pSSD++
Description:
pSSD++ (Probabilistic Species Sensitivity Distribution++) is an open-source probabilistic ecological risk assessment framework for deriving microplastics hazard thresholds. Building on traditional SSD and PSSD approaches, pSSD++ uniquely integrates Monte Carlo simulations to transparently propagate uncertainty across particle traits, toxicological mechanisms, and environmental variability. By leveraging the expanded ToMEx 2.0 toxicity database, pSSD++ accounts for intraspecies variability, assessment factor uncertainty, and the alignment of laboratory test particles with those found in real-world ecosystems. This results in more protective and realistic hazard thresholds for both marine and freshwater systems, supporting robust, science-based environmental management of microplastics. The framework is adaptable, open for community input, and recommended for researchers and regulators seeking transparent, precautionary, and data-driven microplastics risk assessment.
pSSD++ is implemented as an R package, installable directly from GitHub at ScottCoffin/ToMEx2.0_EcoToxRisk. The repository includes all code and data required to reproduce analyses, with large simulation files available via Zenodo (DOI: 10.5281/zenodo.16740504). The package is designed for transparency, reproducibility, and adaptation to new datasets or environmental scenarios.
pSSD++ is described and applied in a peer-reviewed study demonstrating how propagating alignment uncertainty can materially change both the central tendency and the uncertainty bounds of derived thresholds across marine vs. freshwater environments and across ERM categories (e.g., food dilution vs. tissue translocation). The study also reports a global sensitivity analysis showing ERM-alignment parameters as dominant drivers of threshold variability
Scope:
- Probabilistic risk assessment for microplastics in marine and freshwater ecosystems
- Incorporates uncertainty from particle traits, toxicological endpoints, and environmental distributions
- Utilizes Monte Carlo simulations and empirical species-level distributions
- Supports tiered threshold derivation and sensitivity analysis
- Open-source code and data available for reproducibility and adaptation
- Community-driven: open to contributions and updates from researchers
Access:
- R package and code: https://github.com/ScottCoffin/ToMEx2.0_EcoToxRisk
- Large simulation files: Zenodo DOI 10.5281/zenodo.16740504
- Publication: Coffin S., Bertrand L., Ahmed K.T., de Souza Leite L., Cowger W., Siña M., et al. (2026).A probabilistic risk framework for microplastics integrating uncertainty across toxicological and environmental variability: Development and application to marine and freshwater ecosystems.Journal of Hazardous Materials, 503 (Feb 1), 141021. doi: 10.1016/j.hazmat.2025.141021.
Keywords:
microplastics, probabilistic risk assessment, PSSD++, Monte Carlo, species sensitivity distribution, uncertainty propagation, hazard threshold, ToMEx, ecotoxicology, aquatic ecosystems