D2.6 - An improved SimpleBox model for improved environmental risk assessment and life cycle impact assessments

Executive Summary

 Persistent, Mobile and Toxic (PMT) substances are of concern for organisms living in surface water bodies because of their indication of high (eco)toxicity in combination with high environmental persistence, due to poor removal from the water phase. Assessment of environmental persistence requires the use of multimedia chemical fate models such as SimpleBox, because these models are able to integrate the impact of substance properties, emission patterns and the dynamics of the environmental system over time. In the current deliverable report the environmental persistence is specified further into aquatic persistence, being the extent to which substances persist in surface water bodies.

Just as for environmental persistence, the assessment of aquatic persistence needs the use of multimedia fate models to integrate the impact of the three factors mentioned above. To this end, the Aquatic Persistence Dashboard has been developed as an improvement of the SimpleBox model. At the end of the PROMISCES project the Simple Box version with the Dashboard will become publicly available at https://github.com/rivm-syso/SimpleBox. The Aquatic Persistence Dashboard enables the user to evaluate the time that a substance remains in the water phase and hence its tendency to flow downstream and eventually reach the ocean. SimpleBox simulates the degradation and transport as dynamic environmental fate processes occurring at regional, continental and global scale systems. By deriving aquatic persistence in this manner, these dynamic processes are integrated. The Aquatic Persistence Dashboard enables the user (exposure/risk assessor or policy maker) to screen the combined PMT properties of a substance as it directly indicates the timescale over which a chemical is anticipated to maintain in surface water bodies.

The sensitivity analyses performed with the Aquatic Persistence Dashboard show that vapor pressure and air-water partitioning behavior of a substance can be of great impact on the aquatic persistence. However, these substance properties are currently not included as PM criterium. As such, it is possible that a volatile substance is defined as a PM substance as it fits the criteria, whereas in reality the substance resides in the atmosphere. The results of the sensitivity analyses thus shows the need to discuss whether vapor pressure or air-water partitioning coefficient should be considered a PM criterium as well.