Each and Every Exposure Opinion Rejected

A federal court recently excluded the specific causation opinions of a plaintiff's expert who asserted the defendant was liable in an asbestos case under a version of the “each and every exposure” theory. See Comardelle v. Pennsylvania General Ins. Co., No. 13-6555 (E.D. La., 1/05/15).

Plaintiffs alleged that decedent was exposed to asbestos and asbestos-containing products manufactured, distributed, and sold by defendants during the course of his employment from 1963 through 1979.  As a result of these exposures, the decedent allegedly contracted mesothelioma, which was first diagnosed in approximately September, 2013.

Among a myriad of other claims, plaintiffs alleged that he was exposed to asbestos-containing coatings, sealants, and mastics manufactured, distributed, and sold by Amchem, including an adhesive called Benjamin Foster.  Plaintiffs proposed to call Dr. Samuel P. Hammar as an expert witness to opine that Benjamin Foster was a substantial contributing factor to the development of the mesothelioma. Amchem moved to exclude or limit this specific causation opinion. Specifically, Amchem argued that Hammar's testimony was a version of the “every exposure” theory opinion, not allowable under Fed. R. Evid. 702 and Daubert v. Merrell Dow Pharms, Inc., 509 U.S. 579 (U.S. 1993).  Rule 702 of the Federal Rules of Evidence governs the admissibility of expert witness testimony. As readers know, Rule 702 provides:

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:
(a) the expert's scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied the principles and methods to the facts of the case.


To qualify as an expert, the witness must have such knowledge or experience in the field or calling as to make it appear that his opinion or inference will probably aid the trier in his search for truth. See United States v. Hicks, 389 F.3d 514, 524 (5th Cir. 2004). Additionally, Rule 702 states that an expert may be qualified based on "knowledge, skill, experience, training, or education." Hicks, 389 F.3d at 524; see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 147 (1999) (discussing witnesses whose expertise is based purely on experience).  A district court should refuse to allow an expert witness to testify if it finds that the witness is not qualified to testify in a particular field or on a given subject. Huss v. Gayden, 571 F.3d 442, 452 (5th Cir. 2009).

The U.S. Supreme Court's decision in Daubert provides the basic analytical framework for determining whether expert testimony is admissible under Rule 702.  See Pipitone v. Biomatrix, Inc., 288 F.3d 239, 243 (5th Cir. 2002). A number of nonexclusive factors may be relevant to the reliability inquiry, including: (1) whether the technique has been tested, (2) whether the technique has been subjected to peer review and publication, (3) the potential error rate, (4) the existence and maintenance of standards controlling the technique's operation, and (5) whether the technique is generally accepted in the relevant scientific community. Burleson, 393 F.3d at 584. The reliability inquiry must remain flexible, however, as "not every Daubert factor will be applicable in every situation; and a court has discretion to consider other factors it deems relevant." Guy v. Crown Equip. Corp., 394 F.3d 320, 325 (5th Cir. 2004); see Runnels v. Tex. Children's Hosp. Select Plan, 167 F. App'x 377, 381 (5th Cir. 2006). 

In a number of cases, plaintiffs and their experts have advanced the argument that every exposure to asbestos is a factor in producing their illness. See Joseph Sanders, The "Every Exposure" Cases and the Beginning of the Asbestos Endgame, 88 Tul. L. Rev. 1153, 1157 (2014). As summarized by the courts addressing the admissibility of such opinions, the "every exposure" theory "posits that any exposure to asbestos fibers whatsoever constitutes an underlying cause of injury to the individual exposed." Krik v. Crane Co., No. 10-7435, 2014 WL 7330901, at *2 (N.D. Ill. Dec. 22, 2014); see also Davidson v. Ga. Pac. LLC, No. 12-1463, 2014 WL 3510268, at *2 (W.D. La. July 14, 2014).

Dr. Hammar's proposed specific causation testimony here was an example of this "every exposure" theory. In his expert report, Dr. Hammar opined that "all asbestos fibers inhaled by an individual that reach the target organ have the potential to contribute to the development of lung cancer, mesothelioma, and other asbestos-related diseases." At his deposition, he went further and opined that "all of the exposures that that individual had who developed mesothelioma, all of those would have contributed to cause his mesothelioma." Accordingly, Dr. Hammar opined based on this "every exposure" theory that if Comardelle was exposed to asbestos released from Amchem or Benjamin Foster adhesives, those exposures would have been a substantial contributing cause of his disease.

Amchem then moved to exclude Dr. Hammar's testimony that exposure to its product was a substantial factor in causing Comardelle's mesothelioma. According to Amchem, this "every exposure" theory opinion did not pass muster under Rule 702. Amchem criticized as wholly unsupported Dr. Hammar's leap from the general causation premise that every asbestos exposure increases the risk of mesothelioma, to the specific causation opinion that Comardelle's exposure to this product necessarily caused or contributed to his mesothelioma. Amchem also faulted Dr. Hammar for failing to consider any facts or data specific to Comardelle's exposure to this particular product.

The court noted several recent "every exposure" decisions in other courts.  In Smith v. Ford Motor Co., the district court excluded Dr. Hammar's opinion that a plaintiff's exposure to brake dust caused his mesothelioma because "each and every exposure to asbestos by a human being who is later afflicted with mesothelioma, contributed to the formation of the disease." No. 08-630, 2013 WL 214378, at *1 (D. Utah Jan. 18, 2013). The Smith court held that opinion to be inadmissible and agreed with the growing number of published opinions from other courts that have reached a similar result: that the every exposure theory as offered as a basis for legal liability is inadmissible speculation that is devoid of responsible scientific support. Accord Anderson v. Ford Motor Co., 950 F. Supp. 2d 1217 (D. Utah 2013).

In Davidson v. Georgia Pacific LLC, the district court likewise rejected a causation opinion based on the "every exposure" theory, concluding that the theory is not testable and consequently cannot have an error rate, thus failing to satisfy two Daubert factors. 2014 WL 3510268, at *5. The court also faulted the expert for failing to rely on any data that would show that any particular defendant's product actually caused plaintiff to develop mesothelioma.

The court agreed with Amchem that Dr. Hammar's proposed specific causation opinions in this case were unreliable and inadmissible. Although there may be no known safe level of asbestos exposure, this does not support Dr. Hammar's leap to the conclusion that therefore every exposure a plaintiff had to asbestos must have been a substantial contributing cause of his mesothelioma. This kind of blanket specific causation opinion was not based on or tied to the specific facts and circumstances of any of Comardelle's exposures to asbestos and it ignored any differences or nuances of duration, concentration, exposure, and the properties of the fibers to which he may have been exposed.

Instead of explaining how Dr. Hammar could reliably opine that Benjamin Foster was a cause of Comardelle's mesothelioma, plaintiffs referred cursorily to a broad array of cases, studies, and regulatory materials. But none of those citations plugged the impermissible gap in Dr. Hammar's reasoning from the general causation proposition that exposure to asbestos increases the risk of mesothelioma, to the specific causation opinion that in this case Comardelle's exposure to Benjamin Foster  was a cause of his mesothelioma giving rise to liability. See, e.g., Anderson, 950 F. Supp. 2d at 1225 (excluding testimony despite plaintiff's citation to numerous scholarly articles and scientific studies because those materials were not specific to the type of exposure).

Accordingly, the court concluded that Dr. Hammar's specific causation opinions as to Benjamin Foster (and all other exposures at issue in this case), were an unreliable product of the "every exposure theory" and must be excluded.

 

Texas Supreme Court Offers Causation Guidance in Mesothelioma Cases

The Texas Supreme Court ruled that a defendant will not have to pay a $12 million verdict in an asbestos case because there was inadequate proof the company’s products actually caused the alleged injury. See Bostic, et al. v. Georgia-Pacific Corp., No. 10-0775 (Texas 7/11/14).

In Borg-Warner Corp. v. Flores, 232 S.W.3d 765 (Tex. 2007), the court had discussed the standards imposed by Texas law for establishing causation in asbestos-disease cases. Flores had concerned a plaintiff suffering from asbestosis. This case involved mesothelioma, and the court held that the standard of substantial factor causation recognized in Flores also applied to mesothelioma cases.  The court did not impose a strict but-for causation standard, but held that the plaintiffs had failed to offer legally sufficient evidence of causation, and accordingly it affirmed the lower court's judgment.

Under section 431 of the Restatement Second of Torts, the Texas court had held that to establish causation in fact the plaintiff must prove that the defendant’s product was a substantial factor in causing the disease, and that mere proof that the plaintiff was exposed to “some” respirable fibers traceable to the defendant was insufficient. The word substantial is used to denote the fact that the defendant’s conduct has such an effect in producing the harm as to lead reasonable persons to regard it as a cause, using that word in the sense of responsibility.  Proof of mere frequency, regularity, and proximity of potential exposure to asbestos (sufficient in some states) is in Texas
necessary but not sufficient, as it provides none of the quantitative information necessary to support causation under Texas law.  While the plaintiff was not required to establish causation with “mathematical precision,” the court clearly required defendant-specific evidence relating to the approximate dose to which the plaintiff was exposed, coupled with evidence that the dose was a substantial factor in causing the asbestos-related disease.

In rejecting a standard that “some” exposure would suffice, the court recognized that most chemically induced adverse health effects clearly demonstrate thresholds; so, there must be reasonable evidence that the exposure was of sufficient magnitude to exceed the threshold before a likelihood of causation can be inferred. Plaintiffs urged that the standards established in Flores were not applicable in a mesothelioma case because relatively smaller quantities of asbestos can result in mesothelioma.  The court concluded that the Flores framework for reviewing the legal sufficiency of causation evidence lent itself to both types of cases. Even in mesothelioma cases proof of “some exposure” or “any exposure” alone will not suffice to establish causation. While the experts in this case testified that smaller amounts of asbestos exposure can result in mesothelioma, that fact alone does not merit a different analysis. With both asbestosis and  mesothelioma, the likelihood of contracting the disease increases with the dose. 

The court noted that If any exposure at all were sufficient to cause mesothelioma, everyone would suffer from it or at least be at serious risk of contracting the disease. Everyone is exposed to asbestos in the ambient air; it is plentiful in the environment, especially if you’re a typical urban dweller.  Plaintiff's expert confirmed that we all have some asbestos in our lungs, but that background levels are sufficiently low that they do not cause disease; instead, multiples of fibers many times over were required to cause mesothelioma.

More fundamentally, if the court were to adopt a less demanding standard for mesothelioma cases
and accept that any exposure to asbestos is sufficient to establish liability, the result essentially
would be not just strict liability but absolute liability against any company whose asbestos-containing product crossed paths with the plaintiff throughout his entire lifetime. However, exposure does not always result in disease. The court said it had never embraced the concept of industry-wide liability on grounds that proof of causation might be difficult. 

If an “any exposure” theory of liability was accepted for mesothelioma cases because science
has so far been unable to establish the precise dose below which the risk of disease disappears, the same theory would arguably apply to all carcinogens. The any exposure theory effectively accepts that a failure of science to determine the maximum safe dose of a toxin necessarily means that every exposure, regardless of amount, is a substantial factor in causing the plaintiff’s illness. This approach negates the plaintiff’s burden to prove causation by a preponderance of the evidence.

Further, said the court, there are cases where a plaintiff’s exposure to asbestos can be tied to a defendant, but that exposure is minuscule as compared to the exposure resulting from other sources. Proof of any exposure at all from a defendant should not end the inquiry and result in automatic liability. The Restatement Third of Torts provides that when an actor’s negligent conduct constitutes only a trivial contribution to a causal set that is a factual cause of harm, the harm is not within the scope of the actor’s liability.

The any exposure theory is also illogical in mesothelioma cases, where a small exposure can
result in disease, because it posits that any exposure from a defendant above background levels
could impose liability, while the background level of asbestos should be ignored. But the expert
testimony in this case was undisputed that the background level varies considerably from location
to location. The court could not see how the theory can, as a matter of logic, exclude higher than normal background levels as the cause of the plaintiff’s disease, but accept that any exposure from an individual defendant, no matter how small, should be accepted as a cause in fact of the disease. Under plaintiffs'  any exposure theory a background dose of 20 does not cause cancer, but a defendant’s dose of 2 plus a background dose of 5 somehow does.

Expanding on the notion of substantial factor, the court noted that in the Havner decision it had enunciated principles in toxic tort cases that (1) expert testimony of causation must be scientifically reliable, (2) the plaintiff must establish the elements of his claim by a preponderance of the evidence, and (3) where direct evidence of causation is lacking, scientifically reliable evidence in the form of epidemiological studies showing that the defendant’s product more than doubled the plaintiff’s risk of injury appropriately corresponds to the legal standard of proof by a preponderance of the evidence. These principles, said the court, should apply to asbestos cases. As to the
availability of scientific studies, asbestos-related disease has been researched for many decades and the population of potentially affected persons numbers in the millions. A more than doubling of the risk must be shown through reliable expert testimony that is based on epidemiological studies or similarly reliable scientific testimony. 

Multiple-exposure cases raise the issues of how the finder of fact should consider exposure
from sources other than the defendant, what proof might be required as to those other sources, and who has the burden of proof regarding those other sources. These are difficult questions, said the court, but a plaintiff should be required to establish more than a doubling of the risk attributable to the defendant’s product;  the court did not require a plaintiff to track down every possible source of asbestos exposure and disprove that those other exposures caused the disease. In multiple-exposure cases few if any plaintiffs could ever establish which particular fibers from which particular defendant caused the disease.  However, when evidence is introduced of exposure from other defendants or other sources, mere proof of more than a doubling of the risk may not suffice to establish substantial factor causation. Suppose, hypothesized the court, a plaintiff shows that his exposure to a particular defendant’s product more than doubled his chances of contracting a disease, but the evidence at trial also established that another source of the substance increased the chances by a factor of 10,000. In this circumstance, a trier of fact or a court reviewing the sufficiency of the evidence should be allowed to conclude that the defendant’s product was not a substantial factor in causing the disease.

 

State Supreme Court Reaffirms Death of Single Fiber Theory

The Pennsylvania Supreme Court recently reaffirmed several important principles in toxic tort exposure, specifically asbestos, cases. See Howard, et al. v. A.W. Chesterton Co., et al., Nos. 48 EAP 2012, 49 EAP 2012 and 50 EAP 2012 (Pa. Sept. 26,2013).

Plaintiff alleged personal injury from exposure to dust from defendant's asbestos-containing products. The common pleas court awarded summary judgment in favor of defendants/appellants, reasoning that plaintiff's deposition testimony failed to establish that he breathed asbestos-containing dust from the products manufactured or distributed by appellants, and the court also found expert affidavits submitted by plaintiffs represented insufficient proof of actual exposure.  On appeal, the Superior Court reversed on the basis that dust may have been invisible to the naked eye, and the expert affidavits were sufficient to establish exposure to dust which was a substantial causal factor in plaintiff's injury.

The Supreme Court reversed the intermediate appeals court, and in so doing reaffirmed several key principles of state law:

--The theory that each and every exposure, no matter how small, is substantially causative of disease may not be relied upon as a basis to establish substantial-factor causation for diseases that are dose-responsive. See Betz v. Pneumo Abex, LLC, 44 A.3d 27, 55-58 (Pa. 2012). 

-- Relatedly, in cases involving dose-responsive diseases, expert witnesses may not ignore or refuse to consider dose as a factor in their opinions. See id.

-- Bare proof of some de minimus exposure to a defendant’s product is insufficient to establish substantial-factor causation for dose-responsive diseases. See Gregg v. V-J Auto Parts, Inc., 943 A.2d 216, 225-26 (Pa. 2007).

-- Relative to the testimony of an expert witness addressing substantial-factor causation in a dose-responsive disease case, some reasoned, individualized assessment of a plaintiff’s or decedent’s exposure history is necessary. See Betz, 44 A.3d at 55-58.

-- Summary judgment is an available vehicle to address cases in which only bare de minimus exposure can be demonstrated and where the basis for the experts testimony concerning substantial-factor causation is the any-exposure theory. See Betz, 44 A.3d at 55-58; Gregg, 943 A.2d at 227.

In an interesting procedural twist, during arguments before the Supreme Court, plaintiff conceded that the Superior Court had erred in its ruling -- an apparent attempt to have the Supreme Court not reiterate the points that some lower courts in the state inexplicably continued to not apply.  Nevertheless, in light of the intensely protracted nature of asbestos litigation, the Court decided to provide at least some limited guidance.  Indeed, as explained in detail in the unanimous decision in Betz, the any-exposure opinion is simply unsupportable both as a matter law and science.

 

(Note that my colleague Mark Behrens was involved in the amicus briefing on behalf of the Coalition for Litigation Justice.)

Medical Monitoring Claim Rejected in Rail Spill

The Sixth Circuit recently rejected the medical monitoring claims of a putative class of residents of a small Ohio town who alleged exposure to chemicals released after a CSX Transportation Inc. train accidentally derailed. Jonathan Hirsch et al. v. CSX Transportation Inc., No. 09-4548 (6th Cir. Sept. 8, 2011).

On October 10, 2007, thirty-one cars of a CSX train derailed and caught fire near the town of Painesville, Ohio. As a precaution, emergency personnel removed about 1,300 people from the surrounding half-mile radius. Most of what burned in this fire was non-toxic, but nine of the cars were carrying potentially hazardous materials. The plaintiffs claimed that 2,800 tons of burning material were sent into the surrounding atmosphere, and that, as a result, the level of dioxin in their town was significantly elevated.

While the fire was still burning, several residents of the town brought suit against CSX;  the district court did not allow the plaintiffs to pursue an independent cause of action for medical monitoring, but decided a court-supervised medical monitoring was available as an equitable remedy under Ohio law. See Wilson v. Brush Wellman, 817 N.E.2d 59, 63-65 (Ohio 2004); see also Day v. NLO, 851 F. Supp. 869, 880 (S.D. Ohio 1994).  Defendant then moved for summary judgment, which was granted. The district court held that the plaintiffs had failed to meet their burden to show that (1) the dioxin released into the air by the fire is a known cause of human disease; and (2) that the named plaintiffs were exposed to dioxin in an amount sufficient to cause a significantly increased risk of disease such that a reasonable physician would order medical monitoring. The plaintiffs timely appealed.

The court of appeals focused on the issues of causation and injury. Rather than traditional personal injuries, the alleged injuries consisted solely of the increased risk of—and corresponding cost of screening for—certain diseases that, according to plaintiffs, were more likely to occur as a result of the train crash. Assuming that Ohio would recognize such an injury, the remedy would be a medical monitoring program that would spare the Plaintiffs these expenses. But were plaintiffs actually at such an increased risk of disease that they were entitled to a medical monitoring program? Not every exposure, not every increased risk risk of disease warrants increased medical scrutiny. For the plaintiffs to prevail, there must be evidence that a reasonable physician would order medical monitoring for them.

Plaintiffs hired several experts to try to meet this burden. (No Daubert issue raised; the issue was sufficiency, not admissibility.). They offered a chemical engineer who tested the community for levels of dioxin. He assumed a normal background level of dioxin at 4 parts per trillion and took measurements around Painesville to compare with this baseline. His measurements
showed elevated levels near the crash site.  Plaintiffs had a chemist who speculated about train cargo, nature and amounts; then, a physicist who plotted the dispersion and concentration of the chemicals from the fire on a map for the purpose of showing which members of the community were exposed to what levels of dioxin. Then a medical doctor used this map to determine who in the community was likely exposed to levels of dioxin above what the EPA considers acceptable—levels at which the risk of cancer increases by "one case in one million exposed persons."

The court of appeals saw at least two problems with this offer.  One issue was the use of the regulatory level. The expert not only accepted the risk of one in a million as the threshold for monitoring, but appeared to have halved it. “One should be afforded the benefit of medical
monitoring, if one has sustained a dose equal to or in excess of 50% of the EPA maximum.” There was little explanation as to why he believed that reasonable physicians would order expensive and burdensome testing for such a small risk, but he explained he wanted "to err on the side of patient safety.”  However, a one-in-a-million chance is small. Indeed, it is proverbially small. If something has a one-in-a-million chance of causing cancer in an individual, then it will not cause cancer in 999,999. For some perspective, the National Safety Council estimates a person’s lifetime risk of dying in a motor vehicle accident as 1 in 88. The lifetime risk of dying in “air and space transport accidents” is roughly 1 in 7,000. The risk of being killed by lightning
is roughly 1 in 84,000, while the risk of being killed in a “fireworks discharge” stands at around 1 in 386,000. So, a small risk and no basis to say it called for medical monitoring.  Certainly the EPA didn't base its standard on any medical monitoring analysis.

Second, the doctor based based his assessment on the exposure map.  But the map was unreliable. The estimate of the total material burned was speculative. The expert admitted that “the fire temperature, particle size distribution, and fire area were not established.” And there were other sources of exposure not accounted for.

Plaintiffs thus alleged only a risk that bordered on legal insignificance, and failed to produce evidence establishing with any degree of certainty that they had even this hypothetical risk.

Summary judgment affirmed.

State Supreme Court Holds Causation Evidence Insufficient

The Vermont Supreme Court recently held that a plaintiff's evidence that exposure to benzene allegedly caused his cancer was insufficient to get to the jury.  Blanchard v. Goodyear Tire & Rubber Co.,  No. 2010-250 (Vt. 8/5/11).

Plaintiff was diagnosed with non-Hodgkin's lymphoma, and he attributed the onset of the disease to benzene exposure that allegedly occurred between 1968 and 1973 while he was a teenager playing on a ball field on the grounds of the former Goodyear rubber manufacturing plant. That  plant operated in Windsor, Vermont from 1936 to 1986. He sued, alleging that the field itself was polluted and that there was a gully in the outfield that transported foul-smelling and oily stormwater discharge away from the manufacturing plant.

Defendants moved for summary judgment. The lower court concluded that plaintiff was not entitled to present his case to a jury because he had provided insufficient evidence to support an inference that he had been exposed to benzene in any amount, let alone an amount that could have caused his illness, nor sufficient expert testimony sufficient to eliminate other potential causes of his disease. On appeal, plaintiff argued that his circumstantial evidence of causation was sufficient to present his case to the jury.

The state Supreme Court noted that the plaintiff could not survive the motion for summary judgment on his toxic tort claim unless he was able to point to evidence suggesting a probability, rather than a mere possibility, that (1) he was exposed to the specified chemical at a level that could have caused his physical condition (general causation); and (2) the exposure to that chemical did in fact result in the condition (specific causation).  In a toxic tort case, general causation addresses whether a substance is capable of causing a particular injury or condition in a population, while specific causation addresses whether a substance caused a particular individual's alleged injury. E.g., King v. Burlington Northern Santa Fe Ry. Co., 762 N.W.2d 24, 34 (Neb. 2009). General causation is typically shown through epidemiological studies, and plaintiffs in toxic exposure cases in Vermont generally must demonstrate specific causation by submitting evidence concerning the amount, duration, intensity, and frequency of exposure. Citing  Henricksen v. ConocoPhillips Co., 605 F. Supp. 2d 1142, 1157 (E.D. Wash. 2009) (citing several appellate court cases holding that experts testifying as to specific causation must pay careful attention to amount, intensity, and duration of exposure).

The court recognized that in some toxic tort cases it is impossible to quantify exposure with hard proof, such as the presence of the alleged toxic substance in the plaintiff's blood or tissue and the precise amount of the toxic substance to which an individual plaintiff was exposed. Plourde v. Gladstone, 190 F. Supp. 2d 708, 721 (D. Vt. 2002).  Therefore, expert testimony on toxic injuries may be admissible where dosage or exposure levels have been established through sufficient reliable circumstantial evidence. While it is not always necessary for a plaintiff to quantify exposure levels precisely, the courts generally preclude experts from testifying as to specific causation without having any some measurement or reasonable estimate of a  plaintiff's exposure to the allegedly harmful substance. Finally, a defendant's concession that its product contains a carcinogen, say benzene, does not excuse a plaintiff from having to show the benzene contained in defendant's product is capable of causing the illness at issue.

When direct evidence of the precise amount of exposure to a toxic substance is limited, some courts have allowed expert witnesses to use a differential diagnosis process as a method of proving specific causation. We have posted before about the mis-use and mischaracterization of this process.  Differential diagnosis is a scientific analysis entailing the weighing of relevant evidence, listing all likely explanations of the patient's observed symptoms or injury, then eliminating all but one.  Some courts have made the leap from allowing the process designed to arrive at a diagnosis (what disease caused the symptoms) to arrive at a cause (what substance caused the disease). However, said the state court, even the courts that do recognize differential diagnosis are reluctant to admit causation testimony based on a differential diagnosis where the proffered expert possesses only weak circumstantial evidence that some exposure occurred and makes insufficient effort to scientifically evaluate or estimate the degree of exposure or dosage. Also, and significantly, standing alone, the presence of a known risk factor is not a sufficient basis for ruling out idiopathic origin in a particular case, particularly where most cases of the disease have no known cause. In such cases, analysis beyond a differential diagnosis is required.

Here, plaintiff pointed to three bits of circumstantial evidence. First, he offered statements made by himself and boyhood friends concerning their alleged exposure to chemicals from the Goodyear plant when they were teenagers playing ball on a field adjoining the plant.  Second, plaintiff relied on the testimony of the project manager for an environmental firm hired by Goodyear in 2007 to conduct a site investigation in response to a clean-up agreement reached by Goodyear and the State of Vermont. The 2009 report stemming from the investigation listed contaminants of concern, including petroleum products containing benzene, that could have been released into the environment. Third, plaintiff relies upon the testimony of his two experts, who testified that occupational exposure to benzene is generally associated with a risk of non-Hodgkin's lymphoma, and that plaintiff's cancer was not caused by an immunodeficiency disorder, one of the known causes of that form of cancer.

That evidence "falls well short" of what plaintiff would be required to show in order to prevail in a jury trial. Indeed, if a jury were to find in favor of plaintiff on the evidence relied upon by plaintiff, said the court, "we would have to overturn the verdict." In the end, plaintiff's suspicion that his cancer was caused by exposure to benzene on the Goodyear ball field when he was a teenager was purely speculative. There was no way to know whether any benzene-containing product actually contaminated the ball field.  And there was no evidence indicating the amount or concentration of benzene that was present, even assuming some was. Nor was there any evidence indicating plaintiff's level of exposure to any benzene that may have been present on the field. Nor was plaintiff able to point to studies indicating a risk of cancer posed by exposure to limited amounts of benzene from petroleum products in an outside environment.  

Further, plaintiff could not rely upon differential diagnosis to overcome the complete lack of evidence as to the level of any exposure to benzene. A large percentage of cases of plaintiff's type of lymphoma are of unknown origin. Thus plaintiff's experts could not rule out all other causes, an essential part of the differential diagnosis.  E.g., Whiting v. Boston Edison Co., 891 F. Supp. 12, 21 n.41 (D. Mass. 1995) (concluding that differential diagnosis cannot be used to explain disease where 90% of cases of disease are of unknown origin).
 

Federal Court Grants Daubert Motion and Summary Judgment in Toxic Tort Cases

A federal court last week dismissed consolidated toxic tort suits brought against Alcoa Inc. and other defendants brought by employees of Lockheed Martin Corp. who claimed they were exposed to beryllium used in the manufacture of airplanes. Neal Parker et al. v. Brush Wellman Inc. et al., No. 04-cv-606; Timothy Berube et al. v. Brush Wellman Inc. et al., No. 08-cv-2725(N.D. Ga. 9/17/10).

The dozen plaintiffs in the cases were current or former employees of Lockheed Martin Corp.at its Marietta, Georgia plant site; plaintiffs alleged they had a variety of job responsibilities, time periods of employment, and work areas at the Lockheed facility. Lockheed’s Marietta Facility was purchased by the U.S. Government in 1942 and is leased and operated by Lockheed. Since 1952, Lockheed has produced the beryllium-containing C-130 Hercules airlifter, the C-5 Galaxy, the C-141 Starlifter, and the F/A-22 Raptor Air Dominance Fighter at its Marietta location. Each defendant was alleged to have manufactured component parts for Lockheed using copper-beryllium or aluminum-beryllium alloys.  Plaintiffs alleged that defendants failed to provide Lockheed with sufficient and accurate warnings pertaining to the beryllium contained in the manufactured products. Specifically, plaintiffs asserted a failure to warn claim, arguing that the warning materials that the defendants provided did not adequately communicate the health risks associated with the use of beryllium nor did they describe the methods that would reduce such risks.

Defendants filed a Daubert motion to exclude the testimony of Dr. John Martyny, plaintiffs' causation expert, and a companion motion for summary judgment. The Court ordered a Daubert hearing to clarify the evidentiary and factual background for the expert witness’s opinion and an evidentiary hearing regarding the motions to compel and summary judgment.

Since beryllium is generally recognized in the medical community as being able to cause the type of harm plaintiffs alleged –beryllium-related sickness– the Daubert analysis here focused on specific or individual causation to the plaintiffs, the plaintiff-specific questions: was plaintiff exposed to the toxin, was plaintiff exposed to enough of the toxin to cause the alleged injury, and did the toxin in fact cause the injury? The Eleventh Circuit has recognized that in order to carry
this causation burden in a toxic tort case, a plaintiff must demonstrate the levels of exposure that are hazardous to human beings as well as the plaintiff’s actual level of exposure to the defendant’s toxic substances before he or she may recover.

Here, the link between the expert’s opinion and the dose relationship was a key element of the analysis. Indeed, the hallmark of the science of toxic torts is the dose-response  relationship.  Exposure is only the opportunity for contact. Dose is what enters the body. While Dr. Marytny indicated, based on his experience and anecdotal evidence, that plaintiffs may have been exposed to beryllium at the plant, he did not indicate the level, frequency, duration or particle size of this exposure which would indicate the dose from these defendants’ products.  Importantly, Dr. Marytny did not produce any evidence that even a low-dose exposure resulted from defendants’ products. In fact, Dr. Martyny admitted that he could not opine as to the individual product or products that were the source of the alleged exposure.

Secondly, Dr. Martyny’s theory had not been appropriately tested.  The company itself did some sampling, and every air sample indicated that airborne beryllium concentrations were below the analytical reporting limit (<0.001 μg/sample) and thus also less than the OSHA PEL for beryllium.  Theoretically, defendants’ products could have been placed in an environmental chamber and the various machining procedures could have been reenacted to determine the particle production and size. While clearly this would not be as conclusive as personal sampling data for each plaintiff, this evidence would at least minimally indicate that bio-available beryllium from defendants’ products was possible, said the court.  But plaintiffs did no such testing.  Furthermore, no published studies documented levels of beryllium released by workers working with beryllium-aluminum in the aircraft industry.

Without such data, the expert's opinion merely assumed that plaintiffs’ injuries must have been caused by defendants’ products because the defendants produced  beryllium parts which were sold to Lockheed. However, nothing in his opinion linked these products to the alleged exposure of the plaintiffs nor ruled out other manufacturers’ products that were also present at the Marietta facility. 

Thus, the expert's opinion was excluded, and absent a reliable causation opinion, summary judgment was also appropriate.

The court the offered an alternative basis for the summary judgment on the failure to warn claim -- the sophisticated user doctrine. If a sophisticated user’s employees have knowledge that a particular risk of harm exists and yet allow the harm to occur, this knowledge may bar other employees’ claims against the product manufacturer. The supervising employees’ knowledge –the knowledge of the sophisticated user– can bar other employee’s claims against the product manufacturer. And the user’s knowledge does not need to encompass the precise, physical nature of the hazard presented by his use of the product; it is sufficient if he is aware generally that the use being made of the product is dangerous.

Here, Lockheed was a sophisticated user of beryllium alloys. Lockheed, as a part of the beryllium
industry, had as much access to information regarding beryllium safety as anyone else. For more than forty years, Lockheed  used the Department of Defense’s “Handbook for Metallic Materials and Elements for Aerospace Vehicle Structures” which provides guidelines for proper beryllium use. Lockheed issued its own “Safety and Industrial Hygiene Standard" which recognized that beryllium dust and vapors can cause respiratory problems. Lockheed recognized that it should order “medical monitoring” for those within the exposed worker population. The record made clear that the employer was a sophisticated user; summary judgment was appropriate on this basis as well.

California's Proposed "Green Chemistry" Regulations Move Forward

California's proposed "green chemistry" regulation took another step closer to completion last week, as the state Department of Toxic Substance Control (DTSC) submitted the draft regulations to begin the final official rulemaking process.  The public has until Nov. 1, 2010 to make comments.  Under state law passed in 2008, the regulations must be finalized before 2011.

As readers know from previous posts, "green chemistry" is the state's effort to require that chemical products be designed in such a way as to reduce the use or generation of hazardous substances and reduce health and environmental risks, with a clear emphasis on finding alternatives to "chemicals of concern."  Two bills passed in 2008 by the legislature mandated that DTSC develop regulations for identifying and prioritizing chemicals of concern, to create methods for analyzing alternatives to existing chemicals, and to create a mechanism for regulatory response, including possible restrictions or bans on certain chemicals.  The laws also created a Green Ribbon Science Panel to advise DTSC, and provided for a Chemical Information Clearinghouse that will make chemical risk information more accessible to the public.

Earlier in 2010, the agency released a draft Safer Consumer Product Alternatives regulation, then held public meetings and workshops and took written comments.  Last week, the final, slightly revised draft, was issued. DTSC’s regulations call for identifying and prioritizing chemicals in consumer products, for conducting an alternatives assessment, and then an appropriate  regulatory response.

The proposed regulations call for creation of a proposed initial list of Chemicals under Consideration by June 1, 2012, and, from that an eventual list of Priority Chemicals by July 1, 2012. Similarly, the agency is to create a proposed initial list of Products under Consideration (because they contain the relevant chemicals) by March 1, 2013, and eventually a final list of Priority Products by December 1, 2013. In making this determination, the regulations offer a long list of relevant factors, including usage, distribution, disposal and life cycle issues, use by sensitive sub-populations, and a host of toxicity parameters.  One thing for manufacturers to watch: it is unclear how the DTSC will weigh and balance these and other factors. Especially important will be the relative emphasis on realistic, feasible exposure scenarios and dose, as opposed to theoretical risks in the lab.  A second area of potential concern here is that while the proposed regulations include a fairly detailed (and likely lengthy) petition process to challenge regulatory response decisions, they apparently do not include a similar ready process to seek removal of a chemical or product from the priority lists.  Thus, manufacturers and relevant trade associations will have to closely monitor the draft/proposed lists and jump into the comment period before the lists are finalized. Food, drugs, and a few other products are exempt, but the potential list of "consumer products" is quite large.

In the second phase involving Alternative Assessments, product makers will have to provide what may become a quite complex and expensive assessment of potential alternatives to the chemical/product, including a look at hazards, potential exposures, and life cycle.  For example, if the lead of the assessment team works for the manufacturer, the Assessment must be reviewed and verified by an independent third-party consultant.  It is unclear what data DTSC will want to see here, including whether the agency will require additional, new toxicity testing of a product or an alternative.  This may be especially onerous for smaller companies, and for newer technologies (think nano?) in which the existing body of data may not be as robust. One area for companies to watch here is the protection, or lack thereof, of trade secret information.  Ingredients in a product, and possible alternatives that make the product safer, are often a key part of intellectual property, a competitive advantage.  The regulations purport to offer some trade secret protection, but it s not crystal clear how the DTSC will apply this principle.

After receiving the Alternative Assessment, the DTSC is to decide on the best method, if any, to mitigate paternal risks with the product, ranging from no further action to recalls and bans.

The regulations offer a good reminder to double-check company knowledge and comfort with the supply chain, components and agreements, risk sharing provisions, insurance coverage, etc.

Court Excludes Toxic Tort Causation Testimony

A federal court has excluded plaintiffs' expert testimony in litigation alleging personal injury and property damage from releases at a Midwest refinery.  Baker, et al. v. Chevron USA Inc., et al., No. 05-cv-00227 (S.D. Ohio Jan. 6, 2010). In the absence of necessary expert testimony, the claims were subject to summary judgment.

Plaintiffs in this case were residents of the villages of Hooven and Cleves, Ohio, who asserted claims for personal injury and property damage allegedly resulting from the Gulf Oil refinery, now owned by defendant Chevron USA.  Gulf operated a gasoline refinery which was situated on the eastern edge of Hooven from 1930 to 1985. Gulf also refined diesel fuel, jet fuel, and fuel oil at the refinery and operated an asphalt plant at this location. Gulf and Chevron merged in 1985, and Chevron closed the refinery in 1986.

Plaintiffs alleged that Gulf’s operation of the refinery resulted in the release of millions of gallons of gasoline and diesel fuel.  But these plaintiffs did not claim injuries resulting from groundwater contamination. Rather, they asserted injuries allegedly caused by air emissions from the refinery and, in particular, the benzene contained in those emissions. Benzene is ubiquitous in the ambient air and is a component or constituent of vehicle exhaust and cigarette smoke. In the petroleum industry, benzene is found in small amounts in gasoline.

For case management purposes, the matter was bifurcated between personal injury claimants and property damage claimants. The parties were permitted to select bellwether plaintiffs for each trial group. This opinion dealt with the claims of the bellwether personal injury claimants, and a key issue, as is often the case in toxic tort litigation, was causation.

Regarding their alleged benzene exposure, plaintiffs offered a three-step procedure. First, expert Dr. Cheremisinoff calculated a gross amount of benzene released from the refinery through emissions. Then, using those calculations, Dr. Rosenfeld, plaintiffs’ second expert, used an air flow model to calculate the cumulative dose of benzene to which each plaintiff was exposed. Third, using those dose estimates, a third expert, Dr. Dahlgren, submitted opinions that each plaintiff’s dose of benzene was sufficient to cause her illness. 

Chevron moved to exclude Dr. Dahlgren's opinions under Daubert, and for summary judgment contingent  upon the striking of  plaintiffs' causation evidence. The principal argument raised was that Dr. Dahlgren’s opinions were unreliable because there was an insufficient scientific or medical basis to conclude that the doses of benzene to which plaintiffs’ were exposed were large enough to have caused their illnesses. Relatedly, Chevron contended that there is an insufficient scientific or medical basis to conclude that benzene even causes some of the illnesses alleged. The Court held a hearing on Chevron’s Daubert motion during which Dr. Dahlgren and Chevron’s medical expert also testified.

In a toxic tort case, the plaintiff must present evidence of both general causation and specific causation. General causation establishes whether the substance or chemical at issue is capable of causing a particular injury or condition. Specific causation relates to whether the substance or chemical in fact caused this plaintiff’s medical condition. Without expert medical testimony on both general causation and specific causation, a plaintiff’s toxic tort claim will fail.

In this case, Dr. Dahlgren offered causation opinions based largely on epidemiological studies. (Epidemiology is the study of the incidence, distribution, and etiology of disease in human populations.) Epidemiology is usually considered highly probative evidence on general causation in toxic tort cases. The court may nonetheless exclude expert testimony based on epidemiological studies where the studies are insufficient, whether considered individually or collectively, to support the expert’s causation opinion. Nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert. A court may thus conclude that there is simply too great an analytical gap between the data and the opinion proffered.

A couple of parts of the court's detailed analysis are worth highlighting for readers of  MassTortDefense:

First, Dr. Dahlgren’s reliance on the “one-hit” or “no threshold” theory of causation in which exposure to one molecule of a cancer-causing agent has some finite possibility of causing a genetic mutation leading to cancer. The court noted that while the one-hit theory has been accepted for purposes of establishing regulatory safety standards, it has not been accepted as a reliable theory for causation under Daubert standards.  See Allen v. Pennsylvania Eng’g Corp., 102 F.3d 194, 199 (5th Cir. 1996) (“Scientific knowledge of the harmful level of exposure to a chemical, plus knowledge that the plaintiff was exposed to such quantities, are minimal facts necessary to sustain the plaintiffs’ burden in a toxic tort case.”); McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1240 (11th Cir. 2005) (holding that district court erred by not excluding plaintiff’s expert’s causation opinion because he neglected dose-response relationship); Henricksen v. ConocoPhillips Co., 605 F. Supp.2d 1142, 1162 (E.D. Wash. 2009) (excluding expert’s opinion pursuant to Daubert where “he presumed that exposure to benzene in gasoline can cause AML in any dose.”); National Bank of Commerce v. Associated Milk Producers, Inc., 22 F. Supp.2d 942, 961 (E.D.Ark. 1998), aff’d, 191 F.3d 858 (8th Cir. 1999); Sutera v. Perrier Group of Am., Inc., 986 F. Supp. 655, 667 (D. Mass.
1997). Moreover, since benzene is ubiquitous, causation under the one-hit theory could not be established because it would be just as likely that ambient benzene was the cause of plaintiffs’ asserted illnesses.

Second, the court noted that to the extent that Dr. Dahlgren relied on the evidence that plaintiffs were exposed to benzene in excess of regulatory levels, that is insufficient to make his opinions admissible. The mere fact that plaintiffs were exposed to benzene emissions in excess of mandated limits is insufficient to establish causation. Nelson v. Tennessee Gas Pipeline Co., 243 F.3d 244, 252-53 (6th Cir. 2001); David L. Eaton, Scientific Judgment and Toxic Torts- A Primer in Toxicology for Judges and Lawyers, 12 J.L. & Pol’y 5, 39 (2003) (“regulatory levels are of substantial value to public health agencies charged with ensuring the protection of the public health, but are of limited value in judging whether a particular exposure was a substantial contributing factor to a particular individual’s disease or illness.”). This is because regulatory agencies are charged with protecting public health and thus reasonably employ a lower threshold of proof in promulgating their regulations than is used in tort cases. Allen, 102 F.3d at 198.

Third, the court focused on the issue of the link between cited literature and the actual specific opinion given. The court recognized that an expert’s opinion does not have to be unequivocally supported by all epidemiological studies in order to be admissible under Daubert. But here, the opinions expressed in Dr. Dahlgren’s revised report were based "on a scattershot of studies and articles which superficially touch on each of the illnesses at issue." The expert had not differentiated the cases in any way and simply assumed that each reference supported his causation opinion on each and every illness. That clearly was not the case. Also, none of the cited studies supported an opinion that benzene can cause the illnesses from which plaintiffs suffer at the extremely low doses or exposures experienced in this case. Even if it is medically accepted that benzene can cause disease at high doses, Dr. Dahlgren could not cite any paper finding that the relevant low cumulative exposure significantly increases the risk of developing the injuries.

The court, therefore, found that the expert's causation opinions were not reliable under the standards enunciated by Daubert and, consequently, inadmissible. Without Dr. Dahlgren's testimony, the plaintiffs were unable to establish that their illnesses were caused by alleged emissions from the plant, the court observed, and so granted Chevron's motion for summary judgment on all four bellwether personal injury plaintiffs.
 

Summary Judgment In Benzene Case: Failure To Prove Dose

A federal court has granted summary judgment in a toxic tort suit in which plaintiff alleged he contracted a bone disease because of his long-term exposure to trace amounts of benzene in oil-based paint. Smolowitz v. The Sherwin-Williams Co., 2008 WL 4862981 (E.D.N.Y. Nov. 10, 2008). Plaintiff failed to offer sufficient evidence under New York law of exposure level.


In order to prevail in a toxic tort case, plaintiffs must present sufficient evidence to support a finding that defendants' products caused plaintiffs' injuries. Proof of causation requires establishing both “general” causation and “specific” causation.  General causation bears on whether the type of injury at issue can be caused or exacerbated by the defendant's product. Specific causation bears on whether, in the particular instance, the injury actually was caused or exacerbated by the defendant's product.  The fundamental principle of toxicology is that the dose makes the poison: substances that are benign or even beneficial at a certain level can be toxic at another. Even when general causation is clear, a plaintiff must show that he or she was exposed to a sufficient dose of the substance to have caused the disease. Under New York law, plaintiffs must establish both general and specific causation through expert testimony

Plaintiff Richard Smolowitz worked as a drywall taper and spackler over a thirty year period beginning in the 1950s and ending in the early 1980s. Plaintiff alleges that his exposure to benzene in paints caused him to contract myelodysplastic syndrome (“MDS”).  A central factual issue in this case, said the court, was the level of exposure to which plaintiff was subject, and whether that level of exposure can cause MDS. First, plaintiff was not a painter, but alleged he worked in areas where paint products were regularly used. Second, the solvents used in defendants' oil based paints contained only a trace contamination of benzene due to the fact that the products are based on petroleum, and it is not always possible to remove all of the benzene during the manufacturing process.

In early motion practice, plaintiff's counsel represented that he would provide the testimony of expert witnesses who could prove that plaintiff was exposed to oil based paints with sufficient levels of benzene to cause his illness. Eventually, he relied on the opinions of plaintiff's treating physician, Dr. Silverman, to provide expert testimony on issues of general and specific causation. The doctor reported he was currently treating plaintiff for MDS; that Smolowitz reported a history of exposure to oil based paints, thinners and benzene during a 35-year period; and that in his opinion it was “likely to a reasonable medical probability, that Mr. Smolowitz's exposure to benzene during the years that he worked as a dry-wall mechanic is causative for his current hematologic condition.”

The court concluded that Dr. Silverman's testimony was inadequate to prove either general or specific causation. The conclusory statement that based upon plaintiff's reported history it was likely to a reasonable medical probability that Mr. Smolowitz's exposure to benzene during the years that he worked as a dry-wall mechanic is causative for his current hematologic condition, had substantial deficiencies. First, there was nothing in this statement that suggests that Dr. Silverman was aware of or had quantified the precise amount of benzene to which plaintiff was exposed. No proof of dose. Second, Dr. Silverman did not offer any opinion as to whether that limited level of benzene exposure, whatever it was, can cause the disease. In the absence of sufficient evidence from an expert or a treating physician of the plaintiff's exposure level, plaintiff could not prove the essential causation element of the claim.
 

Eighth Circuit Affirms Exclusion Of Causation Expert In Toxic Tort Case

The 8th Circuit has upheld the trial court’s decision that a plaintiff who alleged she was injured by drinking water from a bottle filled with freon did not have adequate and valid expert evidence of causation. Bland v. Verizon Wireless, 2008 WL 3474178 (8th Cir. August 14, 2008).

Plaintiff alleged that she inadvertently left her water bottle behind in a store, and an employee of defendant sprayed compressed air into her water bottle “as a joke,” believing the water bottle belonged to a fellow employee. At home, plaintiff opened the bottle which “made a-kind of pressurized noise.” She took a drink, then decided to smell the contents, taking a big whiff which made her cough. She then allegedly took another drink.

Plaintiff later reported to her doctor that after drinking from the bottle she coughed, which persisted for nearly an hour. She also described a “sore sensation in her throat” and for the next few days a “raspy sensation in her lungs.” Plaintiff alleged she developed a headache which persisted for about two weeks. Later testing at the University of Iowa Lab determined the bottle contained 820 parts per million (ppm) (.08%) of difluoroethane, a freon compound.

Plaintiff was later seen by a Dr. Sprince, complaining of shortness of breath when running. Her lung function test results were basically normal. Dr. Sprince eventually diagnosed her as having “exercise-induced asthma.” Dr. Sprince later theorized that “[b]ased on the initial clinical findings, [a] strong temporal relationship between the inhalation of freon and the occurrence of respiratory symptoms, and the subsequent response to pre-exercise treatment with inhaled bronchodilator” that plaintiff's exercise-induced asthma was caused by the inhalation of freon.

Plaintiff sought to use the testimony of this treating physician, Dr. Sprince, to establish a causal link between inhalation of freon and the alleged exercise-induced asthma. The district court excluded Dr. Sprince's testimony because Dr. Sprince's proffered testimony as to causation did not satisfy the standards for admission of expert scientific testimony under Daubert.

The 8th Circuit affirmed, noting first that a treating physician's expert opinion on causation is subject to the same standards of scientific reliability that govern the expert opinions of physicians hired solely for purposes of litigation.

The first problem with Dr. Sprince's causation testimony was that she failed scientifically to eliminate other possible causes as part of her differential diagnosis. In particular, her own testimony acknowledged the cause of exercise-induced asthma in the majority of cases is unknown. Where the cause of the condition is unknown in the majority of cases, an expert cannot properly conclude, based upon a simple differential diagnosis, that exposure, here to freon, was the most probable cause of the injury. As a practical matter, Dr. Sprince's causation opinion could not possibly be based upon a reasonable degree of medical certainty. Where the majority of cases of exercise-induced asthma have no known cause, and where Dr. Sprince failed to do an investigation and analysis of plaintiff's home or other environments in search of other possible causes, the district court did not abuse its discretion in determining Dr. Sprince's differential diagnosis did not satisfy Daubert.

Second, plaintiff’s expert did not know what amount of exposure to freon causes, or involves an appreciable risk of causing, asthma, and had no good grounds for determining whether plaintiff  was exposed to a sufficient dose to have caused her asthma. Dr. Sprince could not determine or estimate the amount of freon plaintiff was actually or probably exposed to. The expert could not extrapolate from the existing data because the gap between the data identified (exposure facts) and Dr. Sprince's proffered opinion was simply too great an analytical gap to support admissibility. Critical to a determination of causation is characterizing exposure. In a toxic tort case, the magnitude or concentration of an exposure should be estimated and the temporal aspects of the exposure should be determined --whether the exposure was short-term and lasted a few minutes, days, weeks, or months, or was long-term and lasted for years. Dr. Sprince lacked knowledge regarding what level of exposure to freon constitutes an appreciable risk of causing asthma and the specific concentration and degree of exposure to the freon. Similarly, plaintiff’s expert did not offer as evidence any personal experience with treating other patients following a similar exposure, admitting she had no such experience.

Finally, the expert’s heavy reliance on temporal proximity, without more, was insufficient to establish causation. In the absence of an established scientific connection between exposure and illness, or compelling circumstances, the temporal connection between exposure to chemicals and an onset of symptoms, standing alone, is entitled to little weight in determining causation. See Moore v. Ashland Chem., Inc., 151 F.3d 269, 278 (5th Cir.1998). It is not always irrelevant, said the court. The temporal relationship often will be one of several factors, and the weight to be given to the temporal relationship will differ depending on the strength of that relationship. But in this case, the district court properly discounted all the other factors supporting Dr. Sprince's opinion leaving only temporal proximity to support Dr. Sprince's causation opinion. And that was not enough, especially when plaintiff did not make an appointment with a doctor until two to three weeks after the incident.