Pyrethroid sediment toxicity data and risk assessment: … · 2015-11-25 · Pyrethroid sediment toxicity data and risk assessment: challenges associated with highly hydrophobic chemicals

Pyrethroid sediment toxicity data and risk assessment: challenges associated with highly hydrophobic chemicals

Jeffrey Giddings (Compliance Services International)Ted Valenti (Syngenta Crop Protection)Paul Hendley (Phasera)Tianbo Xu (Bayer CropScience)

on behalf of the Pyrethroid Working Group

SETAC North America - November 2015 © Pyrethroid Working Group 2015 Slide 1

The Pyrethroid Working Group (PWG) is a US task force whose members include AMVAC Chemical Corporation, BASF Corporation, Bayer CropScience LP,

FMC Corporation, Syngenta Crop Protection LLC, and Valent U.S.A. Corporation

PWG and its member companies have conducted many spiked sediment tests with pyrethroids

2003-2005 (FIFRA re-registration) 10-d and 60-d Chironomus, 28-d Leptocheirus; natural and OECD

sediment; 4 pyrethroids

2008-2009 (California pyrethroid re-evaluation) 10-d Hyalella; 4 natural sediments with range of characteristics, and

OECD sediment; cypermethrin

2009-2010 (California pyrethroid re-evaluation) 10-d Hyalella, 10-d Chironomus; OECD sediment; 8 pyrethroids

2012-2013 (FIFRA Registration Review) 10-d Hyalella; natural sediment; 8 pyrethroids

2013-2015 (FIFRA Registration Review) 42-d Hyalella, 60-d Chironomus, 10-d and 28-d Leptocheirus; natural

and OECD sediment; 9 pyrethroids

SETAC North America - November 2015 © Pyrethroid Working Group 2015 2

Equilibrium Partitioning (EqP) is the basis for understanding the toxicity of pyrethroids in sediments

Hydrophobic organic compounds (HOCs) such as pyrethroids partition between particulate organic matter (POM), dissolved organic matter (DOM), and freely dissolved fractions.


POM DOM

Free

EqP theoryOnly the freely dissolved fraction in sediment or water is bioavailable and can cause toxicity to aquatic organisms.

Equilibrium Partitioning (EqP) is the basis for understanding the toxicity of pyrethroids and other HOCs in sediments

For risk assessment, the USEPA Office of Pesticide Programs (OPP) expresses sediment toxicity endpoints in terms of both bulk sediment concentrations (normalized to organic carbon) and pore water concentrations.


Measuring freely dissolved HOCs in pore water (or in surface water) can be extremely challenging.

As an alternative to direct measurement of freely dissolved HOCs, concentrations can be estimated from sediment concentrations using partition coefficients (KOCs).

KOC = Csediment/Cpore water

PWG has developed reliable pyrethroid KOC values – previous data were diverse, uncertain, and based on older analytical methods

Previous KOC values compiled by Laskowski (2002) were, until now, considered the best available data and were widely used for exposure modeling and risk assessment.

PWG derived new KOC values for 9 pyrethroids using uniform methods (batch adsorption) and sediments (the same natural pond sediment and OECD formulated sediment used in toxicity tests), and are therefore fully comparable and more robust than previous values.

PWG derived KOC values using both Liquid-Liquid Extraction (LLE), which measures total pyrethroids, and Solid-Phase Microextraction (SPME), which measures freely-dissolved pyrethroids.


Pyrethroid Laskowski (2002)(KOC‐LLE)

Freshwater sediment (KOC‐LLE)

Freshwater sediment (KOC‐SPME)

OECD formulated sediment (KOC‐LLE)

OECD formulated sediment (KOC‐SPME)

Bifenthrin 237,000 671,000 4,228,000 1,034,000 2,982,000Cyfluthrin 124,000 768,000 3,870,000 1,543,000 2,363,000

Cypermethrin 310,000 1,719,000 3,105,000 1,287,000 3,190,000Deltamethrin 704,000 1,403,000 4,350,000 1,180,000 2,978,000Esfenvalerate 252,000 1,309,000 7,220,000 1,485,000 4,399,000Fenpropathrin 43,000 604,000 1,126,000 779,000 1,142,000λ‐cyhalothrin 326,000 802,000 2,056,000 827,000 3,024,000Permethrin 277,000 1,505,000 6,075,000 760,000 2,653,000Tefluthrin 211,000 2,054,000 1,932,000 3,397,000 3,527,000

Pyrethroid KOC values from batch adsorption studies

KOC-SPME vs KOC-LLE (measured using batch adsorption test system)


Natural pond sediment OECD sediment

• As expected, KOC-SPME values are much greater than KOC-LLE (tefluthrinis an exception).

• Both sets of KOC values are generally greater in natural sediment than OECD sediment (again, tefluthrin is an exception), but the difference is within 2x.

• KOC values are similar (within a factor of 6x or less) across pyrethroids.

Batch adsorption

test

Measurement of KOC under standard batch adsorption test conditions

Pre-equilibrate 200 mL 0.01M CaCl2 with 2 g dry wt sediment for 24 h by shaking (1:100 sed:water)

Add appropriate amount AI Shake 24 h Centrifuge 15 min 10,000g.

Decant Measure KOC-LLE & KOC-SPME

BATCH ADSORPTION TEST


Treat 100 g sand with AI in solvent – allow solvent to evaporate

Mix sand with ~3 kg wet sediment for 4 hours

Store 7 days at 4oC, roll 2 h, store 6 days, roll 2 h

Mix thoroughly, weigh aliquots (100 g) into 300-mL test containers, add 175 mL lab water above sediment (approx. 1:2 sed:water)

Allow to settle for 20-24 h at 20/23oC Gently remove overlying water Centrifuge remaining sediment to obtain

pore water Measure KOC-LLE & KOC-SPME in pore water

SEDIMENT TOXICITY TEST CONDITIONS

Measurement of KOC under sediment toxicity test conditions involves a fundamentally different experiment

Pre-equilibrate 200 mL 0.01M CaCl2 with 2 g dry wt sediment for 24 h by shaking (1:100 sed:water)

Add appropriate amount AI Shake 24 h Centrifuge 15 min 10,000g.

Decant Measure KOC-LLE & KOC-SPME

BATCH ADSORPTION TEST


Sediment toxicity

test

Pyrethroid KOC measurements under toxicity test conditions differ considerably from batch tests

Batch adsorption test system vs toxicity test conditions (KOC-SPME)



• Unexpectedly, KOC-SPME values are much lower when measured under toxicity test conditions than in batch adsorption test systems.

• The same trend is even more apparent with KOC-LLE values (not shown).

• KOC-SPME values measured under toxicity test conditions should be used to estimate freely dissolved pore water concentrations in sediment toxicity tests.

KOC is used to estimate pore water concentration from measured bulk sediment concentration and %OC

Example: Bifenthrin in natural pond sediment under toxicity test conditions


Bulk sediment concentration = 40 μg/kg dry wt

OC-normalized sediment concentrationSediment OC = 3.1%40/0.031 = 1300 μg/kg OC = 1.3 μg/g OC

Pore water concentrationKOC-SPME under toxicity test conditions = 1,030,0001.3/1030000 = 0.0000013 μg/mL = 0.0013 μg/L


Freely dissolved pore water toxicity matches water-only toxicity to Hyalella azteca, as predicted by EqP


10-d pore water LC50s (calculated from bulk sediment LC50 using KOC-SPMEmeasured under sediment tox test conditions) compared with 4-d LC50s from water-only test. Dashed lines indicate agreement within ±5x.

Summary and conclusions

The toxicity of pyrethroids in sediment is a function of the pyrethroid concentration freely dissolved in pore water (this is the basis of EqP theory).

Freely dissolved concentrations in pore water (or in the water column) are challenging to measure directly but can be calculated based on partitioning coefficients (KOCs).

KOCs measured under sediment toxicity test conditions are lower than under batch adsorption conditions.

KOCs measured under sediment toxicity test conditions should be used to estimate pore water concentrations in sediment toxicity tests.

Results of pyrethroid toxicity tests with Hyalella azteca in sediments and water corroborate the EqP theory.


Thank you!

[email protected]

13SETAC North America ‐ November 2015 © Pyrethroid Working Group 2015

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Pyrethroid sediment toxicity data and risk assessment: … · 2015-11-25 · Pyrethroid sediment toxicity data and risk assessment: challenges associated with highly hydrophobic chemicals