Analytical and Relative Potency Factor Approach for Effective Evaluation of Polycyclic Aromatic Hydrocarbons Betty Krupka, Scott Kirchner, and Vanessa Macwan Edison, New Jersey CDM ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are chemicals that include organic compounds containing either two or more, or three or more, fused rings made up of hydrogen and carbon atoms. PAHs are persistent and primarily occur in the environment as complex mixtures produced from the incomplete combustion of substances containing hydrocarbons. Using a weight-of- evidence approach, the United States Environmental Protection Agency (EPA) has determined that 24 PAHs are carcinogenic based on toxicological similarities to the indicator compound benzo(a)pyrene. EPA has proposed using a relative potency factor (RPF) approach for estimating the cancer risk of PAH mixtures by summing doses of component PAHs using scaled doses of the individual PAHs relative to the potency of benzo(a)pyrene. Previously, RPFs were developed for seven carcinogenic PAHs by EPA in PAH analytical methods were compared for their potential effectiveness to yield useable data to evaluate all 24 carcinogenic PAHs necessary for the EPA’s proposed RPF approach for use in risk assessment. The application of the methods for specific matrices, target compounds, quality control procedures, and reporting limits are evaluated and presented to add better understanding of analytical methods for data end users such as risk assessors. This information will assist in the selection of the appropriate method that can be applied to their study. Particular attention is paid to the method reporting limits and the analytical and sample matrix factors that affect data evaluation and application in risk assessments. Controlling the variables associated with method reporting limits is instrumental in enhancing the effectiveness of the data when applying derived results to the PAH mixture risk evaluation. CURRENT AND PROPOSED RELATIVE POTENCY FACTORS SW , EPA 625, 525 OR CLP SOM01.2 WITH OR WITHOUT SELECTIVE ION MONITORING (SIM)  Relatively easy to secure – EPA approved methodologies  Lower cost (approximately $200 per sample)  Used when high concentrations of PAHs are suspected  Compound peaks quantified from “non-analog” internal standard  Limited clean up – can not rigorously clean up a sample if matrix interference observed  Reporting limits for soils: gas chromotography/mass spectroscopy (GC/MS) 170 µg/kg; GC/MS-SIM 3.3 µg/kg  Reporting limits for water: GC/MS 5.0 µg/L; GC/MS-SIM 0.1 µg/L POLYCYCLIC AROMATIC HYDROCARBONS BENZO(A)PYRENE TOXICITY  Group B2 probable human carcinogen  Benzo(a)pyrene carcinogenicity is based on a mutagenic mode of action  Ecological and human health effects include forestomach, larynx and esophagus papillomas and carcinomas  Interactions among PAH mixtures do not occur at low (environmental) levels of exposure  Oral Slope Factor: 7.3 per mg/kg-day  Drinking Water Unit Risk: 2.1 x per µg/L  Currently there are 7 PAHs considered by the EPA to be carcinogenic  Toxicity of the PAHs are assessed using relative RPFs to Benzo(a)pyrene CONCLUSION  Additional carcinogenic PAHs are not routinely analyzed  Need to work closely with laboratory to identify method reporting limits and method development REFERENCES Agency for Toxic Substances & Disease Registry Polycyclic Aromatic Hydrocarbons. 8/1995. Website: AXYS Analytical Services Ltd. Ion Chromatograms for Benzo(a)pyrene. Website: EPA Integrated Risk Information System (IRIS) (online database of toxicity measures). Website: U.S. Geological Survey Determination of Semivolatile Organic Compounds and Polycyclic Aromatic Hydrocarbons in Solids by Gas Chromotography/Mass Spectrometry. Website: Mixed method approach:  To take advantage of the long holding times for soils and sediments, (frozen up to one year prior to extraction) (USGS, 2006) - collect samples for the laboratory to hold and freeze  Utilize the GC/MS approach to identify areas with high PAH concentrations via calibration standards or library search  For post remedial confirmatory samples to cleanup levels use the isotope dilution method  Lower reporting limits can confirm that the site is cleaned below applicable risk threshold ION CHROMATOGRAMS FOR BENZO(A)PYRENE MIXED METHOD APPROACH METHOD OF ISOTOPE DILUTION GC/MS WITH SIM  Currently rather specialized – not an EPA approved method  Generally higher cost (approximately $450 per sample)  Most useful for identifying low concentrations of PAH  Compound peaks quantified from isotopically labeled analogs of target PAHs  Sample extracts can be cleaned more rigorously since each target has a labeled analog  Reporting limits for soils: 0.5 ng/g to 1.0 ng/g  Reporting limits for water: 5 ng/L to 10 ng/L  Benzo[g]chrysene  CAS No  C22-H14  Cyclopent[h,i]- aceanthrylene  CAS No  CPhiACEA  3,4-10,11-12,13- Tribenzofluoranthene  CAS No  TBF  Fluorene  CAS No  C13-H10  Benzo(a)pyrene  CAS No  C20-H12  Benzo[k]fluoranthene  CAS No  C20-H12 AnalyteCAS No. Residential Soil Residential Air TapwaterMCL (µg/kg)(µg/m 3 )(µg/L) Benzo(a)pyrene ANALYTICAL METHOD Low level reference sample Benzo(a)pyrene – concentration = 3.27 ng/g Peak 1 (all peaks labeled from top channel) = matrix Peak 2 = benzo(e)pyrene Peak 3 = matrix Peak 4 = benzo(a)pyrene Peak 5 = matrix Peak 6 = pyrene Ion abundance Ratio = 0.19 D12-benzo(a)pyrene – concentration = 2120 ng absolute / 10.3 = ng/g = 87.5% recovery Peak 1 = d12-benzo(e)pyrene Peak 2 = d12-benzo(a)pyrene Peak 3 = d12-perylene Ion abundance Ratio = 0.23 Relative Potency Factors PAHProposed RPFCurrent RPF Anthanthrene0.4-- Benz(a)anthracene Benzo(a)pyrene11 Benz[b,c]aceanthrylene, 11H Benzo(b)fluoranthene Benz[e]aceanthrylene0.8-- Benzo[g,h,i]perylene Benz[j]aceanthrylene60-- Benzo[j]fluoranthene0.3-- Benzo(k)fluoranthene Benz[l]aceanthrylene5-- Chrysene Cyclopenta[c,d]pyrene0.4-- Cyclopenta[d,e,f]chrysene, 4H Dibenzo[a,e]fluoranthene0.9-- Dibenzo[a,e]pyrene0.4-- Dibenz[a,c]anthracene4-- Dibenz(a,h)anthracene101 Dibenzo[a,h]pyrene0.9-- Dibenzo[a,i]pyrene0.6-- Dibenzo[a,l]pyrene30-- Fluoranthene Indeno(1,2,3-cd)pyrene Naphtho[2,3-e]pyrene0.3-- EPA REGIONAL SCREENING LEVEL D12-BENZO(A)PYRENE BENZO(A)PYRENE Highlighted values indicate PAHs currently considered carcinogenic by EPA.