Environ. Sci. Technol. 1994,28, 1669-1673
Identification of Halogenated Compounds in Chlorinated Seawater and Drinking Water Produced Offshore Using n-Pentane Extraction and Open-Loop Stripping Technique Nina K. Krlstlansen,' May Frmshaug, Kjersti T. Aune, and Georg Becher
Department of Environmental Medicine, National Institute of Public Health, Geitmyrsveien 75,N-0462 Oslo, Norway Elsa Lundanes
Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway The formation of byproducts in chlorinated seawater used for drinking water production on three oil installations was investigated with the use of n-pentane and open-loop stripping extraction. The use of capillary gas chromatography (GC) with electron capture detection (ECD) and mass spectrometry (MS) revealed the presence of a great variety of bromine-substituted aliphatic and aromatic compounds in both chlorinated seawater and tap water. Tribromomethane and dibromoacetonitrile were found in tap water in the range of 19-27 kg/L and 0.9-1.6 pg/L, respectively, and these major byproducts were most efficiently extracted with n-pentane. However, the openloop stripping technique was better suited for extraction of halogenated compounds present at the low nadograms per liter level, suchas the iodinated trihalomethanes. When using n-pentane for extraction of chlorination byproducts, the formation of artifacts such as 3-bromo-2-methyl-2butanol and other halogenated C g compounds was observed. These compounds were presumably formed from the reaction of excessive halogen with traces of olefins in the solvent. While ammonium sulfate only partly prevented the formation of the artifacts, sodium thiosulfate was efficient as a quenching agent and completely destroyed reactive halogen.
seawater cooling distribution system. Since the same water is also used as the raw water source for drinking water production, the presence of halogenated byproducts must be considered which may pose a potential health risk to the consumers. The main objective of the present study was to identify volatile halogenated compounds suspected to be present in a wide concentration range (low ng/L to high yglL) in chlorinated seawater and in drinking water produced on oil platforms. Furthermore, we wanted to compare the performance of n-pentane extraction and open-loop stripping technique. The halogenated compounds were determined by gas chromatography combined with electron capture detection and mass spectrometry. Experimental Section
* Address correspondence to this author at her present address: Norwegian FoodResearchInstitute, Osloveien 1,N-l430As, Norway; e-mail address: nina.kristiansen@ matforsk.nlh.no.
Chemicals, Reagents, and Glassware. Carbon disulfide and n-pentane were of glass-distilled grade, obtained from Rathburn (Walkerburn,Scotland). Sodium hypochlorite was obtained from BDH Laboratory Supplies (Poole, England). Other chemicalsand reagents used were of analytical grade. Stock solutions of standards containing 1 mg/mL were prepared in acetone or n-pentane by dissolving 50 mg of each compound in 50 mL; dilutions were freshly prepared prior to use. All solutions were stored at 4 "C. Synthesis of 3-bromo-2-methyl-2-butanol was performed according to the procedures described by Dalton et al. (13) and Cavanagh et al. (14). Glassware was cleaned with HC1 and then successively rinsed with deionized water, ethanol, and acetone. All glassware used for the n-pentane extraction were kept in an oven at 150 "C for 1h prior to use. For the open-loopstripping analysis, 1.5-mg charcoal filters (Bender & Hobein, Zurich, Switzerland) were rinsed with carbon disulfide and flushed with nitrogen prior to use. The stripping gas nitrogen was purified with molecular sieve, charcoal, and Tenax. The bromide ion concentration was determined by neutron activation analysis performed by the Institute for Energy Technology (Kjeller, Norway). The amount of DOC in potable water was determined on a Technicon autoanalyzer I1 in our laboratory while DOC in seawater was determined using a Dohrman DC analyzer 190 at the Norwegian Institute for Water Research (Oslo, Norway). Sampling. Water samples of 11L with no headspace were collected at the oil platforms, transported to the laboratory, and stored at 4 "C. The samples were analyzed within 10 h. Two or three replicates were taken both for the n-pentane analysis and for the open-loop stripping analysis. The chlorine doses used and the concentration of DOC and bromide in the water samples are presented in Table 1. Tap water on platforms I and I1 were produced
0 1994 American Chemical Society
Environ. Sci. Technol., Vol. 28, No. 9, 1994 1669
Introduction It is well-documented that water chlorination for disinfection purposes may lead to the formation of a wide range of chlorinated compounds from natural organic material (1-4). The major byproducts identified are trihalomethanes (THM),dihaloacetonitriles (DHAN),and halogenated acetic acids. Enhanced bromide levels in chlorinated raw water used for drinking water production result in the formation of brominated and mixed bromo/ chloro organic compounds (5-10). This is explained by oxidation of bromide to hypobromous acid, which can react with organic precursors to form the brominated byproducts. On many offshore installations, potable water is produced by desalting seawater which contains variable amounts of dissolved organic carbon (DOC) and a substantial amount of bromide (67 mg/L) (11). DOC concentrations from 1to 3 mgiL are often found, but can vary widely depending on the location of the platform and the season of sampling (9, 12). The seawater is chlorinated primarily for protection against marine fouling in the
0013-936X/94/0928-1669$04.50/0
Table 1. Characteristics of Water Samples from Participating Oil Platforms8 platform platform platform I I1 I11 seawater intake level (m) seawater chlorination dose (mg/L) platform I CSW TW
-50 0.5
-65 0.7
platform I1 CSW TW
DOC (mg/L)
2.9
