PARENT SESSION
38 - Soil and Sediment Contamination
8:00 AM to 6:30 PM, Tuesday, 14 May 2002
Exhibition Area

(38-36) Deposition and accumulation of polydimethylsiloxane in sediments of the upper Mississippi River (USA).

Powell, David^*,1,2, Sandheinrich, Mark², Rada, Ronald², Engstrom, Danial³, ¹ Environmental Sciences, Midland, Michigan² River Studies Center, La Crosse, Wisconsin³ St. Croix Watershed Research Station, Marine on St. Croix, Minnesota

ABSTRACT- Sediment cores were analyzed to reconstruct the historical deposition of polydimethylsiloxane (PDMS) in Lake Pepin, a natural lake in Navigation Pool 4 of the Upper Mississippi River. Concentration of total organosilicon extracted by tetrahydrofuran (defined as ^THFSi_tot) was measured in four ²¹⁰Pb-dated sediment cores. Generally, concentrations of ^THFSi_tot were greatest in surface sediments (range 3.2 to 9.3 g/g dry weight) and decreased with depth to a relatively constant background (range 0.3 to 0.7 g/g dry weight). Concentrations of PDMS were calculated as the difference between measured concentration of ^THFSi_tot and the mean concentration of ^THFSi_tot in sediments deposited before 1940 (prior to the manufacture of silicones). Concentrations of PDMS in surface sediments ranged from 2.9 to 8.6 g/g dry weight. Concentrations of PDMS were not appreciable in sediments deposited at the core sites before 1970, suggesting that PDMS may naturally degrade upon burial in the sediments. Nonetheless, historical deposition of PDMS at the core sites was determined largely by the mass of suspended solids discharged with treated municipal wastewater in the Twin Cities Metropolitan Area of Minneapolis/St. Paul and by increased disposal to wastewater of PDMS in the form of consumer products and process aids.

Key words: polydimethylsiloxane, silicone, sediment, deposition