Research co-authored by the American Cleaning Institute (ACI) presents a spatially referenced environmental exposure model for down-the-drain substance emissions in Europe. The model covers the 27 European Union member states, as well as Norway, Switzerland and UK. It builds on the global modeling framework that leverages the well-established iSTREEM model used in the US, according to ACI.

iSTREEM is an in-stream environmental exposure model which predicts the concentration of a chemical used in “down-the-drain” products. It promotes product stewardship and regulatory compliance for chemical suppliers and manufacturers of formulated products of all sizes across commodity groups.

The research is available in Integrated Environmental Assessment and Management.

The model uses European data on wastewater treatment plant infrastructure and location, along with global spatial datasets on population, river flows and routing. It estimates environmental concentrations of chemicals disposed of via household drains. The model accounts for key environmental processes such as river connectivity, in-stream chemical routing and degradation.

LAS, Alkyl Sulfates & Oxybenzone and Octinoxate

Four consumer-use chemicals with down-the-drain disposal routes were used as case studies:

• Linear alkylbenzene sulfonate and alkyl sulfate – common surfactants found in laundry detergents
• Oxybenzone and octinoxate – UV filters used in personal care products

Monitoring data representing spatial variability across Europe were used to compare against the model’s outputs. The model delivers predictive yet conservative estimates. The 90th percentile modeled concentrations align with monitored values within a factor of 2–8 across all case studies.

“This model represents an important advancement in exposure assessment tools for environmental safety evaluations,” said co-author Darius Stanton, ACI director, regulatory science. “It enables more consistent, science-based decision-making and supports global efforts to evaluate chemical exposure responsibly.”

The model can be used in prospective chemical safety assessments, comparing predicted environmental concentration levels with established predicted no-effect concentration (PNECs) levels. It demonstrates compatibility with tiered risk assessment approaches by producing results in line with real-world monitoring data.

Paper co-authors include Susan A. Csiszar, Chiara M. Vitale, and Kyle S. Roush (Procter & Gamble); Raghu Vamshi and Brenna Kent (Waterborne Environmental); Ryan Heisler (International Collaboration on Cosmetics Safety); Heather Summers (Integral Consulting); Emily E. Burns and Iain Davies (Personal Care Products Council); Darius Stanton (American Cleaning Institute).