Exposure to uranium and co-occurring metals among pregnant Navajo women

Abstract

Navajo Nation residents are at risk for exposure to uranium and other co-occurring metals found in abandoned mine waste. The Navajo Birth Cohort Study (NBCS) was initiated in 2010 to address community concerns regarding the impact of chronic environmental exposure to metals on pregnancy and birth outcomes. The objectives of this paper were to 1) evaluate maternal urine concentrations of key metals at enrollment and delivery from a pregnancy cohort; and 2) compare the NBCS to the US general population by comparing representative summary statistical values. Pregnant Navajo women (N = 783, age range 14-45 years) were recruited from hospital facilities on the Navajo Nation during prenatal visits and urine samples were collected by trained staff in pre-screened containers. The U.S. Centers for Disease Control and Prevention (CDC), National Center for Environmental Health's (NCEH) Division of Laboratory Sciences (DLS) analyzed urine samples for metals. Creatinine-corrected urine concentrations of cadmium decreased between enrollment (1st or 2nd trimester) and delivery (3rd trimester) while urine uranium concentrations were not observed to change. Median and 95th percentile values of maternal NBCS urine concentrations of uranium, manganese, cadmium, and lead exceeded respective percentiles for National Health and Nutrition Evaluation Survey (NHANES) percentiles for women (ages 14-45 either pregnant or not pregnant.) Median NBCS maternal urine uranium concentrations were 2.67 (enrollment) and 2.8 (delivery) times greater than the NHANES median concentration, indicating that pregnant Navajo women are exposed to metal mixtures and have higher uranium exposure compared to NHANES data for women. This demonstrates support for community concerns about uranium exposure and suggests a need for additional analyses to evaluate the impact of maternal metal mixtures exposure on birth outcomes.

Keywords: Maternal biomonitoring; Metal mixtures; Metals; Navajo birth cohort study; Uranium; Urine.

Figure 1.

Study area map illustrating the location of abandoned uranium mines (red X), Navajo Nation boundaries and the location of enrollment facilities.

Figure 2 –

Summary of surveys and biomonitoring samples selected for analysis

Figure 3.

Bean plot illustrating the distribution and median concentration for urine creatinine-corrected metal concentrations, stratified by enrollment (during 1^st or 2^nd trimester) and delivery (collected after 36 weeks gestational age or when a pregnant mother was admitted to the hospital for labor). Reference population (NHANES) median concentrations are plotted as a dashed line for each metal.

Figure 4.

Correlation heat maps for seven metals at enrollment (1^st or 2^nd trimester) and delivery. Units are μg/g-creatinine. An * indicates a p-value <0.05.