ENVIRONMENTAL POLICY ANALYSIS
INDUSTRIAL REGULATIONS
Toxics Release Inventories: Opportunities for Improved Presentation and Interpretation CHARLES Q. JIA ANTONIO DI G U A R D O Department of Chemical Engineering and Applied Chemistry University of Toronto Toronto, Ontario M5S 1A1 D O N A L D MACKAY Environmental aad Resource Studies Trent University Peterborough, Ontario K9J 7B7
Considerable effort and expense are devoted to the acquisition and publication of Toxics Release Inventory (TRI) data, but it is suggested that this invaluable environmental information resource is underexploited and can be misinterpreted. A more accurate expression of the impact of these discharges can be developed through indices that combine the emission data with toxicity, environmental persistence, and the potential for multimedia partitioning. We propose two indices beyond what has been previously suggested: one that weights toxicity and persistence and another that weights toxicity, persistence, and environmental mobility, which was deduced using multimedia fate models. These approaches are illustrated, and the advantages and problems discussed. We hope that by adopting these or similar approaches, TRI data may be better interpreted, and thus may play a more effective role in voluntary chemical stewardship.
Greater regulatory attention now is being devoted to pollution prevention and to generally reducing the quantities of toxic chemicals released into the environment. This strategy contrasts with the traditional end-of-pipe approach, which seeks to ensure that concentrations released to local environments are tolerable. The strategies actually are complementary, and both are necessary if local, regional, and global environments are to be protected. A key tool in the U.S. strategy of pollution prevention to reduce emissions is the annual EPA Toxics Release Inventory (i), which has encouraged industries to reduce emissions to avoid the embarrassment of being prominent on lists of dischargers, such as the Fortune magazine list (2). Indeed, there is a growing belief that such adverse publicity is n o w a m o r e effective i n s t r u m e n t for encouraging corporate boards to implement emission controls than the cumbersome and adversarial legal system. Canada has adopted the TRI approach in its National Pollutant Release Inventory (3). Industry have developed similar voluntary inventories. For example, the Canadian Chemical Producers Association has published two years of emission data for 225 substances and included projections five years into the future (4) Gathering, analyzing, and publishing TRI data is an expensive and time-consuming process. Thus, data and findings should be exploited to the maximum extent possible, interpreted, and summarized in a correct, unbiased, and easily understandable format. Our purpose in this article is to discuss methods of further exploiting TRI data to improve communication, policy formulation, and priority setting. The data must be reasonably accurate and complete, and ultimately must include all sectors of society, such as municipal discharges as well as emissions from fuels and combustion. Horvath et al. (5) recently reviewed and discussed this issue, addressing a p proaches like that of Davis et al. (6) in which toxicity, persistence, and bioconcentration potential may be combined with emission quantity to give a hazard index They pointed out the folly of adding masses of different pollutants to obtain a total mass giving an example of two companies A and B that emit to the atmosphere 1641 x 104 lb and 726 x 104 lb of chemicals respectivelv However when adjusted for toxicity by miiltiplyin** hv a
toxicity weighting factor of 1 mg/m 3 divided bv the threshold limit value (TLV) the adjusted toxicity indices are 17 and 78 srjectivelv So although Company B emits less ma terial the emissions are of greater toxicity and the rnmpany's impact prnhably is greater A n n i e
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son of state emissions shows that Louisiana emits to the atmosphere about 60 times the quantity emit8 6 A • VOL. 30, NO. 2, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
0013-936X/96/0929-86AS12.00/0 © 1996 American Chemical Society
ted in Arizona, but this factor drops to about 3 when adjusted for toxicity. By analogy, it would be equally misleading to compare the wealth of individuals by comparing tiieir bank balances but ignoring the different currencies that define their assets. As Horvath and colleagues noted, several indices and scoring systems have been devised in an attempt to weight emissions, but such attempts are fraught with difficulties (5). The TLV, for instance, is not intended for use in an environmental setting. Effects on wildlife or humans arising from bioaccumulation may not be included properly. There are several adverse effects, such as carcinogenicity, narcosis, reproductive effects, ozone formation, ozone depletion, and global warming, that are different in nature and cannot be easily or meaningfully added to give a total expression of effect or even proximity to effect. Despite these problems, this approach has merit because a kilogram of 2 3 7 8-tetrachlorodibenzo-p-dioxin and a kilogram of sulfuric acid have different impacts when discharged to a lake The Toronto Star named Kronos Canada Ltd ri e cir Montreal as "the country's biggest polluter" of 1993 because the Environment Canada Inventory showed that it discharged 6fi 000 metric tons of sulfuric arid into water noting that piratory problems Modeling in stages We suggest a sequence of stages of sophistication by which TRI data can be processed, interpreted, communicated, and assigned priorities. As a foundation for this discussion, it is useful to show how reported emissions are related to prevailing concentrations, which are in turn presumably related to effects. As shown in Figure 1, if there is a "box" of air representing, for example, the atmosphere of an urban region, then if the emission rate of chemical is E (g/ h), and steady state is achieved with losses by advection, reaction, and transfer to other media such as soil with corresponding rate constants kA,fcH,and fcp (h_1), ,hen the average eoncentration in the welll mixed box of air, CA, will be CA = EI[V{kA +fcR+fcT)](g/m3) (1) where V(m3) is the volume of air. Defining this volume requires judgment about appropriate mixing heights. Expressing the toxicity as a concentration C r (g/m3), which may be an environmental quality objective, standard, or guideline or a no-observableeffect level, a concept similar to the TLV, allows the proximity to this level to be best expressed as the dimensionless quotient CAICr or Q. Obviously, a low value of Q is preferred: Q = CAICT = El[V{kA + kR + kr)CT] (2) For similar toxic modes of action or effects, Q can
FIGURE 1
Mass balance An illustration of a steady-state mass balance of a chemical in a "box" of fir
TABLE 1
Stages of data interpretation Suggested indices (0) derived from emissions {E), where CTcm is a toxicity-based concentration of chemical "c" in medium "m"; x c m is persistence of chemical "c" in medium "m," and Fcl is the intermedia mobility fraction of chemical "c" from medium " i " to medium " i . "
be added for various substances to give a total Q. It is unlikely that a meaningful toxicity-based Cr quantity for ozone depletion or global warming can be defined, but a potency factor could be substituted. We suggest a four-stage approach in which die TRI data are subjected to increasingly sophisticated interpretation. (The indices derived for each stage, Qj to Q4, are summarized in Table 1.) In Stage 1, die simplest data presentation, emissions are merely presented and expressed as lb/year or kg/year. It is not meaningful—in fact it is highly misleading—to add emissions of different chemicals. Of course, it is acceptable to add emissions of the same chemical from different sources to give a series of chemicalspecific Q quantities. Existing TRI data satisfy this stage, although there are issues of data accuracy and VOL.30, NO. 2, 1996/ENVIRONMENTAL SCIENCE & TECHNOLOGY/NEWS " 8 7 A
FIGURE 2
TABLE 2
Emissions to air Fate of pentachlorobenzene when discharged to air
Emission quantities Emissions of two chemicals from sources A and B into three media (t/year). Source A A B B
Air
Water a
Soil
1000 (QCB ) 250 (QCB) 500 (styrene) 250 (styrene) 500 (QCB) 1000 (QCB) 3000 (styrene) 6000 (styrene)
100 (QCB) 100 (styrene) 100 (QCB) 500 (styrene)
^Pentachlorobenzene.
TABLE 3
Considering toxicity Selected toxicity-based concentrations (CT) of chemicals in three media.
completeness. For ranking purposes, direct emissions can be added and compared. But a simple multichemical index is not feasible at this stage because the data are too extensive for a simple evaluation, and our knowledge about impacts is too limited. In Stage 2, a second level of data presentation is accomplished by calculating and documenting the index Q2 as £/CT. This is essentially the approach advocated by Horvath et al. (5) in which they deduced and added values of 57TLV. A related index ii the quantity released (g), which divided by the CT is the critical volume of the environment that may reach CT. This measure has been used in life cycle assessment to compare emissions. It enables quantities of different chemicals to be added, which is justifiable only when the medium is the same and it is the medium in which the CT applies, when the effects corresponding to the CT are similar so that 3dditivity is a reasonable supposition, and when the rate constants are similar for all the chemicals. The first two constraints are the most serious Thus, it is de~ sirable to separate a carcinogenicity index from an ozone depletion index, for example. Individual indices could be added but an emission to water obviously should not be added to an emission to air Different indices must be deduced and presented for emissions to air, to water, and to soils. It may be preferable to retain kg/year as the dimensions of the index by multiplying by a reference CT of say 1 mg/m3, as was suggested by Horvath (5). What may emerge is a matrix of indices with receiving media on one axis and effects on the other. A problem with this approach is the implicit assumption that the rate constants are similar, that is, the overall environmental persistences are similar. If they are not, which usually is the case, it may be necessary to proceed to a third level of sophistication, which takes persistence into account. Stage 3 adjusts Stage 2 indices based on chemical persistence. In Stage 3, the persistence of chemicals is defined for each receiving medium /, giving Q3ii = .Ej/ICEcj:) Cxi] or EfalCjj (3) where xi is the chemical's persistence in the me8 8 A • VOL. 30, NO. 2, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Chemical
Air, mg/m3
Water, |ig/L
Soil, |ig/g
Pentachlorobenzene Styrene
0.5 2.6
0.03 4
0.05 5
TABLE 4
Considering persistence Estimated persistence of chemicals in three receiving media (years). Chemical Pentachlorobenzene Styrene
Air
Water
Soil
0.011 0.0008
0.036 0.015
2.6 0.048
dium and is expressed here as the reciprocal of the total removal rate constant. It is also the residence time, or ratio of amount present to input (or output) rate. It is questionable whether the advection term, kA, should be included. Advection does not remove the substance from the medium, but removes it from the local or regional medium. It seems appropriate to include advection for regional evaluations and exclude it for global evaluations. Again it may be desirable to retain the dimensions of kg/ year by dividing by a reference persistence of say one year. Extensive compilations of atmospheric reaction persistences, or half-lives, are now available largely as a result of the studies by Atkinson (8). Persistences in other media are less well documented, but estimates are becoming available (9,10). Reaction persistences can also be estimated from multimedia environmental models. If values of i{ could be agreed on for each chemical and medium, the index Q3 could replace Q2 in Table 1, giving a more meaningful estimate of exposure relative to a no-effect exposure. The primary advantage is that short-lived chemicals are now more tolerated. Commercial substitution of a short-lived chemical for a long-lived chemical reduces the index and could reduce a company's
contribution. Indices can be added for ditierent chemicals with similar enects. But addition is not possible across media because of differences in concentration units and media volumes. A problem with this stage is that intermedia transport processes are not properly included. For example, benzene emitted to water probably evaporates rapidly but would not be included in the air index.
FIGURE 3
Emissions to water Fate of pentachlorobenzene when discharged to water
The most sophisticated model The full multimedia behavior of the chemical is included in Stage 4. The aim is to include in an index that fraction of the mass of the chemical that is discharged to one medium but later is transported to another medium. Estimating this fraction requires either the use of a multimedia mass balance model or a broad database of chemical fate observations. We believe that it should be possible to agree on reasonable, typical fractions. At this stage, it is necessary to discuss features of existing multimedia models that can contribute to establishing these fractions. Several multimedia models are available, such as ChemCAN {11}, CalTOX (12), HAZCHEM (13), SimpleBOX (14), and that of Cohen et al. (15). The Society of Environmental Toxicology and Chemistry recently reviewed these models and their applications (16). The models essentially are more complex treatments of the simple equations presented earlier, in which connected boxes represent air, water, sediments, soils, and possibly fish, vegetation, and groundwater. A generic version has been described by Mackay et al (17) If inputs are defined, average regional concentrations can be deduced for diese media. To illustrate this approach, Figures 2,3, and 4 show the results of multimedia calculations for pentachlorobenzene (QCB) when emitted into air, water, and soil. The model used is described in the series of "Illustrated Handbooks" by Mackay et al. (10), to which the reader is referred for details. In Figure 2, when 1000 kg/h of QCB is emitted to air, the amount in air is 98,100 kg, and the nominal persistence in air is 98 hours. The actual persistence is 97 h, because the total influx to air including evaporation from soil and water is 1007 kg/h. Additional amounts are expected of 53,800 kg in soil, 3650 kg in water, and 13,000 kg in sediment, giving a total amount of 168,550 kg and thus an overall multimedia persistence of 169 h Figure 3 gives similar data for emission to water the persistence in water being 318 h and in total 1572 h For soil in Figure 4 the overall persistence is 22 400 h Several important conclusions can be drawn from these depictions of chemical fate. First, if emissions to all three media occur simultaneously, the fate is the sum of the weighted individual emissions. Figure 5, then, shows a total emission of 1000 kg/h of which 100 is to air, 600 to water, and 300 to soil. It is exactly the sum of 0.1 of the quantities in Figure 2 plus 0.6 of Figure 3 plus 0.3 of Figure 4. This linear additivity is a result of the exclusively linear equations used in the model. Overall environmental persistence depends on how the chemical is discharged to the environment. It is misleading to state that a chemical such as DDT lasts three years in the environment with-
FIGURE 4
Emissions to soil Fate of pentachlorobenzene when discharged to soil
out specifying how it enters the environment. The total environmental persistence can be much longer than the persistence in the receiving medium, as is shown in Figures 2 and 3. Each medium has a specific chemical persistence, independent of the nature or quantity of chemical emission. For example, in all the figures the persistence in water is about 320 h (13 days) calculated as the ratio of the amount in water to the total rate of input to water by emission and intermedia transport. The persistence in air is 97 h (4 days), in soil 22,400 h (2.5 years), and in sediment about 12,000 h (1.4 years). These quantities correspond to the xK values introduced earlier in Stage 3. In all cases, the proportions of the loss processes from each medium are constant. For example, of the total input to water, there is always fractional loss by reaction FR of 0.01, by advection FA of 0.32, by intermedia transport to air FWA of 0.58, and by transport to sediment F w s of 0.09. These fractions are fundamental properties of the chemical and the environmental medium and are independent of VOL. 30, NO. 2, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 8 9 A
plicity only the indices for air are given in Table 6. We have Considering transport rounded off some Environmental mobility fractions of pentachlorobenzene and styrene. numbers to two significant figures to Pentachlorobenzene Styrene avoid giving a false To air To water To soil To air To water To soil impression of accuracy, but even one From air 1 0.01 0.002 From air 1 0.0003 0.0001 significant figure acFrom water 0.58 1 0 From water 0.31 1 0 From soil 0.08 0.008 1 From soil 0.46 0.009 1 curacy might be questionable. Stage 1: Source B clearly discharges more of both chemicals, 1600t/year emission rates or how the chemical enters the enof QCB (500 t/year into air) plus 9500 t/year of styvironment. They are essentially a ratio of the indirene (3000 t/year into air) versus the 1350 t/year (1000 vidual loss-rate constant to the total-rate constant. t/year into air) and 850 t/year (500 t/year into air) disWe term these intermedia transport fractions (FWA charged by Company A Adding these quantities shows and Fws) as environmental mobilities. They are inthat B discharges 2 3 times as much to air as A and 5 0 structive, because they indicate the multimedia partimes as much in total B is clearly the more signifititioning tendencies of a chemical, and useful, becant discharger cause they enable the total inputs to Medium 1 to be deduced as the sum of direct emission £\ and inStage 2: Considering only discharges to air, when direct emissions via Medium 2 as E2F21 and Methe weighting for CT is included in the total, A and dium 3 as B each discharge a weighted 2200 t/year. Although Ep . The amount present in Medium 1 B's discharges are greater in quantity, they are less is thus approximately toxic, so the impacts on air expressed as Q2 be(E^ E2F21 + E3F31)T1 (4) come similar. A and B are now comparable in imand the concentration is this quantity divided by the pact. To retain the units of t/year, CT is divided by a volume V|. There is no actual need to run a multireference concentration, such as 1 mg/m3. media model for every assessment; all that is needed Stage 3: Again for air, because QCB has longer peris to use the model, experience, or judgment to essistence, the indices Q3 become 22 t/year for A and timate the mobility fractions F{: and the persis12 t/year for B. A now has nearly twice the impact tences Tj. of B because the chemical is more toxic and persisUsing this approach, the index for Medium 1 be- tent. The Tj is divided by a reference persistence of comes one year. Q41 = {Ex + E2F21 + E3F3l)x1l C^ x (5) Stage 4: When mobility is taken into account, the where Ev E2, and E3 are emissions to media 1, 2, and indices Q for both rise because of evaporation from 4 3; F2t is the mobility fraction from 2 to 1; and F3l is water and soil to an approximately equal 26 t/year. the mobility fraction from 3 to 1. A similar apThe increase in B is caused by the large discharge to proach is used for the other media. The advantage water, of which 58% of the QCB and 31% of the styof this approach is that all sources and pathways are rene evaporate. The two sources are now equal in improperly included, and the full multimedia behavpact on air. ior of the chemical is assessed. This is particularly important when a volatile substance is discharged A meaningful presentation to soil or water or when the bulk of emissions are to This example shows that the numerical presentaair and there is substantial atmospheric deposition tion of TRI data to assign priorities or responsibilto soil and water. Again separate indices are reity is far from simple. There is an understandable dequired for each combination of medium and effect. sire to reduce the data to simple quantities to identify This multimedia model assumes that 10% of the the primary problems and assign priorities. But this region is covered by water and the rest is covered by is difficult because chemicals differ in toxicity, persoil. Clearly, the fraction of area covered by water varsistence, and environmental mobility. The quantiies from region to region, which will affect the F„ values. It may be desirable to define different mobility ties characterizing these properties can vary by several orders of magnitude. fractions for different regions. Deposition from air to The simplest presentation of TRI data (Qj) docwater is more important in Michigan than in New uments quantities of various chemicals discharged Mexico. by various sources to various media. But it should Illustrating the concept be explicitly stated, as it is in EPA reports, that these quantities bear no relation to impact. If the intenTo illustrate this approach, we consider a simple case of dischargers A and B, which discharge QCB and sty- tion is to extend the interpretation to assess impact, then the index Q2 assists by weighting only toxrene, as shown in Table 2. Selected CT data are given in Table 3 based on published criteria {18-20} and icity. Q3 weights both toxicity and persistence. Q4 is the most comprehensive, weighting toxicity, persissuggestions by the authors for illustrative purtence, and environmental mobility. poses. Estimated persistences and environmental mobility fractions are given in Tables 4 and 5, respecFrom the viewpoint of environmental science, Q4 tively. Although indices for three media can be is the most meaningful, but even it requires sepadetermined using the proposed approach, for simrate assessment of air, water, and soil. It is not clear TABLE 5
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TABLE 6
All approaches
FIGURE 5
Emissions to three media Fate of pentachlorobenzene when discharged to air, water, and soil
Indices determined using the proposed approach for air (t/year).
if a single consolidated multimedia index of environmental impact could be devised. There is a compelling case for quantifying the uncertainties in indices and in any rankings that may flow from these indices. All the input quantities, emissions, effect levels (CT), and physical chemical and reactivity parameters from which persistence and mobility are deduced contain errors that will propagate through the calculation to give uncertainty in Q. For some chemicals the uncertainty may be intolerable. It is debatable whether expressions of uncertainty will be used, or even understood, but the scientific community has an obligation to express it as part of the communication. TRI data errors have been discussed by EPA {21), and it is likely that a reasonable target is a factor-of-two error. Accordingly at least for the immediate future only one significant figure accuracy is justified Indeed it may be preferable t"fl 11 QP
ranges such as half or even whole decades Obviouslv there is a need to quantify and communicate uncertainty and imDlement policies with a full awareness of this issue Implementing Q2, Q3, and Q4 will require the environmental science community to arrive at some level of agreement about the key properties of the chemicals. We regard this as feasible, at least for the well-studied, high-volume chemicals for which there are extensive fate and effects data. Surely, this is possible after the decades of funding research, monitoring, and assessment. The incentive to improve TRI interpretation flows from the need of industry and regulators to assign resources to high-priority issues and not squander them on trivial problems. Such resources could help agencies identify those chemicals requiring reporting on an annual or less frequent basis reduce the regulatory burden on industry and focus it where it is most needed If TRI data are to play a more effective role in volu.nt3.rv chemical stewardship then some ^vstem of meaningful data weighting must be devised that takes into account fate and effects in a rigorous and transDarent way. We have suggested the elements of one such system. In the absence of such a system, TRI data will rpmain an interesting and useful but an expensive nnHprpyniniteH anri orrasionallb misuspd ensiro'nmental information resource.
References (1) 1992 Toxic Release Inventory Public Data Release. Office of Pollution Prevention and Toxics (7408). U.S. Environmental Protection Agency: Washington, DC, 1994; EPA/ 745/R-94/001. (2) Rice, E Fortune 1993, 114-22. (3) Summary Report: The 1993 National Pollutant Release Inventory. Canadian Environment Protection Act; Environment Canada: Ottawa, 1995; Cat. No. En40-495-l/1995E.
(4) Reducing Emissions: 1993 Emissions Inventory and FiveYear Projections. Canadian Chemical Producers' Association: Ottawa, 1994. (5) Horvath, A. et al. Environ. Sci. Technol. 1995, 29(2), 86A90A. (6) Davis, G. A. et al. Chemical Ranking for Potential Health and Environmental Impacts (Draft Report). University of Tennessee, Center for Clean Products and Clean Technology: Knoxville, TN, 1993; U.S. Environmental Protection Agency Cooperative Agreement No. CR 816735. (7) McAndrew, B. Toronto Star, April 27, 1995. (8) Atkinson, R. In/. Phys. Chem. Reference Data, 1989, Monograph No. 1, 1-246. (9) Howard, P. H. et al., Eds. Handbook of Environmental Degradation Rates. Lewis Publishers: Chelsea, MI, 1991. (10) Mackay, D.; Shiu, W. Y.; Ma, K. C. Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals, Vols. I-IV. Lewis Publishers: Chelsea, MI; CRC Press: Boca Raton, FL, 1992-94. (11) Mackay, D. et al. ChemCAN: A Regional Level Hi Fugacity Model for Assessing Chemical Fate in Canada, in press. (12) McKone, T. E. Ca/TOX, A Multimedia Total-Exposure Model for Hazardous Waste Sites Part 2: The Dynamic Multimedia Transport and Transformation Model; Lawrence Livermore National Laboratory: Livermore, CA, 1993; No. UCRL-CR-111456Ptll. (13) ECETOC, HAZCHEM: A Mathematical Model for Use in Risk Assessment of Substances (Special Report No. 8); Brussels, Belgium, 1994. (14) van de Meent, D. SimpleBOX:A Generic Multi-media Fate Evaluation Model; RIVM: Bilthoven, Netherlands, 1993; Report No. 6727200001. (15) Cohen, Y. et al. Environ. Sci. Technol. 1990,24,1549-58. (16) Cowan, C. E. et al. The Multi-Media Fate Model: A Vital Tool for Predicting the Fate of Chemicals; Society of Environmental Toxicology and Chemistry (SETAC); SETAC Press: Pensacola, FL, in press. (17) Mackay, D.; Paterson, S.; Shiu, W. Y. Chemosphere 1992, 24, 695-717. (18) "Canadian Environmental Protection Act—Priority Substances List Assessment Report: Pentachlorobenzene"; Environment Canada: Ottawa, 1993; Cat. No. En40-215/26E. (19) Priority Substances List Assessment Report: Styrene. Canadian Environmental Protection Act: Environment Canada: Ottawa, 1993; Cat. No. En40-215/24E. (20) Interim Canadian Environmental Quality Criteria for Contaminated Sites. Canadian Council of Ministers of the Environment: Winnipeg, Manitoba, Canada, 1991; CCME EPC-CS34. (21) Toxics in the Community. U.S. Environmental Protection Agency: Washington, DC, 1990; EPA/560/4-90-017. VOL.30, NO. 2, 1996/ENVIRONMENTAL SCIENCE S TECHNOLOGY / NEWS * 9 1 A
