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Veldeman, E. Ph.D. Dissertation, University of Antwerp (UIA), Belgium 1991;p 249. Xhoffer, C. M.Sc. Thesis, University of Antwerp (UIA), Belgium, 1987. Mamane, Y.; Miller, J.; Dzubay, T. G. Atmos. Environ. 1986, 20,2125-2135. Post, J. E.; Buseck, P. R. Environ. Sci. Technol. 1984,18, 35-42. Degens, E.; Buck, B. Cruise S O 45-B Report; LembarSumbawa Bear-Surabaya, 1986. Hood, D. W. Environ. Sci. Technol. 1967,I, 303-305. Rona, E.;Hood, D. W.; Muse, L.; Buglio, B. Limnol. Oceanogr. 1962,7,201-206. Laevastu, T.; Thompson, T. G. J . Mar. Res. 1958,16,192. Slowey, J. F.; Jeffrey, L. M.; Hood, D. W. Nature 1967,214, 377-378. Merlini, M. In Impingement of Man on the Oceans; Hood, D. W., Ed.; John Wiley & Sons, Inc.: New York, 1971;pp 461-486. Cattel, F. C. R.; Scott, W. D. Science 1978,202,429-430. Kremling, K. Nature 1983,303,225-227.
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Hunter, K. A. Mar. Chem. 1980,9,49-70. Chow, T. J.; Patterson, C. C. Earth Planet. Sci. Lett. 1966, I, 397-400. Otten, P. PbD. Dissertation, University of Antwerp (UIA), Belgium, 1991. Ingri, J.; Ponter, C. Chem. Geol. 1986,56, 105-116. Williams, J. D. H.; Jacquet, J. M.; Thomas, R. L. J. Fish. Res. Board Can. 1976,33,413-429. Filipek, L.H.;Owen, R. H. Chem. Geol. 1981,33,181-204. Johannesson, J. K. Analyst 1955,80,840-841. Graham, W.F.; Piotrowicz, S. R.; Duce, R. A. Mar. Chem. 1979,7, 325. Wallace, C. T., Jr.; Duce, R. A. Mar. Chem. 1975,2,522. Chester, R.; Murphy, K. J. T. Sci. Total Environ. 1986,49, 325-338. Kolaitis, L. Ph.D. Dissertation, University of Antwerp (UIA), Belgium, 1988.
Received for review December 9, 1991. Revised manuscript received May 18, 1992. Accepted June 12, 1992.
Life-Cycle Biomagnification Study in Fish Dick T. H. M. Slim,* Wlllem Selnen, and Antoon Opperhuizen
Research Institute of Toxicology, Environmental Chemistry Group, State University of Utrecht, Padualaan 8, P.O. Box 80058, NL-3508 TB Utrecht, The Netherlands
A life-cycle biomagnification model is presented for the bioaccumulation of polychlorinated biphenyls (PCBs) in fish; the model includes biotransformation, life stage, sex, and growth of the fish. Biomagnification of PCBs was studied in the guppy (Poecilia reticulata). Juvenile guppies (first generation) were fed PCB-contaminated food for 30 weeks. Thereafter, elimination was studied for 2 years. Second-generation guppies which were born in the period of elimination were also analyzed for PCBs. Low absorption efficiencies of the PCBs in juvenile guppies were found during their first life stage but efficiencies increased with age. Elimination of the PCBs can be described with pseudo-first-order kinetics. The processes that caused the decrease in the concentrations of the PCBs were growth, biotransformation, and mother-to-young transfer. In the case of the higher chlorinated biphenyls, growth dilution was the only important process. Biotransformation was the most important factor for congeners with all ortho positions substituted with chlorine and at least one pair of adjacent unsubstituted places. Second-generation guppies and their parents contained similar PCB concentrations at the same time. This may be caused by a vitellogenin-mediated transport from mother to young. Decachlorobiphenyl is probably eliminated via the offspring only.
Introduction Polychlorinated biphenyls (PCBs) and other hydrophobic chemicals are found in many compartments in the environment. High concentrations are found in organisms that are at the top of the food chain, such as bear, capelin, seal, tomcod, and whale (1-9). These predators accumulate significant portions of their body burden from their food. Fish usually take up hydrophobic chemicals via the water. Extremely hydrophobic chemicals, however, such as PCBs, may also accumulate via the food chain (10-19). Uptake of extremely hydrophobic compounds via water is of minor importance, due to their extreme low solubility in water and to high sorption by biota, such as plankton 2162
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and particles in the water (20,21).In the case of extremely hydrophobic compounds, it is thus important to examine the kinetics of uptake via food, i.e., biomagnification. In fish, biomagnification is the ratio between the uptake of chemicals from food and their clearance (Figure 1). The more hydrophobic a compound, the more it biomagnifies (22). Bruggeman et al. (22)fmt described biomagnifcation with a first-order one-compartment model. The biomagnification factor K, of a compound is the ratio between the concentrations in fish and food at steady state. Steady state, however, is not easily reached and K,,, is difficult to measure. Whereas there is only one route of uptake (via food), there are several processes which decrease the concentration in fish; these include biotransformation (km),growth (y), elimination via water (k,) or mother-to-young transfer (kr).Steady state, however, does not necessarily imply an equilibrium. Kinetic factors often determine whether or not equal chemical fugacities are reached in each phase. At steady state, no changes are observed in the concentrations in fish if the food contains a specific concentration. Hitherto, several biomagnification models have heen devised. Although they are useful, they do not adequately predict the concentration of extremely hydrophobic compounds. In addition, kinetic data are scarce. Furthermore, experimental errors and variations in methodology may cause a considerable spread in biomagnification data (13, 23). Factors such as long-term uptake and elimination rate constants have not been determined, are poorly understood, or are difficult to calculate in the laboratory (24). Long-term kinetics is not well-described. From one long study with guppies it was, however, concluded that elimination was better described by a two-compartment model than by a one-compartment model (25). In addition, the influence of growth, sex and reproduction, and biotransformation needs to be investigated more extensively. Growth is usually assumed to be a first-order process that only decreases the concentration of the chemical and
0013-936X/92/0926-2162$03.00/0
0 1992 American Chemical Society
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I biotransformation , krn
Figure 1. Blomagnlficatlon klnetlcs of hydrophobic chemicals for fish: cM,concentration In food; c,, concentration In fM E , uptake etfidency; f, feeding rate; 7 , growth rate constant, kp,ellmlnatbn rate constant of physlcochemlcalellmlnatlon; k,, biotransformationrate constant; k,, elimination rate constant for reproduction.
thus is regarded as a first-order elimination rate constant. However, growth may also change physiological properties which subsequently influence biomagnification kinetics. Results of field and laboratory studies on growth are not adequately described by biomagnification models. For instance, steady state was not reached in a wild-life study where a linear increase in PCB concentrations was found in growing rainbow trout between 6 and 12 years old (26). In a laboratory study, no steady state was reached in nongrowing guppies which were fed PCB-contaminated food (25). These field and laboratory studies show that a steady state is not easily reached in growing or nongrowing fish that take up hydrophobic compounds from food. On the other hand, steady state did seem to be reached after PCB-contaminated food was fed to adult nongrowing guppies (27-29) and in growing rainbow trout (30). However, the absolute amounts of PCBs in rainbow trout continued to increase in time. It is thus very likely that the concentrations of the PCBs would increase further if the fish were to stop growing. Growth thus may affect steady-state conditions, but existing biomagnification models cannot predict this. The one-compartment biomagnification model does not include sex differences. A few data, however, do suggest different kinetics in males and females. Bruggeman et al. (28) observed higher half-lives of PCBs in male guppies compared to females, which suggest that sex influences kinetics. In addition, the possible transfer of chemicals from females to young fish has not been thoroughly investigated. This transfer may be regarded as a discontinuous elimination route which has not been taken into account in food chain modeling, although it may be important. An elimination route via the offspring could explain the lower half-lives of chemicals in female fish relative to males. The role of the biotransformation of hydrophobic compounds in a biomagnification model needs more attention. Although biotransformation may be very slow, it may nevertheless be the dominant process for the elimination of extremely hydrophobic compounds that show a very slow physicochemical elimination. In general, hydrophobic compounds such as PCBs are biotransformed very slowly (31-34). So far, studies of several processes, such as growth, sex, reproduction, and biotransformation, have yielded contradictory results. These contradictions have not been taken into account in existing biomagnification models. Furthermore, it is not yet clear to what extent different concentrations of the chemical in food influence biomagnification. In the guppy, Opperhuizen and Schrap (29) found absorption efficiencies of PCBs to be lower at higher concentrations in the food. Clark and Mackay (B),however, found that absorption efficiencies were independent of the concentration. However, uptake efficiencies from food with the same concentrations of chemicals decreased
Figure 2. Structures of PCB congeners in general and those used In the present study. Compounds 8-8 are assumed not to be blotransformed; f-h are assumed to be blotransformed: (a) IUPAC 52, (b) IUPAC 80, (c) IUPAC 153, (d) IUPAC 194, (e) IUPAC 209, (f) IUPAC 54, (g) IUPAC 104, and (h) IUPAC 136; 0 , ortho; m, meta; p, para; n , m = 1, 2, 3, 4, 5.
with higher feeding rates (35). Concentration-dependent uptake efficiency therefore requires further investigation. It can be concluded that a one-compartment biomagnification model is not appropriate. Several processes that may be very important are neglected. In the present study, a life-cycle model is presented which includes growth, sex, reproduction, life stage of the fish, long-term kinetic rate constants, and biotransformation. The aims of the present study are 5-fold (i) to compare biomagnification in juvenile and adult fish; (ii) to obtain elimination rate constants for compounds which eliminate very slowly; (iii) to quantify the influence of biotransformation on the biomagnification of PCBs; (iv) to quantify the transfer of PCBs from adult to offspring; (v) to establish a life-cycle model for the biomagnification of hydrophobic compounds in fish.
Experimental Section Chemicals. The test chemicals (IUPAC number, purity) are illustrated in Figure 2: 2,2’,5,5’-tetrachlorobiphenyl (52, 98.2%), 3,3’,5,5’-tetrachlorobiphenyl (80, 86.7%), 2,2’,6,6’-tetrachlorobiphenyl (54, 84.3%), 2,2’,4,6,6’-pentachlorobiphenyl (104, 97.5 % ), 2,2’,3,3’,6,6’-hexachlorobiphenyl (136, 88.9%), 2,2’,4,4’,5,5’-hexachlorobiphenyl (153, 99.5%), 2,2’,3,3’,4,4’,5,5’-octachlorobiphenyl(194, 98.5%), and decachlorobiphenyl(209,95.4%). The purity of the PCBs was determined by GC-ECD. All PCBs were obtained from Analabs. Hexane (Janssen Chimica) was glass-distilled before use. Fish. Guppies (Poecilia reticulata) were reared in our laboratory and were kept in 30-L aquariums which were aerated and cleaned with a charcoal filter. A 12-h day/l2-h night cycle was used. Water temperature was 20 f 2 “C, and oxygen concentration always exceeded 7 ppm. The hardness of the water was 189.8 mg (CaCOS).L-’, and pH was 8.0. The number of fish in each group is listed in Table I. In the course of the experiment 140 fish vanished in group I, and 65 and 53 fish vanished in group 11and in the control group, respectively. Although the number of fish decreased, the total mass of fish increased. Some fish do not grow a t all, since they do not survive maturation. This partly explains the decrease in the number of fish during the present study. When fish die they may be eaten by other guppies in the aquarium. Cannibalism is a wellknown phenomenon for the guppy (37). A large decrease in the number of guppies was observed particularly in Environ. Scl. Technoi., Vol. 26, No. 11, 1992 2163
Table I. Concentrations of PCBs [mge(kg of food)-l] in Food and Numbers of Fish group initial no. of fish
I
I1
328
306
192
9.58 6.94 6.14 8.09
