To the best of our knowledge, this study is the first in the city of Rio de Janeiro to investigate prenatal exposure to As, Cd, Pb and Hg and the neurodevelopment of children up to 6 months of age.
Maternal and umbilical cord blood geometric means for As were higher in the “fail” group for DDST-II in the six month, statistically significant for maternal blood. Some studies have investigated the effect of prenatal exposure to As on neurological infant development. Liang et al. (2020), in a prospective Chinese birth cohort study (Ma'anshan Birth Cohort-MABC) on 2315 six-month-old infants, observed associations between umbilical cord serum As concentration (median = 1.89 µg /L) and suspected developmental delay in the personal-social domain (Liang et al, 2020). Wang et al. (2018), in a cross-sectional study carried out in Shanghai (n = 892), observed that newborns with a low neonatal behavioral neurological assessment (NBNA) score exhibited higher concentrations (median, interquartile range) of umbilical cord As (3.93, 1.27–8.21 µg/L) than those with a high NBNA score (0.61, 0.23–1.50 µg/L). Tolins, Ruchirawat, & Landrigan, (2014), concluded in a review study that intrauterine exposure may be associated with neurodevelopment deficits, even at exposure levels below current safety guidelines (10 µg/L in drinking water), with manifestations detected only later in life. Those authors also observed that certain factors, such as sex, concomitant exposures and exposure time, modify developmental As neurotoxicity.
No associations between fails in the neurodevelopment domains and maternal or cord blood Cd, Pb, and Hg concentrations in our study population were observed. Nevertheless, in a systematic review study, Asmus et al (2016) reported a body of studies demonstrating associations between high child exposure to Hg in the Brazilian Amazon and poor neurobehavioral assessment results. Marques et al (2007, 2009), evaluated the neuromotor development of 82 six–month-old children, in the Brazilian Amazon and observed an inverse and significant correlation between hair Hg contents and neurodevelopment delay (r = -0.333; p = 0.002) (Marques et al, 2007; Marques et al, 2009; Asmus et al, 2016).
Birth conditions and nutritional status are known to interfere in child neurodevelopment (Halpern et al., 1996; Costa et al., 2015; Hirvonen et al., 2017; Allotey et al., 2018). Halpern et al. (1996), in a study carried out in the city of Pelotas, southern Brazil, with 1362 one-year-old children, observed the occurrence of neurodevelopmental failures through the application of the DDST-II, inversely associated with birth weight. Higher birth weights were observed herein in the “not fail” group, although not statistically significant.
We report herein a positive correlation between maternal age and Pb (0.29; p = 0.05) and Hg (0.34; p = 0.02) levels in umbilical cord blood (Table 2). Other studies have also reported that maternal age is associated with higher Pb and Hg levels in umbilical cord blood (Bjerregaar & Hansen, 2000; Arbuckle et al, 2016; Bocca et al, 2020; Hadavifar et al, 2020). This may be due to the accumulation of these metals in the body (Bocca et al, 2019). The higher Hg and Pb concentrations in umbilical cord compared to maternal blood can be attributed to increased glomerular filtration rates during pregnancy, resulting in higher renal elimination (Selevan, Kimmel & Mendola, 2000). A significant positive correlation was observed between As, Cd, Pb, and Hg concentrations in maternal and umbilical cord blood, as previously described by Figueiredo et al (2020).
The maternal and cord blood geometric means for Cd were higher in the non-white ethnic group, significant only for maternal blood. Some studies suggest that higher biological Cd levels may be associated to a more socioeconomically vulnerable population, including lower socioeconomic favored ethnicities (Lewin et al, 2017; Bulka et al 2019), as is the case of the non-white population in Brazil.
Associations between gestational age and metal concentrations has been investigated in many studies (Ettinger & Wengrovitz, 2010; Kumar et al, 2017; Ashrap et al 2020). In the present assessment, maternal blood Pb concentrations were significantly higher in preterm children (gestational age > 34 weeks and < 37 weeks). No associations were observed between maternal or cord blood As concentrations and gestational age.
No significant associations were observed between mother age, income, education, ethnicity or tobacco or alcohol use and the “fail” and “not fail” groups. The differences between the results reported herein and other studies may be due to sample size, metal concentrations, the type of test used to assess neurodevelopment and the influence of sociodemographic factors and lifestyle (Bellinger, 2009). The long-term development of the investigated children may alter the results, as other areas of child development will be better analyzed with a longer observation time.
A limitation of this study comprises the individual analysis of each metal without considering their potential interactions and the small number of participants. Despite this, these findings provide information on environmental prenatal exposure to metals and potentially adverse neurodevelopment effects on newborns, encompassing sociodemographic and lifestyle data.