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

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

2 PWG and its member companies have conducted many spiked sediment tests with pyrethroids (FIFRA re-registration) 10-d and 60-d Chironomus, 28-d Leptocheirus; natural and OECD sediment; 4 pyrethroids (California pyrethroid re-evaluation) 10-d Hyalella; 4 natural sediments with range of characteristics, and OECD sediment; cypermethrin (California pyrethroid re-evaluation) 10-d Hyalella, 10-d Chironomus; OECD sediment; 8 pyrethroids (FIFRA Registration Review) 10-d Hyalella; natural sediment; 8 pyrethroids (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

3 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 Free DOM EqP theory Only the freely dissolved fraction in sediment or water is bioavailable and can cause toxicity to aquatic organisms. SETAC North America - November 2015 Pyrethroid Working Group

4 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 (K OC s). K OC = C sediment /C pore water SETAC North America - November 2015 Pyrethroid Working Group

5 PWG has developed reliable pyrethroid K OC values previous data were diverse, uncertain, and based on older analytical methods Previous K OC 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 K OC 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 K OC values using both Liquid-Liquid Extraction (LLE), which measures total pyrethroids, and Solid-Phase Microextraction (SPME), which measures freely-dissolved pyrethroids. Pyrethroid Laskowski (2002) (K OC LLE ) Freshwater sediment (K OC LLE ) OECD formulated Freshwater sediment sediment (K OC SPME) (K OC LLE ) OECD formulated sediment (K OC SPME ) Bifenthrin 237, ,000 4,228,000 1,034,000 2,982,000 Cyfluthrin 124, ,000 3,870,000 1,543,000 2,363,000 Cypermethrin 310,000 1,719,000 3,105,000 1,287,000 3,190,000 Deltamethrin 704,000 1,403,000 4,350,000 1,180,000 2,978,000 Esfenvalerate 252,000 1,309,000 7,220,000 1,485,000 4,399,000 Fenpropathrin 43, ,000 1,126, ,000 1,142,000 λ cyhalothrin 326, ,000 2,056, ,000 3,024,000 Permethrin 277,000 1,505,000 6,075, ,000 2,653,000 Tefluthrin 211,000 2,054,000 1,932,000 3,397,000 3,527,000 SETAC North America - November 2015 Pyrethroid Working Group

6 Pyrethroid K OC values from batch adsorption studies K OC-SPME vs K OC-LLE (measured using batch adsorption test system) Natural pond sediment OECD sediment As expected, K OC-SPME values are much greater than K OC-LLE (tefluthrin is an exception). Both sets of K OC values are generally greater in natural sediment than OECD sediment (again, tefluthrin is an exception), but the difference is within 2x. K OC values are similar (within a factor of 6x or less) across pyrethroids. SETAC North America - November 2015 Pyrethroid Working Group

7 Measurement of K OC under standard batch adsorption test conditions BATCH ADSORPTION TEST 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 Batch adsorption test Measure K OC-LLE & K OC-SPME SETAC North America - November 2015 Pyrethroid Working Group

8 Measurement of K OC under sediment toxicity test conditions involves a fundamentally different experiment BATCH ADSORPTION TEST 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 K OC-LLE & K OC-SPME Sediment toxicity test SEDIMENT TOXICITY TEST CONDITIONS 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 4 o C, 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 h at 20/23 o C Gently remove overlying water Centrifuge remaining sediment to obtain pore water Measure K OC-LLE & K OC-SPME in pore water SETAC North America - November 2015 Pyrethroid Working Group

9 Pyrethroid K OC measurements under toxicity test conditions differ considerably from batch tests Batch adsorption test system vs toxicity test conditions (K OC-SPME ) Natural pond sediment OECD sediment Unexpectedly, K OC-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 K OC-LLE values (not shown). K OC-SPME values measured under toxicity test conditions should be used to estimate freely dissolved pore water concentrations in sediment toxicity tests. SETAC North America - November 2015 Pyrethroid Working Group

10 K OC 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 concentration Sediment OC = 3.1% 40/0.031 = 1300 μg/kg OC = 1.3 μg/g OC Pore water concentration K OC-SPME under toxicity test conditions = 1,030, / = μg/ml = μg/l SETAC North America - November 2015 Pyrethroid Working Group

11 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 K OC-SPME measured under sediment tox test conditions) compared with 4-d LC50s from water-only test. Dashed lines indicate agreement within ±5x. Natural pond sediment OECD sediment SETAC North America - November 2015 Pyrethroid Working Group

12 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 (K OC s). K OC s measured under sediment toxicity test conditions are lower than under batch adsorption conditions. K OC s 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. SETAC North America - November 2015 Pyrethroid Working Group

13 Thank you! SETAC North America November 2015 Pyrethroid Working Group