Abstract

Unconventional oil and gas operations (UOG), which combine hydraulic fracturing (fracking) and directional drilling, involve the use of hundreds of chemicals including many with endocrine disrupting properties. Two previous studies examined mice exposed during early development to a 23-chemical mixture of UOG compounds (UOG-MIX) commonly used or produced in the process. Both male and female offspring exposed prenatally to one or more doses of UOG-MIX displayed alterations to endocrine organ function and serum hormone concentrations. We hypothesized that prenatal UOG-MIX exposures would similarly disrupt development of the mouse mammary gland. Female C57Bl/6 mice were exposed to approximately 3, 30, 300 or 3000 μg/kg/day UOG-MIX from gestational day 11 to birth. Although no effects were observed on the mammary glands of these females prior to puberty, in early adulthood, females exposed to 300 or 3000 μg/kg/day UOG-MIX developed more dense mammary epithelial ducts; females exposed to 3 μg/kg/day UOG-MIX had an altered ratio of apoptosis to proliferation in the mammary epithelium. Furthermore, adult females from all UOG-MIX-treated groups developed intraductal hyperplasia that resembled terminal end buds, i.e., highly proliferative structures typically seen at puberty. These results suggest that the mammary gland is sensitive to mixtures of chemicals used in unconventional oil and gas production, at exposure levels that are environmentally relevant. The impact of these findings on the long-term health of the mammary gland, including its lactational capacity and its risk of cancer, should be evaluated in future studies.

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