Systematic Consideration of Parameter Uncertainty and Variability in Probabilistic Species Sensitivity Distributions

Area of Science:

• Environmental Science
• Ecotoxicology
• Risk Assessment

Background:

• Species sensitivity distribution (SSD) is standard for deriving predicted no-effect concentrations (PNEC).
• Traditional SSD methods are data-intensive and struggle with variability in exposure conditions and material types, especially for nanomaterials.
• Probabilistic SSD (PSSD) offers improvements but requires further refinement for uncertainty and variability.

Purpose of the Study:

• To enhance the probabilistic species sensitivity distribution (PSSD) approach by better accounting for input data uncertainty and variability.
• To develop a new PSSD method (PSSD+) incorporating probabilistic uncertainty factors and species weighting.
• To assess the robustness and applicability of the PSSD+ method for calculating PNEC distributions.

Main Methods:

• Implemented probabilistic elements for uncertainty factors using probability distributions.
• Developed the PSSD+ method using a Monte Carlo routine to compute 10,000 PSSDs.
• Extracted the hazardous concentration for 5% of species (HC5) for each PSSD to create a PNEC distribution.
• Included an option for species weighting based on biome composition.
• Applied PSSD+ to existing data sets for carbon nanotubes and silver nanoparticles.

Main Results:

• The PSSD+ method demonstrated robustness in PNEC calculation, with uncertainty factor distributions and species weighting.
• The approach effectively handles both small and comprehensive data sets, yielding PNEC distributions that accurately reflect available data.
• Sensitivity testing indicated the method is relatively insensitive to missing data points, provided the most sensitive species is included (max variation of mean PNEC by a factor of ~2).

Conclusions:

• The PSSD+ approach provides a reliable and robust method for deriving PNEC distributions, effectively managing data uncertainty and variability.
• This enhanced method is suitable for various data set sizes, crucial for chemical risk assessment, particularly for nanomaterials.
• The PSSD+ method improves the accuracy and reliability of environmental risk assessments by providing a more comprehensive understanding of PNEC.