Table 6.
Summary of studies addressing co-occurring exposures to neurotoxicants and their effects on neurobehavioral tests in infants (adapted and expanded from Dórea 2017a,b).
| Neurotoxic Agents | Aim of study: | Neuro-behavioral Tests (age): Outcomes | Reference (Country) |
|---|---|---|---|
| MeHg; EtHg | To compare the effect of time Hepatitis-B shots (<24h or >24hs after birth) on neurodevelopment. | Gesell Developmental Schedules (6 months): Infants immunized 2–4 days after delivery showed no significant difference in neurodevelopment compared to the group immunized within 24 h. | Marques et al. 2007 (Brazil) |
| MeHg; EtHg | To use Principal Component Analysis as a screening of variables linked to pre- and post-natal Hg exposure. | Gesell Developmental Schedules (6 months): Principal Component Analysis discriminated variability of neurodevelopment outcomes associated with variables that included pre- and post-natal Hg exposure. | Marques et al. 2008 (Brazil) |
| Hg2+; MeHg; EtHg | To evaluate the association between infant Hg and Gesell Developmental Schedules. | Gesell Developmental Schedules (6, 36, 60 months): Length of lactation was positively correlated with GDS scores and hair-Hg concentrations were negatively correlated with Gesell Developmental Schedules scores. | Marques et al. 2009 (Brazil) |
| MeHg; EtHg | To study the neurodevelopment of infants exposed to thimerosal in tetanus-diphtheria vaccines during pregnancy. | Gesell Developmental Schedules (6 months): No difference was observed. | Marques et al. 2010 (Brazil) |
| PCB; MeHg | To study a birth cohort to clarify the effects of PCB and MeHg on infants’ neurodevelopment. | Neonatal Behavioral Assessment Scale (3days): MeHg adversely affects neurobehavioral function. | Suzuki et al. 2010 (Japan) |
| MeHg; EtHg | To compare Hg effects on neurodevelopment of infants from one urban center and two rural villages. | Gesell Developmental Schedules (6 months): A higher score of neuro-development was negatively associated with exposure to additional TCV-EtHg in urban infants. | Dórea et al. 2012 (Brazil) |
| PCB; MeHg; Pb | To examine the effects of prenatal exposure to PCBs, MeHg, and Pb on cognitive development infants. | Fagan Test of Infant Intelligence; A-not-B test; Bayley Scales of Infant Development–2nd Edition (6.5 and 11 months): Outcomes of impairment in specific domains were different for the tested neurotoxicants; Hg was associated with poorer performance on A-not-B test. | Boucher et al. 2014 (Canada) |
| MeHg; EtHg; Pb; Al | To study the neurodevelopment of children living in the vicinity of tin-ore kilns and smelters and of children living in a fishing village. | Bayley Scales of Infant Development–2nd Edition (6 and 24 months): Mental Development Index and Psychomotor Development Index were lower at 24 months of age for children living in the vicinity of tin-ore kilns and smelters. | Marques et al. 2014 (Brazil) |
| MeHg; EtHg | To study Hg exposure and neurodevelopment in children from a tin-ore open-pit mine. | Bayley Scales of Infant Development–2nd Edition (6 and 24 months): There was a significant sex difference with boys showing more sensitivity related to Bayley Scales of Infant Development–2nd Edition delays and Thimerosal-containing vaccines. | Marques et al. 2015 (Brazil) |
| MeHg; EtHg | To study neurodevelopment of children in relation to prolonged breastfeeding and Hg exposure. | Bayley Scales of Infant Development–2nd Edition (6 and 24 months): MeHg and EtHg exposure did not show a significant dose effect (related to the length of breastfeeding) on neurodevelopment among groups. | Marques et al. 2016b (Brazil) |
| MeHg; EtHg | To study neurodevelopment of children exposed to MeHg and EtHg. | Bayley Scales of Infant Development–2nd Edition (6 and 24 months): There was a significant delay in Bayley Scales of Infant Development related to the combined exposure to Hg. | Marques et al. 2016a (Brazil) |
EtHg: ethylmercury; MeHg: methylmercury; PCBs: polychlorinated biphenyls; TCV: Thimerosal-containing vaccines