Products Liability Law Daily Wrap Up, CAUSATION—CHEMICAL PRODUCTS—Mo. App.: Directed verdict for herbicide manufacturer upheld in consumer’s cancer case, (Jun 26, 2025)

By Pankhuri Bhatnagar, B.A. LL.B.

A consumer’s failure to present admissible expert testimony on specific causation was fatal to his negligence and strict liability claims.

In an action brought against an herbicide manufacturer by a man who allegedly developed cancer from exposure to the product’s harmful chemical content, the Missouri Court of Appeals upheld a trial court’s directed verdict in favor of the manufacturer. The lower court did not improperly interpret the evidence, make credibility determinations, or limit expert evidence since the consumer’s oncologist testified only that the chemical exposure increased the risk of developing the disease and not that it actually caused the man’s illness. Motions to recall or modify this clear and consistent conclusion amounted to an impermissible attempt to revise earlier expert disclosures (McCostlin v. Monsanto Co., No. ED112532 (Mo. App. June 24, 2025)).

Background. A man allegedly developed non-Hodgkin’s Lymphoma (NHL) due to his exposure to Roundup, a glyphosate-containing herbicide manufactured by Monsanto Company. He and his wife brought suit against the manufacturer for strict liability (design defect and failure to warn), negligence, misrepresentation, violations of consumer statutes, and loss of consortium. Their toxicologist opined that the man’s inhalation exposure to glyphosate was equivalent to 13–33 eight-hour days of spraying. Based on this calculation, their oncologist believed that it was “more than likely” that the cancer was caused by exposure to Roundup. A trial court partly granted Monsanto’s motion to exclude these opinions, allowing the toxicologist to testify that exposure exceeded threshold values identified in dose-metric studies but not that such dosage causes cancer. The oncologist could opine that such exposure increased the risk of developing NHL. The manufacturer later renewed its motion, arguing that the man’s trial testimony materially differed from his deposition, rendering the experts’ opinions—based on the earlier testimony—unreliable. At trial, the toxicologist recalculated and concluded that the man had 9.59 eight-hour exposure days to Roundup while the oncologist testified that this exposure may have “contributed to the risk of developing NHL.” Monsanto moved for a directed verdict on the ground that the second expert did not show causation, only risk. The court granted Monsanto’s motion and denied the individuals’ motion to recall that expert to clarify his opinions. The consumers appealed.

Causation. The consumers claimed that their oncologist’s testimony established causation and cited cases which held that causation is a jury question. Under Missouri law, both strict liability and negligence claims require proof of both general and specific causation per Huett v. Branson, 675 S.W.3d 514, 521 n.3 (Mo. App. E.D. 2023) and in toxic tort cases, causation must generally be shown by expert testimony. Here, there was no “battle of the experts” leading reasonable minds to draw different conclusions on causation and making the issue fir for a jury per Nadolski v. Ahmed, 142 S.W.3d 755, 761 (Mo. App. W.D. 2004). Rather, the issue arose from a lack of expert evidence since the sole specific causation expert consistently opined that Roundup exposure was a possible risk factor for causation, and “[a]ssurance of possibility is not of itself … sufficient to make a submissible case.” Linton v. Carter, 634 S.W.3d 623, 629 (Mo. banc. 2021). The consumers argued that the oncologist was only required to opine that the herbicide contributed to disease development based on a differential diagnosis, independent of epidemiological dose thresholds. The court disagreed, noting that the expert admitted that epidemiological studies were essential to his conclusions and those studies supported a 10-day exposure threshold. The 9.59-day period was only marginally less, but the court could not supply the missing evidence or give the individuals benefit of speculative or forced inferences. Aughenbaugh v. Williams, 569 S.W.3d 514, 523 (Mo. App. E.D. 2018).

Interpretation and credibility. The consumers argued that the trial court misapplied the directed verdict standard by viewing evidence in favor of the manufacturer and improperly made credibility determinations reserved for a jury. The court disagreed, observing that their oncologist’s statement that he “had an opinion” on causation did not equate to testimony that Roundup did cause the lymphoma. After the recalculation of exposure days, the oncologist testified about risk rather than causation. Thus, the findings that the expert “no longer testified concerning causation” and “never gave an opinion on specific causation” were not credibility assessments but accurate summaries of his testimony which did not support a claim for reversible error.” Parkside Fin. Bank & Tr. v. Allen, 688 S.W.3d 83, 89 (Mo. App. E.D. 2024).

Recall denial. The consumers contended that they should have been permitted to recall the oncologist to clarify that his trial testimony meant to convey causation. They invoked precedents encouraging correction of erroneous statements and recanting testimony claimed to be perjury. State v. Byrd, 676 S.W.2d 494, 504 (Mo. banc 1984). But the court concluded that the oncologist did not misspeak, nor was he alleged to have given false testimony. His testimony clearly and consistently referred to “risk,” not causation. Thus, the trial court’s refusal to permit recall was not an abuse of its discretion.

Redirect scope. Lastly, the consumers challenged a sustained objection during the toxicologist's redirect examination, where he attempted to testify that the man’s “actual exposure hours were 153.5 or 19.19 exposure days” and that 9.59 days was a bottom estimate. This court rejected the challenge, finding that the testimony exceeded the scope of redirect and violated the consumers’ prior stipulation that only the 9.59 figure would be presented to the jury. The court emphasized that redirect is limited to clarifying issues raised in cross-examination. The attempt to introduce a higher exposure figure was not a clarification but a backdoor attempt to revise earlier expert disclosures. As such, the trial court properly sustained the objection.

The case is No. ED112532.

Judge: Wright, M.

Attorneys: Jonh F. Garvey, Jr. (Staas & Halsey LLP) for Mark McCostlin. Timothy J. Hasken (Bryan Cave Leighton Paisner LLP) for Monsanto Co.

Companies: Monsanto Co.

Cases: CourtDecisions CausationNews ChemicalNews ExpertEvidenceNews EvidentiaryNews MissouriNews