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Use of Solid Phase Microextraction (SPME) to Assess the Contribution of PAHs to Toxicity of Sediments at a Former Manufacturing Plant. Battelle Sediment Conference Jacksonville, Florida February 5, 2009 Susan Kane Driscoll, Margaret McArdle, and Pieter Booth. Introduction.
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Use of Solid Phase Microextraction (SPME) to Assess the Contribution of PAHs to Toxicity of Sediments at a Former Manufacturing Plant Battelle Sediment Conference Jacksonville, Florida February 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 • 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 Units CSED/CW = fTOC・ Koc where: 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.
Two-Phase Model for Calculating the Sum of Toxic Units CSED/CW = fNPOC・ KOC+fBC・KBCCW 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
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
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