A concentration is not a dose. Converting one into the other is where most of the contestable judgement in a toxic tort matter actually lives.
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Dose reconstruction is the discipline of estimating how much of a substance entered a particular person's body, over what period, from evidence that is almost always incomplete. It combines measured or modeled environmental concentrations with the specifics of the receptor — where they lived and worked, how long they were there, what they drank, how much air they breathed, what they did each day — and it produces a number that both sides will fight over. The work is genuinely quantitative and genuinely uncertain at the same time, which is an uncomfortable combination to present. Reconstructions that survive challenge tend to share one feature: they state their assumptions plainly and carry a range, rather than presenting a single figure with unearned confidence.
Each element is separately contestable, and a weakness in any one of them undermines the estimate as a whole.
What the substance measured — or can be modeled to have measured — at the place the person actually was, not at the fence line or the source.
Inhalation, ingestion, or dermal contact. Each has its own uptake behaviour and its own set of receptor factors.
How long and how often, across a period that may span decades and several residences or jobs.
Age, body weight, breathing rate, water consumption, and activity patterns — children are not small adults for these purposes.
What the site and the surroundings were like during the exposure period rather than today, after remediation or closure.
The range the estimate honestly supports, and which assumptions drive it. Omitting this is the most common avoidable weakness.
How a defensible reconstruction is built.
Nearly every downstream question — causation, damages, class definition — takes the exposure estimate as its input.
Opponents rarely start with the medical literature. They start by asking how the exposure number was produced, which assumptions drive it, and what happens to the conclusion when a defensible alternative assumption is substituted.
Decades, where the documentary record supports it — occupational and community exposure reconstructions routinely address periods from the 1950s onward. What governs is not elapsed time but the survival of records: process descriptions, material purchases, emissions inventories, employment files, and any contemporaneous monitoring. Where those exist the reconstruction can be reasonably constrained; where they do not, the honest estimate carries a wide range, and a wide range is sometimes still decisive because even the low end exceeds a threshold that matters.
Modeled concentrations are routinely accepted where measurement is impossible, which in historical exposure matters is most of the time. What draws challenge is not modeling itself but modeling that runs on default inputs when site-specific inputs were available, that is not calibrated against whatever measurements do exist, or that is presented without any assessment of uncertainty. A model validated against even sparse contemporaneous data is materially stronger than one that was never tested against reality.
They make it additive and more contestable. A cumulative dose across several locations requires a defensible estimate at each, and each is separately attackable — which is why opposing experts often concentrate on the periods with the weakest documentation rather than on the analysis as a whole. It also raises apportionment: where more than one source contributed, the question of how much came from the defendant's operation becomes its own dispute, usually resolved with a combination of modeling and source attribution work.
The recurring pattern is extrapolation beyond what the method supports — using a screening-level tool to produce a litigation-grade number, adopting conservative regulatory defaults designed to be protective and presenting them as best estimates, or reaching a conclusion the underlying data cannot constrain. Courts assess whether the expert applied the same rigor they would apply in their own practice. An exposure estimate produced by a method the field uses, applied the way the field applies it, with uncertainty stated, is on far firmer ground than one built for the occasion.
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