Papers of the Month
By Sara Amolegbe
Fracking chemicals linked to breast tissue changes
Prenatal exposure to chemicals used in unconventional oil and gas (UOG) extraction, also known as fracking, altered mammary gland development in female mice, according to a new study by NIEHS grantees. The researchers saw effects from a mixture of 23 commonly used UOG chemicals at levels that were observed in drinking water in regions experiencing UOG operations.
Researchers added the UOG mixture or a control substance without UOG chemicals to the drinking water of pregnant mice. Chemical doses were equivalent to either concentrations measured in drinking water near drilling operations or measurements in industry wastewater. After the pups were born, the team analyzed the mammary tissue of females at two points in time — before puberty and in early adulthood.
The researchers reported striking changes in the morphology of the pups' mammary glands in early adulthood. In UOG-exposed mice, they saw structures resembling terminal end buds, which are mammary structures that are normally only found at puberty. The structures were not seen in the control mice. Further examination with tissue-level and immunohistochemical tools revealed ducts with excessive layers of epithelial cells that might have been precancerous. No changes were observed in the mice before puberty.
According to the authors, their results suggested that the mammary gland is sensitive to mixtures of chemicals currently used in UOG production, and more research is needed to examine the potential risk of breast cancer in women living near UOG operations.
Citation: Sapouckey SA, Kassotis CD, Nagel SC, Vandenberg LN. 2018. Prenatal exposure to unconventional oil and gas operation chemical mixtures altered mammary gland development in adult female mice. Endocrinology 159(3):1277–1289.
PFAS exposure linked to body weight regulation
A new study by NIEHS grantees suggested that exposure to perfluoroalkyl substances (PFASs) might make it harder to keep weight off after dieting. The researchers found that levels of PFASs in the blood were linked to greater weight gain in study participants who had recently shed pounds, especially women. People with higher blood levels of PFASs also had lower resting metabolic rates overall, meaning they burned fewer calories during normal daily activities.
The study authors used data from the two-year Preventing Overweight Using Novel Dietary Strategies Lost trial, a clinical trial in which overweight and obese individuals followed controlled weight reduction diets that restricted daily caloric intake. In the trial, weight loss generally occurred in the first 6 months, followed by 18 months of gradual weight regain.
As part of the study, five specific PFASs were measured in participants’ blood. Researchers observed that the higher the blood levels of PFASs, the more weight was gained back after the initial period of weight loss. Higher blood levels of these PFASs were also correlated with lower resting metabolic rates during the weight regain period.
Taking these two associations together, the researchers proposed that certain PFAS chemicals might contribute to weight gain by lowering the body’s resting metabolic rate, a novel pathway through which PFASs interfere with human body weight regulation.
Citation: Liu G, Dhana K, Furtado JD, Rood J, Zong G, Liang L, Qi L, Bray GA, DeJonge L, Coull B, Grandjean P, Sun Q. 2018. Perfluoroalkyl substances and changes in body weight and resting metabolic rate in response to weight-loss diets: a prospective study. PLoS Med 15(2):e1002502.
Toxin formed during oxidative water treatment process
Common water treatment methods that remove phenols and other hazardous compounds may produce low levels of toxic byproducts, according to a new study by NIEHS grantees. Phenols, which can contaminate drinking water, are often removed with a water treatment process that converts hydrogen peroxide into hydroxyl radicals using ultraviolet (UV) light. In this process, hydroxyl radicals oxidize the phenols, transforming them into other compounds.
Researchers evaluated the toxicity of these transformation products using a technique that assesses the formation of protein adducts, which can indicate disruption of protein structure or function in the body. They demonstrated that phenols can react with hydroxyl radicals to form toxic compounds known as enedials and oxoenals. Although this chemical reaction was previously observed in the gas phase, the authors wrote this was the first experimental evidence of the reaction occurring in water.
According to the authors, the results highlighted the potential risks of using oxidative treatment on contaminated drinking water sources, and the need to understand and address the fate of toxic byproducts throughout the water treatment process. They also showed that their technique could be used as a sensitive method to identify reactive products formed during oxidative water treatment.
Citation: Prasse C, For B, Nomura DK, Sedlak DL. 2018. Unexpected transformation of dissolved phenols to toxic dicarbonyls by hydroxyl radicals and UV light. Proc Natl Acad Sci U S A 115(10):2311–2316.
Legionnaires’ disease linked to Flint drinking water change
NIEHS grantees and colleagues found that an estimated 80 percent of Legionnaires’ disease cases that occurred during an outbreak in Genesee County, Michigan, could be attributed to the city of Flint’s drinking water supply being changed to the Flint River.
The researchers conducted a detailed statistical analysis of data on Legionnaires’ cases in the Michigan counties of Genesee, Wayne, and Oakland from 2011 to 2016. They determined that in 2014 and 2015, there was an increase in the risk of acquiring Legionnaires’ disease across the Flint water distribution system that was consistent with a system-wide proliferation of Legionella pneumophila bacteria. Based on their calculations, the researchers attributed an estimated 80 percent of Legionnaires’ cases during this period to the change in the water supply.
They found that the risk of a Flint resident having Legionnaires’ disease increased as the amount of free chlorine in their water decreased. The analysis also suggested that the 0.2 or 0.5 parts per million chlorine residual levels recommended by regulatory agencies might not be sufficient to protect communities from L. pneumophila exposure when water quality conditions support strong growth of the bacteria, which was the case in Flint during and immediately after the water change.
Citation: Zahran S, McElmurry SP, Kilgore PE, Mushinski D, Press J, Love NG, Sadler RC, Swanson MS. 2018. Assessment of the Legionnaires' disease outbreak in Flint, Michigan. Proc Natl Acad Sci U S A 115(8):E1730–E1739.