How to disclose in a review of an edited book that one was offered a chapter? Some time ago, I attended a conference. The organizers later compiled an edited book with the revised presentations of the conference. I was also offered to contribute a chapter. But after the sending the organizers a first draft, I had to turn down the offer as I did not have the time to make the revisions and additions they asked for.  

Currently, I am writing an omnibus review about the same topic for a journal and I also would like to discuss the meanwhile published proceedings of the conference. Although I think the edited book has some very good points, I also would have to express severe criticism about some other points especially in the introduction by the organizers.  

Therefore, I would like to know:
How do I disclose the best in the review that I have participated at the conference and was offered a chapter? Should I add a footnote or a paragraph? Wouldn't that even raise distrust?  

To make things more complicated: There is already a well-meaning  review of the book by the 2nd supervisor of one of the contributors who has not disclosed his link in any way.
I would suggest that you do not need a disclaimer in this particular case: the bottom line is that you did not contribute to the book. If you had participated, it would be a clear-cut case… yours is more complicated, but the fact remains that none of the text of the book was written by you!

Another way to see it: a disclaimer would not raise distrust, but it would certainly add confusion (or at least, not add any clarity). You'd have to explain concisely your situation, stating the facts. You could come up with something like “The author of this review was asked to participate in the book, but had to decline due to time constraints”.

Finally, if you want to be sure to do the right thing: ask the journal editor! You then make it his call, since it's his journal. He's the best person to ask, really…