W4 PM Sediment Quality Assessment
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in Ballroom 4

(PAG-1117-553613) Measuring the extent of PAH contaminated shoreline sediments at spill sites in Prince William Sound, Alaska.

Page, D¹, Boehm, P², Brown, J², Bence, A³, Neff, J⁴, ¹ Bowdoin College, Brunswick, ME² Exponent Inc., Maynard, MA, USA³ ExxonMobil Upstream Research Co., Houston, TX, USA⁴ Battelle, Duxbury, MA, USA

ABSTRACT- A field study was done in 2004 to estimate the areal distribution and concentrations of polycyclic aromatic hydrocarbons (PAH) in intertidal sediments at 12 sites in Prince William Sound (PWS), Alaska, once heavily oiled by the 1989 Exxon Valdez oil spill (EVOS) and found to contain buried EVOS remnants in 2002. A hierarchical analytical approach used a rapid colorimetric field screening test, based on the sediment solvent extract color, to give estimates of the total PAH concentration (TPAH) for many samples, backed up by more accurate and precise laboratory methods applied to subsets of field samples. This increased the ability to identify hotspots, in keeping with EPA recommendations. The assessment process has 6 steps: (1) Locate visual evidence of surface oil/tar. (2) Draw a site map and lay out a sampling grid (10-m spacing) over the intertidal area at low tide; (3) Dig pits 50 cm deep on the grid; (4) Perform the qualitative field colorimetric test on sediments from each pit to estimate TPAH and record the results in the ranges <1 ppm; 1-10 ppm; >10 ppm. (5) Expand the gridded area if significant TPAH levels are detected colorimetrically; (6) Based on the colorimetric results, select 5 samples at each site for same-day shipboard PAH immunochemical analysis (SDI RaPID™ PAH) as a calibration check and, based on immunoassay data, select samples for full laboratory analysis to determine PAH sources. A total of 226 pits were dug. A combined area of 211 m² of sediment is estimated to have TPAH exceeding the 4 ppm Effects Range-Low sediment quality guideline value. Immunochemical analyses of 85 samples from the 12 sites yielded TPAH values ranging from 0.001-10.3 ppm (wet wt.), with 3 of the 85 samples exceeding 4 ppm at 2 of the 12 sites. The contaminants are mixtures of 2-3 ring spill related petroleum PAH and 4-6 ring background combustion product PAH. Mussels and clams collected at these sites have tissue PAH of similar composition to the PAH in the sediments but at levels within the range of non-spill sites, except for 2 locations. The median TPAH from all sources was 5 ppb (n = 25; dry wt.) for mussels and 54 ppb (n=20; dry wt.) for clams, indicative of low bioavailability of any spill remnants present. This study shows how a hierarchical approach can be used to rapidly map, quantify, and characterize spill remnants at oil spill sites.

Key words: Exxon Valdez, PAH, Site Mapping