Prenatal Metal Mixtures and Birth Weight for Gestational Age in a Predominately Lower-Income Hispanic Pregnancy Cohort in Los Angeles

Abstract

BACKGROUND: Reduced fetal growth increases the risk for adverse health outcomes. Growing evidence suggests that metal exposures contribute to reduced fetal growth, but little is known about the effects of complex metal mixtures. OBJECTIVES: We investigated the impact of a complex mixture of metals on birth weight for gestational age (BW for GA) in the Maternal and Developmental Risks from Environmental and Social Stressors study, a predominately lower-income Hispanic pregnancy cohort in Los Angeles, California. METHODS: Cadmium (Cd), cobalt (Co), mercury (Hg), nickel (Ni), molybdenum (Mo), lead (Pb), antimony (Sb), tin (Sn), and thallium (Tl) were measured by inductively coupled plasma mass spectrometry (ICP-MS) in maternal urine samples collected in early pregnancy (median GA: 13.1 wk). Speciated urinary arsenic (As) (inorganic+monomethyl+dimethyl As) was measured by high-performance liquid chromatography coupled to ICP-MS. Primary analyses focused on a mixture of seven metals that have previously been associated individually with fetal growth (i.e., As, Cd, Co, Hg, Ni, Pb, Tl) (n = 262). In exploratory analyses, we additionally examined three metals that have been less studied in relation to fetal growth (i.e., Mo, Sb, Sn). Covariate-adjusted Bayesian kernel machine regression was used to investigate metal mixture associations with BW for GA z-scores. RESULTS: In primary analyses, Hg and Ni ranked highest as predictors of BW for GA. An inverse linear association was estimated for Hg, whereas a positive association was estimated for Ni at low-to-moderate concentrations. A potential interaction between Hg and Ni was also identified. In our exploratory analysis, Sb ranked highest as a predictor of BW for GA, followed by Hg and Ni. CONCLUSIONS: Our findings suggest that in this understudied population, Hg may reduce fetal growth, whereas Ni may promote fetal growth. We also identified Sb as a potential metal of concern for this population, which merits additional investigation.

Mercury and Prenatal Growth: A Systematic Review

“…Many studies reported more than one primary effect estimate: a total of 49 results were reported across the 27 studies. A total of 33 estimates from 22 studies reported no evidence of an association [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ]. Evidence of an inverse association between mercury and birth weight was found in 16 estimates from 11 studies [ 25 , 34 , 36 , 37 , 40 , 41 , 45 , 46 , 47 , 48 , 49 ] and possible patterns between studies that may explain these findings will be explored in the following paragraphs.…”

“…The first group of results included investigations of mercury concentrations using whole blood or urine during the first trimester [ 28 , 35 , 37 , 41 , 49 ]. Three prospective studies of pregnancies in South Korea [ 37 ], fishing areas of the USA [ 28 ], and Los Angeles, USA [ 35 ] each found no evidence of an association with birthweight.…”

“…The first group of results included investigations of mercury concentrations using whole blood or urine during the first trimester [ 28 , 35 , 37 , 41 , 49 ]. Three prospective studies of pregnancies in South Korea [ 37 ], fishing areas of the USA [ 28 ], and Los Angeles, USA [ 35 ] each found no evidence of an association with birthweight. A UK-based cohort study reported similar results from mothers who consumed fish, but a negative association in mothers with diets lacking fish (−57 g per μg Hg/L, CI: −112.5 to −1.5) [ 41 ].…”

Invited Perspective: Metal Mixtures and Child Health: The Complex Interplay of Essential and Toxic Elements

“…We have certainly known for decades that nutritional status can affect the toxicity of some pollutants (Mahaffey and Vanderveen 1979). Other examples of interactions between trace elements and metals related to a variety of child health outcomes also are beginning to emerge (Howe et al 2020a(Howe et al , 2020b(Howe et al , 2021Liu et al 2018). However, in many of these cases, the results suggest that the positive association between the trace element and these outcomes may be attenuated at higher levels of the toxic metal.…”

“…We have certainly known for decades that nutritional status can affect the toxicity of some pollutants ( Mahaffey and Vanderveen 1979 ). Other examples of interactions between trace elements and metals related to a variety of child health outcomes also are beginning to emerge ( Howe et al. 2020a , 2020b , 2021 ; Liu et al.…”