How De Groot was caught by CAS in an illegal act and was cancelled

In 2017 I decided it was time for a fourth edition of Patch testingTo give the new book extra cachet, I decided to add a CAS number to all 4900 chemicals in this edition. CAS is the abbreviation for Chemical Abstract Service, part of the American Chemical Society ( This organization gives all individual chemical substances a unique number,

the CAS number. Remarkably enough, although those numbers can be found in all kinds of databases, the copyright rests with CAS, so you have to ask permission (= you have to pay) for permission to use a larger collection of CAS numbers. I did manage to get permission from the Chemical Abstract Service to use the numbers without having to pay and I felt that was quite an accomplishment, as their opening bid was 3,000 USD. But it certainly didn't go without a fight, because there was some old sore at CAS. Let me explain to you why.

In 2014 or 2015 I had started writing a new book on contact allergy to and chemical composition of essential oils. While searching in literature, I came across a few thousand substances that are or may be present in one or more essential oils. I included all of them in the book, of course with a CAS number. In the digital library of the University of Groningen I had access to the database of the CAS via SciFinder. I had to create an account for that and log in every time. It had certainly not escaped my attention that you were allowed to use the CAS numbers only for scientific research or personal use.

 However, use for commercial purposes (such as our book) was strictly prohibited. I then looked at the CAS site and immediately realized that a license to use the data could get quite expensive, the rates started at about 2000 USD. Well, what to do? If I behaved properly, I would spend more money on CAS numbers than I ever would earn in royalties. So I did what I often do: apply De Groot's ruse. This means: pretending nothing is wrong and hoping that it will go away on its own. But to be honest: every time I logged in, it just gnawed at me a bit.

Okay, so I went to work and it all went smoothly, until ….. after half a year or so I suddenly couldn't log in to SciFinder anymore. The ICT of the UMCG could not help me and advised me to contact CAS, because that is where the problem lay. As you will understand, I didn't feel much for that. It seemed De Groot's ruse had failed and the CAS had cancelled me. So I had to switch to other databases to search for CAS numbers. This went smoothly for many chemicals, but some were difficult or impossible to find. For many chemicals, more than one CAS number is often listed (which is in fact impossible), for example because in the pre-computer era a chemical substance was given a CAS number and later the same substance, which was designated by a synonym, had obtained a different number. Only the CAS database itself contains all correct and unique numbers. It all went pretty well, but the affair did not really sit well with me.

De Groot is caught with illegal use

At one point I received a call from the dermatology department of the UMC Groningen. They had sent me an email and asked me to respond to it. When I asked which email address they had used, it turned out to be my UMCG email address. UMCG email address? Did I have a UMCG email address? Yes, since 2008 or so, but of course I had long forgotten that, because I have no business there and had therefore never logged into my email account. And believe it or not, I could still find the password for it in my old papers. However, login failed. I called the ICT helpdesk. The ICT guy laughed heartily, because my password had already expired 6 years ago! Got a new one and logged in. About 500 emails grinned at me. Among them I also found 2 emails from CAS from 8 and 6 months before….....

So people at CAS had noticed that I had looked up and copied CAS numbers daily for months in a row and had apparently started googling my name. Now I could be found on my website, which I used to sell my book Patch testing. There was also a button 'Contact Allergen Database' on that website. If you clicked on that you could read that I was planning to make a digital database of all known allergens with all kinds of data (just like in Patch testing) including …… the CAS numbers. The employees of the CAS had also found that plan of mine and had concluded that I was working on that database. That was an incorrect, but understandable assumption. In the first email they summoned me to stop doing this and to contact them to discuss a license. When I didn't respond, they emailed me again 2 months later and announced that I was black listed……. Bummer! Well, what was wisdom? Of course I could pretend my nose was bleeding, but I had a problem. All those illegally obtained CAS numbers would of course end up in the book Essential oils: Contact allergy and chemical composition. And in the contract I had signed with the publisher of that book I had guaranteed that I had not infringed any third party copyright and that if it came to a lawsuit in the US I would pay the costs! In a country, therefore, where you as a client have already lost 50 dollars when the lawyer's secretary answers the phone.……

Deep in the dust

So the decision was made quickly, I had no choice. I emailed the CAS explaining the situation, why I hadn't contacted them (because I didn't know about their email), that I'm just a simple retired dermatologist, that 100 books would be sold at the most, and that the cost of licensing would be many times the royalties to be earned. But more importantly: just like before in practice, I acted vulnerable, very humble and modest. They were indeed absolutely right, I had not followed the rules, offered my sincere apologies and announced that I would improve my life. DEEP IN THE DUST, as media  say about politicians these days, even when they only apologize and say sorry.

Allergic contact eczema due to the use of arnica tincture (left) and arnica ointment (top right). 'Arnica' is an extract of the plant Arnica montana (arnica; photo bottom right, taken from Wikipedia) and is used in herbal 'medicines' (phytotherapeutics) for all kinds of ailments. Although swelling (edema) is a characteristic of allergic contact eczema, the massive thickening of the right leg is very remarkable

Humility and apologies help

It worked. I received an email back in which I was thanked for the detailed explanation and that my honesty and openness were very much appreciated. I was then referred to the Dutch branch of CAS to discuss the matter. That went well and with a few friendly emails and phone calls I received written permission to use the CAS numbers. But I can't log in to SciFinder since then (although, I have a new position now in Amsterdam, I can try, of course).

Okay, now I go back to where I started. I also needed permission from CAS for the CAS numbers in Patch testing because of that copyright. The fact that I had found all those numbers in PubChem, ChemIDPlus and some other chemical online databases made no difference, because of the copyright principle. Now you will understand why getting permission came with some effort and not without a struggle. I had already built up a good relationship with the Dutch CAS branch. I had promised the CAS agent that I would thank him in an Acknowledgment in the book for his assistance in obtaining CAS's approval and sent him a copy of Patch testing signed by the author. Prerequisite was, however, that I had to state that the numbers had not been verified by CAS (one of their earning models) and may therefore contain errors. The later books (Monographs in Contact Allergy) also contain CAS numbers, but there are a maximum of about 500 per book and that is allowed without approval. All's well that ends well, but I was very worried at times, that's for sure.


This text is also in Chapter Patch testing 4th edition, but it has been given a separate page here in order to be found more easily.


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