The Superfund Basic Research Program (SBRP), in collaboration with the Environmental Protection Agency (EPA) Technology Innovation Program, presents the 2008 edition of Risk e Learning: "Bioavailability - Metals, Organics, and Use at Hazardous Waste Sites". This series of online seminars focuses on the science and policy issues of incorporating bioavailability into risk and exposure assessments. Largely drawing from the successful SBRP Bioavailability Workshop: "Assessing Bioavailability as a Determinant of Pollutant Exposure" held in Tampa, FL (February 2008), the web seminar series features SBRP-funded and other academic researchers and EPA senior staff. The first seminar "Bioavailability of Metals" was May 28th, the second seminar "Bioavailability of Organic Compounds: Methods and Case Studies" is June 11th, and the third seminar "Use of Bioavailability Information at hazardous Waste Sites" is June 18th.
This, the second of the three sessions, will feature Dr. Edward Neuhauser, Principal Environmental Engineer, National Grid, and Dr. Danny Reible, the Bettie Margaret Smith Chair of Environmental Health Engineering at the University of Texas.
Dr. Neuhauser's presentation is titled: True Measurement of PAH Bioavailability in Sediments - Traditional regulatory guidance for screening PAH contaminated sediments have used the total EPA 16 parent PAH's and have correlated these values with summary values from a wide variety of studies. This approach has given very inconsistent results when comparing the EPA total 16 PAH's with actual laboratory toxicology testing. This study has developed a PAH measurement method, the Solid-Phase Microextraction (SPME) method, that actually measures the true bioavailability of PAH's in sediments. The SPME method does not measure the total amount of PAH's present in a sediment sample, but rather only that fraction of PAH's in sediments that are actually present in sediment pore water and are available to benthic organisms. This research has shown that the actual PAH toxicity is concentrated in the alkylated low molecular weight PAH's and that 5- and 6-ring PAH's actually contribute very little to sediment toxicity.
The definition of exposure and risk to contaminants in sediments depends upon access to those contaminants, the extent to which accessible contaminants are bioavailable and the extent to which contaminants accumulate in organisms of interest. Dr. Reible's presentation will focus on efforts to understand and quantify these processes. Recent research associating interstitial water concentrations of PAHs and PCBs to bioaccumulation in benthic organisms will be reviewed. This research has provided an increasingly strong basis for the use of interstitial water concentrations as an indicator of bioavailability, bioaccumulation and ultimately exposure and risk of these contaminants to the benthic community. Building on this basis, field deployable solid phase microextraction devices were developed and used to evaluate bioavailabilty and mobility of organic contaminants in sediments. The use of these devices to assess, in situ, mechanisms and rates of chemical transport and the effectiveness of permeable containment or sorptive barriers (sediment caps) will be summarized.
The session will be moderated by Dr. Karl Gustavson, Contaminated Sediment Liaison to US EPA, US Army Engineer Research and Development Center.