HWF NOTES ©
A REVIEW OF DIOXIN EMISSIONS AND CEMENT KILNS
Jim Woodford and David Gossman
Brief Historical Perspective Related to Dioxin Health Risk Awareness
Dioxins first began to gain notoriety in the United States, from a public perception point of view, as a byproduct from the manufacture of a defoliant widely used in Vietnam known as Agent Orange. Some returning U.S. pilots and soldiers linked their adverse health effects to exposure to Agent Orange. Then in 1976, a chemical factory explosion in Seveso, Italy exposed thousands of people to high doses of dioxins. Residents were found to contain 10,000 times the typical human tissue concentration of five to six parts per trillion (ppt). Had dioxin been as toxic as laboratory studies predicted, the entire population would have been devastated. As it turns out, the adverse health effects from this exposure was primarily a condition known as chloracne.
It is of significant interest to note that there were children in Seveso, Italy that were exposed to a level of dioxin which was three times the amount, relative to their body weights, that would kill a guinea pig. These children, however, did not die and their chloracne conditions eventually cleared up, leaving some minor scarring. Fifteen years later, the population reportedly exhibits no increased health problems.
Times Beach, Missouri and the Initiation of a USEPA Dioxin Toxicity Reassessment
Then in late 1982 and early 1983, the U.S. Government permanently evacuated all 2,240 plus residents of Times Beach, Missouri as a result of dioxin contaminated oil having been previously spread on many of the surrounding dirt roads. But even though the US Government spent approximately $40 billion to evacuate the town in an effort to protect the citizens, in an ABC TV news presentation on the prime time show, 20/20, a reporter and his camera crew were allowed to film government investigators wearing "moon suits" to take soil samples, while the anchor man and his crew walked around in normal dress.
Finally, in 1992, the EPA under then Administrator William Reilly, initiated a review of EPA's dioxin policy as a result of scientific studies that were indicating that dioxin was "no riskier than spending a week sunbathing." An EPA scientist, largely responsible for the Times Beach evacuation decision (Dr. Vernon Houk) had revisited that decision and decided that the evacuation had been a highly conservative over-reaction and unnecessary. The World Health Organization came out in support of the revised view of dioxins by suggesting a new limit on "safe" daily intake of dioxins that was 1600 times greater than recommended by the EPA. That was 1992.
Underscoring the unknowns in determining dioxin toxicity, the EPA Administrator who took William Reilly's place, Carol Browner, is reportedly giving indications about the data from the Reilly initiated study that dioxin is even more toxic than originally thought. Many scientists who have seen the soon-to-be-released study say that the review/reassessment does in fact support the 1992 reason for initiating the study, which was that dioxin is less toxic than originally thought, contrary to some of the preliminary unofficial press leaks. It is frustrating and unfortunate that two entirely different opinions can be generated from the same study, but it emphasizes the uncertainty of risk assessments. Given that risk assessment is a mathematical exercise, and that there are so many unknowns and assumptions involved in the process, slightly different assumptions can result in very different risk assessment conclusions. What compounds this particular regulatory situation, however, is the anti-combustion attitude and agenda of EPA Administrator Carol Browner. This attitude was evident when she headed the Florida Department of Environmental Resources, and it seems rather clear that she is trying desperately to interject this biased agenda into the existing U.S. combustion regulations.
Cement Kilns and Dioxins
Prior to the William Reilly decision to reassess dioxin toxicity, the boiler and industrial furnace (BIF) rules were in the making from before May 6, 1987 when the BIF rules were first proposed, until after February 21, 1991 when the BIF rules were finally promulgated. The BIF rules were health based and compliance provided estimated protection from the likelihood of cancer to less than 1 in 100,000. Dioxin testing was required if stack emission hydrocarbons were above 20 ppm, if dioxin containing wastes were to be burned, or if the inlet temperature to the air pollution control device for the kiln fell within the temperature range of 450F - 750F. This testing was for the purpose of quantifying dioxin emissions. The BIF rules were at least five years in the making before promulgation, and then experienced at least two years of the learning curve and regulatory addendum when the new EPA Administrator, Carol Browner (appointed approximately one year earlier) announced her Hazardous Waste Reduction and Combustion Strategy on May 18, 1993. This new combustion strategy ignored the health risk provisions of BIF, which took over five years to develop, and sought to impose stringent dioxin standards on cement kilns based upon municipal waste combustors, a technology completely unrelated to that of cement kilns. The proposed standard was 30 ng/dscm (based on the sum of all tetra through octa dioxin and furan cogeners). This move was controversial, particularly since these proposed standards had not received the required public input. Consequently, under threat of a lawsuit, Administrator Browner backed off from immediate implementation of the proposed standard.
Within just a few months of this action, various conference attendees began to hear about the workings of an EPA proclaimed dynamic document that was being called CETRED, short for Combustion Emissions Technical Resource Document, which was intended to be a revised/new approach to dioxins and particulate matter incorporating EPA's maximum achievable control technology methodologies. This approach entails looking at the best 12% of a given technology and then setting standards according to this pronouncement of what has been deemed the maximum achievable control technology, congressionally intended to be based upon what is actually happening within a given technology/industry. This document was released in June of 1994. Rather than provide a full blown critique of the document at this time, suffice it to say that the best 12% were not gleaned from each technology/industry, such as cement kilns and hazardous waste incinerators, but rather all waste combustors were lumped together. Plus, misrepresented European standards were presented as how limits and regulations can/should be established. EPA intends to use CETRED to impose dioxin TEQ standards of 0.12 ng/dscm @ 7% oxygen and total tetra-octa cogeners of 9.4 ng/dscm @ 7% oxygen, depending upon the chosen CETRED option. A reanalysis of the corrected CETRED raw data base, by a qualified statistician, reveals that even these proposed limits are conservatively skewed. The proposed TEQ standard of 0.12 ng/dscm @ 7% oxygen becomes 0.442 ng/dscm and the total tetra-octa congeners of 9.4 ng/dscm @ 7% oxygen becomes 34.9 ng/dscm. But, even given the technical problems with CETRED, EPA is ignoring the five to seven years that went into developing a health based BIF standard, declared by EPA to be protective of human health and the environment, in order to impose a technology based standard based upon non-cement kiln technology assessment. In short, EPA intends to impose an ill-founded technology based standard over the BIF regulations that EPA spent years designing to be protective of human health and the environment.
Discussion of Dioxin Testing and Possible Formation Mechanism
Initial dioxin emissions testing for cement kilns centered around the requirements found in the BIF regulations. Since stack testing results were required by the twenty-first of August, 1992, the bulk of the current cement kiln dioxin testing data base was accomplished in 1992. If required, BIF dioxin testing was to be used as part of a health risk assessment. With the exception of perhaps one cement kiln out of the 22 kilns at 15 different locations that did test for dioxins, all were in compliance with the health based BIF regulations. While there have been many points of contention concerning the technical practicality and implementableness of the BIF regulations, the health based limitations have not been a point of contention.
Dioxin formation mechanisms in cement kilns are not clear at this time. There does appear to be some type of dioxin emission relationship with temperature, as evidenced by data introduced in at least three presentations at the 1994 Air & Waste Management Association BIF conference which was held in Kansas City, Missouri. EPA clearly believes there is a temperature relationship as evidenced by the dioxin testing requirements in the BIF regulations for kilns with air pollution control device (APCD) temperatures within the range of 450F to 750F. However, beyond this basic temperature relationship assumption there is little definitive data on dioxin formation mechanisms in cement kilns.
With the increased interest in dioxin emissions, more and more dioxin emissions test data is becoming available. One cement manufacturer has collected test data which suggests that the use of a spray system just prior to the APCD resulted in reduced dioxin concentrations in stack emissions. Another cement kiln conducted dioxin testing in order to experiment with temperature reduction in the APCD, only to find that this had no effect whatsoever on dioxin emissions. A third cement manufacturer discovered that dioxin concentrations going into the inlet to the APCD were actually higher than that found in stack emissions. At first pass, this data might appear confusing, but when differences between cement kilns are taken into account, perhaps this data suggests that there is some type of destruction mechanism associated with some APCD systems. It would not be unreasonable to speculate on the role of increased alkalinity. The data does suggest that APCD temperature may not be as directly related to dioxin formation as what is currently thought by EPA. Another set of cement kiln dioxin testing suggests that dioxins are formed before emissions ever actually reach the APCD. Evidence for this comes from the comparison of dioxin emission concentrations right after the chain section in the kiln was revamped to dioxin emission concentrations when the chain section was thoroughly worn and nearing replacement time. The concentrations increased from when the chain section was new to when the chain section was well worn. Comparing the two extremes provided an opportunity to investigate the affect of a longer heat exchange zone within the kiln. Preliminary indications are that the longer heat exchange zone promoted the formation of dioxins. This occurred before the emission gases ever reached the APCD.
The data from these test situations indicates that there is probably a temperature relationship associated with dioxin formation in cement kilns, however it appears that the effect of temperature on dioxin formation may occur within the cement kiln rather than in the APCD as currently promoted by EPA. This same kiln has successfully reduced stack emission hydrocarbon concentrations by changing to a lower kerogen (source of hydrocarbons) containing raw material and while dioxin concentrations have been reduced, the reduction has not been proportional to the reduction in hydrocarbon input into the kiln. It is not totally illogical to assume a direct relationship between hydrocarbons that enter the kiln with the raw feed and the formation of dioxins in cement kilns, however it is of additionally significant interest to note that the cement kiln with the highest concentration of stack emission hydrocarbons (from rich kerogen bearing raw materials and consequently not combustion related) does not have the highest dioxin emission concentrations within the highly tested universe of hazardous waste burning cement kilns. While not conclusive, the test data discussed here strongly indicates a different temperature relationship associated with dioxin formation in cement kilns than that currently promoted by EPA, yet the hydrocarbon concentration in some raw materials vs. dioxin formation data also confirms that the specific dioxin formation mechanisms are not fully understood.
In the USEPA document CETRED, referenced earlier in this report, dioxin formation mechanism discussions include the role of oxygen, carbon monoxide, hydrocarbons, hydrogen chloride and even fly ash. This discussion is almost exclusively based upon the data base that has been collected for municipal waste combustors. No direct relationship has been demonstrated for any of these parameters in cement kilns. The dioxin levels emitted from hazardous waste burning cement kilns in the United States are protective of human health and the environment according to the boiler and industrial furnace regulations; regulations that include the extremely conservative approach of the maximally exposed individual (MEI). This hypothetical MEI is assumed to be exposed to worst case emissions for seventy years but must exhibit no greater risk of cancer than one person in 100,000 people. It is difficult to imagine a more conservative estimate than this. The issue of dioxins will most probably never disappear, but at what point and at what cost are we safe enough? The current data suggests we are already there.
According to G.W. Gribble, in a recent issue of Environmental Science & Technology, two research groups have concluded that forest and brush fires are major sources of PCDDs. It has been estimated the annually, on average, as much as 60 kilograms of PCDDs are produced in Canadian forest fires alone. By some estimates, this is approximately 10 times more than the amount formed in the 1976 Seveso Italy incident. There were, of course, lightening induced "natural" forest fires even before mankind harnessed fire. Consequently, dioxins have been around for a very long time. While we don't have to be glad about the ubiquitous nature of dioxins, mankind has clearly co-existed with dioxins for thousands of years. Dioxin production from cement manufacturing is hardly a drop in a bucket compared to naturally occurring sources. A tremendous amount of time and money has been spent by EPA and industry to get a handle on dioxins and it seems that the conclusion can readily be made that cement kilns are not major emitters of dioxins and that the health based dioxins considerations, found in the boiler and industrial furnace regulations, are truly protective of human health and the environment.