Document g2LrEvr7YZBLY8mJvNnevBgvq

ENVIRONMENTAL TRANSPORT AND OCCURRENCE OF PCB's IN 1975 Ian C. T. Nisbet, Ph.D.* Abstract Despite curtailment of some dispersive uses, envi ronmental levels and rates of transport of PCB's have not changed greatly since 1972. This is probably due in part to the continued release of materials in service prior to 1971 and in part to time lags in environmental transport and dissipation. Surprisingly high concentrations of PCB's matching Aroclor 1254 are still being found in air, in precipita tion, and in dry fallout. As yet, there is little evidence that significant quan tities of PCB's are being leached from dumps. Human exposure to PCB's is higly variable. Some sport fishermen and breast-fed infants have especially high intakes. Almost nothing is known about the environmental behavior of chlorinated dibenzofurans. I think the organizers of the conference may have expected me to compose a global transport model while this session was going on. I have not attempted to do this, except to make some quick calculations on the back of an envelope. My general conclusion from what I have heard to day and yesterday about the release and concentrations of PCB's in the environment in 1975 is that most of what we have learned since 1972 is reasonably consistent with the very crude model that Sarofim and I con structed in 1972. That is not to say that the model was right. All it says is that our ignorance about the exact rates and routes of transport of PCB's in the environ ment is nearly as profound in 1975 as it was in 1972. I have found only one area where there does seem to be substantial quantitative discrepancy between our 1972 model and the data generated subsequently ; that is,the numbers reported to us here and published in the interim, t on concentrations in air and air transport. We have heard some numbers of the order of 200 parts per trillion of PCB's in snowmelt, reports of numbers of the "Director, Scientific Staff, Massachusetts Audubon Society, Lincoln, Massachusetts 01773. tPersson, B., Ornis Scandinavica, 2:127-135 (1971); Sodergren, A., PCB-Conference // 7972:15-18 (National Swedish Environment Protection Board, 1973); Bengtson, A. A. and A. Sodergren, Ambio, 3:84-86 (1974); Munson, T. 0., Ch. 6 in Upper Bay Survey (Westinghouse Electric Corporation, Final Re port to the Maryland Department of Natural Resources, in press). order of 100 nanograms per cubic meter for concfj tion of PCB's in air, and the number of the order < -- 200 and locally up to 2,000 nanograms per s{|j meter per day for rates of dry deposition. These a| somewhat higher than we anticipated on the basis model. ; If we extrapolate up on the back of an envef basis from 200 nanograms per square meter per day J the whole continent, that comes out to be somethin! the order of 1,000 tons. Similarly, if you extrapolate from 100 parts per trillion in rainfall over the enf continent, you get something of the order of 1,000 tin Now, it may be that the numbers we heard biased toward urban areas. Where the concentration PCB's may be higher than they are in the United Stal as a whole. Even so, we are now being given numlj that suggest that at least 1,000 tons of PCB's per If are falling out onto the terrestrial environment of w United States in rain and particulate matter. That! "a about as large as numbers we had envisaged for toil releases of PCB's into the air in 1971. What makes) problem worse is that nearly all the PCB's that are fouj| in dry fallout, in the air, and in precipitation look jig Aroclor 1254, whereas we had thought that only ab*c| half of the materials released into the environment eyf in 1971 would be Aroclor 1254, and a good deal q them would be Aroclor 1242. So it seems to me that aerial releases and aerj| transport are rather larger than anything we coujj account for according to our knowledge of the uses an releases that we surveyed in 1972. We need to find oil where all this material in the air resembling Arocli|| 1254 is actually coming from. One possibility is that it may be coming from leak| from supposedly sealed uses. Perhaps we ought to looking at transformers to see how much PCB's vapori? from them. I would now like to go to the six questions which;| posed at the beginning of this session and see what1 have learned in the course of this conference toward solving these outstanding problems. 1. What happens to chlorinated dibenzofurans in thej environment? I think the answer is that still we knovij almost nothing. We know they are being released intQJ the environment, since they are present in small quantha ties in commercial PCB's. Dr. Kuratsune in his presentarl tion yesterday indicated that they are actually formed inj the environment during use, and Dr. McKinney's presen-| tation suggested they might be formed by metabolism! DfiEBNfcANT'S 254 {16 EXHIBIT TOWOLDMONOQ46433 m-K'' m. ijhider certain circumstances. On the other hand, Dr. flisebrough's presentation suggested that they are not retained in the bodies of birds even when they are ^ifigested; that conflicts with Dr. Kuratsune's information ^ftt they are retained extraordinarily efficiently in Rhuman tissue. .What happens to PCB's in dumps? Again, we know .tiW: ' almost nothing. Some numbers were mentioned yesteri 'Jay for water leaking out of dumps; I did some back-of- |0e.envelope calculations which suggested that the ^-quantities 0f PCB's escaping are not yet very significant, fr One is talking about quantities of the order of hundreds -of kilograms per year nationwide--certainly not more |jtfian a few tons. t3. Are PCB's in sediments going to be covered up or are they going to be continually recycled? There have ^.jjeen some hints in what has been said today that they are going to be recycled. The information from Ms. McDermott about PCB's in areas where there is shipping Inactivity, and information from Dr. Munson about the movement of PCB's in suspended sediments around -Chesapeake Bay suggests that these PCB's in shallow waters are not going to stay there and be covered up and disappear. They are going to be with us for a long time into the future. 4. Is it correct that tetrachloro-biphenyls and lower chlorinated species are rapidly degraded and is there sig nificant human exposure to these lower species? I think that we have had very adequate evidence here that tetrachloro isomers are indeed degraded rather rapidly, but not as rapidly as we would like. Dr. Sanborn's pres entation just now suggested that in fish the major differ ence in the efficiency of uptake, retention, and metabo lism comes between trichlorobiphenyls and tetrachlorobiphenyls, and that fish do indeed retain tetrachlorobiphenyls fairly efficiently. That was supported by data from the National Fish Monitoring Program, which suggested that a substantial fraction of the PCB's in the fish look like Aroclor 1242 and 1248; that means that they include substantial quantities of tetrachlorobiphenyls. This in turn implies that humans are exposed to tetrachlorobiphenyls. Although the tetrachlorobiphenyls appear to be rare in human tissue, what that tells us is that humans do not retain tetrachlorobiphenyls. It does not tell us that they are not exposed to them. This has some important implications from the regu latory point of view. We may have to consider, for ex ample, whether Aroclor 1016 is environmentally "safe," in the sense that modest releases can be regarded as acceptable. These data indicate that releases of Aroclor 1016 into water will lead to human exposure, at least to tetrachlorobiphenyls. 5. What is the extent of human exposure? The data derive from two sides, monitoring of human tissue and monitoring of human food. Human tissue monitoring tells us that human exposure is very widespread. Human food monitoring tells us that most PCB's in human food are in fish. Unfortunately, that makes it very difficult to esti mate human exposure quantitatively, because we know from the fish monitoring program that the levels of PCB's in fish are extraordinarily variable in space. Despite the large number of samples that have been taken by the Canadian program and by the FDA, it is very difficult to define an average exposure. I would go so far as to say that an "average" exposure is a meaning less concept, because some individuals who live in areas where fish residues are high will get exposures 100 times greater than the average, whereas those persons who live in areas where there is little contamination, or who do not like fish, will get very little. Nevertheless, we do have s&me numbers for human dietary exposure. The Total Diet Program in the United States gave a figure of the order of 9 micrograms per day for the intake of the average adult. I also did some calcu lations from Mr. Graham's figures on the Canadian com mercial fish to see how many kilograms of PCB's were brought in in Canadian commercial fish and what frac tion was eaten. That led me to a figure around 5 micro grams per day for the average intake of the average per son in the Canadian population. We have to remember that the average adult does not eat much fish. Unfortunately, these figures are quite misleading because it is very easy for an individual who is a sports fisherman and who catches salmon, or trout, or chub to take in very much more than that. One calculation in our 1972 paper indicated that it would be very easy for a fisherman or a member of his family to average 300 micrograms per day: this would represent about 4 micrograms per kilogram per day for an adult. One important point is that exposure of breast-fed infants is likely to be very much greater than that of any adult, even- an individual who likes fish. Although Dr. Kutz did not give numerical estimates of PCB levels in human milk in this session, earlier data suggest that a typical level would be around 30 parts per billion.* This leads to an estimate of 4--5 micrograms per kilogram per day intake for the average breast-fed infant. There would *PCB levels reported in human milk have been in the range 10--100 ppb: Risebrough, R. W., and V. Brodine, Environment 12:16-27 (1969); Westoo, G., Nore'n, K., and M. Andersson, Var Fdda, 22:10-31 (1970); Acker, L., and E. Schulte, Naturwissenschaften, 57:497 (1970); Savage, E. P., Tessari, J. D., Malberg, J. W., Wheeler, H. W., and J. R. Bagby, Pesticides Moni toring Journal, 7:1-5 (1973). A concentration of about 30 ppb would correspond to the median level of about 1 ppm reported in human fat. 255 TOWOLDMONOQ46434 be many above the average and many below. Accordingly, when considering averages, we should remember that certain individuals are going to get 10 to 100 times the exposure of the average person, as calcu lated from an average diet. 6. The most complicated question posed in 1972: what would be the effect of Monsanto's curtail ment of dispersive uses? A number of speakers yesterday and today have talked about decreases of PCB levels in certain areas or compartments of the environment. For example, there have been decreases in the total dietary intake estimated from the FDA Total Diet Program, in the frequency of findings of PCB's in milk and fish in the FDA's surveillance samples, and in runoff into the Southern California coastal waters. On the other hand, we have also heard about some levels that have not changed, particularly levels in fish in Lake Michigan. There are three reasons why the curtailment of sales by Monsanto in 1971 should not have been expected to lead to an immediate reduction in environmental levels. One is that not all the closed system uses are actually closed. There are some losses that we heard about today, even from transformer and capacitor uses, which are systems as closed as we are likely to get. Secondly, and more important, there is still a large backlog of products containing PCB's, that were in service prior to 1971, which are still in service and are still being discarded and still leaching. Some of the users of hydraulic fluj(j; transfer fluids, compressors, and so on, are probabf using PCB's that they had several' years ago. Ceif the scrapping of capacitors and any losses thaf result from disposal of transformers are going to releases for years into the future. Finally, there is an environmental inertia: it long time after the input into the environment is ci for the levels in fish, for example, to go down. The lags will depend on the part of the system under sideration; it is evidently quite short for muss# Southern California, but is longer for the fish in' same area. Time lags have been quite short for the lings, which reflect terrestrial uses, and for soil resicfi The time lag is likely to be long for somewhere like Michigan, which is a closed system, with a large resefi of PCB's in the sediment. So I think we should not h! hoped for a very rapid decline in PCB's since 1971. On the other hand, it has been somewhat appointing that it has been so difficult to find | change in the first 3 or 4 years. 1 One of the longest time lags of all is likely tob human tissue, because there is evidence that PCB's retained for an extremely long time in human tissue, will probably have to wait for some considerable tii after PCB levels have declined in fish before we significant decline in human tissue residues. 256 TOWOLDMONOQ46435