Improving Passive Sampling to Detect Low-Level...
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Chemistry Department SCCWRP Dr. Gi Beum Kim (Visiting Scientist from South Korea) 1 Improving Passive Samplers to Detect Low-Level CECs
Transcript of Improving Passive Sampling to Detect Low-Level...
Chemistry Department SCCWRP
Dr. Gi Beum Kim
(Visiting Scientist from South Korea)1
Improving Passive Samplersto Detect Low-Level CECs
Background
Why do we need passive samplers?
1. Detection of trace environmental contaminants is difficult with conventional methods
• CA Ocean Plan Goals for DDTs and PCBs (30 day average conc.)− ΣDDTs = 0.00017 ug/L − ΣPCBs = 0.000019 ug/L
• Standard method using 1-L sample Mostly “non-detect”
* reporting limit in ng/L
• Analyzing larger volume water samples is expensive, time-consuming and uses a lot of solvents.
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Compound Los Angeles San Gabriel Desired RL*River River
17b-estradiol <1.25 <1.25 0.1permethrin <0.17 1.72 0.1
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Biol
ogic
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ffect
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log Total Concentration of HPAH
%Mortality
BRI
Background
Why do we need passive samplers?
2. Total concentrations are not always informative
Current methods that target bulk (“total) concentration are not always predictive of effects (e.g. toxicity, bioaccumulation)
Methods that measure the freely dissolved concentration (Cfree) can better represent true exposure
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0.001 0.01 0.1 1 10 100 1000
Toxic> 41 TU
Sur
viva
l (%
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Porewater PAH34 Conc. (Toxic Units)
Nontoxic< 5.2 TU
Area of Uncertainty
Probit Analysis of EPA H. azteca 28-day Tests
Cfree (∑PAH 34)
What are passive samplers and what do they measure?
Background
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Passive samplers are made of polymers with ahigh surface area/volume ratio
Polymers: low density polyethylene (LDPE)polydimethylsiloxane (PDMS or “silicone”)
Shapes: polymer coated glass fibers, stainless needlesthin films or sheetscoating thickness: 10-100 um
Passive samplers measure Cfree of organic chemicals
Cfree is better correlated with bioaccumulation and toxicity than total conc.
What else can passive samplers accomplish?
Background
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Obs
erve
d T
issu
e(µ
g/kg
lipi
d)
Predicted Tissue = Cfree x Kow
in oligochaetes
PCBs & PAHs
Development and Standardization of PSD Method for CECs
Many passive sampling methods and applications (field, lab) are available
No broad consensus or guidance on which methods are “best” or “ready”
SETAC Workshop on PSMs for contaminated sediments brought 50 experts
together in 2012
Regardless of method/application, standardized methods are needed.
Standardized methods for Cfree are needed
Goal
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OUR GOAL
Develop and standardize lab-based methods
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1. Select model CECs of interest (PBDEs, pyrethroids)
2. Standardize lab-based methods for sediment Cfree usingwell-known polymers (e.g. LDPE, PDMS)
3. Test different polymers for less hydrophobic CECs
4. Develop strategy to correct lab-based Cfree for field applications
Approach
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Results
1. Select Model CECs for Standardization
• Many contaminants of emerging concern (CECs)
• Expert Panel recommended monitoring of CECs fromdifferent chemical/use classes
• CECs selected• Pesticides : fipronil, bifenthrin (a pyrethroid)• Flame retardant ; PBDE-47
• Compare behavior of model CECs to behavior of legacycompounds (PCBs, DDTs, PAH)
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CP
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BDE-47
Results
2. Standardize equilibration time, polymer massPassive sampler - 5-25 mg Polyethylene (PE)Sample - Sediment slurry (water added to ensure better mixing)Spiking - Model Compounds (incl. pyrethroids, PBDEs)Exposure period - 20 days with shaking
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<PE>
Lab-based method accelerates measurement of Cfree
3. Modifying polymer improved sorption of fipronil
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Control MeOH MeOH/EE IPA EE
Fipronil and its metabolites are moderately hydrophobic CECsWe tested sorption of fipronil by different polymers acrylic (PMMA) worked bestWe modified PMMA by solvent swelling to improve sorption Ethyl ether is best
Results
mean log Kow ~ 3.5
Modifying acrylic improves sorption of slightly soluble CECs (like fipronil)
mean log Kow ~ 6
PCBs
Fipronil
4. Correcting Cfree under field conditions
phenanthreneanthracene
fluoranthrenepyrene
Temperature (℃)
Log
Par
titio
n co
effic
ient
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Results
Challenges in the field:• Static conditions delay equilibrium time • Temperature and salinity can affect the freely dissolved concentration (Cfree)
Correction factors can be applied to include field parameters in the calculations of the freely dissolved concentrations
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Next Steps
• Compare lab and field based Cfree measurements for sediments• Identify sources and direction of transport of CECs • Calibrate food-web bioaccumulation models • Couple passive samplers to directly measurements of toxicity /benthic
community index in sediment assessment triad
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Future
ChemistryCtotal Cfree
(Today ) (Future)
Benthic Community
Toxicity -Bioscreening
assay
AdvancedSediment
Assessment Triad
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Questions ?
<Stained cutting board showed the chemicals absorbed in passive samplers>
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Background
Why do we need Passive Sampler?
2. Total concentrations are not always informative
Current (Convention) method Bulk or total conc. Not always predictive of impacts
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0
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100
0.001 0.01 0.1 1 10 100 1000
Toxic> 41 TU
Sur
viva
l (%
)
Porewater PAH34 Conc. (Toxic Units)
Nontoxic< 5.2 TU
Area of Uncertainty
Probit Analysis of EPA H. azteca 28-day Tests
Cfree (∑PAH 34)
Passive sampler method Freely dissolved conc. (Cfree) Be a better metric of exposure
Probit Analysis of EPA H. aztec 28-day Tests
<Cfree>
Particulate
Dissolved organic carbon
( ; chemicals)
<Ctotal>
How you can benefit from using passive samplers
Future
Category Item Passive Sampler Convention Method
Economic Time of analysis 1 day 4 days
Cost Cheap Very expensiveScientific Detection limit Low Low ~ medium
Measurement Cfree Ctotal
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