Final Report on the Amended Safety Assessment of Sodium Polynaphthalenesulfonate and Sodium Naphthalenesulfonate

Abstract

Sodium Polynaphthalenesulfonate (SPNS) and Sodium Naphthalenesulfonate (SNS) are sodium salts of naphthalene sulfonic acid. SPNS was used as an emulsion stabilizer, surfactant—hydrotrope, and/or surfactant—suspending agent at concentrations between 0.1% and 0.4%, in a wide range of products, including one lipstick. SNS is described as a surfactant—hydrotrope; no current uses were reported, but information was provided indicating that use concentrations would be typically below 2%. SNS is manufactured by reacting naphthalene with sulfuric acid to produce a sulfonic acid, which is then reacted with sodium hydroxide to produce the final product. The polymer form uses the sulfonic acid intermediate in a reaction with formaldehyde and water under conditions of heat and pressure to form the polymer sulfonic acid form, to which sodium hydroxide is added to make the final SPNS. The residue level of formaldehyde was 0.09%. Only around 1% of SNS in a 1-mg/ml solution applied to porcine skin penetrated the skin after 24 h, a similar amount was found noncovalently bound to the skin, and the concentration of material applied to the surface of the skin was largely unchanged. Both chemicals were not toxic in acute oral or dermal studies. In a subchronic oral toxicity study in rats, the effects noted were increases in urinary sugar in females and urine protein concentrations in males. Although undiluted SPNS was not a significant eye irritant in rabbits, undiluted SNS was a moderate eye irritant in rabbits. At 2%, SNS was a minimal eye irritant in rabbits. Undiluted SNS was at most a mild irritant in Guinea pigs, and was nonirritating at 20% and 2%. In a delayed contact hypersensitivity test in Guinea pigs, 30% SNS used in the induction phase and in the challenge phase produced no reactions. In a Guinea pig maximization test, 1% SNS used with Freund's complete adjuvant (FCA) injected in the initial sensitization, 50% SNS applied topically in the second sensitization, and up to 30% SNS applied topically in the challenge phase did not produce any irritation or sensitization. Both ingredients were negative in Ames mutagenesis assays. In clinical studies, SNS was neither an irritant (tested up to 2%), cumulative irritant (tested up to 1%), nor a sensitizer (tested up to 1%). The Panel considered the low penetration in concert with the low concentrations of use of these ingredients and the absence of significant overall toxicity and the limited negative genotoxicity findings sufficient to support a conclusion that SNS and SPNS are safe as used in cosmetic formulations intended to be applied to the skin. Use of SPNS in a lipstick formulation, was not considered to be different from application to the skin in that the barrier properties of the skin do not apply when these ingredients may contact mucous membranes or may be ingested. Accordingly, the Panel concluded that the available data are insufficient to support the safety of SNS and SPNS in cosmetic formulations that may contact mucous membranes or be ingested. The additional data needed to make a safety assessment for these uses include dermal reproductive and developmental toxicity data and one genotoxicity assay in a mammalian system, and if that study is positive, then a 2-year dermal carcinogenicity study using National Toxicology Program (NTP) methods may be needed.