cleanup levels for dioxin-contaminated soils

Cleanup Levels for Dioxin- Contaminated Soils

Joel S. Hirscbborn

Joel S. Hirscbborn is President of Hirscbborn C Associates in Weaton, Maryland He bas worked on Superfind cleanups and remedial tecbnologies since tbe program’s tnception in 1980, originally at the Congressional Oflike of Tecbnology Assessment and since 1990 as a consultant to companies, community groups, and government agencies. Many of the cleanup sites be bas worked on have involved dioxin- contaminated soils.

EPA’s use of a 1 partper billion (ppb) level for dioxin contamination in residential soils is shown to be too high and notprotective ofpublic health. It was derived in a 1984 cancer risk assessment by another federal agency, but it is inconsistent with risk-based levels of 2 to 4partsper trillion Qpt) obtained by using EPA ’s standard risk assessment methods. EPA has called the 1 ppb level a policy-based level, which correctly distinguishes it from a risk or health-based cleanup standard. The 1984 assessment is shown in this article to have considerable shortcomings. For over a decade, dioxins have been left in soils at levelsposing health risks and sometimes at levels that EPA is legally required to address. Moreover, noncancer effects have been ignored, but recent work has shown them to support action at lowppt levels. To pmtectpublic health, be consistent with current scientific knowl- edge and other EPA policies, reduce confusion in the environmental management communiv, and be responsive to public demandsfor stringent dioxin cleanups, new EPA policy guidance for dioxin soil cleanups is needed, and key elements arepresented in this article. In an ad hoc fashion, EPA Region 4 has recently used a 200 ppt dioxin cleanup level for residential soil, acknowledged to correspond to a one-in-ten-thousand cancer risk, at two Superfund sites, which environmental professionals should be aware oJ This suggests a shqt in EPA policy.

For soil cleanup decisions at most Superfund sites, EPA has used 1 ppb of dioxin contamination for over a decade. At issue is whether this level is protective of public health, especially for land used for residential purposes. Although given originally as the concentration of the most toxic dioxin isomer, it now is given as toxic equivalent (TEQ) concentration. TEQs are obtained from using toxic equivalency factors (TEFs) for certain dioxins and furans that convert or normalize concentrations to equivalents for the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which has a TEF of one.

Surprisingly, even though there has been remarkable attention to dioxins, there has been little critical examination of the widely used 1 ppb cleanup level. Even though a remarkable amount of work on risk assessment, exposure parameters, and dioxin toxicity has taken place in recent years, EPA has never formally reexamined its 1 ppb cleanup level. This article critically examines the historical roots and scientific basis for the 1 ppb level, presents alternative values obtained by using EPA’s

CCC 1051 -5658/97/070363-18 0 1997 John Wiley & Sons, Inc.

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JOEL S. HIR~CHHORN

EPA has develuped risk assessment procedures and established presumptive numerical values fir key parameters.

standard risk assessment methods, presents relatively new information from the Agency for Toxic Substances and Disease Registry (ATSDR) that supports a more stringent cleanup level, presents information on EPA’s use of 1 ppb in the Superfund program at several sites, and examines how its use compares to other EPA policies. Exhibit 1 presents important historical events, discussed in this article, to help the reader grasp the complex background of the dioxin soil cleanup issue in the Superfund program.

SOURCE OF THE 1 PPB VALUE A paper published in 1984 by Centers for Disease Control (CDC) staff

presented 1 ppb standard,’ but the figure had probably been disseminated within government in 1983. CDC used a cancer risk assessment based on doses for 10-6 risk, and for residential exposure to contaminated soil. CDC said that 1 ppb was “a reasonable level at which to begin consideration of action to limit human exposure for contaminated soil.”

For Superfund decisions, a 1989 EPA memo has been cited by EPA as setting a policy of using the 1 ppb figure as an action or health concern

The memo cited the CDC paper as the source of the 1 ppb figure. The memo was for a particular Superfund site decision and was not issued as EPA policy guidance. Importantly, the memo noted that “1 ppb does not represent a fine line between safe and unsafe conditions as the term ‘action level’ implies.” The problem is that it has been used in exactly that way, and the challenge is to better understand why this has happened. The memo did not cite EPA’s 1985 health assessment for dioxin^.^ EPA still uses the 1985 dioxin cancer potency.

In 1987 EPA released the results of its National Dioxin Study,4 which included soil contamination data for some Superfund sites, but the laboratory testing detection limit was only 1 ppb for about 75 percent of the sites, meaning that levels below that were largely unaccounted for, as if they were unimportant. If dioxin TEQ levels below 1 ppb are of health significance, then rather than using EPA’s method 8280 for dioxin testing which has a generic detection limit of 1 ppb, only method 8290 with a detection limit of 1 ppt is appropriate. The continued use of 1 ppb as a cleanup standard has sometimes resulted in the less accurate laboratory method being used, leading to unreliable data for lower dioxin levels.

EPA RISK ASSESSMENT EPA has developed risk assessment procedures and estabtished

presumptive numerical values for key parameters. EPA Region 3 issues a widely used set of risk-based concentrations, based on 10“ risk, including values for residential soil inge~tion.~ Its value for TCDD is 4 ppt.

Changes in the parameters used in risk calculations can change this value, even for what seems the same basic residential exposure and risk level. For example, an EPA contractor for the Escambia Treating Company Superfund site, Pensacola, Florida, calculated a soil level of 2 ppt TEQ for residential exposure and risk. This figure reflected three exposure pathways of ingestion, inhalation, and dermal exposure, which was

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CLEANUP LEVELS FOR DIOXKN-CONTAMINATED SOILS

1982

1983

1984

1985

Exhibit 1. Important Events for Soil Dioxin Cleanup

CDC urged evacuation of Times Beach, Missouri, because of dioxin- contaminated soil; dioxin becomes national environmental issue

Senior EPA official forced to resign because of support for company’s position on dioxin contamination in Michigan

Paper published by CDC scientists presented 1 ppb dioxin cleanup level

EPA scientist questioned 1 ppb level for dioxin contamination in Midland, Michigan

I YEAR I

1985

1986

1987

EPA Dioxin Health Assessment; dioxin cancer toxicity greater than CDC’s

Company attempted to get EPA to raise dioxin cleanup level from I ppb to 10 ppb for Times Beach

ATSDR supported 1 ppb cleanup level

1987

1988

1989

1994

1995

Air Force cleanup used level of 100 ppt that EPA and CDC supported

EPA used 1 ppb cleanup standard for residential soil in Times Beach ROD

EPA memo to ATSDR, subsequently cited as basis for 1 ppb standard, but actually said that 1 ppb did not define safe-unsafe boundary

EPA draft dioxin reassessment reports issued, dioxin toxicity reconsidered

ATSDR Public Health Assessment for Escambia Superfund site cited 50 ppt level for noncancer health effects

1995

1995

1995

ATSDR scientists published paper supporting 40 ppt dioxin soil cleanup level because of noncancer health effects

Tifton, Georgia EPA study ignored dioxin levels below 1 ppb in community

ATSDR supported EPA Tifton action, ignored noncancer effects

~~

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1996

1996

~~~ ~ ~

EPA used 200 ppt dioxin cleanup level for residential exposure at two Superfund sites, acknowledged as lo4 cancer risk level

EPA Region 4 analysis found 79% of Superfund cleanup decisions used 1 ppb or greater, but 9% used levels in 4-7 ppt range

JOEL S. HIR~CHHORN

CDC’s exposure model used assumptions to obtain uptake doses that merit attention.

appropriate because soil in an adjacent community had been contaminated by dioxin for many years. EPAs 4 ppt is for ingestion only and is more appropriate for soils on a cleanup site. The state of Georgia publishes a cleanup value corresponding to 4.8 ppt and North Carolina uses 4.1 ppt, both presumably following EPA risk methods, but probably with some minor change in one or more exposure parameters.

Another overlooked issue is exposure to other site contaminants, especially PCBs because they are related to dioxins in molecular structure and toxicity and because they are present at some cleanup sites along with dioxins. EPA has not yet determined TEFs for PCBs, which hampers site evaluation for both PCBs and dioxins. In its draft dioxin reassessment, EPA has said that PCBs could double or triple TEQ values, and a leading dioxin expert has said that dioxin TEQs should be doubled to account for contributions by PCBs, as cited recently in a new book on dioxin.6 Recent research supports this view of PCBs.’

DIFFERENCE BETWEEN EPA AND CDC SOIL LEVELS All risk assessments use the same basic method. But they are used and

presented in different ways. EPA’s value of 4 ppt was obtained by asking the question: what level of dioxin contamination in soil corresponds to a 10“ cancer risk, assuming various parameters for ingestion from residential exposure? But CDC asked: assuming a level of 1 ppb TCDD in soil and various exposure parameters, is this level of health concern? There are two basic components of risk assessment: (1) determining an uptake dose from the contaminated soil, and (2) determining a risk-based dose from toxicity data. EPA used one set of toxicity data, while CDC used that one plus another in the literature. CDC used a range of lo4 doses C.028 to 1.428 pg/kg-day), and the low dose came from the toxicity data also used by EPA, but the highest doses came from the other data set. The dose range allowed a risk range to be calculated. The lowest cancer dose equated to a risk of 2.3 x for 1 ppb dioxin contamination and various exposure assumptions.

However, the lower limit dose does not correspond to the value obtained in 1985 by EPA and is still used-.006 pg/kg-day. This smaller dose resulted from use of a higher toxicity or cancer potency than most of the data used by CDC. This lower EPA dose, together with CDC’s exposure assumptions, results in a risk of 1.1 x lo4 for 1 ppb dioxin, which is above the risk level requiring action by EPA under the National Contingency Plan.

CDC’s exposure model used assumptions to obtain uptake doses that merit attention. For example, it assumed that the 1 ppb level might be in 100 percent, 10 percent, or 1 percent of soil, and that some soil had no dioxin contamination. This is like assuming that 1 ppb is a maximum value, but not necessarily the average level over an area. EPA data are normally average levels. CDC assumed a 12-year half-life for TCDD in soil, meaning that exposure over decades would not be to the initial level, but to much lower levels. Remarkably, the same CDC paper also said that “The half-life of TCDD in soil is not known.” A brief discussion noted that the degradation by ultraviolet light required certain chemical circumstances,


CLEANUP LEVELS FOR DIOXIN-CONTAMINATED S o u

and that biodegradation would occur “at a very slow rate.” Although there is no consensus on soil half-life for dioxins, what appears to be the best estimate is 25 to 100 years.’ CDC’s assumptions lowered uptake dose and health risk.

CDC used higher ingestion rates of soil for children than EPA does, but the levels for adults were the same. Various assumptions were used for dermal and inhalation uptakes, not all of which agree with EPA values. The overall impact of all CDC’s assumptions was determined. EPA’s smaller 10‘ dose was used while maintaining the other parameters the same as CDC used. The result is 9.4 ppt for TCDD in soil. Because this is greater than the 2 ppt obtained for a similar multipath exposure by using EPA’s procedures, all of CDC’s data reduced total exposure and dose, and therefore risk, as compared to EPAs method.

CDC concluded: “The excess lifetime cancer risk for exposure to residential soil with a peak TCDD contamination level of 1 ppb ranges over 4 orders of magnitude, from above to below lo”.” Over time, EPA and others have ignored CDC’s risk range for 1 ppb and, especially, that risks lower than resulted from a cancer potency lower than that used by EPA and less conservative exposure assumptions. If EPA’s cancer potency and exposure assumptions are used, an average concentration of 1 ppb has a risk of 5 x lo4, which is high. The 1 ppb level is not a 10“ risk-based concentration. It is a value that CDC associated with a range of 10“ risk cancer doses, that were all greater than EPA’s value, and exposure conditions that in total resulted in less dioxin uptake than with EPAs exposure parameters. Paustenbach et al. examined the CDC cleanup level and found that much lower levels could be supported, such as 10 ppt, if certain cancer potency, exposure factors, and low risk levels are used, but the information did not affect EPA’s cleanup leveL9

CDC’S POLICY RECOMMENDATION The CDC statement that 1 ppb “is a reasonable level at which to begin

consideration of action to limit human exposure for contaminated soil” was given in the paper’s abstract. But in the paper’s summary, CDC said “We have concluded that residential soil levels greater than 1 ppb TCDD pose a level of concern.” These are two very different statements. The term “concern” is far from a tight, scientific concept, but the second statement appears to offer a definitive scientific conclusion. The 1 ppb level is not compatible with EPA’s value of 4 ppt, because CDC did not specify a safe-

The policy statement is inconsistent with EPA’s scientific findings and risk assessment procedures.

unsafe boundary on the basis of risk, but only what it postulated to be an unsafe level, assuming that “concern” equates to unsafe or unacceptable risk. But the semantic confusion is whether a statement about an unsafe level of concern pertains to dioxin levels below it.

The abstract’s statement was apoZicy recommendation for government to use a 1 ppb level to decide whether or not to take action, such as soil cleanup or relocation of residents, that EPA adopted. As the above analysis has shown, the policy statement is inconsistent with EPA’s scientific findings and risk assessment procedures, is not fully supported by CDC’s findings, and has resulted in the incorrect belief or assertion that levels

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JOEL S. HIR~CHHORN

I f CDC had said that contamination levels below 1 ppb posed a health concern, EPA’s decisions on soil cleanup would have been greatly affected, and costs would have been much higher.

below 1 ppb are not of health concern and, therefore, are safe. Certainly, EPA’s persistent use of the 1 ppb has implicitly been based on that interpretation.

The CDC paper had other related statements, including “A soil level of 1 ppb TCDD in residential areas is a reasonable level at which to express concern about health risks” (emphasis added). This phrase is not equal to the policy recommendation of “at which to begin consideration of action.” Another CDC statement was “Although from these calculations levels of TCDD below 1 ppb are, for practical purposes, considered not to reach a level of concern, several additional considerations related to the risk assessment calculations should be pointed out to decision-makers involved in risk management.” In fact, the paper had several critical caveats, such as acknowledging “insufficient information about exposure of people to soil, and insufficient information about intake of TCDD by humans from such soil.” Also, “whether a certain level of TCDD in soil will give rise to concern has to be evaluated on a case-by-case basis.” N o such caveats accompanied the abstract’s policy recommendation. Nor did they support use of 1 ppb as a presumptive cleanup standard.

The CDC study had been conducted because of the highly publi- cized dioxin contaminated sites in Missouri that EPA’s Superfund program was addressing in a highly politicized atmosphere. CDC was charged with determining “what level represented an unacceptable risk to the population living in these contaminated areas.” However, before the CDC risk assessment, at the end of 1982, CDC had already issued a warning that Times Beach should be completely evacuated on the basis of soil contamination data. In other words, CDC was asked to do what ATSDR was subsequently created for. If CDC had said that contamination levels below 1 ppb posed a health concern, EPA’s decisions on soil cleanup would have been greatly affected, and costs would have been much higher.

There would not have been an impact on relocation because EPA had decided in early 1983 to buy out all residents. That decision had been supported by the CDC warning several months earlier. The Missouri buyout was seen as an attempt by EPA to “reverse the agency’s tarnished image,”’O because at the time EPA was in turmoil, under intense public scrutiny, and top political appointees were dismissed o r resigned. Later, attention shifted to soil cleanup. In 1986, Syntex attempted to get EPA to increase the soil cleanup level from 1 ppb to 10 ppb to save 65 percent of cleanup costs that it and other companies were responsible for. In fact, the uncertainties and caveats in the CDC paper could be used to support such an effort, making 1 ppb seem like a political compromise. EPA’s attempts to have companies pay for Superfund cleanups, which accelerated in the late 1980s, conflicted with reducing the dioxin cleanup level below the CDC figure, even though it was inconsistent with EPA’s own risk assessment data. In 1988 EPA used the 1 ppb level in its decision for Superfund cleanup at Times Beach, Missouri. It set the stage for EPA’s dioxin soil cleanup level becoming policy-based rather than risk- or health-based.

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CLEANUP LEVELS FOR DIOXIN-CONTAMINATED SOILS

In 1988, in a paper about the Missouri cleanup, EPA officials noted that

Semantically, the use of the term “acceptable” to describe the dioxin cleanup level was akin to CDC’s use of the term ‘%oncent,” and both skirted the more scientific issue of whether the level was actually a riak- based safi level.

the 1984 CDC paper served as the basis for EPA establishing “1 ppb as an acceptable cleanup level for dioxin-contaminated soils in residential areas.”” They also explained how the agency had “requested additional information from CEH [Center for Environmental Health component of CDCI, and more recently from the Agency for Toxic Substances and Disease Registry (ATSDR), concerning acceptable dioxin concentrations in soils for residential and non-residential areas.” They noted that the evaluation “supported the continued validity of the 1984 study by Kimbrough, et al.” But there was no citation to an actual document. Semantically, the use of the term “acceptable” to describe the dioxin cleanup level was akin to CDC’s use of the term “concern,” and both skirted the more scientific issue of whether the level was actually a risk-based safe level.

NONCANCER HEALTH EFFECl‘S A recent paper by ATSDR staff addressed noncancer health effects and

possible levels of dioxins for cleanup decisions.lz This is important, because over the past few years there has been increasing recognition that noncancer health effects of dioxins may be more important than cancer impacts. For example, a recent successful environmental book said “Dioxin acts like a powerful and persistent hormone that is capable of producing lasting effects at very low doses-doses similar to levels found in the human population. . . . Dioxin and dioxin-like PCBs are known to affect the immune system as well as many parts of the endocrine ~ystem.”’~ Another recent survey indicated that dioxins cause reproductive, immunological, and endocrine effects.14 The ATSDR authors noted that “recent studies suggest that noncancer end points may be more sensitive indicators of dioxin exposure,” and derived a value of 40 ppt for chronic exposure of children, which is called an environmental media evaluation guide (EMEG) by ATSDR. EPA has also used a childhood-only basis for soil cleanup levels of noncarcinogenic ~0ntaminants.I~ EPA’s draft dioxin reassessment indicated that the “no effects” level for cancer and noncancer endpoints may be very similar. In other words, both the ATSDR and EPA works support a cleanup level in the low ppt range, in contrast to the 1 ppb level.

Moreover, the ATSDR authors also concluded that “No absolutely safe exposure (i.e., above zero) can be identified.” The cancer dose-response models used by EPA and CDC (i.e., linear multistage) also assume that even one molecule can result in cancer.16Although a recent analysis using EPAs dioxin toxicity data showed only a cancer risk from one TCDD rn~lecule,’~ and toxicologists and other professionals debate how low- dose cancer risks should be assessed, public concerns about dioxin exposure and Superfund site cleanup levels are increasing because of noncancer effects.

Moreover, the ATSDR authors acknowledged the need to address incremental exposures resulting from multiple, background, and past sources of dioxin exposures. They noted that “ingestion of homegrown


JOEL S. HIR~CHHORN

vegetables and fruit, and derma/dust inhalation exposure of those working in the garden must be considered” and that “special attention must be paid to the exposure of children playing on contaminated soil.” In other words, depending on varying background exposures for different people in different locations, an additional exposure from a cleanup site may be more or less important in causing new or additional health effects. All such conditions “suggest the need to further lower the TCDD levels in soil in order to lower the total exposure,” according to the ATSDR authors. They recommended that although the 1 ppb level “may be appropriate guidance value . . . to the extent that parameters of exposure and/or human factors would suggest the existence of at risk or vulnerable population groups, alternative values such as these outlined in this paper should be considered.” Also, there have been recent findings of synergistic estrogenic effects among PCBs and pesticides which strongly suggest similar interactions with dioxins.lg And this phenomenon also supports the logic of using lower cleanup levels to address noncancer effects.

The 1995 ATSDR Public Health Assessment for the Escambia site used an EMEG of 50 ppt for dioxin TEQ in soil. But ATSDR said “The levels of dioxin-TEQ in off-site soil are unlikely to cause noncarcinogenic health effects,” even though the report gave the maximum level of 950 ppt from 1992 testing. The report also said “Because the cancer risk in people from exposure to dioxin-TEQ is currently under scientific review, we do not know what carcinogenic health effects are likely.” But the draft EPA dioxin reassessment did not nullify the EPA cancer risk information that EPA itself has continued to use, including for the Escambia site. The 50 ppt value was ignored by EPA, which only focused on cancer risks and the 1 ppb level. This author knows of no Superfund site where EPA has used noncancer effects of dioxin to set or influence cleanup levels or other actions such as relocation of residents.

BACKGROUND LEVELS AND INCREMENTAL RISKS There is a critical need at Superfund sites, especially when dioxin

contamination is found in residential soils, to determine the local background level of dioxins in soils and the level of dioxins in blood lipids in people plausibly exposed to site dioxins and those not so exposed. Background data serve two purposes. One is to decide whether soil contamination is significant. The other is to determine whether an exposed population has prior or multiple exposures.

The issue of prior exposure is extremely important, although often overlooked in cleanup decision making. Dioxins “result in greater toxicity from repeated small doses than from a single dose because of their induction of enzyme systems, changes in immunological function, and long retention times within the body.”19 Therefore, residents, including former site workers, may be especially vulnerable to additional, incremental exposures, especially from site cleanup activities. Sherman emphasized that “continuous exposure.. .results from chemicals that are retained within the body, although ongoing external exposure has ceased. [Wlhen taken into the body [dioxins] are slowly, if ever, eliminated. Thus, although the overt exposure may cease,

The issue of prior exposure is extremely important, although often ~ ~ e r l ~ ~ k e d in cleanup decision making.

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CLEANUP LEVELS FOR DIOXIN-CONTAMINATED SOLS

the person remains exposed throughout a significant portion of his or her lifetime, and the adverse effects become cumulative.” Establishing prior dioxin exposure and body burden is, therefore, extremely relevant to setting appropriate cleanup standards.

A recent study reported the proper use of off-site control soil samples to obtain background dioxin levels.2o Interestingly, the average background TEQ level was higher than the cleanup site’s level, and both were very low (less than 3 ppt). The background levels were explained as resulting from the impacts of traffic on a major highway in an otherwise rural area. The data supported the conclusion that the cleanup site was not

True background soil levels for dioxin TEQ will usually be around 1 PPt.

contaminated by dioxins, There is no scientific support for dismissing dioxin contamination

below 1 ppb as merely background concentrations, an approach often used by EPA, unless data are obtained from control samples at some distance from the site and other plausible point sources. Using data from locations near a cleanup site or on it, which is sometimes done, provides overly high levels that are not true background levels. Higher than normal background soil and blood levels for an exposed population provide the basis for lower dioxin cleanup levels, either on or off the Superfund site, or both.

Background soil levels of dioxins in North America vary widely, from 2.26 to 13.66 ppt TEQ, according to EPA.” This range is not surprising, because some geographical areas, even at significant distances from point sources, have been affected by air deposition of dioxin-contaminated particles from waste incineration, industrial manufacturing, and other sources. Also, EPA assumed nondetects equal to half the detection limit, which is EPA’s procedure for risk assessment,z2 but this procedure is not necessarily used when Superfund data are reported. A study cited by EPA on dioxin background exposures in the United States assumed only a .96 ppt TCDD soil level, compared to EPAs average of 8 ppt TEQ. In this author’s opinion, true background soil levels for dioxin TEQ will usually be around 1 ppt.

The background level issue and paying attention to multiple exposures to dioxin were examined in a 1985 EPA analysis that focused on findings of dioxin soil contamination in Midland, Michigan, where Dow Chemical operated a plant that had produced pesticide chemicals having dioxin contamination and incinerated chemical wastes.23 The EPA risk assessor argued that 1 ppb was probably not appropriate to evaluate the findings. EPAs data showed the average level of TCDD (TEFs were not set until 1989) to be 48 ppt in Midland residential and public access soils, as compared to 2.4 ppt in Middleton, Ohio, a comparable industrial city. The average level around the perimeter of the Dow Chemical plant was 327 ppt, compared to 2.2 ppt around a steel mill in Middleton. Dow Chemical had obtained its own data on soil levels in a number of industrial cities and reported an average of 2.2 ppt. The EPA risk assessor argued that the Midland levels were not normal background levels, and were especially significant because many residents had been exposed as workers at the Dow Chemical plant, that people had been exposed to soil and air dioxins

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JOEL S . HIR~CHHORN

EPA’s actions f ir the Escambia site in Pensacola also illustrate problems related to background levels.

for decades because of releases from the facility, and that they had eaten homegrown vegetables and fish from a local river which were probably contaminated by dioxins.

Here was a specific case where site-specific circumstances showed the need to use levels below 1 ppb as of health concern, and to use a lower level for cleanup and relocation decisions. Like the Missouri situation, here too there was a political dimension, because in early 1983 there was a controversy involving a senior EPA official, forced to resign, based in part on actions that allowed Dow Chemical to affect EPAs decisions on dioxin contamination in Michigan. It is clear that the Missouri and Midland cases were the precedents for EPA’s use of the 1 ppb level as a policy-based figure.

EPAs actions for the Escambia site in Pensacola also illustrate problems related to background levels. In 1995 soil sampling was done in the residential community close to the Escambia site, part of which is adjacent to the Escambia site and part a little more distant and even closer to another Superfund site (Agrico Chemical). Samples were also taken from four areas outside this immediate community but only slightly further away. EPA has acknowledged levels of dioxin contamination of health concern only in a small portion adjacent to the Escambia site, where the average level was 587 ppt TEQ, but where several locations had levels above 1 ppb. The area a little further away from the Escambia site had an average of 70 ppt, and the next more-distant area had 7.3 ppt. In the neighborhood closer to the other Superfund site, which is more distant from the Escambia site, the average was 12.4 ppt. For the four areas outside the residential community, a school yard had 7 ppt, a baseball field had 7.5 ppt, a vacant lot had 22.7 ppt, and a residential yard had 7.8 ppt.

EPAs position was that all the areas, except the one adjacent to the Escambia site (where the 1 ppb level was exceeded), did not pose health risks and that they had not been affected by the Escambia site. No data were obtained, however, to determine background levels in the Pensacola area. Nearly all dioxin levels were above the 2 ppt determined for residential exposure and risk, including two areas where children spent time (the baseball field and school). It should also be noted that some residents were exposed as workers at the former Escambia operation, that the dioxin contamination of the residential soil had initially occurred many years before the site entered the Superfund program, that an EPA removal action that excavated an enormous amount of contaminated soil and piled it on the site had probably caused some releases of dioxin, that soils were contaminated by several other highly toxic chemicals, and that there were pervasive health problems in the community. Thus, the issue of incremental dioxin risk was relevant as evidenced by an ATSDR Health Consultation for the Escambia site prepared in 1992 and its review by the ATSDR Health Activities Recommendation Panel. Because of “likely” worker exposures at the operating wood-treating company and because “off-site exposures may have occurred,” the panel recommended a health evaluation of residents living near the site. Most importantly, it was to include physical examinations and laboratory tests. These were not implemented, however.



The prospective approach is valid for cleanup sites themselves, for which assumptions about future land use, such as residential use, are appropriate.

The testing for dioxin in blood lipids would have provided important data regarding past exposures to dioxin among residents.

PROSPECTIVE VERSUS RETROSPECTIVE EXPOSURES Dioxin risk assessment work has focused on prospective residential

exposures and whether residual soil levels after cleanup would pose unacceptable health risks. Oddly, however, in many cases dioxin contamination is found in residential soils where people have already been exposed to the levels found. The prospective approach is valid for cleanup sites themselves, for which assumptions about future land use, such as residential use, are appropriate. But the retrospective approach for off-site areas accounts for additional incremental dioxin risk for dioxin- contaminated residential areas with previously exposed populations.

CDC's work for Missouri was such a situation, yet its analysis was only prospective. Instead of using a half-life to calculate lower dioxin levels for future exposures, it should have worked backwards to obtain higher levels for the people exposed to the soil in the past. As in the Missouri, Midland, and Pensacola cases, for many situations the retrospective approach is necessary, and the 1 ppb level-and even EPA's levels of 2 to 4 ppt-are not necessarily protective when additional incremental dioxin risk is considered.

CONSISTENCY WITH CLEANUP LEVELS FOR OTHER SITE CONTAMINANTS

At most Superfund sites, soil contaminants are designated as "contaminants of concern," and EPA sets cleanup levels as preliminary or final remediation goals. In many cases, these are based on 10" risk and residential exposure. In those cases, when dioxins are also site contaminants, the issue arises as to how EPA can use 1 ppb when, according to EPAs own risk numbers, the lo4 risk is 2 to 4 ppt. Reasonable people question how the government can use the 10" risk level for every toxic chemical except dioxin, which EPA acknowledges to be the most toxic chemical. Moreover, if some soil with up to 1 ppb dioxin remains after cleanup, then residual risks are lo4, negating the benefit of cleaning up the other contaminants to 10" risk levels.

EPA SOIL SCREENING VALUES EPA has established generic soil screening levels for 110 chemicals, for

use in the Superfund program.24 These are based on lo4 risk and residential soil ingestion exposure. They can serve as preliminary or final remediation goals, unless site-specific information is used to support other levels. But no value was presented for dioxin. The explanation from EPA is that a policy decision had already selected 1 ppb, and that EPAs dioxin reassessment is ongoing.

EPA'S USE OF THE 1 PPB LEVEL A good example of the current problem is an EPA study in 1995 that

tested residential area surface soils in a small town, Tifton, Georgia, with


JOEL S. HIR~CHHORN

I l l The corrected TEQs, moreover, indicate levels of health concern at all distances Fern the cleanup site.

a number of toxic waste sites. EPA dismissed the findings of dioxin in all 14 samples solely on the basis that they were below 1 This author’s analysis of the data found that the sample locations could be divided into three groups, based on distance away from the MarzoneKhevron Superfund site. It was found that the five residential soil samples closest to the site (about a quarter mile or less) had an average dioxin TEQ level of 65.2 ppt (with a maximum of 120 ppt). For the three locations further away, the average was 5.9 ppt. For the six locations about one-half to a mile away the average was 2.6 ppt. However, the detection limits were unusually high for the 8290 method, suggesting systematic underestimates of TEQ dioxin. This was compounded by the procedure of ignoring all nondetects. EPA guidance is to use one-half the detection limit. Correcting the data resulted in TEQs for the three zones given above of 66.8, 14.4, and 10.5 ppt, with increasing distance from the Superfund site. This is strong evidence that dioxins had migrated from the site into the surrounding community by means of airborne transport of dioxin-contaminated soil particles (from the cleanup site or from the original industrial operation at that site). The corrected TEQs, moreover, indicate levels of health concern at all distances from the cleanup site.

Although ATSDR reviewed the data for EPA, it simply said that the levels found were below health concern, without providing any explanation or analysis, and ignored the EMEG of 40 ppt for noncancer effects, exceeded at three locations near the site. No problems with the data were noted. Neither EPA nor ATSDR noted, at the time the study report was released, that no testing of dioxins had ever taken place at the two toxic waste sites fitting categories known to likely have dioxin contamination (pesticide and wood-treating sites).

Subsequently, when testing showed widespread dioxin contamination at the Marzone/Chevron site, where EPA had previously established pesticide cleanup levels for risk from residential exposure, EPA attempted to dismiss all findings below 1 ppb, choosing to focus on one area with levels well above 1 ppb (maximum of 3 ppb). For these test results, one-half detection limits were used for nondetects. The position that dioxin contamination in the main former pesticide factory surface soil was just background, and not a result of pesticides, was inconsistent with the average level of 45 ppt TEQ (maximum of 276 ppt) findings of dioxin in subsurface soil (greater than surface soil levels) and chemical storage tank contents, and the lack of measuring background TEQ in the Tifton area. Where subsurface dioxin levels were substantially greater than in surface soils, levels of site pesticides were also correspondingly greater than in surface soils, providing additional support for concluding that dioxin contamination was caused by some pesticides handled at the site. EPA Region 4 has recently decided to use a cleanup level of 200 ppt for dioxin in soil, acknowledging that it corresponds to a lo4 cancer risk, even though the risk-based cleanup levels for pesticides at the Marzone site were based on cancer risk.

In 1996, EPA Region 4 conducted an analysis of dioxin cleanup levels at Superfund sites (unpublished). Over 12 years, 20 (61 percent) sites used

74 R.EMEDIATION/SUMMER 1997

CLEANUP LEVELS POR DIOXIN-CONTAMINA~D SOILS

the 1 ppb level, and six (18 percent) used levels greater than 1 ppb and 7 (21 percent) less. In three cases (9 percent), the cleanup levels were low, between 4 to 7 ppt, at about the 10“ risk level. Nevertheless, EPA officials often state that it would set a dangerous precedent if a value less than 1 ppb was used. The “danger” is economic, namely that a lower cleanup or action level increases the costs of cleanups and relocations, and might affect decisions already made and cause more cleanup. New residential areas built on soil previously cleaned up to 1 ppb would be vulnerable.

Legally, it is clear that the 1 ppb value is, at best, only guidance, but it was never issued by EPA as guidance. At various times, EPA has stated that the 1 ppb level is an action level, a screening level, and a level of health concern. It is not, however, a rigid cleanup standard having statutory or regulatory standing. Yet as concerns about Superfund costs, funding, and liabilities have increased, EPA’s desire to impose the 1 ppb level has increased. The 1989 EPA memo had cited the important caveats of the 1984 CDC paper about making decisions on the basis of site-specific circumstances. A 1992 EPA memo on the strategy to be used in the Superfund program for addressing information from the Agency’s dioxin reassessment made no mention of the program’s use of 1 ppbSz6 Ways in which decisions could be reopened were presented and a commitment was made to “use the best science available in making its decisions.” But the proper policy statements by EPA have not resulted in retrenchment from EPA’s use of 1 ppb as the presumptive dioxin cleanup standard. Only a few Superfund site decisions have used lower levels, and they were not major sites.

Data on other types of cleanup sites, federal and state, are difficult to obtain. In 1988, a paper discussed “the first commercial dioxin cleanup in the United States” using a mobile incinerator in 1987 in Gulfport, Mississippi and it noted that “The goal of the Air Force project is to reduce dioxin levels in the soil to less than 0.1 ppb and then to delist the soil as safe. Agroup consisting of U. S. EPA, the Centers for Disease Control (CDC) and the Dioxin Disposal Advisory Group (DDAG) have agreed on this ~tandard.”~’ Clearly, this cleanup level was inconsistent with the 1 ppb level presented in the CDC’s 1984 paper and with EPA’s use of the 1 ppb standard in Missouri and for many years thereafter, indicating that in 1987 the 1 ppb standard had not solidified at EPA. As another example, some years later a cleanup at the Naval Seabees Center, Gulfpoint, Mississippi used a dioxin cleanup level of 5 ppt to remove contaminated soil with about 100 ppt dioxins. And the state of Florida is using a 7 ppt level for a lo4 risk and has asked that it be used for the cleanup of the Coleman-Evans Wood Preserving Superfund site. If a state has some type of standard, require- ment, or criterion for a lower dioxin cleanup level, such as those also mentioned for Georgia and North Carolina, then EPA can be compelled by statute to use it.

it is that the 1 ppb value is, at best, only guidance, but it

EPA as guidance. never issued by

LEGAL VIOLATION The 1 ppb level corresponds to a risk over lo4 according to EPA’s risk

data. Under the federal National Contingency Plan (NCP) governing the


JOEL S. HIRSCHHORN

In 1994 EPA established universal treatment standards as part of its land disposal restrictions program under the 1984 Hazardous and Solid Waste Amendments.

Superfund program, such risks require EPA action, There is some confusion over what current risk requires EPA action versusfuture risk and cleanup goals, because of the NCP's risk range of lo4 to 10". But NCP language, EPA guidance, and recent General Accounting Office reports made it clear that current risks above lo4 require EPA action,28 usually by taking a removal or emergency action, or an interim remedial action. EPA does not have to achieve future residual risks of lo", but under the NCP if it does not, it must explain why. Usually, the reason is nonresidential exposure. Using EPA's figure of 4 ppt, lo4 risk equates to a soil level of 400 ppt (appropriate for cleanup site soils), and using 2 ppt it is 200 ppt (appropriate for residential soils). In other words, when data reveal levels above these, EPA is legally required to take action. Conversely, when EPA ignores levels below 1 ppb and above these lower levels, it is not complying with the NCP.

At the Escambia, Pensacola site in 1992, after EPA had completed a removal action that consisted of a massive excavation of contaminated soil to protect groundwater, it tested soil in a few residential backyards immediately over the site's fenceline and found dioxin, ranging from 34 to 950 ppt TEQ with an average of 316 ppt. It used a sample for background very near these locations and on the Escambia site itself that had 14 ppt. Three years later, EPA obtained more dioxin data showing even higher levels in residential soils (average of 587 ppt TEQ and maximum of 3 ppb in the area closest to the site). Four years after the original evidence of dioxin contamination in the residential area, EPA had not taken any action, such as soil removal, soil covering, or relocation of residents to protect public health against risks greater than lo4. The residents were not helped by ATSDR's Public Health Assessment in 1995, which raised no concerns about dioxin. EPA Region 4 has recently decided to use the 200 ppt level for dioxin cleanup for the off-site residential areas near the Escambia site, acknowledging that it corresponds to the lo4 cancer risk level, but ignoring noncancer health effects.

TREATMENT TECHNOLOGY It is also relevant that in 1994 EPA established universal treatment

standards as part of its land disposal restrictions program under the 1984 Hazardous and Solid Waste Amendments. The treatment standard for TCDD is 1 ppb, which apparently was taken from the policy-based level of 1 ppb for cleanups. This standard can be applied to technologies used to detoxlfy dioxin-contaminated soil. It provides a disincentive for achiev- ing lower levels. It also suggests problems because of land disposal of soils with dioxins at lower concentrations that pose health threats.

EPA's original concerns in the 1980s about cleanup costs, especially if treatment technology such as incineration was used, are less warranted today. There are more technologies than ever, including BCD dechlorina- tion developed by EPA and licensed to several companies that have commercialized it, a Canadian technology that destroys dioxins, and several commercial solvent separation techn~logies .~~ It is possible to achieve residual levels to low ppt levels. Increasing competition has



Changing to a scientifically credible health- based dioxin cleanup level has been seen by subsequent EPA managers as threatening.

reduced unit costs. People concerned about dioxin exposure have learned about these newer technologies.

DIOXIN CLEANUP AND RISK MANAGEMENT POLICY Since the late 1980s, EPA has used an increasingly inconsistent and

technically indefensible basis for decisions about dioxin-contaminated soil. The 1 ppb level was based on a risk assessment by CDC that had deficiencies and to some extent misrepresented its results to present a simple policy decision rule with enormous economic implications. There was considerable demand for that dioxin cleanup level in the mid-1980s. Now, however, there is no credible scientific, health-based, or logical defense for using the 1 ppb figure. The translation of CDC’s risk assessment results into a Superfund action level and EPA’s initial uses of it occurred during the aftermath of the 1983 backlash against the environmental policies of the Reagan administration. But many senior EPA managers still believed in those policies, and they established a policy-based dioxin cleanup standard that has prevailed.

Changing to a scientifically credible health-based dioxin cleanup level has been seen by subsequent EPA managers as threatening. Rather than focusing on health risks, they manage bureaucratic risks. Lower dioxin soil cleanup levels could result in demands to reopen past cleanup decisions that, in combination with more stringent cleanup decisions, would require higher federal appropriations for the Superfund program at a time when they are being decreased. Yet this problem only worsens with time as more decisions are based on 1 ppb. Concerns about cleanup costs are valid, especially by government officials, but using 1 ppb that poses health risks as a solution is not viable public policy.

Another concern of EPA managers is that use of a lower dioxin cleanup level could affect regulatory permitting and public acceptance of various industrial and waste management facilities. This raises a conflict between protection of public health and concerns about impacts on sources of dioxin, such as industrial and municipal waste incinerators. As Silbergard and deFur observed, “much of the continuing delay by government in implementing comprehensive management of [dioxin] risk arises not only from scientific uncertainty but also from the politics and economics of controlling specific dioxin sources.”

An attractive delay strategy for Superfund managers is waiting for EPA’s final dioxin reassessment, because it is commonly understood it will take years to complete. Their risk management means letting successors inherit this problem. The final report is not likely to remove the fundamental problems with the 1 ppb level. The dioxin soil cleanup issue has been successfully kept at the Superfund program level, allowing EPA to ignore its inconsistencies with larger Agency goals and commitments. EPA’s continuing use of 1 ppb, however, undermines its goals of using good science, common sense, and risk management to improve decisions and public confidence. Ultimately, there are institu- tional risks and penalties that can be minimized only by taking the initiative to correct the dioxin cleanup problem. Ironically, the 1 ppb

&MEDIATION/~UMMER 1997 77

JOEL S. HIR~CHHORN

level was a consequence of an EPA crisis in 1983 and it could precipitate another one.

EPA s inability to retreat from the 1 ppb level reveals more than bureaucratic inertia, however. Over the past decade, a climate of bureaucratic loyalty has emerged. It intimidates lower level Superfund site managers and prevents them from departing from the “company line” by using lower dioxin levels for cleanup and relocation decisions. This is difficult because as front-line managers, they get the demands from angry people for more effective dioxin testing and cleanups and for relocation of residents. Defending EPA’s 1 ppb is increasingly difficult.

PUBLIC PERCEPTIONS Policy aside, use of 1 ppb, rather than 2 or 4 ppt based on EPA risk

methods, can only be logically interpreted as either EPA rejecting its own risk assessment methods and results or EPA acting as if a dioxin cancer risk greater than lo4 is acceptable, which violates the law. When cleanup levels for other contaminants are set on the basis of 10“ risk, either by means of risk assessment or use of EPAs soil screening levels, use of 1 ppb is even more untenable. How can EPA defend using its risk numbers for all chemicals except the more toxic dioxins?

Use of 1 ppb erodes public confidence in risk assessment, as revealed by advice given to community groups addressing dioxin cleanup sites: “It doesn’t matter if the risk level is one-in-a-million, one-in-one-hundred- thousand, or one-in-ten-thousand. “10 amount of additional exposure is acceptable and a risk assessment approach that attempts to define a negligible or acceptable risk is i r re le~ant .”~~

The public, now well informed (some would say inflamed) about dioxin, also knows that noncancer health effects are now probably more significant than cancer, particularly if synergistic interactions with pesticides and PCBs occur. For noncancer effects, ATSDR staff have shown that 1 1 1 The scientific

community has sent a clear message that there is no safe level of dioxin eaposure.

dioxin levels much lower than 1 ppb are appropriate. All the available scientific information supports using low ppt dioxin TEQ for cleanup and relocation decisions. The scientific community has sent a clear message that there is no safe level of dioxin exposure. The ubiquitous presence of dioxins should cause cleanup decisions to recognize other exposures, not to dismiss levels of dioxin below 1 ppb because “dioxin is everywhere.” EPA’s use of 1 ppb literally adds insult to injury.

CONCLUSIONS This risk, historical, and policy analysis provides support for new EPA

Superfund guidance that specifies the 2 and 4 ppt levels for residential and cleanup site soils, respectively, but permits use of different dioxin TEQ levels if they are supported by site-specific analysis. The guidance should clarify that chronic health effects other than cancer should be considered, that past and other sources of dioxin and PCB exposures should be accounted for, that control samples should be used to determine background levels for specific cleanup sites, that EPA method 8290 should be routinely used, and that nondetects should be converted to one-half their

~



actual method detection limits to calculate TEQs. The guidance should also clarify what types of sites should be tested for dioxins in soils, because cases have arisen where either no dioxin testing was performed or where the testing was performed very late in the Superfund process, even though site information supported dioxin testing. EPA could also provide a framework for evaluating past Superfund site decisions and whether there are grounds for reexamining them. The guidance should make it clear that EPA’s ongoing dioxin reassessment and particularly the draft reports issued by EPA in 1994 should not be cited as a basis for ignoring what remain as official EPA data about dioxin cancer toxicity. Until EPA formally completes its dioxin reassessment, EPA personnel have no right to assume that EPA will change what it considers to be key cancer toxicity data for dioxin.

NOTES 1. R.D. Kimbrough et al., “Health Implications of 2,3,7,8-Tetrachlorodibenzodioxin (TCDD) Contamination of Residential Soi1,”J. Tox. and Env. Health, 14: pp. 47-93, 1984.

2. EPA, memo by J. Winston Porter, head of the Superfund program, to Barry Johnson, head of ATSDR, Jan. 26, 1989.

3. EPA, Health Assessment Document for Polychlorinated Dibenzo-p-Dioxins, EPA/600/ 8-84/014F, 1985.

4. EPA, National Dioxin Study, EPA/530-SW-87-025, 1987.

5 . EPA Region 3, Risk-Based Concentration Table, April 19, 19966; Internet at http:// www.epa ,gov/reg3hwmd/riskmenu. htm.?

6. L.M. Gibbs, Dying from Dioxin, South End Press, Boston, 1995

7. U. Jarnberg et al., “Polychlorinated Byphenyls and Polychlorinated Napthalenes in Swedish Sediment and Biota: Levels, Patterns, and Time Trends, Env. Sct. Tech., 27: pp.

8. D.J. Paustenbach et al., Recent Developments on the Hazards Posed by 2,3,7,8 tetrachlorodibenzo-p-dioxin in Soil: Implications for Setting Risk-Based Cleanup Levels at Residential and Industrial Sites,J. Tox. Enu. Health, v.36, pp. 103- 149, 1992.

9. Id.

10. A. O’M. Bowman, Epifogue, in thepolitics ofHazardous WasteManagemerat, J.P. Lester and A. O’M. Bowman (Eds.), Duke University Press. 1983.

11. R.W. Field and D.J. Sarno, “Times Beach Remedy Selection,” Superfnd‘88, pp. 255-258.

12. H. Pohl et al., “Public Health Assessment for Dioxins Exposure from Soil,” Cbemosphere,

13. T. Colborn et al., Our Stolen Future, Dutton, New York, 1996, pp. 120, 181.

14. J.D. Sherman, ChemtcalExposureandDisease, Princeton Scientific Pub., 1994, p. 175.

15. EPA, Soil Screening Guidance: Technical Background Document, EPA/%O/R-95/128, May 1996.

16. E.K. Silbergard and P.L. deFur, “Risk Assessment of Dioxinlike Compounds,” in Dioxins and Health, A. Schecter (Ed.), Plenumpress, 1994, pp. 51-78.

17. S.E. Hrudey and D. Krewski, “Is There a Safe Level of Exposure to a Carcinogen?” Enu. Sct. Tech., 29:pp. 370A-375A, 1995.

18. S.F. Arnold et al., “Synergistic Activation of Estrogen Receptor with Combinations of Environmental Chemicals,” Science, 272:pp. 1489-1492, June 7, 1996; S.S. Simons, Jr.,

1364-1374, 1993.

3 1 : ~ ~ . 2437-2454, 1995.


JOEL S. HIRSCHHORN

“Environmental Estrogens: CanTwo ‘Alrights’ Make a Wrong?” p. 1451; J. Kaiser, “New Yeast Study Finds Strengths in Numbers,” p. 1418.

19. See note 13.

20. G.R Nemeth et al., “Background Determination of Element and Anthropogenic Compounds in Soils of the Maryland Coastal Plain,” in Supefund Risk Assessment in Soil Contamtnation Studies: Second Volume, ASTM STP 1264, K. Hoddinott (Ed.), American Society for Testing and Materials, 1996, pp. 3-18.

21. EPA,.EAttmatingExposuretoDtoxin-LikeCompounds, Vol. 1: ExecutiveSummary, Draft, EPA/600/6-88/005Ca, 1994.

22. S.B. Floit et al., “Evaluation of the Use of Substitution Methods to Represent Nondetect Data,” In: SuperfundRtskAssessment tn Soil Contamtnatton Studies: Second Volume, ASTM STP 1264, K. Hoddinott (Ed.), American Society for Testing and Materials, 1996, pp. 70-83.

23. EPA Region 5, memo from J. Milton Clark, Health Effects Specialist, to George A. Jones, Chief, Superfund Implementation Group, July 30, 1995.

24. See note 16.

25. EPA Region 4, South Tifton Residential Area Investigation Report, Tifton, GA, Sept. 1995.

26. EPA, memo by D. Clay, head Superfund program, to EPA Administrator, Feb. 27, 1992.

27. J.H. Lanier, “ENSCO MWP-2000 Transportable Incinerator,” in Superfund ‘88, pp. 587- 591.

28. GAO, Superfund-Information on Current Health Risks. GAO/RCED-95-205, 1995; Superfund-Improved Reviews and Guidance Could Reduce Inconsistencies in Risk Assessments, GAO/RCED-94-220, 1994.

29. EPA, Superfund Innovative Technology Evaluation Program-Technology Profiles Seventh Edition, EPA/540/R-94/526, 1994.

30. S. Lester, “Risk Assessment and Dioxin,” Everyone’s Backyard, 14 (2): pp. 24-26,1996.

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cleanup levels for dioxin-contaminated soils

Documents