In the June 11, 2016, edition of the Canada Gazette, Canada’s Department of the Environment and Department of Health published a notice of the availability for public comment two documents concerning coal tars and their distillates: (1) a Draft Screening Assessment (DSA) and (2) a Risk Management Scope (RMS). These documents are mostly focused on coal tars and distillates in industrial settings, but also contain draft screening assessments based on the scientifically problematic information about refined coal tar-based pavement sealant (RTS) that PCTC is far too familiar with. For this reason, PCTC submitted comments on the documents. The comment document is available here.
The DSA included assessments of potential risks to human health based on three scenarios involving possible exposure to RTS. One scenario used data from the problematic USGS study of PAHs in house dust. PCTC believes the house dust data in the USGS study to be of insufficient quality to inform risk assessment or provide a basis for risk management regulation. Nevertheless, these data were used to calculate a Margin of Exposure (MOE) using a value known as a “BMDL10” developed for benzo(a)pyrene by Health Canada, for residents exposed to PAHs in house dust at the levels suggested in the USGS paper. Canada’s DSA reports a “lifetime adjusted MOE” (that is, making appropriate allowances for different age groups) = 15,500.
What does an MOE = 15,500 mean? In its comments, PCTC explains how MOE values are used around the world:
The United Nations World Health Organization Joint Expert Committee on Food Additives (WHO JECFA), the Scientific Committee of the European Food Safety Agency (EFSA, 2005), and the UK Committee on Carcinogenicity (2012) recommend use of MOE > 10,000 as an indicator of low concern for public health….From a real-world perspective, use of an MOE > 10,000 as an indicator of a low level of concern can be viewed as a precautionary approach, adopted by some regulatory agencies out of an abundance of caution.
The Scientific Committee of the European Food Safety Agency (EFSA) says this:
The Scientific Committee is of the view that in general a margin of exposure of 10,000 or higher, if it is based on the BMDL10 from an animal study, and taking into account overall uncertainties in the interpretation, would be of low concern from a public health point of view and might be reasonably considered as a low priority for risk management actions.
The US National Library of Medicine has posted a table explaining what MOE values mean on its web site. MOEs calculated for a few of the common products listed in the table are (click on the table to make it bigger):
Canada’s MOE calculation and its additional findings that exposures during application as well as short duration exposures are unlikely to be a threat to public health emphasizes the point PCTC has been making all along.
PCTC’s comments also weigh in on the ecological assessments summarized in the DSA. Again, the comments are posted here.