The linear no-threshold model of dose-response meant that plaintiffs could continue to prevail on toxic tort claims even though their exposures had occurred in the modern era and thus were tiny fractions of those that led to epidemics in years past. Either courts permitted plaintiffs to rely on a one molecule / one particle theory of causation (consistent with the view that some risk is associated with a single molecule or particle) or they allowed plaintiffs to conflate causation with risk.
Eventually some courts began to grasp the absurdity that follows from basing proximate cause on a "one-hit" model in a world of trillions of hits while others began to take notice of the fact that despite probing larger and larger populations with low exposures epidemiology was unable to verify the linear no-threshold model for numerous diseases; thereby suggesting that there is indeed a threshold for diseases including leukemia (a new case making the latter point is Schultz v. Glidden Company.) Meanwhile we have argued that the old cases got it right – that causation in an individual toxic tort case is unfathomable and that the most sensible approach is to estimate the risk imparted (e.g. by a single molecule); to ask why it makes sense to impose liability for creating a 1:1,000,000,000,000,000,000 chance of harm; and, further asking why it wouldn’t make sense to impose liability for a 1:100,000 or greater risk.
But all of that assumes risk goes to zero or at least continues to decrease as exposure is reduced below previously measured levels. If that assumption is false, if risk starts heading back up as exposure goes down, especially if unpredictably so, then all bets are off. We will have entered another period of great uncertainty, And it’s in such times that toxic tort claims flourish. The horsemen of this new age of uncertainty have published a review paper on the topic and if you want to understand what’s coming, why it’s pitch perfect for the health and wellness movement and why what happened to BPA will be repeated again and again for other chemicals until some new way is established to either verify or refute their claim that dose doesn’t make the poison you need to read it: "Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses"