Variability in site-specific pyrethroid KOC and KDOC partition coefficients and implications for predicted aquatic...

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Aquatic Science

Background:

• Equilibrium partitioning estimates pyrethroid bioavailability (Cfree) in aquatic systems.
• Default organic carbon-water (KOC) and dissolved organic carbon-water (KDOC) partition coefficients are typically used.
• Sorption capacities vary due to differing organic carbon quality.

Purpose of the Study:

• Experimentally measure KOC and KDOC for six pyrethroids in 19 California sediment samples.
• Examine variability in site-specific coefficients compared to default values.
• Assess variability in predicted pyrethroid toxic units and organism survival using toxicity data.

Main Methods:

• Collected 19 streambed sediment samples across California.
• Experimentally measured KOC and KDOC for six pyrethroids (bifenthrin, cyfluthrin, cypermethrin, esfenvalerate, lambda-cyhalothrin, permethrin).
• Utilized sediment/water chemistry and Hyalella azteca toxicity data.

Main Results:

• Measured site-specific log KOC ranged from 5.32 to 7.11; log KDOC ranged from 5.28 to 7.41.
• Toxic units estimated using site-specific and default coefficients explained comparable variance in H. azteca survival.
• Both coefficient types aligned closely with 50% organism survival predictions.

Conclusions:

• Recommends using default coefficients derived from this study's 19 unique sediment samples.
• These default coefficients reflect measured variability and accurately predict pyrethroid bioavailability and toxicity.
• Acknowledges the need to consider uncertainties associated with site-specific factors.