Development and validation of a congener-specific photodegradation model for polybrominated diphenyl ethers

Area of Science:

• Environmental Chemistry
• Photochemistry
• Chemical Engineering

Background:

• Polybrominated diphenyl ethers (PBDEs) are flame retardants with varying bromination levels.
• Phaseout of certain PBDEs necessitates understanding the environmental behavior of remaining formulations, especially deca-BDE.
• Predicting photodegradation is crucial for assessing environmental persistence and transformation.

Purpose of the Study:

• To develop and validate a model for predicting PBDE photodegradation products and concentrations.
• To investigate the photodegradation pathways of specific PBDE congeners under UV light.
• To establish methods for identifying unknown photodegradation products.

Main Methods:

• Calculation of enthalpies of formation for 209 PBDE congeners.
• Determination of relative reaction rate constants for PBDE photodegradation.
• Experimental UV photodegradation studies of BDE-209, BDE-184, BDE-100, and BDE-99 in isooctane.
• Development of a gas chromatography retention time model using multiple linear regression.

Main Results:

• The photodegradation model accurately predicted experimental results for PBDE photochemical reactions.
• PBDE photodegradation follows first-order kinetics, with stepwise bromine loss as the rate-determining step.
• BDE-99 is predicted to remain abundant, while BDE-49 and BDE-66 will increase significantly post-degradation.

Conclusions:

• The developed model provides a reliable tool for predicting PBDE photodegradation products.
• Understanding PBDE photodegradation is essential for environmental risk assessment and management.
• The study elucidates the transformation pathways of PBDEs in the environment, highlighting the formation of less brominated congeners.