Antimicrobial, Preservative, and Hazard Assessments from Eight Chemical Classes

Preservatives, such as isothiazolinones and formaldehyde-releasing
compounds, provide safety and stability in consumer products by preventing
microbial contamination. Yet these ingredients present human and environmental
hazards, including allergic contact dermatitis and aquatic toxicity.
The development of safer alternatives has been stymied by trade-offs
between safety and efficacy. To enable the identification of safer
preservatives, substances from eight functional classes were assessed
for antimicrobial efficacy and human and environmental hazards. First,
130 substances were evaluated for microbial inhibitory activity against
two relevant model microorganisms, Aspergillus brasiliensis (filamentous fungi) and Pseudomonas aeruginosa (Gram-negative bacteria). High-performing compounds within each
class were assessed for hazards across a broad suite of human and
environmental health end points. Four promising compounds were selected
for further testing based on microbial inhibition, hazard profiles,
and commercial availability. These ingredients were tested for biocidal
activity in model home care formulations using methods adapted from
industrial preservative challenge guidelines (USP-51). Two substances
were identified, caprylhydroxamic acid and caprylyl glycol, that provided
adequate preservation and improved toxicity profiles compared to isothiazolinone
and formaldehyde-releasing preservatives. This study highlights trade-offs
between antimicrobial activity and hazards across a broad spectrum
of chemical classes relevant to safer preservative development.