Cross-reactions between xanthates and rubber additives

We previously described allergic contact dermatitis from xanthates used in the recovery of metals from mining ores. We observed cross-reactions with carbamates, believed to be due to the common "dithio" nucleus shared by both groups.

The present study was undertaken to establish the rate of cross-reactions between xanthates and rubber additives.

Between November 2002 and December 2005, 1,220 consecutive patients were patch-tested with sodium isopropyl xanthate 10% in petrolatum (pet) and with potassium amyl xanthate 10% pet and later 5% pet, in addition to the North American Contact Dermatitis Group standard series and other series as required by their conditions.

Fifty-one patients reacted to xanthates, carbamates, or thiurams; 26 reacted to xanthates only, and these reactions were felt to be irritant. Twenty-five patients reacted to xanthates and/or to one or more of the rubber additives, 12 had positive reactions to xanthates and to either carba mix or thiuram mix, 10 reacted to xanthates and carba mix, 9 reacted to xanthates and thiuram mix, and 8 showed positive reactions to xanthates and both mixes. However, 13 patients had positive reactions to carba mix and thiuram mix but did not react to xanthates. Six patients reacted to other rubber additives such as mercaptobenzothiazole, black rubber mix, and mixed dialkyl thioureas. Five of these patients also reacted to xanthates, 4 reacted to xanthates and carba mix, and 3 reacted to xanthates, carba mix, and thiuram mix.

Of patients sensitized to carbamates, thiurams, or mercaptobenzothiazole, 50% exhibit cross-reactions with xanthates. Xanthates are irritants, and their patch-test concentrations should be lowered to 5% or less.