Benzalkonium runoff from roofs treated with biocide products - In situ pilot-scale study

Area of Science:

• Environmental Science
• Ecotoxicology
• Materials Science

Background:

• Biocides, primarily benzalkonium chloride (BAC), are used for roof maintenance to control biological growth.
• BAC is toxic to aquatic ecosystems, raising concerns about its environmental impact from roof runoff.

Purpose of the Study:

• To assess the one-year evolution of roof runoff contamination after BAC biocide treatment.
• To determine the rainfall thresholds required to reduce BAC concentrations below ecotoxicological limits.

Main Methods:

• An in-situ pilot scale study was conducted to monitor roof runoff contamination over a year.
• Benzalkonium ion concentrations in runoff were measured following biocide application.
• Mass balance calculations were performed to account for BAC loss.

Main Results:

• High BAC concentrations (5–30 mg/L) were observed immediately after treatment, decreasing exponentially.
• 175–375 mm of rainfall was needed to lower concentrations below the fish EC50 (280 μg/L).
• Leaching varied by roofing material (ceramic vs. concrete) and tile condition; significant BAC mass was lost, likely via biodegradation.

Conclusions:

• BAC roof treatments lead to significant, prolonged aquatic contamination.
• Roofing material type and condition influence BAC leaching rates.
• Biodegradation may play a role in the environmental fate of BAC on roofs.