Polycyclic aromatic hydrocarbons (PAHs) are thought to account for about 20% of the carbon in the universe (see here, here, and here) and are considered building blocks of life. On Earth, PAHs occur in organic matter, including fossil organic matter (oil, coal), and are constantly being made when organic matter is heated or decays. They are also constantly being destroyed – eaten by microorganisms, degraded by the sun, other natural processes.
PAHs cause headaches for both regulators and the regulated. The headaches are rooted, in part, in history, so this post is a brief introduction to the history of PAHs in the environment, with an example of a regulatory headache exacerbated by government scientists who misrepresented historical data.
Generally speaking, no one makes PAHs on purpose – they are just part of the raw materials and byproducts of modern life. In addition to being present in oil and coal, PAHs are made in wood-burning fireplaces and stoves, in engine lubricants, in compost heaps, in decaying plants in a swamp… wherever organic matter is heated. Thus, humans are now and have, since fire was tamed, been exposed to PAHs. As one researcher put it: Continue reading →
Posted by Anne LeHuray, October 11, 2015
In a rare win for science, the subscription news service Chemical Watch reports that
The European General Court has annulled part of the mandatory classification of the substance CTPHT [coal tar pitch, high temperature], following an appeal by 18 companies.
Its ruling means CTPHT is no longer classified as a substance with category 1 acute and chronic aquatic toxicity…
In its written opinion, which is available here, the Court took note of the very low aqueous solubility of coal tar pitch, which is in contrast with the assumption made by European Chemical Agency’s (ECHA’s) Risk Assessment Committee (RAC) that all of the individual PAHs dissolved in water and were therefore available to aquatic biota. According to the Court’s opinion, the highest tested actual solubility of coal tar pitch was 0.0014%, but the European Commission accepted ECHA’s individual polycyclic aromatic hydrocarbon (PAH) constituent method as the basis of the “category 1 acute and chronic aquatic toxicity” classification. The PAH constituent method resulted in a calculated solubility of 9.2%. The Court concluded
…such a value is not realistic, given that the maximum rate is 0.0014%.
According to Chemical Watch, the Court’s ruling is a landmark case in the EU because, apparently for the first time, it sets limits on the discretionary powers of EU government agencies when assessing chemical risks.
The ruling has significance to how the US EPA assesses PAHs as well. Continue reading →