In this study with two concurrent investigations, we investigated 2249 children aged 0–7 years old and the total lead levels in 294 toys. We found that the plastic toys accounting for a highest proportion (156/294, 53.06%) among the studied toys had the highest lead levels compared with toys of other materials, and playing with plastic toys was a significant risk factor for BLL-increment among children under 7 years old. Together with the findings of the BLLs and toy lead concentrations in the overlapped investigation areas, we suggest the possibility of the potential association between higher toy lead levels and higher BLLs in children under 7 years old.
In this study, we found that the geometric mean of the BLLs of children aged 0–7 years old in shanghai from 2013 to 2014 was 2.02 µg/dL, which was lower than that (4.2) of Chinese children in the same age group investigated nationwide during the same time period(Yan et al., 2020). However, the BLLs reported in this study were still higher than the concurrent BLLs in developed countries among children of similar ages, but lower than the concurrent BLLs in most of the developing countries among children of similar ages. The geometric mean of the BLLs of children aged 1–5 years old in USA from 2013 to 2014 was 0.78 µg/dL(Wang et al., 2021b), and the median of the BLLs of children aged 3–5 years old in Korea from 2012 to 2014 was 1.34 µg/dL(Burm et al., 2016). In Kashmir of India, the mean of the BLLs of children aged 2–4 years old was 4.71 µg/dL around 2018(Rashid et al., 2019). In Enugu of southeastern Nigeria, the mean of the BLLs of children aged 0–5 years old at 2011 was 7.5 µg/dL(Ugwuja et al., 2014). However, in São Paulo of Brazil, the geometric mean of the BLLs of children aged 1–4 years old at 2013 was only 2.16 µg/dL(Olympio et al., 2018).
Consistent with other investigations, we found that plastic toys had the highest average total lead levels, followed by metal toys. Previous studies unveiled that PVC plastic toys and metallic jewelry toys usually had very high lead concentrations(Greenway and Gerstenberger, 2010; Hillyer et al., 2014; Njati and Maguta, 2019; Sanders et al., 2013; Shen et al., 2018). This is because that PVC toys contain lead and cadmium additives, acting as plasticizers so as to make PVC soft and pliable. And the PVC plastic toys accounted for a considerable part of plastic toys. According to Joseph A’s survey, 27.1% of the tested plastic toys were made of PVC plastics(Greenway and Gerstenberger, 2010). In light of our findings, 83.28% of the study children played with plastic toys, and plastic toys accounted for a substantial proportion of the measured toys. Therefore, high lead levels in plastic toys may explain why playing with plastic toys is a significant risk factor for BLL increment in young children and worth attention.
We compared children’s BLLs and toy lead levels in the overlapped investigation areas and raised the possibility that the district with higher toy lead levels may have higher BLLs in young children. This suggested that lead contamination in toys might be a significant contributing factor for children’s BLL increment. Previous studies showed that mouthing behavior played an important role in children’s exposure to environmental contaminants(Tulve et al., 2002). Children are increasingly likely to mouth non-food items since 6 months old, and the high frequency of mouthing hands or objects begins to moderate between 2 and 3 years old(Firestone et al., 2007), then becomes less frequent after 3 years old(Xue et al., 2010). Mouthing of lead contaminated toys may cause the release of lead in toys via contacting with saliva, and ingestion of toy pieces may result in the release of lead into digestive fluids, simulating saliva extraction and gastro-intestinal digestion(Guney and Zagury, 2013; Weidenhamer et al., 2011).
This study had some strengths and limitations. This study analyzed the adjusted association between children’s BLLs and the sampled toys’ materials using epidemiological investigation by strict stratification-random sampling, and compared the BLLs and the toys’ lead levels in overlapped investigation areas. Previous studies only measured toy lead levels or children’s BLLs. Few studies combined these two issues and analyzed the association between them, and fewer studies compared lead levels among toys with various materials. However, this study also had some limitations. First, within the same investigation districts in investigation 1 and 2, the comparisons of the BLLs and the toy lead levels were based on the hypothesis that children tended to buy toys from the supermarket/ toy-stores located in their own districts. Although online shopping was rare in 2013–2014 in China, it is still possible that, in some conditions, parents may buy toys from other districts other than the supermarkets/ toy-stores closest to their home in their own district. Second, in investigation 2, we didn’t measure the toy lead levels in all the 6 districts involved in investigation 1 where children’s BLLs were tested. It would be better if we could directly test the lead levels in toys used by the study children. However, the preliminary findings of this study also provided clues for the potential correlation of children’s BLLs and toy materials. Third, because this study was a cross-sectional investigation, the findings can only be implied that there may be a potential correlation of children’s BLLs with toy materials but not meaning causality. It needs prospective studies to further explore the cause-and-effect relationship between BLLs and toy materials. Fourth, although some important confounders such as some demographic characteristics and toy-biting behaviors were adjusted, other important potential confounders such as exposure to other sources of lead contaminations (battery manufacture or recycling, electronic waste, food cans, candies, cosmetics, traditional remedies, ceramic glazes, jewelry and others) were not considered.