05	0.0236	0.045	0.0622	0.131	1.7E-07	9.4E-08	1.2E-06	0.00033	0.0019	0.0096	0.012
A22	8E-05	2.8E-05	6.5E-05	0.0227	0.0278	0.2178	0.268	1.7E-07	5.8E-08	4.1E-06	0.00032	0.0012	0.0335	0.035
A23	0.0001	4.7E-05	2.9E-05	0.0286	0.0468	0.096	0.171	2.1E-07	9.8E-08	1.8E-06	0.0004	0.002	0.0148	0.017
A24	8E-05	3.6E-05	4.7E-05	0.0228	0.0362	0.1553	0.214	1.7E-07	7.6E-08	2.9E-06	0.00032	0.0015	0.0239	0.026
A25	0.0001	6.1E-05	6.9E-05	0.0299	0.0614	0.2315	0.323	2.2E-07	1.3E-07	4.4E-06	0.00042	0.0026	0.0356	0.039
A26	7.2E-05	6.7E-05	4.1E-05	0.0207	0.0672	0.1356	0.223	1.5E-07	1.4E-07	2.6E-06	0.00029	0.0028	0.0208	0.024
A27	9.3E-05	4.8E-05	1.9E-05	0.0266	0.0476	0.0639	0.138	2E-07	1E-07	1.2E-06	0.00038	0.002	0.0098	0.012
A28	7.9E-05	4.5E-05	5.6E-05	0.0225	0.0452	0.1869	0.255	1.7E-07	9.5E-08	3.5E-06	0.00032	0.0019	0.0287	0.031
A29	5.9E-05	5.9E-05	2.8E-05	0.0168	0.0587	0.0928	0.168	1.2E-07	1.2E-07	1.8E-06	0.00024	0.0025	0.0143	0.017
A30	6.8E-05	6.8E-05	3.8E-05	0.0196	0.0684	0.1256	0.214	1.4E-07	1.4E-07	2.4E-06	0.00028	0.0029	0.0193	0.022

Table 5 show the oral and dermal cancer risk, total cancer risk (TCR) and hazard Index (HI). The HI of Pb, Cd and As from via oral and dermal routes ranged from 0.126-0.409 indicating es no significant non-carcinogenic health risk. The total cancer risk (TCR) of Pb, Cd and As were within the generally acceptable risk range of $1.4\times {10}^{-4}-1.4\times {10}^{-6}$.

Table 5.

Oral and Dermal cancer risk, Total Cancer and Hazard index of Pb, Cd and As in children toys.

Sample	Oral Cancer Risk			Dermal Cancer Risk	Total Cancer Risk	Hazard index
	Pb	Cd	As	As
A1	7E-07	2.1E-05	4.2E-05	2.6E-06	6.6E-05	0.188
A2	7.8E-07	2E-05	7E-05	4.4E-06	9.6E-05	0.262
A3	6.1E-07	3.2E-05	6.8E-05	4.3E-06	0.0001	0.281
A4	5.6E-07	2.1E-05	4.9E-05	3.1E-06	7.4E-05	0.202
A5	7E-07	1.7E-05	3.3E-05	2.1E-06	5.3E-05	0.155
A6	5E-07	1.1E-05	8.2E-05	5.1E-06	9.8E-05	0.256
A7	8.5E-07	2.5E-05	5.3E-05	3.3E-06	8.3E-05	0.234
A8	7.1E-07	2.1E-05	4.8E-05	3E-06	7.3E-05	0.205
A9	5.9E-07	9.5E-06	6.2E-05	3.9E-06	7.5E-05	0.203
A10	5.1E-07	1.6E-05	8.4E-05	5.3E-06	0.00011	0.276
A11	1.1E-06	3E-05	6.1E-05	3.8E-06	9.6E-05	0.276
A12	4.5E-07	1.2E-05	3E-05	1.9E-06	4.5E-05	0.126
A13	9.3E-07	1.1E-05	8.9E-05	5.6E-06	0.00011	0.289
A14	7.9E-07	2.6E-05	8.3E-05	5.2E-06	0.00011	0.309
A15	9.5E-07	1.9E-05	9.8E-05	6.2E-06	0.00012	0.335
A16	1E-06	2.6E-05	8.4E-05	5.3E-06	0.00012	0.32
A17	8.9E-07	3.1E-05	7.3E-05	4.6E-06	0.00011	0.302
A18	8.3E-07	2E-05	5.1E-05	3.2E-06	7.5E-05	0.213
A19	8.9E-07	2.5E-05	0.00012	7.6E-06	0.00015	0.409
A20	9.1E-07	2.3E-05	8.2E-05	5.2E-06	0.00011	0.304
A21	7E-07	1.7E-05	2.8E-05	1.8E-06	4.8E-05	0.143
A22	6.8E-07	1.1E-05	9.8E-05	6.2E-06	0.00012	0.303
A23	8.5E-07	1.8E-05	4.3E-05	2.7E-06	6.5E-05	0.189
A24	6.8E-07	1.4E-05	7E-05	4.4E-06	8.9E-05	0.24
A25	8.9E-07	2.3E-05	0.0001	6.6E-06	0.00014	0.361
A26	6.2E-07	2.6E-05	6.1E-05	3.9E-06	9.1E-05	0.247
A27	7.9E-07	1.8E-05	2.9E-05	1.8E-06	5E-05	0.15
A28	6.7E-07	1.7E-05	8.4E-05	5.3E-06	0.00011	0.286
A29	5E-07	2.2E-05	4.2E-05	2.6E-06	6.7E-05	0.185
A30	5.8E-07	2.6E-05	5.7E-05	3.6E-06	8.7E-05	0.236

4. Discussion

Children's toys may be source of heavy metals. Lead exposure has been implicated in the impairment of cognitive development in children (Jusko et al., 2008; Kaufman et al., 2014) whereas exposure to cadmium and arsenic may give rise to neurodevelopment problems and behavioral disorders in children (Rodríguez-Barranco et al., 2013). These metals are used in stabilizing and recycling of the plastics in addition to being applied in the attractive paint colours of the toys (Guney and Zagury, 2012; Rastogi and Pritzl, 1996). Mouthing of non-food item which peaks at 6-12-month age (39–66 min/day) is a common behavior of children plays the unwanted role of children exposure to these metals (Guney and Zagury, 2014; Smith and Norris, 2003).

According to US CPSC, 0.06% Pb by weight, or 600 ppm was chosen as the permissible limit of Pb in paint on items intended for children (United states Consumer Product Safety Commission, 2019) but was further reduced to 0.009% (Library of Congress, 2008).

The Pb, Cd and As levels in all the toys in this study were below the limit set by the European Union migration units for toy safety which includes Pb (90 mg/kg), Cd (23 mg/kg) and As (47 mg/kg) (European Council, 2009). There were higher Pb levels than Cd and As probably due to the preference for Pb because of its better stabilizing property than the other metals preventing free chlorine radicals in polyvinyl chloride PVC from reacting with hydrogen radicals to form hydrochloric acid (Tuczai and Cortolano, 1992). Although some manufactures have substituted Pb for Cd in stabilizing PVC in children products because of reported Pb toxicity, the substitution of Pb with Cd in children's toys may also pose a health threat.

Pb, Cd and As levels in this study were lower than previously reported data by other researchers in Nigeria and other countries. Studies by Omolaoye et al. in 2010 from Nigeria reported higher level Pb and Cd in the range of 2.50–1445.00 mg/kg and 0.50–373.3 mg/kg respectively. Another study by Oyeyeola et al. (2017) also in Nigeria detected high levels of Pb and Cd in a range of 36.1–106 mg/kg and 3.55–40.7 mg/kg respectively. Elsewhere other studies have reported higher levels of Pb, Cd and As than values detected in our study Hillyer et al. (2014); Mateus-Garcia and Ramos-Bonilla (2014); Cui et al., (2015), Ismail et al., (2017) and Negev et al., (2018).bib_Negev_et_al_2018

The metal levels in our study coupled with reports from studies done by Oyeyeola et al., (2017) (Pb-36.1-106 mg/kg) and Ismail et al., 2017(Pb- 1.50-171.67 mg/kg) show there is a decrease in the levels of these metals in children toys when compared with studies before and immediately after the recalls of low-cost toy and jewelry in 2007 by US CPSC in 2007 and strict regulation for Pb in children products. In 2007 alone nearly 6 million toys were recalled in the US (Schmidt, 2008). In 2010, 12 million Mc Donald's cups were recalled due to Cadmium content in the painted coating (CPSC, 2010). Also, in 2010 bracelet were voluntarily recalled due to high levels of Cd.

The THQ, TTHQ, and HI of Pb, Cd and As in the children toys, via oral and dermal exposures were below the threshold of 1. The carcinogenic health risks of these metals were within the acceptable limit $1\times {10}^{-4}-1\times {10}^{-6}$. Although Pb, Cd and As determined in this study did not show any significant health risk but bioaccumulation after chronic exposure may pose health risk in children especially for Pb which has no safe levels in blood.

5. Conclusion

There were low levels of Pb, Cd and As in some ‘‘made in China’’ toys lately imported into Nigeria.

Declarations

Author contribution statement

O. Orisakwe: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper

Z. Igweze: Performed the experiments; Contributed reagents, materials, analysis tools or data.

O. Ekhator: Analyzed and interpreted the data; Wrote the paper.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Competing interest statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.