**4. Discussion**

In the present study, we examined environmental exposure to Pb among 3–7 years old children, living in Pakpoon suburb, Nakhon Si Thammarat Province. The study children were randomly selected from a fishing community, where repair boatyards were located (Figure 2). The results showed that blood Pb levels ranged from 0.03 to 26.40 μg/dL. Although the average blood Pb level of 2.81 μg/dL was below the level of concern of ≥ 5 μg/dL, set by the CDC [17], 11.9% of children had elevated blood

Pb levels ≥ 5 μg/dL. The blood Pb levels recorded for children in the present study appeared to be lower than the levels found in children living in fishing communities in the Tasajera and South Africa. Blood Pb levels in children in Tasajera, Colombian Caribbean coast, ranged from 0.4 to 50.1 μg/dL with 57.1% of study children having blood Pb levels ≥ 5 μg/dL [8]. Blood Pb levels in children of fishing communities in South Africa ranged from 2.2 to 22.4 μg/dL with 74% of study children having blood Pb levels > 5 μg/dL [12]. The 4.8 and 6.2 times higher percentages of high blood Pb in South Africa and Tasajera study might be due to different Pb exposure sources. The South Africa and Tasajera studies both found that living near a lead smelting area was strongly associated with children's high blood Pb levels [8,12]. In contrast, there was no melting of Pb weights in the process of making fishing nets in this Thai study.

**Figure 2.** Boatyards, girls and working-at-home mothers, and a fishing net with lead weights. A total of 311 children were randomly selected from a fishing community in Pakpoon suburb, where repair boatyards existed (**A**,**B**). Girls were nearby while mothers were assembling lead weights to produce fishing nets (**C**). Approximately 180 lead weights are used to make a two-kg fishing net (**D**).

In the present study, we found that parent occupation involving lead weights was associated with 17.54 fold increase in risk of high blood Pb levels in children (*p* < 0.001). This might be attributable to environmental exposure via household Pb dust, water, and food contamination [20] from lead weights used in making fishing nets at home (Figure 2). However, living close to repair boatyards was not associated with high blood Pb levels (*p* = 0.872). Of note, blood Pb levels in both boys and girls of parents producing fishing nets were 2.3 and 2.5 times higher than similarly aged boys and girls of parents with other occupations (*p* < 0.001 for boys and girls). These data confirmed parents' occupation as a strong determinant of blood Pb levels. The levels of Pb in dust, water, and food contamination in the households that used lead weights require a further study. Blood Pb levels in mothers should also be investigated since Pb is readily transported through the placenta.

A child's milk consumption was associated with a 61% reduction in the risk for high blood Pb (*p* = 0.034) and a 43% reduction in the risk of having abnormal growth (*p* = 0.040). Milk has been reported to be a protective factor against Pb toxicity both in humans and experimental animals [21–24]. In an animal study, blood Pb levels decreased in lead-treated mice after nine weeks of daily milk intake. It is suggested that Pb absorption in gastrointestinal tract is reduced by the high calcium levels in milk, and that Pb absorption is enhanced by calcium deficiency [22,23]. In a longitudinal cohort study of children, aged 6–31 months [25], blood Pb levels were negatively correlated with calcium, magnesium, nickel, and zinc. It can be inferred that consumption of food rich in calcium and zinc can reduce Pb absorption. Another possible protective mechanism of milk might be due to organic substances that chelate Pb, thereby reducing Pb absorption and enhancing Pb excretion [21]. The synergism between Pb exposure levels and a lack of milk consumption is unknown. The present study indicated that milk is one of the factors that reduced the risk of high blood Pb levels in children. A quantitative study on milk intake is required.

Potential adverse e ffects of high blood Pb on children's growth was observed; high blood Pb was associated with 2.04 fold increase in the POR for abnormal growth (*p* = 0.050), while seafood consumption was associated with a 1.71 fold increase in the POR for abnormal growth (*p* = 0.036). Likewise, blood Pb and seafood consumption were associated with decreased growth rates in other studies [25,26]. A negative e ffect of Pb on children's growth may involve disruption of the endocrine system, causing circulating levels of insulin-like growth factor 1 to fall [27]. Pb may a ffect osteoblast and osteoclast development via 1, 25-dihydroxyvitamin D3 [28,29]. Exposure to Pb during childhood could a ffect growth in adolescents and adults. This was observed in a longitudinal study in Russia, where children with blood Pb levels ≥5 μg/dL showed the most height decrease at 12–15 years of age [30]. An association between seafood consumption and abnormal growth may be attributable to methymercury in seafood [31]. Thus, children with abnormal growth rates should be monitored. Further information should be sought to identify specific types of seafood and frequencies of consumption.

Interestingly, an e ffect of Pb on BMI increase was seen in girls only. This is a new finding. Gender-specific neurological e ffects of Pb have been seen in prenatal and preschool age exposure conditions [32–34]. Such gender specific e ffects of Pb may be caused by gene-specific DNA methylation patterns in the brain [33]. The gender-specific di fference in BMI needs confirmation. Nevertheless, the association seen between children BMI and parent occupation could be used in growth prediction and obesity prevention programs in children.

In conclusion, the present study provided baseline data on environmental Pb exposure levels experienced by boys and girls, aged 3–7 years together with factors associated with the high blood Pb levels. These data are useful in setting Pb surveillance and Pb toxicity mitigation programs for children of fishing communities. Aspects of environmental Pb contamination need a further investigation. A Pb primary prevention program should be implemented in conjunction with a nutritional promotion campaign.

**Author Contributions:** S.Y. designed the study protocol, obtained an approval from the O ffice of the Human Research Ethics Committee of Walailak University, and supervised the collection of demographic data and biologic specimens; S.Y., D.W. and S.K organized and analyzed the data, created the tables and figures, and revised the manuscript.

**Funding:** This research was funded by National Science and Technology Development Agency (NSTDA), Ministry of Science and Technology, Thailand, gran<sup>t</sup> number FDA-CO-2559-1183-74. The APC was funded by Walailak University.

**Acknowledgments:**This work was cooperated with by the Pakpoon Health Promoting Hospital, PakpoonMunicipality, Nakhon Si Thammarat, Thailand. We thank Steve Nazar and George Kruzynski for editing the English. We also thanks Tanaporn Khamphaya for graphic design.

**Conflicts of Interest:** The authors have no potential conflicts of interest to declare.
