GCI TECH NOTES ©
EPA released their dioxin reassesment in June of 1994. The study was touted as having taken several years, resulting in over 2,000 pages and involving hundreds of scientists. Following release of the EPA dioxin reassessment, newspapers were filled with story after story about the horrible dangers of dioxin reported in the EPA reassessment. The fall out from the release of that dioxin reassessment continues. Incinerators are being challenged all across the country, even incinerators that had already gone through arduous approval processes. Projects in foreign countries are feeling the heat as well. Unfortunately for industry, public perception has apparently failed to notice that all six volumes of the dioxin reassessment are very clearly marked as follows:
This document is a preliminary draft. It has not been formally released by EPA and should not at this stage be construed to represent Agency policy. It is being circulated for comment on its and policy implications. (emphasis added)
In addition, each volume carries a DISCLAIMER which states "This document is an external draft for review purposes only and does not constitute U.S. Environmental Protection Agency policy." And then finally, each and every page is clearly marked; DRAFT--DO NOT QUOTE OR CITE. Yet even though the document is laced with proclamations designed to absolve EPA of any responsibility/liability, the ill effects are thundering across America. Proponents of real science can only attack the dioxin reassessment for what it is, an incomplete researched document designed to forward an anti-combustion strategy, and hope for the best. The dioxin battle has just begun. This months GCI Tech Notes provides some comments on the exposure assessment "document", which consisted of three volumes and over 1,000 pages.
In the section II discussion about dioxin chemical structures and properties, EPA states that "Dioxin-like compounds exhibit little potential for significant leaching or volatilization once sorbed to particulate matter." This statement indicates that even if/when dioxins are associated with cement kiln dust (CKD), or other thermal treatment system particulates, there is "little potential for significant leaching or volatilization" since the dioxins would clearly be "sorbed to particulate matter" by way of the wasted dust.
EPA identifies "Temperature in the range of 250-450°C...as necessary conditions for [CDD/F formation]. These ranges for dioxin formation of 250-450° C coincide with 482° F to 842° F. EPA cites no references for these temperature ranges. This temperature range is presented in such a manner as to infer that it is representative of all dioxin formation in all combustion devices. Given that EPA focuses on municipal solid waste incinerators in their discussion on mechanisms of formation of dioxin-like compounds during combustion of organic materials in Volume II, Chapter 3, there is no reason to believe that any cement kiln data was used to determine this purported temperature range. As a reference point, the EPA BIF regulations identify 450-750° F.
Continental Cement Company has performed numerous dioxin emission tests on their cement kiln. Data is included with these comments that demonstrates higher dioxin concentrations at the entrance to the kiln APCD than at the exit. This runs counter to EPA assumptions concerning temperature and dioxin formation. EPA assumptions are, unfortunately, based upon worst case operating conditions, imposed by the BIF rules, which resulted in highly biased data. Biased data that in no way reflects normal operating conditions. Higher dioxin concentrations at the entrance to the APCD than found at the APCD exit brings the current EPA suggested remedies into serious question as it applys to cement kilns.
EPA presents data in Table II-2, on page 17, which purportedly indicates that "all the countries except Austria estimate that municipal waste incinerators are an important source." There is little or no discussion concerning this claim and the data for each country, presented in Table II-2, which comes from only one study per country. This is, unfortunately, consistent with a number of single study citations found throughout the dioxin reassessment. Apparently, if at least one study has found something to be so, at least something that supports EPA's agenda, then that is good enough for EPA to make a claim, regardless of what other studies or data might exist.
Cement kilns are first mentioned on page 21. EPA states that "limited data suggests that the CDD/F levels in clinker dust and stack emissions of these kilns may be significantly higher than the kilns which do not burn hazardous waste." EPA does indicate that their "suggestion" is based upon limited data, here as in Volume II, pages 3-155 thru 3-164. EPA fails to point out (as perhaps they themselves do not realize) that the hazardous waste fuel burning cement kiln data is representative of absolute worst case operating conditions, as required by the BIF regulations, and not normal operating conditions.
Emissions testing was performed at the Lone Star Industries, Inc. Greencastle, Indiana cement plant, following a modification to their existing electrostatic precipitator. Dioxin emissions data were collected as part of this ESP modification project. Dioxin levels, while burning waste fuel, were very low. The operating conditions under which the testing was conducted were normal operating conditions. These dioxin levels, collected under normal operating conditions in the Summer of 1994, were an order of magnitude lower than dioxin levels collected under worst case BIF operating conditions in 1992.
A number of "major identified sources of environmental release" were identified on pgs. 14-15. The characterization of what some researchers, not highlighted in this report, call "naturally occurring" CDD/CDFs such as those produced by forest fires, (see Env. Sci. Tech. Vol. 28, No. 7, 1994; pg. 315A, 130 pounds of PCDDs annually from Canadian forest fires alone), is only briefly mentioned in the reservoir sources section on page 15. [wood burned in forest fires is later discussed in Volume II, page 3-146, section 3.6.16] While differences of opinion exist in most research environments, EPA has obviously chosen to omit/ignore research indicating that forest fires are possibly the major source of dioxins in the environment. This would mean that dioxins have been "naturally occurring" and accumulating in the environment for thousands of years.
In a dioxin source discussion in Science magazine, editor Phil Abelson discusses another study which examines dioxins from burning wood [T.J. Nestrick & L.L. Lamperaski, Anal. Chem. 54, 2292 (1982)] which found that total dioxins produced from wood burning were as much as 160 micrograms per kilogram. Abelson also points out that a 1978 study reported that wood fuel alone accounted for one fifth of the total domestic energy consumption of developing countries or 1.67 x 109 cubic meters (M.R. de Montalembert & J. clement, Food and Agriculture Organization of the United Nations, Rome, FAO Forestry Paper, No. 42, 1983). Abelson sums up his discussion by pointing out that the burning of 2 to 3 billion metric tons of biomass per year in developing countries, leads to smoke containing on the order of 100 kg of 2,3,7,8-tetrachlorinated dioxin. This exceeds the EPA estimates of total current anthropogenic emissions in the U.S. by at least one order of magnitude.
EPA tries to further erode the idea of forest fires as the major source of dioxins in the discussion of wood burning sources of dioxin on page 23. Here EPA introduces research that hypothesizes that dioxins from forest fires may be resuspended material from aerial deposits rather than originally formed material. It is clear that EPA does not intend to blame natural causes, after all, how does EPA regulate natural causes? If forest fires are a/the major source of environmental dioxins, then EPA is dealing with a very long term problem, perhaps a problem older than the human race. If this is the case, as many scientists believe it is, then EPA is trying to apply short term solutions to this very long term problem. Unfortunately, EPA's short term solution is to heavily burden combustors, a very small segment of industry.
EPA casts further doubt on some of their own assumptions in this reassessment, in particular dioxin emission & deposition. EPA states "These studies are acknowledged to be quite speculative due to the strong potential for inaccuracies in emission and deposition estimates." Yet even with this strong statement casting significant doubt on the procedure, EPA forges ahead; "Bearing these limitations in mind, this procedure has been used here to compare the estimated emissions and depositions in the United States." Why let a "strong potential for inaccuracies" get in the way of a comparison?
EPA cites research that leads them to state "CDD/Fs have been accumulating [in the environment] for many years." Furthermore, in comparing known emissions with deposition rates, "studies may suggest annual deposits exceed emission rates." EPA suggests "one explanation may be that the reservoir sources cause deposition through volatilization/ atmospheric scavenging or particle resuspension." Again, naturally occurring dioxins (resulting from forest fires) could be a/the major source of dioxins, whether EPA wishes to acknowledge it or not.
EPA does at least concede the possibility of "small amounts of dioxin-like compounds... formed during natural fires" and even admits this suggests "that these compounds may (emphasis added) have always been present in the environment." Even though EPA makes this statement, they go on to qualify their admission by stating, "However, it is generally believed that much more of these compounds have been produced and released into the environment in association with man's industrial and combustion practices. "Generally believed among environmentalists? No citations are offered to support this statement. By EPA's own admission, stated in the very next paragraph, "Studies that may be used to assess temporal trends in human exposure to dioxins and furans are extremely limited" (emphasis added).
The COMPDEP model is introduced on page 56. COMPDEP contains modifications of the Industrial Sources Complex (ISC) model (Short Term version), used in BIF, and COMPLEX I, a second level screening model applicable to stationary combustion sources located in complex and rolling topography. Under emission factors on page 57 & 58, EPA refers to atmospheric transport modeling which rely on "actual test data from an incinerator burning organic wastes (sources otherwise unspecified)" as representative of "combustion devices (e.g., scrubbers combined with fabric filters)" and then lists five different types of combustors. Cement kilns are not included.
Cement kilns are listed in Table IV-1 indicating "high" uncertainty in emissions estimates with a high priority for future testing. The table also indicates that data from only 17 out of 212 cement kilns were used/available. It is clear EPA does not put much defensible credence in their cement kiln emission estimates. This has not stopped them from making incriminating suggestions and statements about cement kilns throughout the dioxin reassessment.
Cement kiln dust/clinker is mentioned here as having been tested for CDD/F content. No concentrations are mentioned and no discussion is offered.
EPA states dioxins "exhibit little potential for significant leaching or volatilization once sorbed to particulate matter." This statement indicates that even if dioxins were found in CKD, there would be "little potential for significant leaching."
EPA discusses photogradation studies of "CDDs/CDFs naturally adsorbed to five fly ashes." Fly ash discussions often stimulate CKD discussions. Even though one set of experiments concluded that "the absence of photodegradation [in fly ash] was not due to the absence of a hydrogen-donor organic substance, CKD is not similar to fly ash in many basic properties. In most cases, naturally occurring sources of hydrocarbons in cement raw materials, such as kerogens, ultimately result in some hydrocarbon coating on CKD. This would provide the hydrogen-donor discussed on page 2-21. The possible photodegradation of the CDDs/CDFs in CKD due to the availability of hydrogen-donors could explain the decreased levels of dioxins found in CKD piles. It may also explain why dioxins are not found above background levels where MEI dioxin sampling has occurred. This would suggest that any level of dioxins produced from the cement manufacturing process are being reduced/photodegraded naturally and have little impact on the environment.
EPA states "releases to the air occur primarily from combustors and appear to have the most direct influence on human exposure." Is the word "combustors" used to represent municipal waste combustors or combustors in general? Cement kilns are not specifically mentioned, but can be included by implication. And, what about diesel engine emissions? Some studies have identified diesel engines as a significant source of dioxin emissions. (K.H. Jones, Diesel Truck Emissions, an Unrecognized Source of PCDD/PCDF Exposure in the United States, Risk Analysis, Vol. 13, No. 3, 1993) Also, where does EPA get the notion that dioxins from combustors "appear to have the most direct influence on human exposure." It is widely known EPA has this opinion, but without supporting data it is just that; an opinion.
You know that this reassessment is a highly scientific and unbiased document when a Greenpeace report gets cited.
This section starts on 3-63 and ends on 3-96 (33 pages). Conspicuously absent is any mention of cement kilns. Frankly, this section should more appropriately have been called "Mechanisms of formation of dioxin-like compounds from municipal solid waste incinerators (MSWIs) combustion of organic materials", since MSWIs completely dominate the discussion and cement kilns are not even mentioned. On page 3-64 it is stated "it is possible to identify the central chemical events participating in the formation of CDDs and CDFs by evaluating emission test results from MSWIs in combination with laboratory experiments." The implication of the title of the section is that the section addresses all combustion. It is clear the text deals only with municipal solid waste incinerators. EPA needs to make appropriate distinctions between the various combustors. If EPA actually believes MSWIs are representative of all combustors, then their research and understanding of combustors is sorely lacking. Oddly enough, EPA's own homologue profiles indicate MSWIs are not representative of combustors in general.
It seems of particular interest to note that this section is introduced with the statement; "The specific molecular mechanisms by which CDDs and CDFs are initially formed and then emitted from combustion sources remain largely unknown and are theoretical." (emphasis added) However, three theories are then introduced on pages 3-64 thru 3-91. There is no mention of cement kilns.
EPA seems to imply, in the first paragraph of this section, that you cannot produce dioxins from burning coal. This implication comes from the fact that core sediment dioxin correlated with synthetic chlorinated organic chemical production and did not correlate with coal consumption. Even more confounding is that EPA later discusses dioxins from coal combustion in section 3.6.17. EPA goes on to state "the pattern of levels of CDDs and CDFs in the sediment cores seemed to track the total volume production of synthetic chloroaromatics by the petrochemical industry in the United States, whereas the consumption of coal did not show a good correlation." A positive correlation between two occurrences does not definitively indicate a causative relationship. As has been pointed out by Dr. Bruce Ames, originator of the Ames Carcinogen test, the decline in the population of storks in England can be very nearly graphically paralleled with the decline in human births in England. However, this does not mean that storks bring babies. EPA also makes additional vaguely substantiated attempts, in this section, to discredit "natural sources such as forest fires" as significant contributors of dioxins.
EPA states that a "low" confidence rating is ascribed to the emission factors derived [for hazardous waste incinerators] because stack test data were available for only six of the 190 HWIs in the U.S. and the stack test data used represent only one hazardous waste technology (rotary kiln)." This statement is consistent with Table IV-1 in Volume I, the Executive Summary. What is particularly curious, actually unexplainable, is that cement kilns also have a low confidence rating, yet EPA concludes on page 24 of the Executive Summary that HWIs "appear to be relatively minor sources [of dioxins] on a national scale." Cement kilns on the other hand, even with the same low confidence rating, are identified as "key" source categories on page 21 of the Executive Summary.
This section discusses wood burned in forest fires. Again, the very real possibility that forest fires are the major source of dioxins in the environment continues to get played down. Unfortunately, EPA found only one study that made direct measurement of CDD/CDFs emissions from forest fires. This one study citation was used for EPA to conclude that dioxins primarily come from anthropogenic sources. (page 12, Volume I.) It is quite convenient how these two lone study discussions allowed EPA to make conclusions which ultimately support their anti-combustion strategy.
Then, in the final paragraph of section 3.6.16, EPA makes another attempt to show that dioxin releases from wood burning are questionable significant sources of human exposure. One study cited indicates that 400 year old Eskimo females yielded levels only 15% of current levels. It is interesting to note that half-life discussions throughout this dioxin reassessment address living tissue. No mention is made of possible half-lifes in dead tissue. For the sake of discussion, let us point out that a half-life of 100 to 150 years yields concentrations approximately 15% of current levels. This is not out of the realm of possibility. This would also tend not to support EPA's contention that dioxins from wood burning is questionably significant as a source for human exposure.
These pages specifically discuss cement kilns. Five possible dioxin formation mechanisms are listed on pages 3-156 & 3-157. The listed options demonstrate a lack of understanding of the cement kiln process and cement chemistry. While not news to those of us associated with the cement industry, it is extremely unfortunate that three years after the BIF regulations and seven years after BIF was first proposed, EPA still does not understand cement kilns. Nowhere in these listings is there a mention of organics in raw materials. This is absolutely unbelievable, given the attention over the past two years to raw materials hydrocarbons. There is also no mention of chlorine in raw materials. Both should be considered. The de novo synthesis catalytic agent example of copper chloride is laughable. Copper chloride simply cannot exist inside of a cement kiln.
EPA rationalizes through five points in an attempt to indict chlorine in waste fuels as probable dioxin precursors which EPA thinks helps explain why preliminary data from hazardous waste burning cement kilns exhibited higher dioxin concentrations than nonhazardous waste burning cement kilns. While there may be superficial logic to this argument, cement industry COC data does not reveal any correlation between chlorine input and dioxin concentrations. This lack of correlation is graphically demonstrated on pages 38 & 39 of the Commercial BIF Compliance Test Results - 1992 report, published by Gossman Consulting, Inc.
EPA erroneously states, on page 3-157, "currently, cement kilns that accept and burn hazardous waste as an auxiliary fuel are required under RCRA to characterize pollutant stack emissions, including emissions of CDD/CDFs." Only cement kilns that could not initially meet the 20 ppm HC BIF limit, due to hydrocarbons in the raw material, and/or had high kiln exit temperatures, were required to perform dioxin testing. These requirements resulted in dioxin data that is, consequently, biased towards certain conditions in addition to the fact that all of the BIF data was collected under absolute worst case operating conditions as required by EPA. These significant bias factors are not recognized anywhere within the dioxin reassessment.
This table lists cement kiln dioxin emission data for hazardous waste burning kilns and kilns not burning hazardous waste. EPA presents the data in this table as if it demonstrates a valid correlation. EPA points out "the ratio of total CDDs/DCFs to the TEQ ranges from about a factor of 5:1 to a factor of 1000:1" and "cement kilns which do not burn hazardous waste as supplemental fuel appear to be less variable." EPA cautions against the significance of this comparison by stating "this observation must be tempered by the fact that fewer of these kilns have been stack tested", but fails to point out that the data from hazardous waste burners is biased towards cement kilns with high exit temperature and worst case conditions. Even though EPA cautions against the significance of comparing waste burners with non-waste burners and has pointed out that this data is preliminary, it doesn't stop EPA from making the determination, on page 3-160, that "separate emission factors should be developed for kilns burning hazardous waste and those that do not." Given that the data is biased, thanks to the BIF regulations, it is no wonder EPA sees a difference between hazardous waste burners and non-hazardous waste burners. EPA is in an ideal position. Develop regulations that require kilns to operate under completely unrealistic worst case conditions and then use this worst case data to indict those same kilns as major polluters. This is a clear cut case where EPA either completely misses the implications of compliance with their own regulations or they purposely omitted explanations to prove their predetermined point. Additionally, the data is obviously skewed and, therefore, it is statistically invalid to use averages of the data.
EPA states "the estimated range of potential emissions is assumed to vary by a factor of ten between the low and high ends of the range." This is not the only place in this dioxin reassessment where a factor of 10 is used. What is the statistical justification for this factor of ten? One suspects it is simply a convenient multiplier rather than based on any set of data. A more acceptable method would be to use a median plus or minus 1 or 2 standard deviations. More sophisticated and technically defensible statistical approaches are also available.
EPA states 1.75 dscm/kg as a reasonable estimate of combustion gas volume/kg of materials processed in a cement kiln. Quick calculations on just two sets of BIF data yielded 1.5 and 1.6 dscm/kg. This would mean that EPA's emission factor estimate of 12.4 ng TEQ/kg for hazardous waste burning cement kilns is approximately 10% to 15% too high. EPA calculations were not able to be checked since this "reasonable estimate" came from a Research Triangle Institute memorandum to USEPA's Joseph P. Wood from RTI's Jeffrey W. Portzer. It is unclear as to why estimates were used in the first place since data from the 34 hazardous waste fuel burning BIFs was referenced in this report and at least 14 sets of data were analyzed (page 3-157). Recalculation is necessary for EPA to more accurately represent this "first method" calculation.
EPA points out, on page 3-162, that "The estimated TEQ emission factors used to derive this best estimate of annual TEQ emissions [210 g TEQ for kilns burning hazardous waste and 140 g TEQ for kilns not burning hazardous waste] are given a "low" confidence rating because the mechanisms giving rise to dioxin emissions from cement kilns are largely unknown." (emphasis added)
Discussion on page 3-163 addresses the CKD report to Congress. EPA fails to mention that the report is a draft report and that voluminous comments were offered demonstrating that the CKD report to Congress was filled with bad data. In addition, there was a problem with the analytical methods that were used and the associated quality assurance and quality control. None of this is mentioned. In fact, not only are these accuracy doubt casting issues not raised, but EPA refers to the CKD report to Congress as one that "establishes the factual data for its [EPA's] decision making regarding the appropriate regulatory status...of cement kiln dust (CKD) waste." Factual indeed. EPA also fails to mention that the six hazardous waste burning kilns were targeted because they had exhibited high dioxin concentrations in their stack emissions. Again, the data was biased, but no mention is made of this bias qualifier.
EPA expands on the significance of the 400 year old Eskimo females previously discussed in section 3.6.16 on page 3-150. In section 3.6.16, we learned that the Eskimo females were 400 years old and supported the EPA contention that dioxins from wood burning fires were not a significant source in human exposure even back when wood would have been the primary source of heating and cooking. Now we learn these same two Eskimo females could actually have been only 100 years old and, in addition to demonstrating that dioxins from burning wood are/were not significant sources of human exposure, these two female Eskimos also demonstrate dioxins were less prevalent in ancient times as compared to people currently living in industrial areas. Here is one study, cited differently in two different discussions, apparently to demonstrate two different points. This seems to be an obvious case of EPA manipulating the data, limited as it is to just this one study, in order to demonstrate two different points. This one study of two female Eskimos sure carries a tremendous burden of proof for EPA assertions. How fortunate for EPA that they found this one report. Again, however, EPA admits "Studies that may be used to assess temporal trends in human exposures to dioxins and furans are extremely limited." Amazingly, that still doesn't stop EPA from using this extremely limited data from supporting their ideas.
In general, results from studies presented in this appendix was mixed. It would appear that extracted dioxins from contaminated media is more toxic than the contaminated media itself. Some dioxin contaminated soil was not lethal at all, whereas the extract did produce some deaths in guinea pigs. Dioxin contaminated fly ash was significantly less bioavailable than the dioxin exract from the contaminated fly ash in Wistar rats.
This section is entitled Evaluating Atmospheric Releases of Dioxin-like Compounds from Combustion Sources, however cement kiln data are not included. Specifically, pages 3-6 thru 3-20 discuss dioxin emissions (homologue profiles) from eleven (11) sources other than cement kilns.
EPA discusses the method of converting "the concentrations of TCDD/F mixtures into an equivalent concentration of 2,3,7,8-TCDD," citing four references. It turns out these references are for municipal waste combustors, rather than incinerators or cement kilns. In a most interesting admission, on page 3-8, EPA states "hazardous waste incinerators have not been extensively evaluated for stack emissions of dioxin-like compounds."
Cement kilns are discussed in this last paragraph of section 3.2.2. "The ratio of total PCDD/Fs to the TEQ [ranging] from about a factor of 5:1 to a factor of 1000:1." and "the database on stack emissions of dioxins [from cement kilns] just now coming available" are cited as reasons that no homologue profile was developed.
EPA goes to great lengths to illustrate "that the TCDD-TEQ emission factor derived for the hypothetical incinerator lies well within the range of emission factors developed from measured incineration sources burning a diversity of waste material, but employing similar air pollution control technology." Normally it might make sense to demonstrate the applicability of a proposed model. In this case, however, EPA has pointed out "The emission factors for the dioxin-like compounds from the stack of the hypothetical waste incinerator were derived from actual stack monitoring and emissions testing of an incinerator burning a complex mixture of organic wastes." Since "actual stack monitoring and emissions" were used to determine the emission factors for the hypothetical incinerator, why wouldn't it be expected it would be a good fit? The fact that EPA is going to such great lengths to illustrate how wonderful their model works, when it is admittedly based upon the very same emissions used to confirm how well it works, has to make one a little suspicious.
What seems clear is that EPA has used actual emission data to illustrate their model is predictive. But it seems rather obvious the model is predictive of the actual emission data used to illustrate that the model is predictive. EPA has used circular logic here and it becomes readily apparent EPA simply can not use an extensive enough database to illustrate whether their model is predictive or not. Using one set of data to predict that same set of data is circuitous logic.
EPA discusses the methodology used for estimating dioxins in collected fly ash. The EPA method boils down to an exercise in proportioning. This assumption would not hold true for all cement kiln APCDs, as for instance, ESPs collect dust according to size. With size considerations, surface area is the important factor, not mass. The surface area collected vs. the surface area emitted is critical. The EPA methodology used would significantly overestimate dioxin concentrations in CKD.
In the second paragraph of this section, EPA states "No data could be found which linked stack emissions to an incremental impact to nearby soils." This seems to be a rather telling statement. For Chapter 7 alone, EPA lists 106 references. Out of three years of effort to compile this document and all the input from sources outside of EPA, no data could be found which linked stack emissions to an incremental impact to nearby soils. There is a rather obvious message here. Maybe there is no incremental impact from stack emissions to nearby soils! This certainly did not stop EPA from suggesting methodology which would create an impact mathematically even if one did not exist in real life.
In fact, data has been collected from the MEI for Continental Cement Company in Hannibal, Missouri that revealed dioxin concentrations equivalent to area background levels. Bear in mind the cement plant has been sitting in the same location for approximately 100 years. Approximately 100 years of maximum deposition only to yield dioxin concentrations equivalent to background concentrations. This data would seem to indicate the reason "No data could be found which linked stack emissions to an incremental impact to nearby soils" is because there is no impact! This data has been provided to Region VII and a more comprehensive study is in progress.
Not one of the off-site soil contamination situations listed in this table is linked in any way, shape, or form to a combustion source. EPA has obviously tried to link their imaginary stack emission impact with dioxin contaminated soils which were from chemical contamination. This EPA concocted imaginary link can, in no way, be even remotely associated with stack emissions.
In discussing the potential impact of incinerator emissions on water body bottom sediments, EPA points out "evidence collected so far does not indicate an impact from incinerator emissions." Does this mean EPA will continue collecting evidence until they "find" a link and then ignore the data collected prior to that?
Here, as well as throughout this document, potential impacts of contaminated soil is considered. In this section, impacts of contaminated soils to vegetation are discussed. What is lacking in all of these discussions is consideration of the source of the contamination. In Volume II, Appendix C, EPA has already pointed out that dioxins adsorbed onto fly ash is not as bioavailable as dioxin extract from the very the same contaminated fly ash. Source dependent dioxin bioavailability is a phenomenon that merits further investigation.
Here EPA talks about vegetable uptake ratios. It is evident from the data cited that there is a high variability. Dioxin concentrations in the vegetables are often higher than the soil concentrations. One possible explanation for this observation is some type of dioxin production by the vegetable. Enzymatic conversion of chlorophenols by horse radish peroxidase enzyme, into part-per-million concentrations of both PCDDs and PCDFs was reported in Vol. 15 of Chemosphere in 1986 (page 1577).