U.S. District Court for the District of New Mexico Affirms “But For” Test Is Required to Prove Causation in Toxic Tort Lawsuit

November 3, 2008

In a recent ruling, the U.S. District Court for the District of New Mexico dismissed the claims of residents who lived near a uranium mill because they failed to prove that they would not have developed cancer “but for” their exposure to hazardous substances migrating from the mill.  Wilcox v. Homestake Mining Co., D.N.M., No. CIV 04-534, 10/23/08.  In this opinion, the U.S. District Court for the District of New Mexico followed the jurisprudential trend reinforcing the necessity of establishing “but for” causation in toxic tort lawsuits, which is often disputed by plaintiffs’ attorneys and their designated experts.

This case arises from the alleged release of radioactive and other hazardous substances by Defendants from their uranium milling facility near Milan, New Mexico.  The plaintiffs are residents or former residents of neighborhoods adjacent to the Homestake Mining Company’s uranium milling facility.  The plaintiffs contend that Homestake’s release of hazardous substances into their environment, including their drinking water, caused them to develop various cancers.

Defendant Homestake Mining Company moved for summary judgment against the plaintiffs, alleging that plaintiffs failed to make a prima facie showing of specific causation because plaintiffs’ experts failed to testify in their expert affidavits that “but for” the plaintiffs exposure to hazardous materials released by defendant, they would not have developed cancer.  Plaintiffs’ expert, Dr. Inder Chopra, opined that the exposure “was a contributing factor to [the plaintiff’s] cancer.”  Similarly, Plaintiffs’ expert, Dr. Robert Gale, opined that “the exposure [of plaintiffs] was, more likely than not, a substantial factor contributing to each plaintiff developing cancer.”  According to the Court, under New Mexico law, neither of these opinions were sufficient to establish a prima facie case of specific causation because the opinion did not satisfy the “but for” causation requirement.

Although the Court acknowledged that proof of causation can be particularly difficult in cases such as these, it still declined to lower the standard of proof on causation.  Citing In Re Hanford Nuclear Reservation Litigation, 534 F.3d 986, 1010-1011 (9th Cir. 2008), the Court states that “[w]here the plaintiffs’ alleged injuries are cancer-related, causation poses a particular problem for plaintiffs, since cancer frequently occurs in the absence of any toxic exposure and since it is generally very difficult, if not impossible, to scientifically trace an individual’s cancer to a particular exposure.”

The court dismissed the plaintiffs’ claims, concluding that “there are no genuine disputes as to material issues of fact…[b]ecause Plaintiffs’ experts are not able to testify that, more likely than not, Defendants’ alleged negligence was a but-for cause of their cancers…” and therefore, “Plaintiffs cannot meet their prima facie burden of demonstrating specific causation.”  In reaching this decision, the Court noted that the standard of proof for causation in toxic tort cases in Colorado is analogous to that of New Mexico and that both require that plaintiffs establish but-for causation.  See June v. Union Carbide Corp., 2007 WL 4224228 (D. Colo., Nov. 27, 2007).

In the same way, California law continues to require proof of but-for causation.  The California Supreme Court has held that the trier of fact must determine whether, “but for the negligence [Plaintiffs allege], the harm would not have occurred.”  Viner v. Sweet, 30 Cal. 4th 1232, 1241 (2003); see also Soule v. GM Corp., 8 Cal. 4th 548, 572-73 (1994).  The only current exception to this requirement is when there are “concurrent independent causes, which are multiple forces operating at the same time and independently, each of which would have been sufficient by itself to bring about the same harm.”  CACI 430, citing Viner v. Sweet, 30 Cal. 4th 1232, 1241 (2003); Barton v. Owen, 71 Cal. App. 3d 484, 503-504 (1977); and Rest. 2d Torts § 432(2).

This recent decision in Wilcox v. Homestake Mining Co. demonstrates that courts are continuing to require that plaintiffs meet the higher “but for” standard of causation in toxic tort cases.  The continued vitality of the “but for” standard of causation will likely have important implications for toxic tort cases litigated in a variety of jurisdictions across the country.

Gibson, Dunn & Crutcher has particular expertise in environmental litigation, including nuisance actions, and also handles a range of other environmental and counseling matters nationwide.  To learn more about the firm’s environmental practice, please contact the Gibson Dunn attorney with whom you work, Patrick W. Dennis (213-229-7567, [email protected]) or Jeffrey D. Dintzer (213-229-7860, [email protected]) in Los Angeles, Alan N. Bick (949-451-4211, [email protected]) in Orange County, or Peter E. Seley (202-887-3689, [email protected]) in Washington, D.C.

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