Table 2.

Key findings and study characteristics of studies on metal exposure.

First author (study year)	Toxicant	N	Age at toxicant measure	Toxicant measure	Age at MRI	MRI measure	Exposure main effect
Aschner et al. (2015)	Manganese	58	Newborn	Survey, medical and pharmacy records, blood sample	Newborn	T1R in globus pallidus, putamen	Greater parenteral nutrition and greater total Mn exposure associated with shorter T1R in globus pallidus and putamen. No association with whole blood Mn.
de Water et al. (2018)	Manganese	15	Prenatal	Blood sample	6.3 -7.6 years	Resting state functional connectivity with seeds in bilateral ACC, insula, MFG, superior parietal lobule, R and L globus pallidus	In children with higher prenatal Mn exposure, there was reduced R globus pallidus - dACC functional connectivity and a quadratic association between prenatal Mn and R globus pallidus-IFG connectivity. No other associations survived controlling for all covariates.
de Water, Papazahari as et al. (2019)	Manganese	14	Prenatal, early postnatal, and childhood	Deciduous teeth	12 – 18 years	Resting state functional connectivity with seeds in L and R putamen, L and R caudate, L and R pallidum, and bilateral MFG	Adolescents with higher early postnatal Mn exposure showed reduced functional connectivity between R putamen and L pre and post central gyri and increased bilateral MFG - L mPFC functional connectivity.
Dion et al. (2016)	Manganese	23	9- 15 years	Water sample from kitchen tap, questionnaire	9- 15 years	T1R in globus pallidus, standard PI, pericranial PI	High Mn group (vs. low Mn group) had lower signal intensity on the pericranial PI and longer T1R. No difference in standard PI.
Iannilli et al. (2016)	Manganese	14	N/A	Lifetime residency	14.65 years	Brain activation during olfactory stimulation task, olfactory bulb vol.	Whole brain task analysis: low Mn group had greater activation in secondary olfactory cortex, cerebellum, and SMA. ROI task analysis: low Mn group had greater activation in bilateral insula, R middle cingulate, and PCC. No association between Mn and olfactory bulb vol.
Karcher et al. (2021)	Lead	10,328	9-10 years	Geocoded lead risk	9-10 years	ICV, cortical GMV, subcortical GMV, total SA, total CT, hippocampa l vol	Lead risk associated with smaller ICV, subcortical GMV, cortical GMV, total SA, and total CT. Hippocampa l vol not associated with lead risk. Air pollution also assessed, but no analyses conducted with MRI measures.
Kim et al. (2018)	Lead	150	6 – 17 years	Blood sample	6 – 17 years	10-12 frontal lobe CT ROIs	No effect of lead on any ROI.
Lao et al. (2017)	Manganese	23	9-15 years	Water sample from kitchen tap	9-15 years	Basal ganglia vol. (caudate, putamen, globus pallidus) measured volumetrical ly and with mTBM	Using mTBM, high Mn group displayed larger L and bilateral putamen, but no difference when measured volumetrically.
Marshall et al. (2020)	Lead	9,712	9 – 10 years	Geocoded lead risk	9 – 10 years	Total CT, total SA,cortical vol.	No main effect of lead risk on any MRI measure.
Marshall et al. (2021)	Lead	8,524	9 – 10 years	Geocoded lead risk	9 – 10 years	Subcortical GMV, vol. of hippocampus, amygdala, cerebellum, brain stem, CC sub-regions, putamen, caudate, accumbens, pallidum, thalamus, ventricles	Lead risk associated with smaller CC in all sub-regions studied, except anterior CC. No other brain regions associated with lead risk.
Meng et al. (2005)	Lead	12	9 – 13 years	Blood sample	9 – 13 years	MRS voxel in L and R frontal lobe, L and R hippocampus (metabolites : NAA, Cr, Cho)	Peak of NAA, Cr, Cho lower in high lead group in all regions. For NAA, difference between high and low lead groups more pronounced in frontal lobe than hippocampus, and even more pronounced in R frontal lobe than L.
Trope et al. (2001)	Lead	21	Before age 5	Blood sample	8.75 years	MRS voxel in L prefrontal lobe (metabolites : NAA, Cr, Cho, ml).	The NAA/Cr ratio in the L prefrontal lobe was significantly lower in the high lead group.

Note. See notes following Table 9 for table notes and a comprehensive list of abbreviations.