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Cauwenberghe, K. A,; Van Vaeck, L.; Shaffer, S. D.; Thill, A. J.; Belser, W. L., Jr. Science (Washington,D.C.) 1980,
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Hydrocarbons; Jones, P. W.; Leber, P., Eds.; Ann Arbor Science: Ann Arbor, MI, 1979; pp 141-158. Hughes, M. M.; Natusch, D. F. S.;Taylor, D. R.; Zeller, M. V. In Polynuclear Aromatic Hydrocarbons;Bjorseth, A.; Dennis, A. J., Eds.; Battelle: Columbus, OH, 1979; pp 1-8. Bowen, E. J. Adu. Photochem. 1963, I , 23. Peters, J.; Seifert, B. Atmos. Environ. 1980, 14, 117-119. Thomas, J. F.; Mukai, M.; Tebbens, B. p. Enuiron. Sci. Technol. 1968, 2, 33-39. Pitts, J. N., Jr.; Harger, W.; Lokensgard, D. M.; Fritz, D. R.; Scorziell, G. M.; Mejia, V. Mutat. Res. 1982,104,35-41. Katz, M.; Chan, C.; Tosine, H.; Sakuma,T. In Polynuclear Aromatic Hydrocarbons; Jones, P. W.; Leber, P., Eds.; Ann Arbor Science: Ann Arbor, 1979; pp 171-189. Korfmacher, W. A.; Wehry, E. L.; Mamantov, G.; Nutusch, D. F. S. Environ. Sci. Technol. 1980, 14(9), 1094-1099. Daisey, J. M.; Lewondowski, G. G.; Zorz, M. Environ. Sci. Technol. 1982, 16(12), 857-861. Vollman, H.; Becker, H.; Corell, M.; Streeck, H.; Langbein, G. Justus Liebigs Ann. Chem. 1937, 531, 1. Fatiadi, A. J. Environ. Sci. Technol. 1967, 1(7), 570-572. Fatiadi, A. J. J. Chromatogr. 1965, 20, 319-324. Thekaekara, M. P. In Solar Energy Engineering; Sayigh, A. A. M., Ed.; Academic: New York, 1977; pp 40-41. Okabe, H. Photochemistry of Small Molecules; Wiley-Interscience: New York, 1978; pp 237-249. Inn, E. C. Y.; Tanaka, Y. Adv. Chem. Ser. 1959, No. 21,263. Butler, J. D.; Crossley, P. Atmos. Enuiron. 1981,15,91-94.
Received for review July 3,1986. Accepted March 9,1987. This work was supported by the U.S. Department of Energy under Contract DE-ACO6-76RLO-1830 to Pacific Northwest Laboratory.
Persistence of Benz[ a ]anthracene Degradation Products in an Enclosed Marine Ecosystem Kenneth R. Hinga" and Michael E. Q. Pilson Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882
Carbon-14-labeled benz[a]anthracene was introduced into an enclosed marine ecosystem that had planktonic primary production and a heterotrophic benthos. Benz[alanthracene, labeled COz, and operationally defined fractions of labeled degradation products were followed in water and sediments for 202 days. The major fraction of intermediate degradation products was sufficiently water soluble so as not to be readily extractable with organic solvents and at the end was still slowly decaying to COz. Both the parent benz[a]anthracene and degradation products found in the sediment appear to become protected from further alteration after about 2 months and may persist indefinitely.
Introduction Polycyclic aromatic hydrocarbons (PAH) include carcinogenic and toxic compounds. Anthropogenic activities, especially combustion, have greatly increased the flux of PAH to the environment (I). Some pathways for PAH introduction to the marine environment have been quantified (2-7),and the presence of PAH in marine systems, especially those close to populated areas, is well documented (i.e., ref 8 and 9). PAH in the environment may have a direct toxicity, but the primary concern is that they may be acted upon by 648
Environ. Sci. Technol., Vol. 21, No. 7, 1987
mammalian enzymes to become carcinogenic compounds. In the environment, PAH may be photodegraded and biologically degraded, leading to intermediate products before complete remineralization. These intermediate products, if persistent, may present their own health or environmental hazard. For example, fungi produce initial degradation products from PAH that are very similar to the products responsible for carcinogenesis in mammals (10). Biological degradation pathways of smaller aromatics, which can be utilized as sole carbon sources by bacteria, have been determined, but only the initial steps in the degradation of larger PAH, which are only degraded through cometabolism, have been established (111. Similarly, the initial products of PAH photodegradation have been described ( 1 , 2 ) ,but the behavior of the breakdown products in natural environments is not known. Two previous experiments were conducted with radiolabeled PAH in enclosed marine ecosystems to measure the rate of disappearance of the parent and the remineralization rate to C 0 2 under near natural conditions (12, 13). The chemical fractionation used iu these experiments has also permitted a glimpse of the behavior of intermediate products. In both these experiments we noted that intermediate degradation products of four-ringed ?AH, benz[a]anthracene and 7,12-dimethylbenz[a]anthracene, were found at the end of the 230- and 60-day experiments,
0013-936X/87/0921-0648$01.50/0
0 1987 American Chemical Society
respectively (12, 13). In a third experiment with benz[alanthracene, described here, we document in greater detail the long-term persistence of degradation products in sediments and report for the first time water-soluble degradation fractions of moderate persistence.
Experimental Section
Enclosed Ecosystems. The Marine Ecosystems Research Laboratory (MERL) a t the University of Rhode Island maintains 14 large microcosms and is licensed for radiotracer work in four of these. Each microcosm is a fiberglass tank, 1.8 m in diameter and 5.5 m in height, containing 13 m3 of seawater and a 35-cm layer of sediment. Unmodified sediments and water were taken from adjacent lower Narragansett Bay, a fairly typical New England coastal ecosystem, to initiate this experiment. The tank was operated in batch mode with water input or drain only to compensate for periods of excess evaporation or precipitation and was mixed 2 h out of every 6 h with a vertical plunger. The tanks are outdoors, exposed to ambient sunlight, and maintained a t temperatures within 2 "C of the adjacent bay. The fundamental assumption for this type of experiment is that the ecosystem enclosed in the tank has the same components and processes that occur on a chemical scale in the natural coastal system. A number of tank-bay comparisons documenting the similarity between the experimental and the reference natural ecosystem are available (14-26). In spite of some differences in physical properties between tanks and bay, all measured chemical and most biological parameters (e.g., large predators are excluded) fall within the range of measured values for lower Narragansett Bay throughout the year. MERL microcosms have now been operated for 10 years, up to 2 years on one loading of sediment, and continue to appear to contain ecosystems that are reasonable representatives of Narragansett Bay. Most processes that may act on PAH and their derivatives in a coastal system one therefore expects to be present in the MERL tanks and quantitatively similar to those in lower Narragansett Bay. Extrapolating the results from MERL/bay to other environments requires the same judgements as deciding the appropriateness of applying results obtained in any environment to another. I t should be noted that on time scales less than about 15-30 days there can be considerable variations between individual tanks and the bay and between different parts of the bay, in such parameters as the initiation, composition, and duration of blooms, as may be expected from the variability in natural systems. These experiments also do not directly address processes such as large-scale horizontal transports of particle-bound pollutants that may affect their distribution in coastal or ocean systems. Spike and Operation. On February 23,1982,700pCi of [12-14C]benz[a]anthracene(Amersham Corp., 49 mCi/mmol) was introduced into a MERL tank within an oil-water mixture LO give a starting activity in water of 1.19 X lo5 dpm L-l. Prior to use the benz[a]anthracene was charged to a silica gel chromatography column, washed with hexane, and eluted with 4:1 hexane-methylene chloride. No detectable labeled impurities were observed after thin-layer chromatographic analysis of the purified compound, nor were any other PAH found by GC-MS chromatography of the cleaned compound. Preparation of the carrier (15L of seawater plus about 1 g of No.2 fuel oil) used for introduction to the tank was previously described (12). The experiment was run for 202 days. Between days 168 and 173 the water in the tank was partially
drained and replaced with fresh bay water 3 times. This procedure reduced the concentrations of water-soluble labeled fractions in the tank to about 10% of their former levels. The benz[a]anthracene added to the tank, 3.5 mg, gave an initial concentration of 270 ng L-l, which represented 1% of the seawater saturation solubility a t the salinity (about 30%) and the beginning temperature of the experiment (27). Rates of microbial attack on PAH have been found to be elevated in sediments subject to chronic hydrocarbon and PAH contamination (28-30), so the spike was kept to a small size to minimize the possibility of stimulating a high rate of microbial degradation. The concentration of labeled benz[a]anthracene achieved in the experimental sediments was lower than that of normally occurring benz[a]anthracene in the area where the sediments used in this experiment were collected (31). The small size of the spike relative to the ambient background materials as found in these experimental conditions did not facilitate identification of unknown compounds. Identification of specific degradation products was not an objective of these experiments. Sample Collection and Processing. All water column samples were taken during a mixing cycle to ensure that the water column was homogeneous during sampling. Cores were taken with a 2.5 cm diameter stainless steel interface retaining corer (32) and then frozen until extraction. Figure 1 provides a summary of the detailed procedures listed below and identifies the fractions discussed later. Water samples (1-2 L, unfiltered) were extracted 3 times with chloroform (20mL/L), the activity in an aliquot of each extract was counted, and the samples were combined. Beginning on day 20 the water samples were acidified to pH 2 after the initial extractions and extracted twice more with chloroform, and the additional aliquots were counted. Samples of particulate material were obtained by filtering 0.5-2 L of water through a 47 mm diameter glassfiber filter (Whatman GF/A). The filters were placed in 10 mL of scintillation fluid and counted. Duplicate samples were extracted in a single-phase chloroform-methanol-water solution for 8 h, then the solution was converted to two phases by the addition of water, and aliquots of both the chloroform and methanol-water fractions were counted. Total COz was collected by transferring 500-mL water samples to a bottle fitted with two suspended wells, each containing a piece of filter paper and 0.2 mL of phenethylamine, and then acidified to a pH of
