Environmental Occurrence of Polydimethylsiloxane N. J. FENDINGER,* ,² D. C. MCAVOY, ‡ W. S. ECKHOFF, ‡ AND B. B. PRICE ² The Procter and Gamble Company, Sharon Woods Technical Center, 11511 Reed Hartman Highway, Cincinnati, Ohio 45241, and The Procter and Gamble Company, Ivorydale Technical Center, 5299 Spring Grove Avenue, Cincinnati, Ohio 45217 An extensive monitoring program was conducted to determine the occurrence of polydimethylsiloxane (PDMS) in environmental compartments impacted by consumer waste disposal practices. Eight wastewater treatment plants, representative of those found in North America, were monitored to determine PDMS removal during wastewater treatment. Surface waters, sediments, and sludge- amended soils impacted by wastewater treatment plant effluents and sludges were also monitored for a more complete assessment of the environmental fate of PDMS. Newly developed GPC-ICP and/or HPLC-ICP analytical techniques were used to provide insight into the environmental fate of PDMS and anticipated PDMS degradation products. PDMS was found to be highly removed during wastewater treat- ment with effluent concentrations, in most cases, below the quantitation limit of the analytical technique (<5 μg/L). PDMS sludge concentrations ranged from 290 to 5155 mg/ kg and varied as a function of influent concentration and sludge processing method. Sediment levels of <6 mg/ kg were measured near the outfall of the wastewater treatment plants sampled. Measured sludge-amended agricultural soil concentrations ranged from <0.41 to 10.4 mg/kg and were lower than expected in most cases based on calculated PDMS loadings via historical sludge application. The lower than expected PDMS concentrations in sludge-amended soil combined with detection of dimethylsilane-1,1-diol, an expected PDMS breakdown product, suggest degradation of PDMS in the soil environment. Introduction Polydimethylsiloxane is part of a group of man-made orga- nosilicone compounds that range from low molecular weight volatile materials to high molecular weight polymeric materi- als. The focus of this monitoring study was the nonvolatile, polymeric polydimethylsiloxanes (PDMS) represented by the generic formula where n may vary from 10 to >10 000. PDMS is used in a broad range of food, medical, personal care, and household applications (1). In many of these applications, PDMS is disposed into wastewater treatment systems and has the potential to enter the environment as a component of effluents and sludges from wastewater treatment plants. It was the purpose of this study to (1) investigate the levels of PDMS that enter wastewater treatment systems from down the drain sources, (2) observe the behavior of PDMS during wastewater treatment, (3) estimate conse- quent PDMS loadings to the environment, and (4) study the behavior of PDMS in environmental systems. PDMS that enters wastewater treatment systems is ex- pected to partition onto solids and be removed primarily by sorption and sludge wasting given the very low water solubility of PDMS (2, 3). PDMS is expected to remain unchanged during wastewater treatment because of its chemical and thermal stability (3). PDMS not removed on sludge solids will be present in wastewater treatment effluent as a component of the suspended solids. The predominant pathway of PDMS entry into the environment is expected to be as a component in sludge added to soil based on its removal mechanism during wastewater treatment. Recent work by Lehmann et al. (4, 5) and Carpenter et al. (6) have shown that, once PDMS is introduced into the soil environment, it can undergo chemical hydrolysis to low molecular weight dimethylsilane-1,1-diol (DMSD). A similar transformation that occurs at a much slower rate has also been observed in sediments (7). Previous monitoring studies (8-16) focused on PDMS levels in sludges, sediments, and surface waters and did not attempt to understand potential environmental transforma- tions or fate during wastewater treatment. In addition, atomic adsorption and inductively coupled plasma analysis methods used in previous monitoring studies did not provide structural information about the silicone polymer. In this study, we used newly developed gel permeation chromatography- inductively coupled plasma (GPC-ICP) instrumentation (17) to provide concentration and structural information about PDMS found in environmental matrices. PDMS degradation products were measured using a high-pressure liquid chro- matograph-inductively coupled plasma (HPLC-ICP) instru- ment (17). Use of the new analytical techniques coupled with a comprehensive sampling program at wastewater treatment plants has enabled us to better understand the environmental fate of PDMS during wastewater treatment as well as in the receiving environment either as a component in sludge or in effluent. Experimental Section Sampling Locations. Eight municipally owned wastewater treatment plants were sampled across North America during 1993 and 1994. The 1984 U.S. EPA Needs Survey and National Inventory of Municipal Waterworks and Wastewater Systems in Canada were used to identify potential U.S. and Canadian sampling locations. The selected treatment plants varied in size, sludge handling techniques, and treatment type (Table 1). Aspects common to all treatment plants sampled were as follows: wastewater from primarily domestic sources, some form of land application for sludge disposal, and low surface water dilution in the receiving stream. Sampling was done once at all treatments plants except for Columbus, OH, and Kenton, OH, where sampling was done in both 1993 and 1994 to determine the extent of PDMS influent and sludge fluctuations. Sludge-amended soils were collected from agricultural fields that received sludges from the treatment plants monitored. Characteristics of the soils sampled with dates * Corresponding author telephones (513)626-2257; fax: (513)626- 1375; e-mail: fendingernj@pg.com. ² Sharon Woods Technical Center. ‡ Ivorydale Technical Center. CH 3 CH 3 Si CH 3 O Si O CH 3 CH 3 SiCH 3 CH 3 CH 3 n Environ. Sci. Technol. 1997, 31, 1555-1563 S0013-936X(96)00871-1 CCC: $14.00  1997 American Chemical Society VOL. 31, NO. 5, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1555