Use of Solid Phase Microextraction (SPME) to Assess the Contribution of PAHs to Toxicity of Sediments at a Former Manufacturing PlantBattelle Sediment Conference Jacksonville, FloridaFebruary 5, 2009

Susan Kane Driscoll, Margaret McArdle, and Pieter Booth

Introduction

• Former manufacturing and assembly plant

• Several site investigations have been conducted, subject to audit by state

• Area of concern: – Brook

• Contaminants of concern:– PAHs, metals,

phthalates, PCBs, and pesticides

Site Habitat and Surroundings• Urban setting with mixed

industrial, commercial, and residential uses

• Stream quality is impacted by typical urban stressors– Impervious surfaces influence

stream flow– Riparian habitat loss from

development– Degradation from storm water

discharges– Ephemeral water flow limits

fish community

Conceptual Model: Brook

• Assessment Endpoint 2: Reduced survival, growth, or reproduction of benthic invertebrates in the brook

• Measurement Endpoints: Comparison to sediment benchmarks, chronic toxicity tests, and PAH toxicity models

Exposure Assessment: Freshwater Brook• 25 sediment samples screened for metals

and SVOCs• 14 sediment samples selected for further

analysis– Chronic sediment toxicity with Hyallela azteca– Pesticides– 34 PAHs– Total organic carbon– Grain size– Black carbon– Solid-phase microextraction (SPME) and analysis of

34 PAHs in pore water

Freshwater Brook: Sample Locations

Freshwater Brook

• Sediment– Lead was detected up to 6,400 mg/kg– Zinc was detected up to 900 mg/kg– Antimony was detected up to 200 mg/kg– Total PAHs were detected up to 900 mg/kg– Pthalates were detected up to 1,000 mg/kg– Total PCBs were detected up to 1 mg/kg– Total DDT was detected up to 0.09 mg/kg

• Porewater – SPME used to measure PAHs in a subset of

samples

Effects Assessment for PAHs based on U.S. EPA Guidance Documents• U.S. EPA. 2003—Procedures for the Derivation

of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: PAH Mixtures

• U.S. EPA. 2000—Draft Methods for the Derivation of Site-Specific Equilibrium Partitioning Sediment Guidelines (ESGs) for the Protection of Benthic Invertebrates: Nonionic Organics

U.S. EPA ESB Approach

• Calculates “toxic units” for 34 PAHs as:

– Note: EPA FCV provided as mg/kg OC or mg/L

• If Sum-TU for 34 PAHs < 1.0, concentration of total PAHs in sediment is protective of benthic invertebrates

C SED, PAHi

Final Chronic Value PAHi

U.S. EPA ESB Approach

• Three methods used to calculate Σ-TUs:

– One-phase model estimates PAHs in pore water from PAHs in bulk sediment and TOC

– Two-phase model estimates PAHs in pore water from PAHs in bulk sediment, TOC, and black carbon

– Solid phase microextraction (SPME) method directly measures PAHs in pore water

One-Phase Model for Calculating the Sum of Toxic Unitswhere:

CSED = concentration of each PAH in sediment (µg/kg dry wt)

CW = concentration of truly dissolved PAH in pore water (µg/L)

fTOC = weight fraction of TOC (kg organic carbon/kg dry wt)

KOC = organic carbon-water partition coefficient (L/kg)

The equation is rearranged and used to solve for CW. CW for each PAH is divided by its corresponding FCV to calculate a toxic unit.

CSED/CW = fTOC ･ Koc

Two-Phase Model for Calculating the Sum of Toxic UnitsCSED/CW = fNPOC

･ KOC + fBC

･ KBC CW

n-1

where:

CSED = concentration of each PAH in sediment (µg/kg dry wt)

CW = concentration of truly dissolved PAH in pore water (µg/L)

fNPOC = weight fraction of non-pyrogenic organic carbon in sediment (kg non-pyrogenic organic carbon/kg dry wt, calculated from the difference between TOC and black carbon)

KOC = organic carbon to water distribution coefficient (L/kg)

fBC = weight fraction of black carbon in sediment (kg black carbon/kg dry wt)

KBC = black carbon to pore water partition coefficient (L/kg)n = Freundlich exponent, which accounts for nonlinear sorption behavior

(n=0.6) (Accardi-Dey and Gscwend 2002)

An iterative approach was used to solve for CW. CW for each PAH is divided by its corresponding FCV to calculate a toxic unit.

Relationship of log KOW to log KBC

Data from Accardi-Dey and Gschwend 2003

Station TOC (%)

BC as %

of TOC

Lead (mg/kg)

Total (34)PAHs

(mg/kg)

Avg Survival

(%)

Avg Repro

(# offspring)

1 0.6 1.6 7.9 2.0 96 8.22 1.4 0.7 26 10 94 7.33 2.6 2.5 52 11 91 7.44 2.2 12.3 6400 662 78 2.45 2.3 2.4 1100 68 93 7.76 2 1.5 1900 114 84 2.87 2.7 4.5 2500 895 63 3.28 1.7 8.5 2600 150 83 4.59 3.2 2.4 2700 225 2 0

10 1.9 0.5 710 84 94 5.311 1.9 0.5 420 72 93 7.312 2.0 2.1 1200 57 10 1.013 1.4 17.8 340 48 90 6.314 2.0 2.3 240 101 92 4.7

Results of Physical Analyses for the Brook Study Site

Significantly reduced survival = green Significantly reduced growth = yellow

Sum ESB Toxic Units for Modeled and Measured PAH Concentration in Porewater

Concentrations of PAHs in pore water measured by SPME were much lower than predicted from the one-phase or two-phase model, which could be influenced by the values of KBC used in the 1-phase and 2-phase models.

Conclusions of SPME Analyses• PAHs were ruled out as contributing to

observed toxicity

– ΣTU SPME indicates that PAHs would not result in toxicity

– ΣTU for any method (one-phase, two-phase, or SPME) did not correlate strongly with survival and reproduction

Correlation Analysis

• Several metals, PAHs, PCBs, and phthalates were strongly correlated with each other and with survival and reproduction– Lead exceeded probable

effect concentration (PEC) to much greater extent; lead PEC-hazard quotient ranged from 2 to 50

• Target cleanup level for lead set to 1,150 mg/kg

Numbers = Stations

Proposed Remediation Area

Summary and Conclusions

• Previous ERAs indicated that brook sediments adjacent to the plant posed an unacceptable ecological risk and would need to be remediated

• Collecting site-specific data and using innovative approaches in sediment bioavailability provided more realistic estimates of ecological risk and the extent of remediation required in these areas