Environ. Sci. Technol. 1985, 19, 198-199
University, Covallis, OR, 1982, Report 82-01. (11) Cantwell, F.; Puon, S. Anal. Chem. 1979,51,623-632. (12) Horvath, C.; Melander, W.; Molnar, I. Anal. Chem. 1977, 49, 142-154. (13) James, R. 0.;Parks,G. Surf. Colloid Sei., 1982,12,119-216. (14) Schindler, P. W. In “Adsorption of Inorganics a t SolidLiquid Interfaces”; Anderson, M.; Rubin, A., Ed.; Ann Arbor, Science Publishers: Ann Arbor, MI, 1981. (15) Westall, J.; Hohl, H. Adv. Colloid Interface Sei. 1980,12, 265-294.
(16) Stumm, W.; Kummert, R.; Sigg, L. Croat. Chem. Acta 1980, 53, 291-312. (17) Harned, H. S.; Owen, B. B. “The Physical Chemistry of Electrolytic Solutions”; American Chemical Society: Washington, DC, 1958. (18) Westall, J., Oregon State University, Corvallis, OR, unpublished data, 1983.
Received for review January 16,1984. Revised manuscript received May 15, 1984. Accepted September 4, 1984.
CORRESPONDENCE Comment on “FishSediment Concentration Ratios for Organic Compounds” SIR: The examination of fish/sediment concentration ratios by Connor ( I ) provides an instructive comparison of the environmental behavior and fate of chlorinated aromatic hydrocarbons (CAHs) and polynuclear aromatic hydrocarbons (PAHs). However, errors in his eq 3 led him to erroneously conclude that “fish/sediment ratios greater than about 0.01 are higher than could be predicted” and that each of the fish liverlsediment ratios in his Figure 3 “is 3-5 orders of magnitude higher than predicted by assuming an organic content of 1% carbon.” In fact, ratios much higher than 0.01 can be predicted, and the ratios in his Figure 3 are very close to the values predicted by the corrected equation. Thus, fishlsediment ratios predicted by using Connor’s approach are much closer to observed field ratios and therefore even more useful than Connor suggested. Two errors are present in Connor’s eq 3. First, in converting the organic-carbon-normalizedpartition coefficient (KO,) to the mass-normalized, or sediment, partition coefficient (Ksed),one should multiply KO, by f,,, the fraction of the sediment, by weight, composed of organic carbon; Connor expressed f,, as a percent, thereby introducing an error of 2 orders of magnitude into his calculations. The relationship shown in his Figure 1 thus represents ratios for sediments containing 100% organic carbon as stated in the text, not 1% as stated in the figure legend. Second, because K, and f, are in the denominator of the ratio, the log (f,,) term [or, alternatively, log (70 organic carbon/100)] should be subtracted from the right side of eq 3 and not added. This error led Connor to conclude that sediments with less than 100% organic carbon should have a lower fishlsediment concentration ratio, when in fact they are expected to have a higher ratio. The corrected equation for predicting the fish/sediment concentration ratio from Kenaga and Goring’s (2) relationships is log (BCF/Ksed) = -2.872 0.391 log (KO,) - log (f,,.) (1)
+
where BCF is the fish/water bioconcentration factor and KO, is the octanol/water partition coefficient. For an organic carbon content of 1%(Le., f,, = 0.01), the log (BCF/K,,d) ratio increases from 0.30 to 1.67 as log (KO,)varies from 3.0 to 6.5. If the contaminant concentration in fish liver is 25 times higher than the whole-body 198
Environ. Sci. Technol., Vol. 19, No. 2, 1985
concentration, as Connor notes, then the log (fish liver/ sediment) ratio is expected to be 2.87 and 2.39 for a log (KO,) of 6 and f, of 0.01 and 0.03, respectively. These two predicted ratios are near the top and center, respectively, of the cluster of observed values for CAHs shown in Connor’s Figure 3. If the fish/sediment ratios for polychlorinated biphenyls (PCBs) shown in Connor’s Figure 2 are examined separately as freshwater, marine, and laboratory values, the correlation with flushing time is much less evident. The four freshwater ratios, the four largest ratios in the figure, do not show a strong correlation with flushing time. However, they appear to be within an order of magnitude of 45, the steady-state ratio predicted by eq 1, assuming that log (KO,) = 6.47, as reported for Aroclor 1254 (3),and that the sediments are 1% organic carbon. A similar steady-state ratio of 21 is predicted by using the same assumptions and eq 2, based on the equations of Oliver and Niimi (“low exposure”) ( 4 ) and Karickhoff et al. (51, and converting KO,to Ksed: log (BCF/Ksed) = [0.997 log (KO,) - 0.8691 - [log (KO,) - 0.211 - log (f,) (2)
Variation about the predicted fishlsediment ratio is cert,inly to be expected. Kenaga and Goring (2) reported 95% confidence limits of i1.35 for the log (BCF) predicted from log (KO,) and f1.37 for the log (K,) predicted from log (KO,). Also, the slope of the log (fish/sediment) vs. log (KO,) relationship depends upon which equations are used in predicting the ratio. The slope can be positive (eq 1) ( I ) , zero (5,6),nearly zero (eq 2) ( 4 , 5 ) ,or negative (5, 7). Several factors can contribute to variation about the predicted ratio. For example, for certain chemicals, accumulation through the food chain pathway could make the fishlsediment ratio higher than predicted by this analysis (though perhaps still within the 95% confidence limits). I t is not correct to refer to the laboratory bioconcentration factors from the studies cited by Connor ( 2 , 3 , 6 , 8,9) as “96-h”values. Although many chemicals can reach steady-state concentrations in fish in less than 96 h, the more lipophilic chemicals may take several weeks, as Connor notes, and some of the BCFs measured in the cited studies were accordingly made after several weeks of exposure. For example, steady-state BCFs were estimated by Veith et al. (3) from 32-day exposures. Although one technique for rapid estimation of BCFs involves 5-day exposures followed by a depuration period (IO), this technique is used to estimate steady-state BCFs, not 96-h
0013-936X/85/0919-0198$01.50/0
0 1985 American Chemical Society
Environ. Sci. Technol. 1985, 19, 199-199
or 5-day concentration ratios, from estimates of uptake and elimination rates. If all the laboratory-derived bioconcentration factors had been 96-h values, it would have helped explain how field ratios, presumably closer to steady state, could be higher than predictions based on those laboratory values. The field data in Connor’s figures and these corrected calculations suggest that equations developed from laboratory measurements may be useful in predicting the accumulation of CAHs by fish relative to sediments under field conditions. Comparable predictions of fishlsediment ratios for PAHs must account for their more rapid biotransformation in fish. Connor’s approach to predicting fish/sediment ratios thus appears to be more successful than he suggested.
Literature Cited (1) Connor, M. S. Enuiron. Sci. Technol. 1984, 18, 31-35. (2) Kenaga, E. E.; Goring, C. A. I. ASTM Spec. Tech. Publ. 1980, STP 707, 78-115. (3) Veith, G. D.; DeFoe, D. L.; Bergstedt, B. V. J . Fish. Res. Board Can. 1979,36, 1040-1048. (4) Oliver, B. G.; Niimi, A. G. Enuiron. Sci. Technol. 1983,17, 287-291. (5) Karickhoff, S. W.; Brown, D. S.; Scott, T. A. Water Res. 1979,13, 241-248. (6) Mackay, D. Environ. Sci. Technol. 1982, 16, 274-278. (7) Veith, G. D.; Macek, K. J.; Petrocelli, S. R.; Cmol, J. ASTM Spec. Tech. Publ. 1980, STP 707, 116-129. (8) Neely, W. B.; Branson, D. R.; Blau, G. E. Enuiron. Sci. Technol. 1974,8, 1113-1115. (9) Chiou, C. T.; Freed, V. H.; Schmedding, D. W.; Kohnert, R. L. Enuiron. Sci. Technol. 1977, 11, 475-478. (10) Branson, D. R.; Blau, G. E.; Alexander, H. C.; Neely, W. B. Trans. Am. Fish. SOC.1975,104,785-792. t Operated by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-840R21400 with the U.S.Department of Energy. Publication No. 2445, Environmental Sciences Division, ORNL.
James E. Breck
Environmental Sciences Division Oak Ridge National Laboratoryt Oak Ridge, Tennessee 37831
SIR: Breck’s correction of my eq 3 (1)has the happy result of bringing the field data into better agreement with the mathematical predictions. As I noted in the paper, the fish/sediment ratio seems to reach a plateau when flushing times are greater than 100 days. These plateau values also agree nicely with the predicted steady-state ratios from the corrected eq 3. I believe this behavior is less associated with the freshwater nature of these environments as Breck suggests than with the coincidence that all the freshwater data available here happened to be from the environments with the longest flushing times. If all environmental pools were at steady state, presumably flushing time would have little importance. However, input loads can be highly variable, and fishlsediment ratios are one way of reducing this environmental variation.
Breck also shows that a variety of equations could be combined to yield quite different slopes of the fishlsediment ratio with respect to the octanol-water partition coefficient (KO,).Mackay has recently argued that the relationship between the bioconcentration factor (BCF) and KO,should be linear (2). Karickhoff et al. have developed a similar relationship for the soil partition coefficient (K0J (3). Combining these two equations yields a fish/sediment ratio independent of KO,: 0.077 -BCF - KBed fraction organic carbon Of all the various combinations of equations, the simplicity of this relationship makes this equation most appealing. In addition, the variation reported by Mackay and Karickhoff et al. was much smaller than the earlier work of Kenaga and Goring ( 4 ) . From McKay’s and Karickhoff s regression data, I ran Monte Carlo simulations to predict the fishlsediment ratio for a mean log KO, of 4.5 with a variance of 1.0. The resulting fish/sediment ratio had a coefficient of variation of about 14%, a small source of error compared to the other sources of error mentioned in my paper. The predicted fishlsediment ratio (approximately 200) using this equation agrees quite well with the data for the high octanol-water partition coefficient chlorinated hydrocarbons in Figure 3 (1). When the caveats cited in my paper and by Breck are recognized, either version of the corrected eq 3 provides a technique for estimating the maximum concentrations in fish given certain sediment loads. Breck has nicely summarized the appropriate procedures to determine laboratory bioconcentration factors. Much of the earlier data used to develop the first regression equations for bioconcentration factors and octanol-water partition coefficients was based on tests as short as 96 h (ref 5, Table 5-3). Even today the U S . Environmental Protection Agency and the U S . Army Corps of Engineers use only 10-day tests in determining the suitability of dredge spoils for dumping (6).
Literature Cited (1) Connor, M. S. Enuiron. Sci. Technol. 1984, 18, 31-35. (2) Mackay, D. Enuiron. Sci. Technol. 1982, 16, 274-278. (3) Karickhoff, S. W.; Brown, D. S.; Scott, T. A. Water Res. 1979, 13, 241-248. (4) Kenaga, E. E.; Goring, C. A. I. ASTM Spec. Tech. Publ. 1980, STP 707, 78-115. (5) Bysshe, S. E. In “Handbook of Chemical Property Estimation Methods: Environmental Behavior of Organic Compounds”; Lyman, W. J., Ed; McGraw-Hill: New York, 1982; p 5-1. (6) U.S. Army Corps of Engineers “Evaluation of Proposed Discharge of Dredged Material into Ocean Waters”; Environmental Effects Lab: Vicksburg, MI, 1977; G-1.
Michael Stewart Connor U S . Environmental Protection Agency, Boston, Massachusetts 02203
Not subject to U.S. Copyright. Published 1985 by the American Chemical Society
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