Volume II Chapter 3.0 Pages 3 of 10 page next page 4

3.4.2. Manufacture of Halogenated Organic Chemicals - Dioxin/Furan Test Rule Data 3-37

3.4.3. Manufacture of Halogenated Organic Chemicals-Pesticide Data Call-In 3-44

3.4.4. Chlorine Production Using Graphite Electrodes 3-56

3.4.5. Petroleum Refining Catalyst Regeneration 3-59

3.4.6. Additional Chemical Manufacturing and Processing Sources 3-62

3.5. MECHANISMS OF FORMATION OF DIOXIN-LIKE COMPOUNDS DURING COMBUSTION OF ORGANIC MATERIALS 3-63

3.4.2. Manufacture of Halogenated Organic Chemicals - Dioxin/Furan Test Rule Data

Based on evidence that halogenated dioxins and furans may be formed as by-products during chemical manufacturing processes (Versar, 1985), EPA proposed a rule under Section 4 of the TSCA that would require chemical manufacturers and importers to test for the presence of chlorinated and brominated dioxins and furans in certain commercial organic chemicals (Federal Register, December 19, 1985).

The final rule (Federal Register, June 5, 1987) listed 12 manufactured or imported chemicals for which testing was required and 20 chemicals not currently being manufactured or imported that would require testing if manufacture or importation resumed. These chemicals are listed in Table 3-10. The specific dioxin and furan congeners for which quantitation is required and the target limits of quantitation (LOQ) specified in the Rule are listed in Table 3-11.

Under Section 8(a) of TSCA, the final rule also required that chemical manufacturers submit data on manufacturing processes and reaction conditions for chemicals produced using any of the 29 precursor chemicals listed in Table 3-12. The rule stated that subsequent to this data gathering effort, testing may be proposed for additional chemicals if any of the manufacturing conditions used favored the production of dioxins and furans.

To date, data have been submitted to the EPA TSCA Docket for 10 of the 12 chemicals requiring testing, however, not every manufacturer/importer has submitted data for every applicable product (Cash, 1993). Manufacture/import of the other two substances have stopped since the test rule was promulgated. [NOTE: All data and reports in the EPA TSCA Docket are available for public review/inspection at EPA Headquarters in Washington, DC.]

The results of analytical testing for dioxins and furans for the eight chemicals for which data are available in the TSCA docket are presented in Table 3-13. Data submitted for pentabromodiphenyloxide and tetra-bromobisphenol A-bisethoxylate are currently under EPA review. Dioxins/furans were found in four of these eight chemicals.

The chemicals for which positive results were obtained are:

  • 2,3,5,6-tetrachloro-2,
  • 5-cyclohexadiene-1,
  • 4-dione (chloranil),
  • octabromodiphenyloxide,
  • decabromodiphenyloxide,
  • and tetrabromobisphenol-A.
table Table 3-10 Chemicals Requiring TSCA Section 4 Testing Under the Dioxin/Furan Rule table Table 3-11 Congeners and Limits of Quantitation (LOQ) for Which  Quantitation is Required Under the Dioxin/Furan Test Rule and Pesticide Data Call-In
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table Table 3-12 Precursor Chemicals Subject to Reporting Requirements Under TSCA Section 8(a) table Table 3-13 Results of Analytical Testing for Dioxins and Furans in the Chemicals Tested To-Date Under Section 4 of the Dioxin/Furan Test Rule
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table Table 3-14 CDDs and CDFs in Chloranil and Carbazole Violet Samples Analyzed Pursuant to the EPA Dioxin/Furan Test Rule
Table 3-14 presents the quantitative analytical results for the four submitted chloranil samples as well as the results of verification sampling/analysis performed on chloranil by EPA. It should be noted that although testing conducted under this test rule for 2,4,6-tribromophenol indicated no halogenated dioxins or furans above the LOQs, Thoma and Hutzinger (1989) reported detecting BDDs and BDFs in a technical grade sample of this substance.

Total TBDD, TBDF, and PeBDF were found at 84 m g/kg, 12 m g/kg, and 1 m g/kg, respectively. No hexa-, hepta-, or octa-BDFs were detected. Thoma and Hutzinger (1989) also analyzed analytical grade samples of two other brominated flame retardants, pentabromophenol and tetrabromophthalic anhydride; no BDDs or BDFs were detected (detection limits not reported).
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3.4.3. Manufacture of Halogenated Organic Chemicals-Pesticide Data Call-In

In the early 1980s, attention began to focus on pesticides as potential sources of CDDs and CDFs in the environment. Historically, no regulation had been placed on CDD and CDF levels in end-use pesticide products. Certain pesticide active ingredients were known or suspected, however, to be contaminated with CDDs and CDFs (e.g., pentachlorophenol (PCP), Silvex, and 2,4,5-T).

During the mid and late 1980s, EPA took several actions to investigate and control CDD/CDF contamination of pesticides. In 1983, the sale of Silvex and 2,4,5-T was canceled for all uses by EPA (Federal Register, October 18, 1983). EPA entered into a Settlement Agreement in 1987 with PCP manufacturers to allow continued registrations for wood uses (Federal Register, January 2, 1987) but which set tolerance levels for HxCDD and 2,3,7,8-TCDD. TCDD levels were not allowed to exceed 1.0 ppb in any product, and after February 2, 1989 (a gradually phased in requirement), any manufacturing-use PCP released for shipment could not contain HxCDD levels that exceeded an average of 2 ppm over a monthly release or a batch level of 4 ppm.

EPA then issued a Final Determination and Intent to Cancel and Deny Applications For Registrations of Pesticide Products Containing Pentachlorophenol (Including but not limited to its salts and esters) For Non-Wood Uses which prohibited the registration of PCP for nonwood uses (Federal Register, January 21, 1987).

In addition to these cancellations and product standards, EPA's Office of Pesticide Programs (OPP) issued two Data Call-Ins (DCIs) in June 1987. Pesticide manufacturers are required to register their products with EPA in order to market them commercially in the United States. Through the registration process, mandated by FIFRA (Federal Insecticide, Fungicide and Rodenticide Act), EPA can require that the manufacturer of each active ingredient generate a wide variety of scientific data through several mechanisms.

The most common process is the five phase reregistration effort to which the manufacturers (i.e., registrants) of older pesticide products must comply. In most registration activities, registrants must generate data under a series of strict testing guidelines, 40 CFR 158--Pesticide Assessment Guidelines (U.S.EPA, 1988). FIFRA accommodates the fact that some pesticide active ingredients may require additional data, outside of the norm, to adequately develop effective regulatory policies for those products. Therefore, EPA can require additional data, where needed, through various mechanisms as noted above including the DCI process.

The purpose of the first DCI (June 6, 1987), Data Call In Notice For Product Chemistry Relating to Potential Formation of Halogenated Dibenzo-p-dioxin or Dibenzofuran Contaminants in Certain Active Ingredients, was to identify chemicals that may contain halogenated dibenzo-p-dioxin and dibenzofuran contaminants and to quantify and eventually minimize exposure to these contaminants.

The requirements made in this DCI parallel requirements established in the Dioxin/Furan Test Rule promulgated under Sections 4 and 8 of TSCA. (See Section 3.4.2.) The list of pesticide active ingredients to which this DCI applied along with their corresponding Shaughnessey and Chemical Abstract code numbers are presented in Table 3-15.

[Note: the Shaughnessey code is an internal EPA tracking system--it is of interest because chemicals with similar code numbers are similar in chemical nature (e.g., salts, esters and acid forms of 2,4-D)]. All registrants supporting these chemicals were subject to the requirements of this DCI unless their product qualified for a Generic Data Exemption (i.e., a registrant exclusively used a registered product(s) as the source(s) of the active ingredient(s) identified in Table 3-15 in formulating their product(s)).

Registrants whose products did not meet the Generic Data Exemption were required to submit the types of data listed below to assess the formation of tetra- through hepta-halogenated dibenzo-p-dioxin or dibenzofuran contaminants during manufacture. Registrants, however, did have the option to voluntarily cancel their product or "reformulate to remove an active ingredient," described in Table 3-15, to avoid compliance with the DCI.

Table 3-15 Pesticides That Could Become Contaminated With Dioxins If Synthesized Under Conditions Which Favor Dioxin Formation
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. Product Identity and Disclosure of Ingredients:


EPA required submittal of a Confidential Statement of Formula (CSF) based on the requirements specified in 40 CFR 158.108 and 40 CFR 158.120

- Subdivision D:Product Chemistry. Registrants who had previously submitted still current CSFs were not required to resubmit this information.
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. Description of Beginning Materials and Manufacturing Process:
Based on the requirements mandated by 40 CFR 158.120 - Subdivision D, EPA required submittal of a manufacturing process description for each step of the manufacturing process, including specification of the range of acceptable conditions of temperature, pressure, or pH at each step.

. Discussion of the Formation of Impurities:
Based on the requirements mandated by 40 CFR 158.120 - Subdivision D, EPA required submittal of a detailed discussion/assessment of the possible formation of halogenated dibenzo-p-dioxins and dibenzofurans.

The second DCI (dated June 15, 1987), Data Call-In For Analytical Chemistry Data on Polyhalogenated Dibenzo-p-Dioxins/Dibenzofurans (HDDs and HDFs), was issued for a variety of pesticide active ingredients to the individual manufacturers of each ingredient. (See Table 3-16.) All registrants supporting these pesticides were subject to the requirements of this DCI unless the product qualified for various exemptions or waivers. Pesticides regulated by the second DCI were strongly suspected to be contaminated with detectable levels of HDDs/HDFs.

Under the second DCI, registrants whose products did not qualify for an exemption or waiver were required to generate and submit the following types of data in addition to the data requirements of the first DCI:

Table 3-16 Pesticides That Are Suspected To Be Contaminated With Dioxins
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. Quantitative Method For Measuring HDDs or HDFs:

Registrants were required to develop an analytical method for assessing the HDD/HDF contamination of their products.

The DCI established a regimen for defining the precision of the analytical method (i.e., for internal standard--precision within +/- 20 percent and recovery range of 50 to 150 percent, also a signal to noise ratio of at least 10:1 was required).

Target quantification limits were established in the DCI for specific HDD and HDF congeners. (See Table 3-11.)
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. Certification of Limits of HDDs or HDFs:
Registrants were required to submit a "Certification of Limits" in accordance with 40 CFR 158.110 and 40 CFR 158.120 - Subdivision D. Analytical results were required that met the guidelines described above.

Registrants could select one of two options to comply with the second DCI. The first option was to submit relevant existing data, develop new data, or share the cost to develop new data with other registrants. The second option was to alleviate the DCI requirements through several exemption processes including a Generic Data Exemption, voluntary cancellation, reformulation to remove the active ingredient of concern, an assertion that the data requirements do not apply, or the application/award of a low-volume, minor-use waiver.

The data contained in CSFs, as well as any other data generated under Subdivision D, are typically considered Confidential Business Information (CBI) under the guidelines prescribed in FIFRA because they usually contain information regarding proprietary manufacturing processes. In general, all analytical results submitted to EPA in response to both DCIs are considered CBI and cannot be released by EPA into the public domain. Summaries based on the trends identified in that data as well as data made public by EPA are provided below.

To date, more than 100 submissions have been reviewed in response to the two DCIs. The majority have been manufacturing process data in support of waiver requests, analytical method protocols, and sample collection protocols (telephone conversation between S. Funk, EPA - Office of Pesticide Programs (OPP), and J. Dawson, Versar, Inc. on 2/18/93). Analytical results on the levels of tetra- through hepta- HDDs/HDFs have been received and reviewed for 16 distinct pesticide active ingredients (Table 3-17).

In general, the analyses have not revealed HDD/HDF concentrations in excess of the LOQs specified in Table 3-11. For those products in which LOQs are exceeded, the identified contamination levels were generally within an order of magnitude of the LOQ and apply only to one or two congeners per product (telephone conversation between S. Funk, EPA/
OPP, and J. Dawson, Versar, Inc. on 2/18/93). Table 3-18 presents a summary of results recently reported by EPA for CDDs and CDFs in eight technical 2,4-D herbicides.

3.4.4. Chlorine Production Using Graphite Electrodes

The production and use of chlorine gas has involved processes that result in the generation of CDFs (Rappe, 1992a). Chlorine is commonly produced via electrolysis of brine in mercury cells. High levels of CDFs have been found in the graphite electrode sludge from this chemical process and may have been responsible for occupational exposures among workers who handled these sludges. Svensson et al. (1992) evaluated the relationship between blood CDF levels in chloralkali plant workers and direct exposure of these workers to electrode sludges and to dust and earth contaminated with graphite electrode sludge.

Subjects who had been exposed by handling graphite electrode sludge had higher levels of 2,3,7,8-substituted PeCDFs and HxCDFs than reference subjects. Evaluations of congener distribution patterns have demonstrated that the 2,3,7,8-substituted CDFs are the major congeners formed during the chloralkali process (Rappe et al., 1990; Rappe, 1992a).

table Table 3-17 Summary of Analytical Data Submitted to-Date in Response to Pesticide Data Call-In table Table 3-18 Summary of Results for CDDs and CDFs in Technical 2,4-D Herbicides
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Until the late 1970s, graphite electrodes were the primary type of anode used in the chloralkali industry (Curlin and Bommaraju, 1991). Since then, metal anodes have been developed to replace graphite electrodes because of production problems associated with their use (U.S. EPA, 1982; Curlin and Bommaraju, 1991). Currently, no U.S. facilities are believed to use graphite electrodes in the production of chlorine gas (telephone conversation between L. Phillips, Versar, Inc., and T. Fielding, U.S. EPA, Office of Water, February 1993). Although the use of graphite electrodes has been eliminated, the potential for CDD/CDF releases from dump sites containing contaminated sludges may still exist (Svensson et al., 1992; Rappe, 1992a).

3.4.5. Petroleum Refining Catalyst Regeneration

Catalyst regeneration in the petroleum refinery reforming process has been identified as a source of CDDs and CDFs based on testing conducted in Canada (Thompson et al., 1990). According to Thompson et al. (1990), "catalytic reforming is a refinery process which is used to produce high octane gasoline. The reforming process occurs at high temperature and pressure and requires the use of a catalyst. During the catalytic process, a complex mixture of aromatic compounds known as coke is formed and deposited onto the catalyst. As coke deposits onto the catalyst, its activity is decreased.

The high cost of the catalyst necessitates its regeneration. Catalyst regeneration is achieved by removing the coke deposits via burning and activating the catalyst using chlorinated compounds. Burning of the coke produces flue gases which contain CDDs and CDFs along with other combustion products." Thompson et al. (1990) reported total CDD and CDF concentrations of 8.9 ng/m3 and 210 ng/m3, respectively, in stack gas samples from petroleum refinery reforming operations (Table 3-19).

It was also found that the CDD and CDF congener distribution patterns observed were similar to those found in municipal waste incinerator ash and stack samples. Because flue gases may be scrubbed with water, internal effluents may also be contaminated with CDD/CDFs. Thompson et al. (1990) observed CDDs and CDFs in the internal wash water from a scrubber of a periodic/cyclic regenerator (Table 3-20).

The Canadian Ministry of the Environment detected concentrations of CDDs in an internal wastestream of spent caustic in a petroleum refinery that ranged from 1.8 to 22.2 ppb, and CDFs ranging from 4.4 to 27.6 ppb. The highest concentration of 2,3,7,8-TCDD was 0.0054 ppb (Maniff and Lewis, 1988). CDDs were also observed in the refinery's biological sludge at a maximum concentration of 74.5 ppb, and CDFs were observed at a maximum concentration of 125 ppb (Maniff and Lewis, 1988). The concentration of CDD/CDFs in the final combined refinery plant effluent was below the detection limits.

table Table 3-19 CDDs/CDFs in Petroleum Refinery Stack Gas from a Continuous Regenerator Without Scrubber  table Table 3-20 CDDs/CDFs in the Scrubber Wash Water from a Petroleum Refinery Periodic/Cyclic Regenerator
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Insufficient data are available to evaluate CDD/CDF releases from these sources in the United States. However, Beard et al. (1993) conducted a series of benchtop experiments to investigate the mechanism(s) of CDD/CDF formation in the catalytic reforming process. A possible pathway for the formation of CDFs was found, but the results could not explain the formation of CDDs. Analyses of the flue gas from burning coked catalysts revealed the presence of unchlorinated dibenzofuran (DBF) produced in quantities of up to 220 ng/g of catalyst.

Chlorination experiments indicated that dibenzofuran and possibly biphenyl and similar hydrocarbons act as CDF precursors and can become chlorinated in the catalyst regeneration process. Corrosion products on the steel piping of the process plant seem to be the most likely chlorinating agent. Furthermore, CDFs can form by de novo synthesis from chlorinated hydrocarbons like trichloroethylene, methylene chloride, and carbon tetrachloride in the presence of FeCl3 and HCl or Cl2.

3.4.6. Additional Chemical Manufacturing and Processing Sources

Rappe et al. (1989) reported the formation of CDFs (tetra- through octa-chlorinated CDFs) when tap water and double-distilled water were chlorinated using chlorine gas. The CDF levels found in the single samples of tap water and double-distilled water were 35 and 7 pg TEQ/L, respectively. The water samples were chlorinated at a dosage rate of 300 mg of chlorine per liter of water which is considerably higher (by a factor of one to two orders of magnitude) than the range of dosage rates typically used to disinfect drinking water. Rappe et al. (1989) hypothesized that the CDFs or their precursors are present in chlorine gas.

It should be noted, however, that although few surveys of finished drinking water for CDD/CDF levels have been conducted, the few that have been published only rarely report the presence of any CDD/CDF even at low pg/L detection limits and in those cases the CDD/CDFs were also present in the untreated water. (See Section 4.3.)

Several recent studies have been conducted to identify the source(s) of CDD/CDFs found in textiles and at dry cleaning facilities. Horstmann and McLachlan (1994) analyzed 35 new textiles and found total CDD/CDF levels generally less than 50 pg/g; however, some items were as high as 290,000 pg/g. The authors conclude that textile finishing processes are not likely to be the source of the high CDD/CDF levels found because of the apparent randomness of the textiles with high CDD/CDF levels.

However, the authors hypothesize that the use of pentachlorophenol to preserve cotton, particularly when it is randomly strewed on bales of cotton as a preservative during sea transport, is the likely source of the high levels occasionally observed. As discussed in Section 3.4.3, the use of pentachlorophenol (PCP) for nonwood uses has been prohibited in the United States since 1987.

However, Horstmann and McLachlan (1994) comment that PCP is still used in developing countries, especially for purposes of preserving cotton during sea transport. As discussed in Section 3.4.1.5, certain dyes and pigments have also been observed to contain CDD/CDFs and may also contribute to levels found in textiles. Horstmann and McLachlan (1994) also summarize recent research concerning CDD/CDFs in dry cleaning residues and reach the conclusion that new textiles are the source of the CDD/CDFs found.

3.5. MECHANISMS OF FORMATION OF DIOXIN-LIKE COMPOUNDS DURING COMBUSTION OF ORGANIC MATERIALS

The specific molecular mechanisms by which CDDs and CDFs are initially formed and then emitted from combustion sources remain largely unknown and are theoretical. The theoretical basis for conjecture is derived primarily from direct observations in municipal solid waste incinerators and from well conducted laboratory studies. Municipal solid waste incinerators (MSWIs) have been heavily studied from the perspective of eventually finding the specific formation mechanism transpiring within the system, and determining ways to either significantly reduce such opportunities or ultimately hinder the formation kinetics to preclude evolution of these chemicals.

Although much has been learned from these studies, it is still not known how to completely block the formation of CDDs/CDFs during the combustion of certain organic materials in the presence of a source of chlorine. Adding to this complexity is the wide variability of organic materials that are incinerated and thermally processed by a wide spectrum of combustion technologies having variable temperatures, residence times, and oxygen requirements. However, 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 emission of CDDs and CDFs can be explained by three principal theories, which should not be regarded as being mutually exclusive. The first is that CDD/CDFs are present as contaminants in the combusted organic material.

This theory is discussed in Section 3.5.1. The second is that CDDs/CDFs are ultimately formed from the thermal breakdown and molecular rearrangement of precursor compounds, which are defined as chlorinated aromatic hydrocarbons having a structural resemblance to the CDD/CDF molecule. This theory is discussed in Section 3.5.2.

The third theory, similar to the second and described in Section 3.5.3, is that CDDs/CDFs are synthesized de novo; this means they are formed from organic and inorganic substrates comprised of singular or mixtures of molecules bearing little resemblance to the molecular structure of CDDs or CDFs. Section 3.5.4 discusses the generation of coplanar PCBs. Section 3.5.5 discusses the evaluation of naturally occurring CDDs/CDFs by examinations of sediment core data, and Section 3.5.6 provides a closing summary of the three principal theories of formation.