10th Circuit Sheds Light on "But For" Causation. Substantial Factor Causation, Not So Much

In Wilcox v. Homestake Mining Company plaintiffs argued that in toxic tort cases involving an injury with multiple potential causes "causation in such cases may be proven through a substantial factor test, without regard to whether the injuries would likely have occurred in the absence of the defendant's actions." Plaintiffs further argued that a "but for" causation requirement would make recovery all but impossible in toxic tort cases. The court rejected those arguments.

All a plaintiff has to do to get to a jury is to develop testimony that that the putative cause (e.g. radiation) was more likely than not a necessary cause of her injury (e.g. bladder cancer) and if there are multiple tortious sources of that cause then she can avail herself of alternate causation approaches (e.g. Summers v. Tice)  to assert liability against a specific defendant. On the other hand, it's not enough merely to show that the defendant brought plaintiff into contact with one of the known causes of her injury and it's not enough to show that the putative cause is one of the more common causes of that such injuries.

That's helpful. "But for" goes with the first legal causation question: was it more likely than not that the exposure (e.g. 5 fiber/cc yrs amphibole asbestos) was a necessary cause of plaintiff's cancer (e.g. mesothelioma). So where does "substantial factor" go? The court doesn't say. Like most courts it doesn't even say what it is.

Where should "substantial factor" go? We think it makes sense for it to go with the second legal causation question which is "was the exposure (i.e. the risk imposed) unreasonable?" The ability to estimate the ex ante risk of cancer imposed by exposure to a carcinogen allows both qualitative and quantitative assessments of the reasonableness of the defendant's conduct and informs the question of whether a particular exposure was substantial (and thus a basis for liability) or merely de minimis (and so unable to support a liability claim).

As we argued in Borg-Warner and have argued since, in a toxic tort case the ex ante risk imposed is the best measure of the reasonableness of the man (or woman). And that's what "substantial factor" causation ought to be about - determining whether there's some notion of responsibility associated with the particular risk imparted.

The End of Toxic Tort Litigation in Texas?

If a plaintiff's cancer was caused by one molecule or one fiber damaging a single cell's DNA causing it to become malignant, and plaintiff was exposed to billions of molecules or fibers from multiple sources, how could he possibly prove that ,"but for" any single source of exposure or subset of exposures, he would not have developed his cancer? As stated, this is the Summers v. Tice problem traditionally resulting in burden shifting rather than dismissal so long as the conduct of each defendant was tortious.

Similarly, if plaintiff's cancer was caused by the cumulative effect of any one of several subsets of exposures from multiple sources, e.g. if three widgets were sufficient to cause cancer and plaintiff was exposed to one widget from each of A, B, C and D, she could never prove that "but for" A's widget she wouldn't have gotten cancer since the widgets of B, C and D were sufficient to have caused it; and the same would be true if she sued B, C or D. Again, the traditional answer to plaintiff's problem, assuming each defendant's conduct was tortious, has been to shift the burden of proof on causation. See Landers v. Texas Salt Water Disposal Co.

Suddenly the 5th Court of Appeals has in essence held that Borg-Warner v. Flores puts the burden of proof of causation back on plaintiff; doing so in a case in which the defendant stipulated so-called "general causation". See Georgia-Pacific v. Bostic. There's essentially no discussion of the rationale for imposing a "but for" causation proof burden on a toxic tort plaintiff nor is the impact of this monumental shift in Texas law even discussed so maybe the court didn't intend such a result. Indeed it did proceed to discuss substantial factor causation even after concluding that a "but for" burden was borne by a mesothelioma plaintiff with the result being that plaintiff's evidence was held insufficient to "provide quantitative evidence of [plaintiff's] exposure to asbestos fibers from [defendant's product] or to establish [plaintiff's] exposure was in amounts sufficient to increase his risk of developing mesothelioma."

So if you establish an increase in risk you've established substantial factor causation and that's the same as"but for" causation?! This case has a lot of lawyers scratching their heads.

It's time for a clearly articulated definition of "substantial factor" and it's time to get rid of the confusing and, in cancer cases, nonsensical "general causation" v. "specific causation" dichotomy. More on that after I get home.