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ENVIRONMENTAL POLICY ANALYSIS REGULATIONS A Critical Review of the Benefits Analysis for the Great Lakes Initiative DANIEL W. SMITH SMITH Technology Corporation One Plymouth Meeting Plymouth Meeting, PA 19462 A critical review of the Benefits Analysis that accompanies EPA's Great Lakes Water Quality Initiative (GLI) shows that the benefits have been significantly overestimated. Benefits ac- crue from the estimated reduction in human cancer risk as a result of the decrease in point source loading due to the initiative. EPA esti- mated cancer reduction for fish consumers as the product of the numbers of consumers, fish consumption rate, chemical concentrations in fish, percent point source contribution to total loading, expected decrease in loading with GLI, and EPA cancer slope factor. For these compo- nents EPA used values that were higher than likely and that overestimated final benefits. EPA estimated GLI benefits of about $17,000 for each $1 million invested, but using more likely values produced estimated benefits of about $5 for each $1 million invested. Over the long term, one cancer should be averted sometime between now and the year 8086 after an expenditure of about $1.3 trillion. In April 1995, EPA released the Great Lakes Water Quality Initiative (GLI), a controversial, potentially ex- pensive new ruling that could significantiy tighten controls on point source pollution across the Great Lakes. To demonstrate the GLI's cost-effectiveness (J- 3), EPA also released a favorable cost-benefit anal- ysis. In this article the benefits portion of that anal- ysis (4), hereafter called the Benefits Analysis, is critically examined. The Benefits Analysis estimated GLI benefits in two ways: a whole-watershed analysis and a more de- tailed analysis of three Great Lakes Areas of Concern (AOC): Green Bay, Saginaw Bay, and Black River. The whole-watershed analysis estimated reductions in pol- lutants from a random selection of minor and major dischargers across the basin and men extrapolated those figures to the entire watershed. For the AOC subwa- tersheds, reductions in loading from all dischargers were estimated. The whole-watershed analysis considered only human health benefits. The AOC watershed anal- yses also considered other benefits, including "non- use" benefits and benefits to commercialfisheries.How- ever, almost all the benefits to the three AOC subwatersheds were direcdy or indirectly related to re- ductions in risk to human health. The two methods yielded quite different results. Benefits based on the whole-watershed analysis ranged from $0.7 to $6.7 million per year because of reductions in cancer deaths associated with the con- sumption of Great Lakes fish. Based on EPA's esti- mated cost of $60 million to $380 million per year, the whole-watershed analysis predicted that 0.2 cents to 11 cents of benefit could be expected for every dol- lar spent. In contrast, the AOC analyses predicted benefits of, on average, about 72 cents for each dol- lar spent on compliance. Only the whole-watershed analysis will be con- sidered in the following review, because the AOC ben- efit analyses are flawed. They incorporate a crucial polychlorinated biphenyl (PCB) point source load- ing estimate to Green Bay that is known to be in- correct {5-7). EPA's whole-watershed benefits analysis The estimated benefits across the whole water- shed accrue from reduced cancer mortality be- cause of decreases in chemical concentrations in fish. EPA estimated cancer reduction for fish con- sumers in each Great Lake subwatershed with the following equation: Cancer deaths averted = numbers of consumers x fish consumption rate x fish concentrations of chemicals x % point source contribution to total loading x expected decrease in loading with GLI x EPA cancer slope factor 3 4 A • VOL. 31, NO. 1, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS 0013-936X/97/0931-34A$14.00/0 © 1996 American Chemical Society

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Page 1: Environmental Policy Analysis, Peer Reviewed: A Critical Review of the Benefits Analysis for the Great Lakes Initiative

ENVIRONMENTAL POLICY ANALYSIS

REGULATIONS

A Critical Review of the Benefits Analysis for the Great Lakes Initiative DANIEL W. SMITH SMITH Technology Corporation One Plymouth Meeting Plymouth Meeting, PA 19462

A critical review of the Benefits Analysis that accompanies EPA's Great Lakes Water Quality Initiative (GLI) shows that the benefits have been significantly overestimated. Benefits ac­crue from the estimated reduction in human cancer risk as a result of the decrease in point source loading due to the initiative. EPA esti­mated cancer reduction for fish consumers as the product of the numbers of consumers, fish consumption rate, chemical concentrations in fish, percent point source contribution to total loading, expected decrease in loading with GLI, and EPA cancer slope factor. For these compo­nents EPA used values that were higher than likely and that overestimated final benefits. EPA estimated GLI benefits of about $17,000 for each $1 million invested, but using more likely values produced estimated benefits of about $5 for each $1 million invested. Over the long term, one cancer should be averted sometime between now and the year 8086 after an expenditure of about $1.3 trillion.

In April 1995, EPA released the Great Lakes Water Quality Initiative (GLI), a controversial, potentially ex­pensive new ruling that could significantiy tighten controls on point source pollution across the Great Lakes. To demonstrate the GLI's cost-effectiveness (J-3), EPA also released a favorable cost-benefit anal­ysis. In this article the benefits portion of that anal­ysis (4), hereafter called the Benefits Analysis, is critically examined.

The Benefits Analysis estimated GLI benefits in two ways: a whole-watershed analysis and a more de­tailed analysis of three Great Lakes Areas of Concern (AOC): Green Bay, Saginaw Bay, and Black River. The whole-watershed analysis estimated reductions in pol­lutants from a random selection of minor and major dischargers across the basin and men extrapolated those figures to the entire watershed. For the AOC subwa-tersheds, reductions in loading from all dischargers were estimated. The whole-watershed analysis considered only human health benefits. The AOC watershed anal­yses also considered other benefits, including "non-use" benefits and benefits to commercial fisheries. How­ever, almost all the benefits to the three AOC subwatersheds were direcdy or indirectly related to re­ductions in risk to human health.

The two methods yielded quite different results. Benefits based on the whole-watershed analysis ranged from $0.7 to $6.7 million per year because of reductions in cancer deaths associated with the con­sumption of Great Lakes fish. Based on EPA's esti­mated cost of $60 million to $380 million per year, the whole-watershed analysis predicted that 0.2 cents to 11 cents of benefit could be expected for every dol­lar spent. In contrast, the AOC analyses predicted benefits of, on average, about 72 cents for each dol­lar spent on compliance.

Only the whole-watershed analysis will be con­sidered in the following review, because the AOC ben­efit analyses are flawed. They incorporate a crucial polychlorinated biphenyl (PCB) point source load­ing estimate to Green Bay that is known to be in­correct {5-7).

EPA's whole-watershed benefits analysis The estimated benefits across the whole water­shed accrue from reduced cancer mortality be­cause of decreases in chemical concentrations in fish. EPA estimated cancer reduction for fish con­sumers in each Great Lake subwatershed with the following equation:

Cancer deaths averted = numbers of consumers x fish consumption rate x fish concentrations of chemicals x % point source contribution to total loading x expected decrease in loading with GLI x EPA cancer slope factor

3 4 A • VOL. 31 , NO. 1, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS 0013-936X/97/0931-34A$14.00/0 © 1996 American Chemical Society

Page 2: Environmental Policy Analysis, Peer Reviewed: A Critical Review of the Benefits Analysis for the Great Lakes Initiative

The number offish consumers, chemical concen­trations in fish, and percent point source contribu­tions vary considerably from lake to lake and were cal­culated on a lake-specific basis. Numbers of fish consumers for each lake were estimated from fishing licenses sold in the watershed. These anglers were then exposed to a lake-specific chemical concentration in fish, and the corresponding value was reduced as a function of a lake-specific percent point source con­tribution. For the other three parameters in the equa­tion, a single value was derived for the Great Lakes wa­tershed as a whole and applied to the calculation for each lake. The number of human deaths from cancer that were averted was then calculated for each lake and summed across all Great Lakes.

The equation above highlights two important points. First, the accuracy of the estimated benefits depends on the accuracy of each value used in the equation. Second, given the power of multiplica­tion, a small consistent bias in the estimation of these values produces a very large inaccuracy in the final estimate. Given the high numbers of licensed an­glers in the Lake Michigan subwatershed and the high chemical concentrations in Lake Michigan fish, about 70% of the current risk and 70% of GLI estimated ben­efits were predicted to accrue to consumers of Lake Michigan fish. Thus, an assessment of the accuracy of each component for Lake Michigan follows. How­ever, the comments below apply generally to each of the lake-specific analyses and to the sum of bene­fits as well.

Fish consumption rates EPA's exposure assessment is based on the follow­ing assumed average consumption rates of Great Lakes fish: low-income minorities, 43 g/day; other mi­norities, 11 g/day; and other sport anglers, 16.7 g/ day. These rates were taken from a study in the state of Michigan (8). In choosing to use these values, EPA made the critical assumption that anglers in the Lake Michigan watershed eat only "recreationally" caught fish from Lake Michigan, even though the study by West et al. included all freshwater sources. Thus, the extrapolation of these consumption values to an­glers in the Great Lakes basin assumes that all an­glers in the Great Lakes watershed eat as much rec­reational fish as do anglers in all of Michigan, and that all anglers in the Great Lakes watershed eat only Great Lakes fish.

These two assumptions are not supported by other existing studies. For example, Wisconsin anglers re­portedly eat considerably less recreationally caught fish, about 12.3 g/day (9), and most of them do not fish the Great Lakes [10). Similarly, those anglers who fish Lake Ontario reportedly eat only about 4 g/day of Lake Ontario fish {11), about one-fourth the daily ration of

fish assumed for Great Lakes watershed anglers. Thus, these other studies suggest that the EPA's assumed consumption rates are much higher than likely.

Fortunately, consumption rates for Michigan an­glers can be checked against numbers offish caught in Lake Michigan. EPAs exposure assessment for Lake Michigan is based on 42,853 low-income minori­ties, 33,900 other minorities, and 980,011 other sport anglers estimated to reside in the watershed. Thus, EPA's exposure assessment assumed the following rate of fish consumption from Lake Michigan:

Low-income minorities: 42,853 people x 0.0431 kg/ day x 365 days/year = 674,000 kg/year

Other minorities: 33,900 people x 0.0110 kg/day x 365 days/year = 137,000 kg/year

Other sport anglers: 980,011 people x 0.0167 kg/ day x 365 days/year = 5,974,000 kg/year

Total fish consumed = 6,785,000 kg/year

Data on the number of fish caught (12), how­ever, indicate that Lake Michigan recreational an­glers catch only enough to supply about 2,200,000 kg per year offish on the table, because about three-quarters of fish mass is lost during gutting, clean­ing, and cooking (13). Thus, the Benefits Analysis is based on a rate of consumption estimated to be 310% higher than the reported catch.

Fish contamination The Benefits Analysis bases the concentrations of chemicals in Lake Michigan fish primarily on data for lake trout. However, these fatty fish are at the top of the food chain and have concentrations of li­pophilic chemicals that are 2-20 times higher than those in other recreationally caught fish. Therefore, conclusions drawn from lake trout data signifi­cantly overestimate the risk to anglers.

To accurately portray this risk, the chemical ex­posure must be based on the mix of species actu­ally eaten. According to EPA's fish catch ("creel") sur­vey (14), chinook salmon make up 37% of the catch, and 25% is made up by yellow perch. About 70% of the catch is salmonids (lake, brown, and rainbow trout, and chinook and coho salmon); perch and wall­eye make up most of the rest. Assuming that the av­erage salmonid tissue can be estimated by the chi­nook salmon data and that the yellow perch have, on average, about one-third of the chemical con­centrations found in the walleye, the average con­centration for Lake Michigan fish can be estimated by the following equation:

Avg. concentration = 0.7 x chinook salmon + (0.25 walleye/3) + (0.05 x walleye)

VOL.31, NO. 1, 1997 /ENVIRONMENTAL SCIENCES TECHNOLOGY/ NEWS • 35 A

Page 3: Environmental Policy Analysis, Peer Reviewed: A Critical Review of the Benefits Analysis for the Great Lakes Initiative

Concentrations used in this equation should also take into account fish preparation. Zabik et al. (13) stud­ied the contaminants in fish prepared and cleaned by methods likely to be used by Great Lakes anglers. Their samples were also geared toward fish sizes similar to those found in creel surveys; this is important be­cause chemical concentrations depend on fish size. Av­erage concentrations for Lake Michigan chinook salmon and walleye, as well as the values used in the GLI Ben­efits Analysis, are presented in Table 1.

As shown, using concentrations in species actu­ally caught and in fish as it is actually eaten produces substantially lower chemical concentrations, and lower exposure levels, than the concentrations used in EPA's Benefits Analysis. The overestimates ranged from a low of 1.3 for DDT to a high of 4.8 for toxaphene. On av­erage, EPA overestimated fish concentrations, the risk offish consumption, and the benefits of avoiding those risks by approximately 250%.

Point source contributions GLI benefits accrue from reductions in external load­ing to the lakes, calculated as the product of point source reductions multiplied by the percent of total loading caused by point sources. Although PCBs and 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD) make up almost all the EPA cancer risk, both compounds are already so tightly controlled that neither was pre­dicted, in the watershed Benefits Analysis, to un­dergo any reduction in loading after the GLI. Thus, the benefits were based on reductions in the banned pesticides: DDT, chlordane, toxaphene, and diel-drin. For these pesticides, EPA "assumed" that point sources contribute 5-10% of total external loading to Lake Michigan. According to the Benefits Analysis, this value is based on two sets of data: unpublished EPA-collected data for four widely used industrial compounds (cadmium, mercury, lead, and PCBs) and point source contributions estimated by Strachan and Eisenreich (15) for PCBs and lead.

Thus, EPA's methods assume that the current sources of the banned pesticides, which were dis­persed widely in the environment and which are now banned, would be similar to source dynamics for compounds that remain in use today. Of this group, the use of cadmium, lead, and mercury is espe­cially misleading; these are naturally occurring heavy metals that are unlikely to approximate the source dynamics of a group of anthropogenic, hydropho­bic, banned chlorinated pesticides. The inclusion of cadmium is particularly inappropriate and also cru­cial to EPA's analysis. It is inappropriate because cad­mium is not considered a problem in the Great Lakes and will, consequently, not have its loading re­duced by the GLI. It is very important because cad­mium has, by far, the highest point source loading of the four chemicals—15 to 40% of total loading due to point sources—almost exactly an order of mag­nitude higher than that found for the more logical surrogate, PCBs.

PCBs are closer to the pesticides in chemistry and production history. According to the unpublished data presented by EPA (4, Table 5.1), only 1.7-3.8% (54 kg/ year) of total PCB loading to the lakes in 1992 could be attributed to U.S. point sources. More recent es­timates of loading, presented in Table 4.5 of the Ben­efits Analysis, suggest that point sources now con­tribute only 27.7 kg/year, producing current point source contribution of 0.8-1.9% of total PCB load­ing. In contrast, on a mass-weighted basis using to­tal loading data for each Great Lake from Strachan and Eisenreich (15), the point source contributions assumed in the Benefits Analysis indicate that 8.2-13% of total PCBs loading to the Great Lakes is com­ing from point sources. Thus, EPA's assumed point source contributions are about an order of magni­tude higher than warranted by the relevant data.

The usage history of the banned pesticides also provides no evidence for significant point source con­tributions. Dieldrin, and its precursor aldrin, were used widely on corn in the Great Lakes states (16), so nonpoint sources are likely to be very signifi­cant. Toxaphene inputs also should be dominated by nonpoint inputs. There are not likely to be signifi­cant point sources of toxaphene to Lake Michigan, because none of the major manufacturers of toxa­phene were in the Great Lakes basin (16,17). The lack of point and aquatic nonpoint sources on the Great Lakes has, in fact, been used to demonstrate that tox­aphene inputs are almost exclusively via atmo­spheric transport from agricultural uses in the south­ern United States (17).

Clearly the use of loading data for these pesti­cides would be the best approach for estimating their current point source contributiorfs. Reliable data for most of these pesticides, apart from DDT, are lim­ited. Total external loading to the Great Lakes is about 580 kg/year of DDT and its breakdown products (15). EPA's random sampling of point sources across the Great Lakes basin estimated that point sources con­tribute a total of about 4.6 kg/year (Table 4.5 of the Benefits Analysis), about 0.8% of total DDT loading— substantially less than EPA's estimate of 5-10% for DDT and the other pesticides. Thus, the point source contribution of 5-10% assumed in the Benefits Anal­ysis is too high by a factor of 6.3-12.6. Conserva-

TABLE 1Chemical concentrations in Lake Michigan fish Comparison of chemical concentrations in fish used in the Benefits Analysis compared with those found in cooked Lake Michigan fish (73). All concentrations are in mg/kg, wet weight. t-DDT concentrations are the sum of DDT, DDE, and DDD concentrations, and t-chlordane concentrations are the sum of a- and g-chlordane, oxychlordane, and cis and trans nonachlor. Chinook salmon concentrations are average values for charbroiled and baked with skin on and skin off from Table S-4 (13\. Walleye values are average for baked, charbroiled, and deep fat fried from Table W-5 (13). Average Lake Michigan fish = 0.7 x chinook salmon + 0.25 x walleye/3 + 0.05 x walleye.

t-DDT t-Chlordane Dieldrin PCBs Toxaphene

Benefits Analysis Concentrations (mg/kg) 0.47 0.27 0.10 2.00 0.96

Cooked chinook (mg/kg) 0.51 0.18 0.09 0.90 0.28 Cooked walleye (mg/kg) 0.10 0.04 0.01 0.23 0.03 Average Lake Michigan

fish (mg/kg) 0.37 0.13 0.07 0.66 0.20 EPA/average fish (%) 130 210 150 300 480

3 6 A • VOL. 31, NO. 1, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY/ NEWS

Page 4: Environmental Policy Analysis, Peer Reviewed: A Critical Review of the Benefits Analysis for the Great Lakes Initiative

tively assuming the former adds another 630% er­ror to the estimated benefits.

Fish concentrations and current loadings Another Benefits Analysis assumption is that present chemical concentrations in fish are in equilibrium with total external loading and that future concen­trations will rapidly equilibrate with future loading. This assumption implies that a given reduction in ex­ternal loading translates, immediately, into the same reduction in fish concentrations. But this ignores the complexity of chemical interactions within the lake ecosystem. It is also contradicted by much observa­tional data and theory suggesting that the sedi­ments and water column act as long-lived reser­voirs for chemicals [18-22). The long residence time of chemicals in the Great Lakes and resulting lags in system response to reductions in loading are actu­ally one of the primary bases for the GLI (23).

Why is this lag relevant to an attempt to esti­mate benefits resulting from the GLI? The chemical concentrations currently measured in fish have not yet caught up with reductions in loading that oc­curred over the past two decades or so. Because cur­rent fish concentrations may be 2, 3, or more times higher than current loading will support, further cuts in external loading will have a lesser effect than that assumed by the Benefits Analysis. Consider the case of Green Bay. According to data presented in EPA's modeling, PCB loading in 1989 was only sufficient to maintain water concentrations at about half of that actually measured. Thus, reducing loading by 9.4% would have only half that effect, e.g., 4.8%, on the final water concentrations in Green Bay.

A recent mass balance for Lake Michigan (24) and mathematical modeling (25) suggest that PCB con­centrations in the lake have not reached a steady-state with external loading. The mass balance esti­mated that total PCBs losses from the lake in 1991 were more than four times higher than total exter­nal loading, suggesting that much of the total load­ing is coming from PCBs stored in the sediments. Similarly, a mathematical model suggests that PCB concentrations in Lake Michigan lake trout are higher than can be sustained by current loading. Accord­ing to this model (25), PCB concentrations in large lake trout are expected to fall about 340% even if ex­ternal loading remained constant into the future. Be­cause smaller recreationally caught fish are likely to respond more quickly to changes in external load­ing, a conservative estimate of current disequilib­rium between loading and contamination for the av­erage food fish would be about 200%.

Cancer slope factors Lastly, the Benefits Analysis uses EPA's cancer slope factors (CSF) as predictors of the most likely events. However, CSFs purposely overestimate most likely cancer risk (26-28). The net effect of this conserva­tive approach will be estimated for PCBs, which rep­resent the bulk of the EPA calculated cancer risk. The CSF for PCBs is based on liver tumor data for fe­male rats from Norback and Weltman (29). This CSF ignores observed suppression of cancers in other tis­sues (30); the male rat data from this same experi­ment, which showed almost no response (31,32); data

from other experiments (33,34); and current meth­ods for classifying tumors (31). In each case, these exclusions result in an overestimate of the cancer rate compared with that predicted by the whole data set. Looking only at liver tumor data for all valid exper­iments, Smith et al. (35) calculated an upper bound potency of 1.9 (mg/kg/dayT1 for Aroclor 1260, about 25% of the value used by EPA. This CSF applies to Aroclor 1260, and other PCB formulations have proven to be either less carcinogenic (30) or not carcinogenic at all (35). Because only about 25% of the PCBs in Lake Michigan fish are Arochlor 1260 (36) with lesser pro­portions in the sediments (37), applications of a can­cer potency factor for Aroclor 1260 to PCBs found in fish, again, probably overestimates most likely cancer incidence resulting from eating fish.

To translate dose in lab animals to dose in hu­mans, CSFs also rely on a conservative body weight scaling factor that also is likely to overestimate risk. Currently, CSFs are based on a ratio of body weights of humans to laboratory animals scaled to the (1/ 3)"1 power, a value EPA itself no longer recom­mends as valid (38). Other federal agencies (e.g., the Food and Drug Administration) converted dose us­ing body weight without scaling at all. If EPA's new proposed scaling factor of (1/4)"1 is correct, use of current CSFs overestimates risk by factors of 55-93%, depending upon whether rats or mice were used in the toxicological studies. On the other hand, in those cases in which the appropriate scaling should be body weight without scaling, the CSF overesti­mates likely risk by factors of 6-14, again depend­ing on whether the critical studies are based on rats or mice. Assuming that scaling to the (1/4)"1 power is correct half the time and that half the potency fac­tors are based on mice and half are based on rat bio-assay suggests a geometric mean overestimate of about 400% [i.e., (1.55 x 1.93 x 6 x 14) ~25].

The CSF is also based on the upper 95% confi­dence interval for the slope as compared with the most likely slope, which represents another system­atic error when attempting to estimate likely can­cer rates. Most likely cancer estimates for a num­ber of Great Lakes pesticides and PCBs ranged from 1.3 to 6 times lower than the 95% upper confidence limits, when both were estimated with the linearized multistage model (39). A value of 200% appears to be a reasonable average estimate for this error.

To calculate the error inherent in using a CSF to predict likely cancer incidence, the following val­ues were used: 200% error for use of the 95% upper confidence limit, 400% for the conservative body weight scaling factor, and 400% for the systematic ex­clusion of contradictory data. This produces an av­erage overestimate of 3200% compared with most likely estimate using all appropriate data. By com­parison, other attempts to quantify the discrep­ancy between the EPA's cancer potency factors and the true most likely estimate have found ratios of 4300 (Sielkin et al., quoted in 40) for dioxin, and about 1.4 billion times for formaldehyde (41). With spe­cific reference to cancer risks posed by consuming PCBs in Great Lakes fish, the Michigan Environmen­tal Science Board (27) concluded that EPA's default methods probably overestimate likely cancer risk by "orders of magnitude."

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Risks overestimated EPA's Benefits Analysis estimated between 17 and 34 cancers would be averted over 70 years for Lake Mich­igan fish consumers. But the product of the com­bined errors reviewed above gives a total estimation er­ror of about 312,000%. Correcting for the 312,000% error produces more likely cancer reductions of between 0.005 and 0.011 cancers over the next 70 years. Assum­ing that the remainder of the watershed is similarly over­estimated, the total cancers averted will not be 25 to 47 over the next 70 years, as suggested by the Benefits Analysis, but between 0.008 and 0.015. This corrected estimate produces a range of likely yearly benefits of $230 to $2140, using the value of $2-10 million of ben­efit for each statistical life saved (4). Comparing the mid­point of the likely benefits with that of EPA's esti­mated costs of 460 million-$380 million per year— $1186 per year in benefits versus $220 million in costs— produces a median cost-benefit ratio of about 185,000 to 1. This represents a benefit of about $5 for each $1 million invested in pollution control. Over the long-term, one cancer should be averted sometime be­tween now and the year 8086 after an expenditure of about $1.3 trillion.

In a specific sense, this review suggests that the GLI should be reconsidered because its costs will likely dra­matically exceed its benefits. In a general sense, tiiis analysis illustrates the problem of estimating the ben­efits of environmental regulation, as well as the spe­cific problem of having an agency review its own pol­icies. I present this critique to spur thought and open debate on these important issues.

Acknowledgments This work was supported, in part, by the Occidental Chem­ical Corporation. I thank Ruth Anderson, Steve Jones, John Westendorf, Alan Weston, Jim Wilson, and Bob Tardiff for their comments. Four anonymous reviewers and the edi­tor were also especially helpful.

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