According to the Web site of the Service du répertoire toxicologique de la CSST: "Commercial xylene is a mixture that contains variable percentages of xylene isomers (ortho-xylene, meta-xylene, and para-xylene), ethylbenzene and some impurities (example: trimethylbenzene, phenol, thiophene, pyridine, toluene, pseudocumene, benzene, nonaromatic hydrocarbons). M-xylene is always the most abundant isomer. The proportion of the different components depends on the origin of the xylene. For example, xylene from petroleum via the catalytic reforming process has the following typical composition: 25% ortho-xylene, 40% meta-xylene, 20% para-xylene, and 15% ethylbenzene; xylene from petroleum via cracked gasoline has the following typical composition: 17% ortho-xylene, 23% para-xylene, 37% meta-xylene, and 23% ethylbenzene." (free translation)
It therefore appears that with commercial xylene, frequently presented as CAS number 1330-20-7 (mixture of isomers), ethylbenzene is always present in a non-negligible proportion. As a result, it is strongly recommended that ethylbenzene be analyzed when the presence of xylenes is suspected.
Laboratory's analytical approaches:
Traditionally, a xylene mixture also containing ethylbenzene is used for calibrating the gas chromatograph for the quantification of xylenes in air samples. With a few exceptions, ethylbenzene has been quantified and "accounted for" in the quantity of xylenes reported for the samples. If the requester had written xylenes AND ethylbenzene on the analytical requisition, the substances were reported separately. In the end, the result was considered as equivalent, regardless of the approach adopted, meaning that the "ethylbenzene-xylenes" pair or only the xylenes were reported.
This approach was motivated by the following information items:
- Ethylbenzene was (and still is) intrinsically linked to xylenes, in the commercial product as well as in the highly pure substance used in the laboratory for instrument calibration;
- Both substances had (and still have) the same TWAEV;
- Recognized scientific knowledge have reported the same health effects on workers for both substances;
- The value of Rm1,2, regarding the ethylbenzene-xylenes pair, was not affected, whether ethylbenzene was reported separately or included in the xylenes.
Current knowledge in the scientific literature3 has made certain adjustments necessary in how analysis requisitions involving the "ethylbenzene-xylenes" pair are handled. In fact, the lowering of the reference value of certain international organizations4 for ethylbenzene as well as the documentation3 of toxic effects for this compound on target organs other than those cited for xylenes now makes it essential to quantify ethylbenzene separately in relation to xylenes.
To do this, the IRSST laboratory has made two modifications to the analytical approach for these compounds:
1) Ethylbenzene analysis is now offered on passive dosimeter IRSST #2695 (3M 3500 passive dosimeter for organic vapours). The method number, the minimum reported value (MRV) and the analytical uncertainty are identical to the method offered on IRSST #2120 active charcoal tube. For more information, consult the data sheet for this product on the IRSST's web site (http://www.irsst.qc.ca/en/-RSST100-41-4.html).
2) From now on, the result reported for xylenes will no longer include the result for ethylbenzene. The result for xylenes will therefore only be the sum of the concentrations of ortho-xylene, meta-xylene and para-xylene. To obtain a result for ethylbenzene for a sample, ethylbenzene will have to be explicitly mentioned on the environmental analysis requisition.
Follow-up with clients in general:
For a 3-month transition period, the IRSST Laboratory Customer Service team will contact clients to confirm ethylbenzene analysis if xylenes are mentioned on the requisition without ethylbenzene appearing. If, despite the information provided above, the requester does not want to have ethylbenzene analyzed in addition to xylenes, a clear remark about this should be written on the analysis requisition in order to avoid any further delay. It is important to note than once the 3- month transition period has passed, the laboratory will not add the analysis of ethylbenzene to an analysis requisition where only xylenes are mentioned.
To users of the SISAT computer-based system:
For personnel in the Québec public health network with access to the SISAT computer-based system, an input aid is available to automatically include ethylbenzene with xylenes (in French only):
- Analysis of charcoal tubes: Forfait-Xylènes et Éthylbenzène sur tube
- Analysis of passive dosimeters: Forfait-Xylènes et Éthylbenzène sur dosimètre passif
Mélanie Huard, M.Sc., chemist
Simon Aubin, M.Sc., chemist, CIH, ROH
1) GOUVERNEMENT DU QUÉBEC. Regulation respecting occupational health and safety, Éditeur officiel du Québec, 2014. (Part 3 of Schedule I).
2) DROLET, Daniel and Guylaine Beauchamp. "Sampling Guide for Air Contaminants in the Workplace (8th edition, version 8.1, updated)," 2012, Studies and Research Projects/Guide technique T-15, IRSST, 152 pages. (Section 1.2)
3) AMERICAN CONFERENCE OF GOVERNMENTAL INDUSTRIAL HYGIENISTS (ACGIH®). Documentation of the Threshold Limit Values and Biological Exposure Indices, 2011, Ethylbenzene, Cincinnati, OH, USA.
4) GESTIS - International limit values for chemical agents - Occupational exposure limits (OELs)