Fracking Chemicals May Alter Mammary Gland Development, Animal Study Finds

Chemicals used in unconventional oil and gas (UOG) operations – fracking and directional drilling – may alter mammary gland development, according to a study recently published in Endocrinology.

The study, led by Susan Nagel, PhD, of the University of Missouri, and Laura N. Vandenberg, PhD, of the University of Massachusetts, is yet another indictment of endocrine disrupting chemicals, especially those used in UOG operations. The researchers point out that more than 1,000 chemicals have been identified in fracking fluids and waste water and/or have been reported to be used by the industry. “Many of these chemicals are known developmental and reproductive toxicants,” the authors write. “Furthermore, recent evaluations found that >100 of these chemicals are known or suspected [EDCs] and water samples collected in drilling-dense or UOG wastewater-affected areas of the United States have exhibited disruption of the estrogen, androgen, progesterone, glucocorticoid, and thyroid receptors.”

Two previous studies exposed mice to a 23-chemical mixture of UOG compounds (UOG-MIX) that are commonly used in these operations. In those studies, the mice displayed altered endocrine organ function and serum hormone concentrations. In the first study, male mice exposed to environmentally relevant doses of UOG-MIX showed decreased sperm counts, increased serum testosterone concentrations, and alterations to the weight of organs like the heart and thymus. In the second study, the researchers evaluated the female siblings and found that these mice had alterations to number and developmental stages of ovarian follicles. The mice also had alterations to the weight of several organs, including the uterus, ovary, and heart.

The researchers hypothesized that UOG chemicals would similarly disrupt the mice’s mammary gland development, since, as the authors write, the mammary gland is a hormone-sensitive organ that is responsive to multiple endocrine inputs during early development. They exposed female mice to varying doses (3; 30; 300; 3,000 μg/kg/d) of UOG-MIX from gestational day 11 to birth. The mice showed no effects on mammary gland development before puberty, but the mice exposed to the 300 or 3,000 μg/kg/d doses of UOG-MIX developed more dense mammary gland epithelial ducts. Females exposed to the lowest dose had an altered ratio of apoptosis to proliferation in the mammary epithelium. “Furthermore,” the authors write, “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).”

The authors conclude that these results suggest that the mammary gland is sensitive to mixtures of chemicals used in UOG production at exposure levels that are environmentally relevant. They go on to write that the evidence for an association between UOG operations and breast cancer is inadequate and that these results suggest that further studies are needed to address this gap. “Future studies are needed to evaluate the many additional chemicals used in, and produced by, UOG processes to better quantify the concentrations of these and other contaminants in environmental samples and to assess the effects of exposure during other sensitive windows of development, including pregnancy and lactation, puberty, and the aging female,” the authors write.

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