Influence of wash aids on Bacillus spore removal from an asphalt parking lot using two spray-based washing methods

The goal of this study was to measure the removal efficacy of Bacillus atrophaeus spores from a parking lot using spray-based washing methods (a pressure washer and a garden hose) and wash aids. B. atrophaeus is a commonly used nonpathogenic surrogate for B. anthracis, the causative agent of anthrax and a deadly bioterrorism agent that would cause major disruptions and damage to public health should it be disseminated over an urban area.

Five wash aids (1 mM sodium chloride, an Instant Ocean® seawater solution, 0.01% Tween 20, 0.01% sodium dodecyl sulfate, and unamended tap water) were used along with two different spray sequences in this study. Across all treatment conditions, 3.7-6.4 log₁₀  colony forming unit were recovered in the runoff water, and 0.15%-23% of spores were removed from the surface of the parking lot.

Pressure washing removed more spores than the garden hose, and for both types of washing methods, the first pass removed more spores than the subsequent passes. The Instant Ocean and Tween 20 wash aids were found to significantly increase the percentage of spore removal when using the pressure washer, but the overall increase was only 1%-2% compared to the tap water alone.

This study provides public officials and emergency responders with baseline spore physical removal information for situations where a corrosive disinfectant might have a negative impact on the environment and washing is being considered as an alternative remediation approach.