## Facts

- Christopher Thompson worked as a brakeman for Southern Pacific Railroad and regularly entered Monsanto’s Luling, Louisiana plant to perform railroad service.
- Thompson developed porphyria cutanea tarda, involving chronic skin lesions and abnormal liver function; potential causes include alcohol use and exposure to certain chemicals.
- Thompson sued Southern Pacific under FELA and sued Monsanto under Louisiana negligence law, alleging workplace chemical exposure caused his disabling condition.
- Thompson initially attributed the condition to hexachlorobenzene exposure, but later shifted to a dioxin-causation theory after Monsanto disclosed dioxin contamination near the tracks and investigations found no hexachlorobenzene at the site.
- Thompson’s chemical-engineering expert testified dioxin in soil can be ingested, inhaled, or absorbed, but could not quantify Thompson’s exposure because he lacked information on where and how long Thompson worked at the plant.
- Thompson’s toxicology expert opined dioxin caused the condition because Thompson worked where dioxin was found and “definitely could have come into contact with it,” but had no knowledge of exposure amount or duration.
- Thompson’s neurology expert stated dioxin exposure could cause Thompson’s symptoms but did not opine that it did so here, citing insufficient information on dioxin concentration and Thompson’s time in the area.
- All five of Thompson’s treating physicians testified dioxin did not cause his porphyria; a specialist attributed it to alcohol use and excluded dioxin in part because Thompson did not develop chloracne.
- Monsanto’s toxicology expert testified measured dioxin levels were too low to cause porphyria under Thompson’s alleged exposure and that reported dioxin-induced porphyria cases involved chloracne, which Thompson lacked.

## Issues

1. Whether Thompson presented substantial evidence that dioxin exposure at Monsanto’s plant probably caused his porphyria cutanea tarda, sufficient to sustain a jury verdict against Monsanto under Louisiana negligence law and federal sufficiency standards.

## Decision

- The Fifth Circuit reversed the district court’s judgment against Monsanto and rendered judgment for Monsanto.
- The court held Thompson failed to provide substantial, non-speculative evidence of causation.
- The court concluded the record showed, at most, a possibility of exposure and causation, not a probability supported by competent proof.

## Legal Principles

- A jury verdict cannot stand on speculation; causation must be supported by substantial evidence linking the defendant’s conduct or condition to the plaintiff’s injury.
- In toxic-exposure negligence cases, the plaintiff must present evidence of meaningful exposure (including some indication of level, frequency, or duration) and expert proof that the exposure probably caused the specific illness.
- Expert testimony that a substance “could have” caused the injury, without data tying dose and exposure conditions to the plaintiff, is insufficient to establish causation.
- Treating-physician testimony and clinical findings that contradict the plaintiff’s causation theory may undermine the sufficiency of the plaintiff’s expert case when the plaintiff cannot quantify exposure or otherwise connect it to the disease.

## Conclusion

The Fifth Circuit set aside the verdict against Monsanto because Thompson’s evidence did not establish that he experienced harmful dioxin exposure at the plant or that such exposure probably caused his porphyria, making the causation case legally insufficient as a matter of law.


Thompson v. S. Pac. Transp. Co., 809 F.2d 1167 (5th Cir. 1987)