CEHN Articles of the Month, March 2015 Issue
Maternal Arsenic Exposure, Arsenic Methylation Efficiency, & Birth Outcomes in the Biomarkers of Exposure to Arsenic (BEAR) Pregnancy Cohort in Mexico
Authors: Jessica E. Laine, Kathryn A. Bailey, Marisela Rubio-Andrade, Andrew F. Olshan, Lisa Smeester, Zuzana Drobná, Amy H. Herring, Miroslav Stýblo, Gonzalo G. García-Vargas, Rebecca C. Fry
Arsenic is a naturally occurring substance, with two forms: inorganic (not produced by living things) and organic (produced by living things). Organic arsenic is not known to be significantly toxic to humans, and is most commonly ingested through seafood. Inorganic arsenic, however, has been shown to cause both serious acute and chronic health issues. Inorganic arsenic (iA) is naturally present in our environment, coming from the Earth’s crust, as well as unnaturally present due to mining, industry, and agriculture. It is found in the soil, groundwater, and air. Several countries have naturally occurring high levels of iA in their soils, including Argentina, Bangladesh, India, Mexico, and the United States.
Many people worldwide are exposed to very high levels of iA through drinking water, and a growing concern in the US is iA-contaminated food. Inorganic arsenic finds its way into foods through naturally contaminated soils and from unnatural soil-contaminating sources, like pesticides, fertilizers, and industrial activities. Some foods of concern are apple and grape juices, and rice and rice products. The latter two are especially worrisome due to the tendency of the rice plant to absorb 10 times more arsenic than other grain crops. Moreover, for many Americans, rice is an important staple in their diet, and additionally, many parents serve rice cereal to infants as a first food. It is also important to note that because the tobacco plant readily absorbs iA from the soil, smoking is another route of exposure to iA.
Women and unborn and born children are considered among the most susceptible to iA exposure, due to their physiological differences in comparison to other individuals in the population. For example, metabolic changes in pregnant women may make them more prone to inefficient processing of iA in the body. Previous studies indicate that individuals exposed to iA, either prenatally or in early childhood, are at risk of cancer and other adverse health outcomes later in life. In addition, some studies indicate that pregnant women who are exposed to iA risk preterm birth, low birth weight, and loss of the fetus. However, more research is needed to confirm the links between maternal altered metabolism, higher iA exposure, and maternal/fetal health.
The BEAR study authors aimed to better understand the effects of iA on pregnant women and their children. Specifically, the authors aimed to monitor the presence of certain metabolites, which are substances produced from metabolism, in the urine of expectant mothers. The metabolites of interest were MMAs and DMAs, which are indicative of iA exposure. The connection of these metabolites to adverse birth outcomes in the newborns of these women was examined. The authors also intended to characterize the extent of iA exposure in pregnant women in Gómez Palacio, Mexico.
200 pregnant women, ages 18-41, were recruited for the BEAR study at the General Hospital of Gómez Palacio in northern Mexico between August 2011 and March 2012. To qualify, the women had to: have lived in Gómez Palacio and its surrounding rural areas for at least one year; exhibit no disease nor pregnancy complications; and not be pregnant with multiple babies. The women were recruited, and their medical histories and urine samples taken, within 24 hours prior to the birth of their children.
The following birth outcome measures were recorded: preterm birth (less than 37 weeks), low birth weight (less than 2, 500 g or 5 lbs 6 oz), less than 10th percentile birth weight, and more than 90th percentile birth weight. All comparison data was acquired in northern Mexico. Drinking water samples for each mother were collected within 4 weeks of delivery. Inorganic arsenic concentrations were measured in the drinking water samples, and metabolite concentrations were measured in the urine samples.
The average concentration of iA in the drinking water tested in the study was 24.6 μg As/L. Women who used municipal drinking water were exposed to much higher levels of iA: the mean iA concentration in municipal water was 23.3 μg As/L, compared to a mean of 0.40 μg As/L of non-municipal water. Approximately 53% of the women in the study were using drinking water that exceeded the World Health Organization’s (WHO) inorganic arsenic concentration standard for drinking water of 10 μg As/L.
The authors’ findings confirmed that presence of iA in drinking water was significantly associated with presence of iA metabolites in urine. Women who used municipal water had a mean metabolite concentration of 49.5 μg As/L in their urine versus a mean of 22.9 μg As/L for women who did not use municipal water.
MMA levels were found to have a significant negative association with newborn weight and gestational age. DMAs were not found to have significant associations with birth outcomes.
The pregnant women of Gómez Palacio were exposed to potentially harmful levels of iA through municipal drinking water, and iA metabolites in the bodies of pregnant mothers, especially MMAs, are related to negative birth outcomes in their babies, namely with regard to weight and gestational age.
Whereas municipal water suppliers in the United States (US) are required to meet the U.S. Environmental Protection Agency’s (EPA) safety standard of 10 μg As/L for arsenic in drinking water, no such regulation exists for private wells. Approximately 13 million people, nationwide, get drinking water from private wells with arsenic levels above the federal standard. Sufficient funding is necessary for public health awareness initiatives to educate target populations about testing their private wells.
There is currently no iA concentration limit enforced for food in the US. The Environmental Working Group (EWG) calls for consumer awareness of arsenic-containing foods and a legally enforced maximum level of arsenic for foods set by the U.S. Food and Drug Administration (FDA). EWG also encourages the FDA to mandate that the food industry must find alternatives for rice syrup, bran, and flour in processed foods. Consumers Union urges: the EPA to phase out arsenic-containing pesticides; the U.S. Department of Agriculture (USDA) and EPA to cease the use of arsenic-containing manure as fertilizer; and the FDA to ban the use of all arsenic containing drugs for animals.
Continued research on iA contamination of food and the long-term effects of early-life exposure to iA should be supported, as should research on techniques and technologies that could reduce the amount of arsenic uptake by plants like rice.