Study of the fate of Bronopol and the effects of antioxidants on N-nitrosamine formation in shampoos and skin creams.

Synopsis The role of antioxidants in preventing nitrosamine (N-nitroso diethanolamine) formation in shampoos and skin creams and the levels of Bronopol (2-bromo, 2-nitropropane-1, 3-diol) addition in relation to the resultant levels of N-nitroso compounds have been studied. The addition of 0.05% BHT, alpha-tocopherol or ascorbate was effective in preventing nitrosamine formation (limit of determination: 2.5 mug kg(-1)) in products preserved with 0.01% Bronopol. At 0.05% Bronopol, 0.2% of all three antioxidants was effective in preventing nitrosamine formation but at 0.1% Bronopol only alpha-tocopherol was effective. Levels of Bronopol found in shampoo formulations stored for 2 weeks at 37 degrees C with initial concentrations of 0.005-0.1% were reduced by 64-86%, independent of the initial concentration. The levels in skin creams stored for extended periods at ambient temperature with 0.01% Bronopol initially were reduced by, on average, 60%. High nitrite levels (NO(2) (-)) were found in formulations containing 0.01% Bronopol but no antioxidants (200-250 mg kg(-1)). Detected levels of nitrite in skin cream formulations were greater than could be formed by stoichiometric decomposition of Bronopol. In formulations with both Bronopol and antioxidants the levels of nitrite were considerably reduced. When alpha-tocopherol rather than BHT or ascorbate was the antioxidant then the nitrite levels were appreciably higher but formation of N-nitroso diethanolamine was no greater. High nitrite levels correlated with the formation of detectable levels of N-nitroso compounds in the absence of antioxidants.