Illustrating the importance of expert testimony in toxic torts, the United States Court of Appeals for the Tenth Circuit recently dismissed a plaintiff’s appeal after finding that the plaintiff’s expert witness (1) provided a flawed methodology for determining benzene caused the plaintiff’s leukemia and (2) failed to rule out idiopathic origins. Hall v. Conoco Inc., 886 F.3d 1308 (10th Cir. 2018).

Plaintiff Samantha Hall sued the operator of a refinery near her childhood home after contracting leukemia. Hall claimed her leukemia was caused by benzene emissions from the refinery. She hired an oncology expert, who proffered to the court a differential diagnosis that Hall’s benzene exposure as a child caused Hall’s leukemia. Ultimately, the district court excluded Hall’s expert’s testimony. Without the link between benzene and leukemia, the district court found that Hall failed to show causation and dismissed her case. The Tenth Circuit affirmed.

The court found several flaws in the plaintiff’s experts’ testimony. First, the oncology expert relied on the refinery’s highest hourly average benzene emissions to calculate Hall’s exposure. The court found that the expert was not qualified to determine which measure of exposure was appropriate to calculate Hall’s exposure. The court was also concerned that the oncology expert mistakenly calculated Hall’s exposure over eight years, when Hall actually lived near the refinery for only four years. The court also questioned a meteorological expert’s qualifications to opine on which means of measuring refinery emissions was best suited to calculating the plaintiff’s benzene exposure.

The court also found that plaintiffs’ causation expert failed to rule out spontaneous causes of Hall’s leukemia. The parties agreed that Hall’s type of leukemia is “frequently caused by idiopathic sources.” Id. Differential diagnoses should address all plausible causes of a disease. Id. The expert’s failure to rule out idiopathic causes was thus a “reasonable” basis for finding a “fatal error tainting the differential diagnosis.” Id. at 1314.