Measures of overall persistence and the temporal remote state

Area of Science:

• Environmental Chemistry
• Multimedia Environmental Models
• Chemical Persistence Assessment

Background:

• Overall persistence (Pov) integrates half-lives and partitioning but suffers from varied definitions.
• Common Pov measures, like steady-state residence time, are sensitive to chemical release patterns.
• A robust persistence indicator independent of release history is needed for environmental risk assessment.

Purpose of the Study:

• To compare different measures for computing chemical persistence (Pov) from dynamic multimedia models.
• To evaluate measures based on environmental mass over time, including equivalence width, mean time, and clearance time.
• To establish a reliable persistence benchmark using the temporal remote state, independent of release patterns.

Main Methods:

• Utilized a dynamic multimedia model to simulate chemical mass in the environment over time.
• Calculated Pov using equivalence width (steady-state residence time), mean time, and clearance time.
• Defined and analyzed the temporal remote state, representing conditions long after emission cessation.

Main Results:

• The mean time in the temporal remote state serves as a reliable, release-pattern-independent persistence benchmark.
• Equivalence width and mean time show strong correlations with the persistence benchmark.
• Maximum equivalence width, achievable with single-media releases, approximates the mean time in the temporal remote state.

Conclusions:

• The mean time in the temporal remote state is a superior indicator of long-term chemical persistence.
• Maximum equivalence width offers a practical estimation of this benchmark using existing steady-state models.
• This research refines chemical persistence assessment in environmental modeling, enhancing risk evaluation.