Absence of free, unbound carbon black in printer toners: a California Proposition 65 study

On February 21, 2003, California's Office of Environmental Health Hazard Assessment (OEHHA) added carbon black to the Proposition 65 list of carcinogens. The listing was based on the reclassification of carbon black as a Group 2B agent (possibly carcinogenic to humans) by the International Agency for Research on Cancer (IARC). However, IARC noted in its evaluation of carbon black carcinogenicity that end users of certain products are not exposed to carbon black per se, because carbon black is bound within the product matrix, and OEHHA has restricted the listing of carbon black to "airborne, unbound particles of respirable size". The objective of the present study was to determine if carbon black is bound within the polymer matrix in printer toners or if free, unbound carbon black is detectable in printer toners. Thirteen toners in five different polymer matrix categories from five manufacturers ranging from small workgroup printers to large production printers were analyzed. Both toners with and without surface treatment additives were included in the present study. The results of the present study showed that carbon black was bound in the polymer matrix of the tested printer toners and that free, unbound carbon black was not detectable in the tested printer toners. Therefore, the results support a conclusion that carbon black in printer toners is not subject to consumer warning under Proposition 65.