Aviation engine oils used on the commercial airline fleet globally all contain tricresyl phosphates (TCPs), according to the hazardous ingredient information listed on product safety data sheets (SDS) and some published chemical analyses of the engine oils and associated fumes. The reported TCP content on an SDS for a specific engine oil product can vary considerably, though, depending on the SDS country of origin. For example, the 2008 US version of the SDS for BP2380 engine oil states that the “product does not contain any hazardous ingredients at or above regulated thresholds,” while the South African version for the same product published in the same year reports 5 – 10% TCP content, by weight, and also 1 – 5% n-phenyl-naphthylamine. In addition to TCPs, safety data sheets for some aviation engine oils list trixylenyl phosphate (TXPs); 0.1-1%, by weight. In Dec. 2013, the European Chemical Agency classified TXP as a Substance of Very High Concern because it is recognized as toxic to reproduction 

Because the engine oil manufacturers appear to report the TCP content of their products unevenly, Professor Chris van Netten of the University of British Columbia analyzed the actual TCP content – both total TCPs and the relative amounts of four TCP isomers – in samples of eight aviation engine oils and three aviation hydraulic fluids. The total TCP content of the eight oils ranged from 2.2 to 5.2% (by weight), and the total TCP content of each hydraulic fluid was zero. The details those analyses are provided in Table 9 of the report. It is notable that the measured TCP content of each of the three BP engine oils (2.80, 2.85, and 4.70%) are markedly higher than each corresponding safety data sheet suggest. Likewise, the measured TCP content in MJOII oil was 5.6% compared to the 1 – 3% claim on the product SDS.

To assist the reader in interpreting the TCP isomer data in Table 9, the following background information may be helpful. There are a total of 10 isomers of TCP that may be present in a given engine oil. It is worthwhile to define both the total TCP content, and the isomeric blend of TCPs in a given engine oil product, because these characteristics will influence the toxicity of the fumes that can be supplied to the cabin and flight deck when the air supply system is contaminated. Aviation engine oil manufacturers can choose between two commercial brands of TCPs blends for their products – Durad 125 by Chemtura, and Syn-o-ad 8484 by ICP Industrial Products. While the particular blend of TCP isomers in each of these products is proprietary, the blends must not contain more than 0.2% (by weight) of the six ortho isomers of TCP, per SAE Aerospace Standard 5780. This leaves a total of four meta and para isomers that may comprise the remaining 99.8% or more of the TCPs in aviation engine oils. Previous published research conducted by Prof. Chris van Netten has confirmed the presence of all four meta/para isomers (mmm, ppp, mmp, and ppm) in samples of aviation engine oil fumes, which is why the relative amounts of those isomers are reported in Table 9 of the report. The relative amount of the tri-ortho isomer of TCP is also listed in Table 9. Any amounts of the remaining five ortho isomers are not listed because the chemical standards for those products were not available. However, as stated, the total ortho isomer content is anticipated to be no more than 0.2%, so the relative content of the remaining five ortho isomers should not contribute appreciably to the total TCPs.