Environmental Fate and Distribution of Cyclic Volatile Methylsiloxane Materials: Modeling and Monitoring Data

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1 Environmental Fate and Distribution of Cyclic Volatile thylsiloxane Materials: Modeling and Monitoring Data Hudson-Delaware Chapter SETAC October 8, 2008 Charles Staples, Ellen Mihaich, Kathy Plotzke, Gary Koserski, Shihe Xu, Reinhard Gerhards and Joe Bazinet

2 Overview Discussion will focus on cyclic volatile methylsiloxane materials (cvms): D4 D5 D6 Si O O Si Si O O Si O Si Si O Si O Si O O Si O Si Si O O Si Si O O Si Si O Overview of media-specific half-lives Evaluation/selection of partition coefficients Fate and transport based on modeling and monitoring Conclusions 2

3 Cyclic Volatile thyl Siloxanes (cvms) Materials Clear, volatile, low-viscosity silicone fluids Beneficial physical and chemical properties adequate evaporation rate low surface tension no odor Used in the manufacture of silicone polymers and in a range of consumer applications including: Personal care Cleaning agents Household care 3

4 Motivation Identified as emerging substances by various authors Muir and Howard, 2006; Chapman, 2006 Are cvms persistent and bioaccumulative? Screening based on single compartment criteria, modeling Show potential for bioaccumulation Do cvms really behave as PBT? Do cvms act as POP s? Long range transport and deposition Screening monitoring conducted (Norway, Sweden, Silicone Industry) has demonstrated that data beyond screening criteria should be evaluated to describe cvms behavior in the environment 4

5 Scientific Approach Tiered approach, based on evaluating Persistence Bioaccumulation Toxicity A tiered approach to overall research plan: Lab studies Modeling Field Studies More Modeling 5

6 Degradation Processes Air Compartment Half-Lives D4 D5 D6 Rxn with OH radical (7.7 x 10 5 molec cm -3 ) 10 d 7 d 5 d Rxn with minerals/uv/ozone/humidity (prelim) <10 d <7 d < 5 d Soil Compartment Clay catalyzed hydrolysis (RH = 100%) < 5 d (80%) < 13 d < 200 d Clay catalyzed hydrolysis (RH = 32%) 1 h (20%) 2 h 33 h Water Compartment Abiotic hydrolysis (ph 7, 25 ºC) 4 d 71 d 401 d Abiotic hydrolysis (ph 7, 12 ºC) 17 d 314 d 6 y Sediment Compartment Biotic/Abiotic degradation??? 6

7 Air Degradation: Summary of the Results to Date Mineral aerosols can significantly remove D4 and D5 from the gas phase of the atmosphere, especially under dry conditions Ozone and Ozone/UV can promote the removal of D4 and D5 from the gas phase by the mineral aerosols Urban-centralized emission substantially reduces the overall half-lives of D4 and D5 in the atmosphere due to the high concentration of hydroxyl radicals in the densely populated regions Data generated to date suggest the half-lives are significantly less than currently reported half-lives 7

8 Sediment Persistence: Issue D4/D5 were deemed persistent in sediment on the basis of the data from a single (bio)degradation study (Springborn 1991) that was not designed to accommodate volatile materials or quantify degradation products. Reassessment of these data does suggest that abiotic degradation is taking place. All mechanisms of degradation, whether biotic or abiotic, should be considered when evaluating persistence. 8

9 Sediment Persistence: Preliminary OECD 308 Results Initial data (through 3 weeks) from an ongoing study based on the OECD 308 guideline indicates that D4 will have a half-life in water/sediment much less than the 365 day criterion Key ln C D4 /C 0 D Half-Life = 47.3 days Incubation Time at 22 o C (Days) Total recovery % Total Recovery D4 Remaining C D4 = Conc. Of D4 at time t = Initial D4 Conc. C o D4 Note Sediment from Sanford Lake MI ph = 6.9 after acclimation Initial D4 Conc.= 0.2 μg/g Sediment All degradation products quantified 9

10 Lipophilicity: Importance for Accumulation Dynamics Property Compound Value Reference Log K ow D Kozerski and Shawl, 2007 D Kozerski, 2007 D SEHSC, 2007 Uptake of highly lipophilic chemicals (log K ow >5) from water (via gills) relative to dietary uptake (via gut) is considered small for most fish species and the importance of dietary uptake of lipophilic chemicals increases with increasing log K ow (Bruggeman et al., 1984; Thomann, 1989; Qiao et al., 2000; Loizeau et al., 2001; Nichols et al., 2001; Borga et al., 2004). 10

11 Empirical bioaccumulation data for D5 Test organism Endpoint Value Reference Pimephales promelas BCF ss 7060 L/kg wet wt. Drottar (2005) Pimephales promelas BCF k L/kg wet wt. Drottar (2005) Oncorhynchus mykiss BMF ss 0.82 (lipid normalized) Calculated from Drottar (2006) and Domoradzki and Woodburn (2008) Oncorhynchus mykiss BMF k 0.32 (includes k 2 + k g for total depuration) Calculated from Drottar (2006) and Domoradzki and Woodburn (2008) Oncorhynchus mykiss BMF k-lipid 0.91 (lipid normalized) Calculated from Drottar (2006) and Domoradzki and Woodburn (2008) Chironomus riparius BSAF * Springborn Smithers Laboratories (2003) Freshwater fish Field BSAF sediment-to-fish 0.79 (mean) (95% confidence range) Calculated from Norden (2005) for Helsinki, Finland * Value may be elevated due to presence of sediment in gut of invertebrate 11

12 Partition Coefficients D4 D5 D6 Mw (g mol -1 ) Log K a AW 2.7 (1.4) 3.1 (1.1) 3.3 (0.8) Log K b OA 4.3 (3.1) 5.1 (4.1) 5.8 (5.1) Log K c OW 6.5 (4.5) 8.0 (5.2) 9.1 (5.9) Log K d OC 4.2 (6.0) 5.2 (7.6) 6.1 (8.6) a asured/estimated K AW (Kochetkov et al values in parenthesis) b asured K OA (values in parenthesis from literature K AW and K OW values) c asured/estimated K OW (Bruggeman et al values in parenthesis) d asured/estimated K OC (estimated K OC = 0.35*K OW ; Seth et al. 1999) 12

13 Emission Scenarios Compartment D4 D5 D6 % Air % Soil % Water

14 The Globo-POP Model Level IV multimedia fate/transport model 10 latitudinal climate zones 9 environmental compartments Air (4), water (2), sediment, soil (2) No assumption of steady-state conditions Inputs Partitioning properties (temp dependence) Degradation rates (temp dependence) Emission scenarios Outputs of interest Fraction degraded Zonally-averaged distributions Amount in Arctic Surface dia Total Global Amount Emitted Arctic Contamination Potential (eacp) = x

15 D4, D5 and D6 Are Different from Known Arctic Contaminants D4 D5 D6 AC-BAP Old K AW Yellow Circles: D4, D5 and D6 with most recent K aw data Old K aw = placement of D6 with old K aw Blue Open Diamonds: 86 known arctic contaminants Brown, T. N.; Wania, F. Environ. Sci. Technol Published on Web. 06/11/

16 Monitoring Data: Information to date No detectable* D4, D5 and D6 were found in sediment and zooplankton in a isolated lake (i.e., Lake Opeongo) No detectable* D4, D5 and D6 in the sediments in Lake Ontario except the sediment sample in Toronto harbor (only sample that may be influenced by direct waste water discharge) No detectable D4, D5 and D6 in water, soil and sediment samples in any remote areas included in Norwegian monitoring program (Norden 2005) Monitoring data to date does not support any evidence of back deposition or long-range transport to the Arctic *thod Detection Limit < 1/3000 times the lowest NOEC for sediment-dwelling animals 16

17 Monitoring of cvms (Lake Ontario) CCGS Limnos (July 2006) - Ship time provided by Derek Muir Station 81 Water depth: 35 m Surface sediment (5 cm) Station 725 Water depth: 10 m Surface sediment (5 cm) Core Station 13 Water depth: 105 m Mysid (104 m) Sediment cores (0.5 cm) Core Station 40 Water depth: 185 m Water (4 m; 100 m) Zooplankton (175 m) Mysid (180 m) Sediment cores (1.0 cm) Core Station 64 Water depth: 230 m Zooplankton (205 m) Mysid (225 m) Sediment cores (0.5 cm) 17

18 Lake Ontario Sediment 300 D4 Concentrations 0 CS 13 CS 40 CS 64 ng/g dw Limit of detection asured Limit of quantitation Depth in core (cm) D4 Concentration (ng/g dw) asured LOD 18

19 Lake Ontario Sediment D5 Concentrations 0 CS 13 CS 40 CS 64 ng/g dw Limit of detection asured Limit of quantitation Depth in core (cm) D5 Concentration (ng/g dw) asured LOD 19

20 Lake Ontario Sediment D6 Concentrations 0 CS 13 CS 40 CS 64 ng/g dw Limit of detection asured Limit of quantitation Depth in core (cm) D6 Concentration (ng/g dw) asured LOD 20

21 Conclusions The chemical space (K OA, K AW, and K OW ) of D 4 and D 5 indicates that these materials will partition mainly to air. cvms materials in the air compartment: Degrade via OH-radical oxidation (half-life 10 d or less) Are fliers (transported in air) Have low deposition potential from air (high K AW, low K OA ) cvms materials in the water compartment: Removed from water by degradation (hydrolysis), deposition to sediment, and volatilization Deposit to sediment in vicinity where emitted Not expected to undergo advective transport 21

22 What Have We Learned? Historically, fate and effects modeling of cvms is subject to a number of errors nearly all of which predict properties which are not consistent with what is currently being measured in the environment. There are a number of reasons for this, including: cvms are very difficult to work with in laboratory testing and therefore the values that are put into fate and effects models have to be reviewed with great care. Many of the models themselves have not been calibrated for materials with the unique properties of cyclic siloxanes. Given the challenges associated with getting accurate environmental and biological fate data, it is imperative that a weight-of-evidence evaluation look at existing environmental data and future monitoring data. The goal of this should be to ground-truth whether the modeling efforts could be under/over-predicting the environmental behavior and occurrence 22

23 Acknowledgments Coauthors: Ellen Mihaich Gary Koserski Shihe Xu Kathy Plotzke Reinhard Gerhards Joe Bazinet Prof. Frank Wania Dr. Derek Muir 23