Researchers at Johns Hopkins found evidence of rises in the bloodstream levels of toxicants known to be stored long term in fat, including PCBs & organochlorine pesticides.
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Paper: https://onlinelibrary.wiley.com/doi/10.1002/oby.22618
Brown, R.H., Ng, D.K., Steele, K., Schweitzer, M. and Groopman, J.D. (2019), Mobilization of Environmental Toxicants Following Bariatric Surgery. Obesity, 27: 1865-1873. https://doi.org/10.1002/oby.22618