EPA Develops Standard Protocols for Disinfectant Residue Analysis on Hard Surfaces

The primary objectives of these protocols are to quantitatively apply disinfectants, determine the residue levels left on surfaces post-application, and establish a standard method for these analyses. This is crucial for ensuring the safety and efficacy of disinfectants used in various environments, particularly those involving food preparation.

Materials and Methods

Phenolic Compounds Protocol

1. Representative Surfaces and Disinfectants:
   • Surfaces: Stainless steel, laminate (e.g., Formica), granite, and ceramic tile.
   • Disinfectants: Various phenolic compounds, including phenol, 2-phenylphenol, 2-benzyl-4-chlorophenol, and 4-tert-amylphenol in forms such as trigger sprays, wipes, and aerosols.
2. Procedure:
   • Disinfectants are applied using a pipette to ensure a known amount is deposited on the test surface.
   • A TQC Scrub Abrasion and Washability Tester is used to perform standardized wiping with lint-free cotton cloths soaked in potable water.
   • Residues are then extracted using methanol and analysed using high-performance liquid chromatography (HPLC) with ultraviolet detection.

Quaternary Ammonium Compounds (QACs) Protocol

1. Representative Surfaces and Disinfectants:
   • Surfaces: Same as for phenolic compounds.
   • Disinfectants: QACs like dialkyldimethyl ammonium salts and benzylalkylammonium dimethyl salts, in forms such as liquid trigger sprays, concentrates, wipes, and aerosol sprays.
2. Procedure:
   • Similar to the phenolic compounds protocol, disinfectants are applied using a pipette.
   • The same TQC tester is used for wiping.
   • Residues are analyzed using liquid chromatography tandem mass spectrometry (LC/MSMS).

Key Findings

Phenolic Compounds

• Residue Levels: The residue levels of phenolic compounds on surfaces varied based on the type of surface and the formulation of the disinfectant. Stainless steel surfaces generally had the least residue remaining after PWR.
• Removal Efficiency: The efficiency of residue removal by wiping was consistent across different wiping materials, with lint-free cotton cloths providing the most reliable results.

Quaternary Ammonium Compounds (QACs)

• Residue Levels: QAC-based disinfectants showed varying residue levels depending on the surface type, with stainless steel again showing the least residue post-PWR.
• Efficiency of Wiping: Similar to phenolic compounds, the use of lint-free cotton cloths was found to be effective in removing QAC residues.

Implications

These standardised protocols provide a reliable method for evaluating the residue levels of disinfectants, ensuring that surfaces, particularly those in food preparation areas, are safe for use after disinfection. The use of mechanical wiping devices and precise application techniques reduces human error and variability, making these protocols robust for regulatory and safety assessments.

The EPA's development of these protocols marks a significant step in standardising the analysis of disinfectant residues, ensuring public health safety and compliance with regulatory standards. These methods can be adapted for various disinfectants, providing a versatile tool for ensuring the cleanliness and safety of hard surfaces in different environments.