Reduction of the mutagenicity of lead chromate-based pigments by encapsulation with silica

13 lead chromate-based pigments were assayed for mutagenicity and toxicity using Salmonella typhimurium TA100. The compounds were assayed with and without S9, both in the presence and absence of the chelating agent, nitrilotriacetic acid (NTA). In general, the use of NTA to solubilize the compounds resulted in mutagenicity and/or toxicity being observed where it had not in the absence of NTA, or being observed at lower concentrations than when water alone was used. Encapsulation of pigments with amorphous silica rendered these pigments non-mutagenic and non-toxic, indicating that the active moieties were biologically unavailable to the bacteria. Varying the percentage of silica encapsulation on one pigment, medium chrome yellow, indicated that 5% encapsulation did not alter the mutagenicity while 10% encapsulation inhibited the mutagenicity without or with NTA.