I understand that this is an old post - but we have just come across this issue as well following on from a recent site audit. The liquid hand soap used by maintenance contains an abrasive material which is a powdered walnut shell. The species is identified as being Juglans Regia. (English Walnut)
I believe that this abrasive is just the shell which has been pulverised/milled into a powder form and is not the nut flesh. The product is being sold as "all natural" and is being manufactured by a reputable chemical/detergent company. There are no warnings on the product for allergen and that it contains "tree nuts".
I read of a man who died after being exposed to powdered walnut shell that was being used as an abrasive in sandblasting. This indicates to me that the walnut shell if not processed appropriately is hazardous to those who are allergic to walnuts. You would think that powdered walnut shell should not be permissible to use in a product that is used for direct skin contact as the risk may be too high and that there should be warnings on the labels of this product.
I'm trying to get more information from the manufacturer - but it looks like we'll also be removing this hand cleaner from our factory - for the health and well being of our maintenance crew and remove the potential for cross contamination of our food products.