Dr. Schwartz letter of on tire burning for fuel.

January 21, 1998


Mr. Daniel Pennington, Chair
Mr. Robert Frazee, Vice-chair
Mr. Wesley Chesbro
Ms. Janet Gotch
Mr. Paul Relis
Mr. Steven Jones
California Integrated Waste Management Board 8800 Cal Center Drive
Sacramento, California 95826


Dear Board Members:

It has come to my attention that the Board has sent my report Domestic Markets for California's Used and Waste Tires out for review in preparation for your January 28th meeting, at which you will reconsider Resolution 97-425. As I will not be attending that meeting, I wish to submit the following statement on the use of waste tires as fuel. In particular, I address the statement in the Board's findings supporting Resolution 97-425 (September 30, 1997) that "...analyses of emissions data as conducted by Dames & Moore, Carnot, and other entities, have found that no statistically significant increase in risk occurs..." I state that the term "no statistically significant increase" conveys the impression to the lay public that burning tires in cement kilns is safe. That interpretation is inaccurate. On the contrary, there is no scientific basis for concluding that burning waste tires in cement kilns is safe .


1. Test Burn Results
In Section II.C. of my report, I reviewed test burns at four California cement kilns and reported the percentage changes in several important types of toxic emissions that are on the Toxic Hot Spots list. These numbers are calculated directly from the test results and do not involve any interpretation. Here are the numbers from the report.
Dioxins and furans showed increases of between 53% and 100% in four tests; polycyclic aromatic hydrocarbons (PAHs) increased in three tests (between 296% and 2230%) but decreased by 68% in a fourth test; lead emissions increased in three tests, by 59%, 388%, and 475%, respectively, and decreased in one test, by 94%; hexavalent chromium increased in one test by 727%, and decreased in two tests by 36% and 87%, respectively.


2. Risk Assessment
In my discussion of risk assessment (Section II.C.), I quoted from the risk ssessment handbook published by the California Air Pollution Control Officers (CAPCOA); this is the officially authorized source for conducting risk assessment under California's Toxic Hot Spots Legislation. The introduction to the handbook contains the following statements about the "uncertainties" (i.e., flaws) in the risk assessment process:


2.1) "Effects of exposure to more than one carcinogen or toxicant are also not quantified in the risk assessment. Many examples of additivity or synergism (effects greater than additive) are known" (CAPCOA, 1993; p. I-3).


2.2) "Additionally, there may be chemicals which pose health risks but are not considered in a given risk assessment for a number of reasons, including lack of information on toxicity" (CAPCOA, 1993; p. I-3).


2.3) "The estimates of cancer potency in humans contain many sources of uncertainty. . . . Differences in these factors . . . cannot be easily quantified and incorporated into risk assessment . . . . Other uncertainties arise in the assumptions underlying the dose-response model used." (CAPCOA, 1993; p. I-4).


Statements 2.1 and 2.2 mean that science cannot tell us how much is left out of the risk assessment model. The risk assessment could be estimating only a small fraction of the total risk because of lack of knowledge of the causal mechanisms of the health effects (the dose- response functions).
When risk assessors or agencies that use risk assessment tell us that the assumptions in a risk assessment model are conservative, they are referring only to that fraction of the risks that are included in the model. However, the part that is left out (not known) could cause an enormous underestimate of the true risks.


3. Virtually nothing is known about the dose-response functions for important categories of health effects, particularly disruptions to the hormone systems of humans, which could produce life long damage in developing infants. Also, virtually nothing is known about the health effects caused by combinations of toxic chemicals that are emitted when burning tires (see items 2.1 and 2.2 above). Without such scientific knowledge, and because some toxic pollutants increase from burning tires, there is no scientific basis for the Board to conclude that burning waste tires in cement kilns is safe.


4. The Board's finding in support of Resolution 97-425 that ""...analyses of emissions data as conducted by Dames & Moore, Carnot, and other entities, have found that no statistically significant increase in risk occurs;..." may be technically accurate but it is deceptive. To researchers, a finding of no statistically significant difference means something very different than it does to the lay public. Researchers know that a finding of "no difference" can occur by chance when, in fact, there is a difference; they know it can be also be an artifact of the way data were defined or analyzed. To the lay public, the statement of "no statistically significant increase in risk" from burning waste tires suggests that it is safe to do so. This interpretation is incorrect. A statistical test using a flawed risk assessment model with highly variable (and suspect) emissions data, provides absolutely no scientific basis for concluding that burning waste tires is safe.



Concluding Comment.


In conclusion, it is clear that the Board's Resolution promoting burning waste tires in cement kilns cannot be supported by scientific evidence that it is safe to do so.
It is likely that an increase in the use of waste tires as fuel will be damaging to the public's health and well being.


Sincerely yours,
Seymour I. Schwartz
Professor, Environmental Science and Policy (UC Davis)


cc: Senator Byron Sher
Assemblymember Debra Bowen
Richard Toshiyuki Drury, Communities for a Better Environment
Leslie Fowler, West Valley Citizens Air Watch
Bonnie Holmes, Sierra Club