Half truths as usual...

General

There are special occasions, where PVC, chloride (salt), wetting and/or compacting of the waste has a serious impact on dioxin foramation. That is the case for backyard barrel burning and inadvertent fires in dumps. That is less the case for accidental fires of houses and warehouses, where incineration conditions in general are better (higher temperatures, less compacted, less wet). But even in worst case conditions, it is not the chlorine level which makes more dioxins, it is the influence of chlorine on the conditions which makes the difference. Moreover, more PVC/chlorine reduces the amount of PM(10 and 2.5), VOC's (benzene) and PAH's. The latter are far more important in carcinogenity and toxicity than dioxins...

A lot of omissions can be found in the latest Greenpeace report about the role of chlorine in dioxin formation. That will be addressed in the last part of this answer page.

Chlorine input and dioxin output in  large scale facilities.

1. Municipal waste combustors:
Original set of data: HCl content in raw waste gas (as surrogate for chlorine content in the waste) and dioxin measurements.	Partial correlation coefficients by the ASME, based on multiple regression, as is appropriate for multi-cause and effect systems like can be expected in incinerators	Single correlation coefficients according to Greenpeace for different facilities, without taking into account design (turbulence), temperature and residence time...

2. Medical waste combustors:
Original set of data: HCl content in raw waste gas (as surrogate for chlorine content in the waste) and dioxin measurements.	Partial correlation coefficients by the ASME, based on multiple regression, as is appropriate for multi-cause and effect systems like can be expected in incinerators	Single correlation coefficients according to Greenpeace for different facilities, without taking into account design (turbulence), temperature and residence time...

3. Hazardous waste combustors:
Original set of data: HCl content in raw waste gas (as surrogate for chlorine content in the waste) and dioxin measurements.	Partial correlation coefficients by the ASME, based on multiple regression, as is appropriate for multi-cause and effect systems like can be expected in incinerators	Single correlation coefficients according to Greenpeace for different facilities, without taking into account design (turbulence), temperature and residence time...

    As one can see, there is ample difference between the Greenpeace interpretation of the data of the three large scale main combustion facilities: municipal, hospital and hazardous waste incinerators. All show as good positive as negative correlations. That simply means that a small change in process conditions has a much higher influence than large changes in chlorine content...

Chlorine input and dioxin output in  backyard barrel burning.

At first glance, PVC input has a tremendous impact on dioxin formation, like more copper, compressing and wetting of the waste has. But chlorine has only a secondary effect, as it lowers the burning temperature and/or augments the residence time, which results in higher dioxin releases.

As you can see, chlorine sources like PVC, chlorine or HCl can be omitted out of the equation, while still obtaining a high correlation. But copper and time and/or temperature can't be omitted. That again confirms that process conditions and copper by far are the most important parameters.

Only in one series of experiments (See: barrel burning), not only dioxins were measured, but also PM, benzene, VOC's, PAH's,... From that experiments, one can learn that a higher PVC content is accompanied by lower PM, benzene, VOC and PAH emissions. With a factor 20 lower for cancerogenity for BaP than for TCDD (in some strains of rats), the emissions of high-PVC trials were less carcinogenic (as far as these contaminants are bio-available) than for low-PVC, because of much lower PM, PAH and benzene emissions. Unfortunately, VOC and PAH emissions were not measured in the new series.

Thus exchanging PVC by alternative plastics can reduce dioxin emissions in worst case scenarios, but will augment PAH emissions (already 3-4 orders of magnitude higher) in the same circumstances. Dioxins don't damage DNA and are cancer promotors only at extreme levels. PAH's break down to DNA damaging oxidized substances and thus are cancer initiators. What a choice... A good case to apply the precautionary principle? But you don't have to choose: just forbid backyard burning (and educate people to don't burn any waste - neither in barrels nor in open fire places or stoves) and let the waste go to state-of-the-art incinerators. Makes a difference of 30,000-120,000 times in emissions. No matter what you burn...

Laboratory experiments .

While we don't have all works referenced by Pat Costner, these that we have contain very interesting information which was omitted by her. Here follows a step by step comparison. For some of the experiments that show a high correlation, nothing is mentioned about the other variables that influence dioxin formation to a much larger extent (temperature, time, turbulence and copper content). Thus not much comment can be given...

Greenpeace:
"Since every molecule of dioxin contains two or more atoms of chlorine, chlorine is an absolute necessity for dioxin formation. Therefore, when no chlorine is present, no dioxins are formed."
Omitted:
But without oxygen or carbon, no dioxins are formed either. The first is used in an alternative for incineration (thermolyses). And the second is type dependent. Carbonised organic materials are good precursors for dioxins (and PAH's), while graphite is not. And even ambient air contains hundreds to thousands times the amount of chlorine that is necessary to form dioxins found at incinerators. And any organic material contains chlorine at hundredthousands to millions of times higher levels than what is built into dioxins...

Greenpeace:
"For example, Katami et al. (2000) found less dioxin output in gaseous emissions with lower chlorine input during the combustion of newspaper with PVC or sodium chloride, as shown in figure 1".
Omitted:
The tests mentioned by Greenpeace to "prove" the relation between chlorine input and dioxin output is by Katami e.a. [63]. But in the graph they made of the testresults, they omitted one of the tests! That was a test with NaCl impregnated newspaper and PE plastic added. While the chlorine content of the fuel was reduced from 3.1% to 2.5%, the dioxin/furan emissions remained the same... Thus may we conclude that PE is a precursor for dioxin formation???

See the difference in graphs:

Further, one can give a lot of critique about the tests and the interpretation of the results:

• Burning chamber temperatures were average from 653 (plain newspaper) to 456 degr.C (newspaper+PVC). Exhaust temperatures between 526 and 416 degr.C. That is right in the range of worst case scenario's like in backyard barrel burning. If that represents the average Japanese waste incineration, then it is no wonder that they still have high dioxin emissions...
• Fuel burned was between 50-60 kg in about 4 hours or 12-15 kg/h, except for impregnated newspaper + PE and impr. newspaper + PVC: 31,76 and 28 kg resp. in 3 hours 20 minutes or 9.5 resp. 8.4 kg/h.
• Caloric content of the different fuels largely differed from each other: ranging from 583 Mcal total (heavy oil - blank test) via 243 Mcal (newspaper) to 131 Mcal for newspaper + PVC or as caloric feed: 146 Mcal/h (oil) via 61 Mcal/h (newspaper) to 39 Mcal/h (newspaper + PVC).
• CO content of the exhaust gases were between 87 ppm (oil) via 1000 ppm (newspaper) to 1500 ppm (newspaper + PVC), pointing to severe differences in process efficiency due to different conditions.
• Their presumption that the metal content of the newspaper was not of relevance is not confirmed by their own figures: iron content was 33,000 ng/g paper, copper content was 8,600 ng/g paper, while chlorine content  in the dioxins which were formed was only 74 ng/g in the worst case...

All together, one can conclude that no conclusion can be drawn from this tests, as different process conditions with a known high influence on dioxin formation were not kept constant. That is as well as for temperature as for time, but probably also for turbulence, as different load conditions also can introduce changes in air flows...
 

Greenpeace:
Numerous studies of laboratory- and pilot-scale combustion systems have found that dioxin formation decreases with reduced chlorine input. The U.S. Environmental Protection Agency (2000) acknowledged this to be the case in their recent review of such studies:
“[R]eview of experimental data clearly indicates an association between chlorine content of feed/fuels and … synthesis of CDDs and CDFs.”
Omitted:
The above statement is true, but what was omitted is how much the chlorine content influences chlorinated organics formation, compared to other influences. As seen in experiments on laboratory and pilot scale (see laboratory experiments), those that show a correlation, have a two-fold increase of PCDD/F with a 12-fold increase in chlorine. Others show a 30% reduction with a tenfold decrease in chlorine content. That is within the variation of measurements of one dioxin sample within one laboratory (+- 30-50%) or between laboratories (up to a five-fold!). Or far within the variation between series with identical experiments (a 3- to 10-fold)...
The U.S. EPA also stated that for large scale combustors:

• "The conclusion that chlorine in feed is not a strong determinant of CDD/CDF emissions applies to the overall population of commercial scale combustors. For any individual commercial scale combustor, circumstances may exist in which changes in chlorine content of feed could affect CDD/CDF emissions. Based on scientific evidence currently available, reduction in chlorine content of feeds to well-controlled commercial combustors is not likely to result in a significant reduction of CDD/CDF emissions, unless the chlorine content could be brought to near zero. For uncontrolled combustion, such as open burning of household waste, the chlorine content of the waste may play a more significant role in rates of CDD/CDF formation and release than is observed at commercial scale combustors."

• "This conclusion [of the ASME] has been questioned in a paper by Costner (1998) [note: of Greenpeace] who claims that many of the facilities assessed by Rigo et al. (1996) show a positive (though small) correlation between chlorine in feed and CDD/CDF emissions. Conversely, Costner (1998) also found that about half the facilities showed a weak inverse relationship."

Greenpeace:
Samples with a higher chlorine content give a higher CP [note: chlorophenols as surrogate for dioxin] emission but tend to reach a plateau value. ... [W]ith added HCl .. it appears that the CP emission increases quite regularly if not linearly with [HCl].” and
"Lowering the chlorine load – by leaving out compostables and PVC -, lowers the CP-level."
Omitted:
The complete work of Kanters and Louw has something more to say: complete elimination of PVC out of the feed had no effect on total CP formation, neither had the complete elimination of the compostables fraction. Only when both were reduced, resulting in a tenfold decrease in chlorine content, a 30% reduction was obtained. That was within the variability of CP measurements (30%) and far within the variability of two series of identical experiments (a 3-fold).

Greenpeace:
“… PCDD/F yields do in fact increase with increasing Cl radicals. … the presence of Cl radicals could be a critical influencing factor on
chlorination and PCDD/F formation.”
Omitted:
Cl *radicals* have no correlation with chlorine in the feed, neither in particulate or gases as they are formed by catalytic oxidation from chloride ions (either salt or HCl) by copper and oxygen. Thus copper and oxygen are the limiting factors, not chlorine...

Greenpeace:
"In another series of laboratory experiments, Wikstrom et al. (1996) varied the chlorine content of an artificial waste by spiking it with PVC or calcium chloride, obtaining the results illustrated in Figure 2." and
"Some scientists who agree that dioxin formation correlates with chlorine input nonetheless oppose policies restricting chlorine input. They contend that, even though restricting chlorine input reduces dioxin formation, other factors have far greater influence. For example, while Wikstrom and Marklund (2001) found a positive chlorine/dioxin relationship, they concluded that “the most important variable for changes in the PCDDs/Fs [dioxins] … formation was disturbance in the combustion condition and not the variation in chlorine content of the fuel“.
Then follows a ridiculous explanation why chlorine input still is important.
Omitted:
Wikström et al. [64], performed far more work than was mentioned by Greenpeace.  The graph shown by Greenpeace is outdated, as more experiments by Wikström et al. were done:

• "This indicates that the chlorine content is of importance for the formation of chlorinated organic compounds, but only at rather high levels [note: that was the result of the first series of experiments]. The condition was not further confirmed in other experiments performed in the laboratory reactor. This indicates that other parameters than the chlorine content are of importance for the formation of chlorinated pollutants."

• "The variation in dioxin formation within each chlorine level is larger than the differences between the eight fuels. Consequently no correlation between the chlorine content and the I-TEQ level in the flue gas could be discerned."

• "The chlorine source and level are unimportant for formation of chlorinated organic pollutants".
• "Combustion efficiency roles the degree of chlorination".
• "Secondary chlorination is more important than the de novo synthesis during low temperature reactions".

Greenpeace:
"Delayed release of dioxins. The 'memory effect', which has been documented in a number of studies (e.g., Gullett et al. (2000) ; Blumenstock et al. (2000) ; Zimmerman et al. (2001) ; Hunsinger et al. (2000) occurs when dioxins are adsorbed onto the walls of incinerator stacks, ducts, etc., and then slowly released. This results in underestimation of the dioxin emissions that might otherwise correlate with a specific rate of chlorine input."
Omitted:
As was clearly stated at the dioxin seminar in Bruges, November 18-20, 2001 , the "memory effect" is indeed important, especially with upsets. But with upsets it is mainly soot/PAH's which precipitate on the walls. Further incineration again forms dioxins from the soot/PAH's. Thus again by catalytic chlorination from carbon sources... That means that you have to wait a long time after such an incident, before one can take conclusions of experiments. But that has nothing to do with the chlorine content of the waste...

Greenpeace:
"In a more specific example, the U.S. Environmental Protection Agency attributed reduced dioxin releases from lead smelters to the phase-out of PVC separators in lead batteries which are processed in such smelters"
Omitted:
The USEPA attributed 1 g I-TEQ dioxins per year to secondary lead smelters in 1987, 1.63 g I-TEQ/a in 1995, both very unimportant (but rising?) quantities. Quantities are from the UNEP world-wide dioxin inventory [60].

Greenpeace:
"For example, Gullett et al. (2000) carried out a series of experiments in which simulated domestic waste with varied quantities of PVC was burned in open barrels and, in one case, in a waste pile. As illustrated in Figure 4, dioxin formation decreased with lower PVC content. In the one test with a waste pile, they found considerably lower dioxin formation than with the open barrel burns."
Omitted:
The latter confirms that burning conditions are far more important than composition...
Further is omitted that the series of experiments included experiments where salt was added (more dioxins), the waste was wetted (more dioxins). Copper was added (more dioxins) and the waste was compacted (more dioxins)...
Further, the researchers tried to make correlations between one or more factors and dioxin formation. The results show that high correlations can be obtained WITHOUT chlorine, PVC or HCl in the equation. The only constant factor was copper, together with time and/or temperature of the incineration. See the results of backyard barrel burning on this page.
That leads us to one possible explanation of why higher dioxins are found with more PVC/chloride/water/compacting in these circumstances: all these factors hinders the incineration, changing the burning temperature and/or time. But that is more than compensated by the reduction of VOC's, benzene and PAH's at lower temperatures.
Only in one series of experiments by Lemieux e.a.[54], not only dioxins were measured, but also PM, benzene, VOC's, PAH's,... From that experiments, one can learn that a higher PVC content is accompanied by lower benzene, VOC and PAH emissions. With a factor 20 lower for cancerogenity for BaP than for TCDD (in some strains of rats), the emissions of high-PVC trials were less carcinogenic (as far as these contaminants are bio-available) than for low-PVC, because of much lower PM, PAH and benzene emissions. Unfortunately, VOC and PAH emissions were not measured in the new series.
That is confirmed by Wikström et al. [64]:

• "The probability of sooth and PAH formation differs between PVC and the other non-chlorinated plastics. The soot and PAH levels were much higher for the non-chlorinated polymers, especially for the polystyrene (PS) plastic. The reasons for the differences in formation are very likely the different burning properties of the polymers. PVC burns as individual particles while PS and PE have a strong tendency to form group flames instead. The individual particle flame utilized the oxygen in the furnace effectively and promoted the oxidation of soot and PAH's."

Conclusion:

You are at level two of the Chlorophiles pages

Created: November 22, 2001.
Last update: January 1, 2002.

Welcome page

Home Page of the Chlorophiles

Chemistry of dioxin formation

Comment on "Pandora's Poison", written by Joe Thornton

For any comment on this or other pages, especially on phthalates:

Chlorophiles@pandora.be