What Exactly Is an Environmentally Relevant Dose?
The term "environmentally relevant dose" is commonly used to characterize the dose of a chemical that is given to laboratory animals in scientific studies. More specifically the term is used to signal that the results of the study are important.
But what does the phrase actually mean? Presumably it means that the dose given to laboratory animals is comparable (i.e., relevant) to the levels that people are actually exposed to from their environment (e.g., diet, drinking water, air).
In that light, a recent press release on a new study from Canadian researchers that referred to environmentally relevant doses of BPA is particularly puzzling. If the study was highlighted in a press release it must be important, right? But were the doses tested really relevant to actual human exposures?
If we know anything about Bisphenol-a (BPA), we know very well how much BPA people are exposed to in daily life. In a study published in 2017, Chinese researchers searched the scientific literature for all available studies that measured the level of BPA in human urine.
Because the human body quickly eliminates Bisphenol-a through urine after exposure, measuring BPA in urine is considered the best way to evaluate BPA exposure.
The researchers found "over 140 peer-reviewed publications, which contained over 85,000 data [points] for urinary BPA concentrations derived from 30 countries." In comparison to this large body of globally representative data, the two doses given to mice in the new study, which the authors described as "environmentally relevant," were approximately 1,000 and 1,000,000 times higher than typical human exposure.
More recently, the Canadian government released its fourth biennial report on exposure of the Canadian population to a variety of chemicals, including Bisphenol-a. Since typical exposure to BPA in Canada is lower than the global average, the Canadian researchers could not have been referring to environmentally relevant doses in Canada.
Not answered by the press release or the new study it highlighted is the most important question - are actual levels of human exposure to BPA safe or not? A resounding answer to that question was recently provided by the U.S. Food and Drug Administration after completion of its CLARITY BPA study. As stated by Dr. Stephen Ostroff, Deputy Commissioner for Foods and Veterinary Medicine at FDA: "our initial review supports our determination that currently authorized uses of BPA continue to be safe for consumers."
So what could account for the wide discrepancy between the "environmentally relevant" doses tested in the new study, and actual human exposure levels? Based on the extensive amount of available data, the doses in the new study are better characterized as environmentally irrelevant.