Noted toxicologist Laura C. Green, Ph.d., recent addressed the recently reported “Yale Study” from Connecticut non-profit group Environment and Human Health, Inc (EHHI)
Comments on the EHHI/Yale study
For many reasons, the EHHI/Yale study does not demonstrate that rubber mulch or crumb rubber pose a significant risk of cancer (or other diseases).
First, the study has not been published (or released in any complete form) nor, to my knowledge, has it been peer reviewed. In fact, contrary to the press release, the study does not appear to have been written up in even an unpublished manuscript. At my request, Nancy Alderman of EHH was kind enough to supply me with a summary of some of the methods and a spreadsheet of the results to date: I have attached these materials to this memorandum.
Second, as far as I can tell, the summary results presented are entirely non-quantitative: there is no indication of the concentrations of any of the detected chemicals, let alone is there any attempt to assess levels of exposure or doses potentially received by children or others playing on or near rubber mulch or crumb rubber. Accordingly, there is no way to judge the degree to which any such exposures might be risky. Since all of us eat, drink, and otherwise contact at least trace levels of many carcinogens daily, it is crucial to be quantitative when assessing cancer-risks (and then acting upon those assessments). Absent at least semi-quantitative estimates of risk, informed judgments simply cannot be made.
Third, to the summary of the study‐methods, the chemicals were detected in methylene chloride extracts of a mixture of ground and ungrounded crumb rubber or rubber mulch — but methylene chloride extraction is not a relevant or reliable means of assessing how rubber mulch in playgrounds might become solubilized or otherwise release chemicals that could then be absorbed across a child’s skin, for example, or across a child’s digestive tract (were he or she to ingest some rubber). For purposes of human health risk assessment, instead of using a non-biological solvent such as methylene chloride, one should use simulated sweat or simulated gastric fluid, as used in the published, peer–‐reviewed study by Pavilonis et al., 2014, for example, cited above.
Fourth, EHHI reports that eight of the chemicals detected in the methylene chloride extracts of at least one of the nine samples of mulch are “probable carcinogens” (there were another five samples of “infill” that are not considered here) — but none of these eight chemicals is so categorized by authoritative bodies, such as the International Agency for Research on Cancer (IARC), the U.S. National Toxicology Program (NTP), or the U.S. Environmental Protection Agency (EPA). Moreover, not one of the putative “probable carcinogens” is consistently detected in the samples of mulch.
For example, EHHI lists pyrene (detected in seven of the nine samples) as a carcinogen, but no rodent bioassays of pyrene are in fact positive; and, per U.S. EPA, “Overall, the database for pyrene is substantial, and the weight of evidence suggests that this PAH is not carcinogenic” (EPA–‐635–‐R–‐08–‐012A). Not surprisingly, then, neither IARC nor NTP lists pyrene as either known or a probable human carcinogen (See Here). Similarly, EHHI lists heptadecane (detected in one of the samples) as a carcinogen, but no rodent bioassays indicate that heptadecane is carcinogenic, and it is not listed as a carcinogen by either IARC or NTP. EHHI lists phthalamide as a carcinogen, but the NTP bioassays for phthalamide yielded negative results in male and female rats and mice, and it is not listed as a carcinogen by either IARC or NTP.
And EHHI lists 9,10–‐dimethylanthracene, fluoranthene, phenanthrene, 4–‐(1,1,3,3–‐ tetramethylbutyl)–‐phenol, and 1–‐methylpyrene as carcinogens; but, again not one of these five chemicals is listed as a carcinogen by either IARC or NTP.
Finally, I would note that the chemicals butadiene and benzene were not detected in this EHHI/Yale study. Recall that these two chemicals are indeed established causes of cancer in humans, and that EHHI had hypothesized that both are present — and presumably bioavailable — at significant concentrations in crumb rubber and rubber mulch. I would add that the elevated temperatures used to dry and to analyze the samples would likely have obscured the presence of either compound, but it remains the case that the causal hypothesis raised by EHHI has yet to be supported by actual data or other reliable evidence.