HEALTH CARE RISK WASTE INCINERATION -
A BRIEF OUTLINE OF THE COMPOSITION, FORMATION, TOXICITY AND DESTRUCTION OF DIOXINS & FURANS
Brian Thomson
MACROtech CC
ABOUT THE SPEAKER
Brian Thomson is a waste disposal “NUT CASE”
He has used his engineering degree and post grad. diploma (Wits 1958 and 1967) to dispose of waste varying from sewage sludge to bank notes; from stinking phenols to gold dust. He has supplied more than 700 plants into 27 countries of the world. He has lived with the evolution of incinerators from a black box with a chimney on top, to highly sophisticated, fully automatic systems.
He has rubbish on the brain – so if he spills a little dirt in the path of those that oppose him, don’t be surprised.
One thing is certain. When he dies, nobody will throw dirt on top of him. He will be cremated – in one of his cremators!
ABSTRACT
There is a world outcry against the emission of dioxins and furans and against equipment that creates these emissions. Health care risk waste incinerators are of special concern due to the PVC content of medical wastes.
Does the man in he street know what dioxins and furans are and why we should be concerned about their presence?
This little chat is intended to bring a little better comprehension to the minds of those who are interested. Following the guideline of “KISS” (keep it simple stupid), some of the concepts may be a little simplistic. I apologize to the purists and technical maniacs that might have wanted a higher level discussion.
HEALTH CARE RISK WASTE INCINERATION -
A BRIEF OUTLINE OF THE COMPOSITION, FORMATION, TOXICITY AND DESTRUCTION OF DIOXINS & FURANS
The Composition of Dioxins and Furans. All combustible waste is made up compounds of carbon, hydrogen and oxygen. These are the major components. Other common components include nitrogen, sulphur and halogens (fluorine, chlorine, bromine and iodine) as well as the OH radical. The molecular structure of these compounds very varied. Most of them, particularly the synthetics such as plastics include many carbon atoms.
The process of combustion breaks these compounds down into simpler compounds containing fewer atoms. The ultimate is reached when the all of the carbon is converted to carbon dioxide. During the breakdown a vast array of intermediate compounds are formed, some more stable, and hence more common than others.
One or two atoms of oxygen can replace one or two of the hydrogen atoms. The oxygen atoms have hooks at each end, so an atom of oxygen can join two benzene rings together. Sometimes two oxygen atoms form a double link between two benzene rings
A PAIR OF BENZENE RINGS LINKED BY A SINGLE OXYGEN IS CALLED A FURAN.
A PAIR OF BENZENE RINGS LINKED BY TWO OXYGEN ATOMS IS CALLED IS CALLED A DIOXIN.
The Addition of Chlorine and Fluorine. The dioxin/furan structure described above consists only of carbon, hydrogen and oxygen. The compounds can be modified by the addition of one or more chlorine or fluorine atoms in place of any of the hydrogen atoms. The addition of one chlorine creates a mono chlorinated dioxin or furan. Four chlorine atoms produce a tetra-chlorinated dioxin or furan. A maximum of eight halogen atoms can be attached to a dioxin pair.
The toxicity of dioxins and furans varies according to the number of halogens attached. A dioxin without any halogens has been proved to be non-toxic. A tetra-chlorinated dioxin is given the highest toxicity rating. It is not only the number of halogens that determines the toxicity rating. The location of the halogens on the structure of the dioxin also has a marked effect.
Two hexagonal benzene rings each with two corners occupied by the linking oxygen atoms have eight potential positions onto which a chlorine or fluorine can be attached. The corners are numbered anti-clockwise with number 1 at the bottom of the right hand ring.
The dioxin that is said to be the most toxic is described as 2,3,7,8 tetrachlorodibenzo-p-dioxin or, more simply as 2,3,7,8 TCDD. It has four chlorine atoms attached - two on one ring in positions 2 and 3 and two on the other ring in positions 7and 8. All other dioxins and furans are less toxic.
TEF and TEQ. The relative toxicity of various dioxins & furans has been established experimentally by men far more qualified than I. These clever people have established a simple system whereby the toxicity of all known dioxins and furans can be expressed as a decimal fraction of the toxicity of 2,3,7,8 TCDD. They have called this the Toxicity Equivalent Factor or TEF. In 1998 the American EPA published a table of TEF values.
COMPOUND / TEFMONO, DI, TRI – CDD / 0
2,3,7,8 Tetra CDD / 1
Other Tetra CDD’s / 0
2,3,7,8 Penta CDD’s / 0.5
2,3,7,8 Hexa CDD’s / 0.1
2,3,7,8,Hepta CDD’s / 0.01
The only Octa CDD / 0.001
· If positions 2,3,7,8 are not occupied by chlorine or fluorine atoms, the TEF is ZERO. Thus, for instance a 1,3,6,7,8 Penta-CDD is not toxic.
· Octa-CDD has all positions occupied by chlorine atoms. It is rated as being cytotoxic – but notice how very small the toxicity is when compared to the “bad boy” Tetra CDD.
· Mono-, Di- and Tri-CDD’s have too few chlorine atoms to fill the 2,3,7,8 positions and are not cytotoxic.
· A Table of TEF Values for furans reveals a similar pattern, except that the values are all significantly lower.
The relatively low or zero toxicity of the vast majority of dioxins is in marked contrast to the statements made by anti-incinerator lobbyists, who refer to “75 dioxins and 135 furans … the most deadly toxins known to man”. The Penguin Dictionary of Chemistry lists “dioxin” as “The incorrect popular contraction of 2,3,7,8-tetrachlorodibenzo-p-dioxin.” The man in the street and most of the vociferous “no-burn” activists are ignorant of how few dioxins can be given a significant toxicity rating.
Waste containing no halogens will form dioxins, but the dioxins are not toxic.
Even if halogens are present, toxic dioxins will not be formed unless conditions favor the formation of dioxin with at least four halogen atoms in the right positions.
The Toxicity of 2,3,7,8 TCDD. It has been stated that 2,3,7,8 TCDD is “one of the most toxic man-made compounds known”. This assessment has apparently been made on the strength of tests done on small caged animals. The validity of the data as applied to humans is questionable. Researchers have not yet sunk to the depths of administering toxic substances to humans in cages. Because it is not feasible to conduct tests on live humans, two compromise options must be considered.
The first is to extrapolate the results from small animals to humans. This is not very satisfactory or conclusive as the toxicity varies hugely even between small animals such as mice and guinea pigs. Literature even differs as to which of the two species is completely immune to dioxins. Reports do, however, agree that one or other is immune.
The second is to look for instances where humans have been accidentally exposed to large doses. Studying cases where humans are exposed to small doses is inconclusive because dioxins are a natural phenomenon, and we all have some dioxin in our systems. Veld fires and numerous other combustion processes all produce a measure of dioxins. Volcanic activity is the largest source of natural dioxins. Studies of people living near to geophysical activity have not shown any measurable correlation between proximity to such activity and cancer or the other diseases attributed to dioxin exposure.
Various authorities have confirmed the statement that:
“There is no such thing as a toxic substance – there is only a toxic dose.”
Positive correlation has been found in cases where people were exposed to massive doses of dioxin. The doses were thousands of times higher than would be caused by emissions from an incinerator chimney. To the best of my knowledge no deaths have ever been directly attributed to dioxins or furans, not even in massive doses. The long term cumulative effects from old, crude incinerators, has been debated and proved to be a problem. However the effect of the tiny quantities that may escape from a modern incinerator is not significant when compared to natural sources.
Large doses of dioxin have been shown to cause a health problem that is not related to cancer. The problem comes in the form of chloracne. Chloracne is a skin disease that shows symptoms like severe acne on exposed parts of the body. It is not chronic and it clears up shortly after the exposure to dioxin is removed.
Can 2,3,7,8 TCDD really be “one of the most toxic man-made compounds known”?
Elimination and/or Reduction. Although the adverse effects of dioxin may be under a cloud of uncertainty, the manufacturers of good quality, sophisticated incinerators take the elimination of high dioxin levels very seriously. Numerous actions are taken to reduce and, eventually eliminate dioxin/furan emissions.
The obvious first step is to eliminate chlorine and fluorine from the waste. This is covered by a “Green Procurement Policy”. The details are beyond the direct control of incinerator manufacturers and are therefor beyond the scope of this presentation except to say that we support the scheme in its entirety.
In practice, the complete elimination of halogens from medical waste is unlikely, if not impossible. Responsible incinerator manufacturers therefor utilize a range of technical options to destroy dioxins and furans.
Dioxins can be eliminated by destroying the benzol compounds at high temperature in the secondary chamber of the incinerator. This can only be effective if the design of the incinerator ensures
· thorough mixing of the air supply and the combustion gases,
· high secondary combustion temperatures above 1000°C,
· high excess air quantities – typically stochiometric plus 100%,
· and sufficient retention time – more than 1 second.
All of the above are inter-related. If, for instance turbulence is insufficient to ensure thorough mixing it may be necessary to increase the retention time or the temperature. For this reason, some authorities are inclined to adopt a “belt and braces” attitude and stipulate more severe operating requirements than those stated above.
When the benzol compounds have been reduced to carbon dioxide, the halogen is released and can be caught and neutralized in a dry or a wet scrubber. The neutralization usually produces a salt that is caught in the wet scrubber or in a dust collector.
A more modern system involves the prevention of dioxin formation by early entrapment of the halogens. A sophisticated loading system and hearth arrangement causes early volatiles to come into intimate contact with partly burnt waste and ash in particular. The ash has a high affinity for acidic compounds such as HCl. The relatively low ash content of the plastics in modern hospital waste reduces the effectiveness of the ash. Nevertheless, an appreciable amount of the halogen can be absorbed.
Thereafter a hot gas, in chamber system neutralizes the remainder of the halogen (and SOx) before the gases leave the incinerator. The concept depends in some measure on the fact that the formation of dioxins is not instantaneous and it is possible to neutralize chlorine more rapidly than it will form dioxin.
Neutralization of acid gases in the incinerator avoids the possibility of “secondary” dioxin formation in flues or the dust collector.
Conclusions.
· Some Dioxins and some Furans are cytotoxic.
· Not all Dioxins and Furans are cytotoxic.
· The majority of Dioxins and Furans are NOT cytotoxic.
· Many of the cytotoxic dioxins have very low TEF ratings.
· In the absence of Halogens (Chlorine & Fluorine), cytotoxics cannot be formed.
· Early neutralization of halogens minimizes the formation of Dioxins and Furans.
· If Dioxins or Furans are formed, a good quality, high tech incinerator fitted with a dry neutralization and dust filtration system will eliminate them.
Produced with the assistance of
MACROtechNOLOGY
Brian Thomson
MACROtech CC
Phone : 433 2013
Fax : 433 2013
Cell : 083 409 7925
April 03