## Facts

- NL Industries, Inc. and Mautz Paint Co. (collectively, the companies) manufactured and sold lead-based paint and/or lead pigments used in paint sold in Milwaukee over many decades.
- Milwaukee alleged that, by the late 1990s, it faced a serious public health crisis from childhood lead poisoning, tied largely to deteriorating lead paint in older housing.
- The City alleged lead paint in residences breaks down into chips and dust that children ingest or inhale, resulting in elevated blood-lead levels across the community.
- The City sued the companies in Wisconsin circuit court asserting public nuisance, conspiracy, and restitution (seeking recovery of municipal response and abatement-related costs).
- The City conceded it could not identify which manufacturer’s paint was present in particular homes where children were poisoned.
- The City presented evidence (including letters and public statements attributed to company/industry officials) suggesting the companies acted in concert to keep selling lead-containing paint products even while aware of the risk to children.
- The companies moved for summary judgment, arguing the City could not prove causation because it could not connect any defendant’s product to any specific child’s poisoning or to particular properties.
- The circuit court granted summary judgment to the companies and dismissed the City’s claims.
- The City appealed to the Wisconsin Court of Appeals.

## Issues

1. Whether the City produced sufficient evidence to create a genuine issue of material fact that defendants’ manufacture and sale of lead-based paint/pigments was a substantial factor in causing the alleged citywide public nuisance of childhood lead poisoning, despite the City’s inability to identify defendants’ products in specific homes.
2. Whether the City’s related conspiracy and restitution theories could be dismissed on summary judgment when they were tied to the same alleged wrongful conduct and causal theory supporting the nuisance claim.

## Decision

- The Wisconsin Court of Appeals reversed the summary judgment in substantial part and remanded for further proceedings.
- The court held the City’s evidence was enough to create a triable issue on whether defendants’ conduct was a substantial factor in causing the alleged public nuisance.
- The court rejected the view that the City’s inability to trace a particular defendant’s paint to a particular home necessarily defeated causation as a matter of law at the summary-judgment stage in this community-wide nuisance case.
- The court also held that, because the nuisance claim should not have been dismissed on summary judgment, dismissal of related conspiracy and restitution claims on the same causation ground was improper at that stage.

## Legal Principles

- A public nuisance is a condition or activity that substantially or unduly interferes with the use of a public place or with the activities of an entire community.
- In Wisconsin, nuisance liability still requires causation: the nuisance must be a cause of the plaintiff’s harm, and recoverable damages must be the natural and proximate consequence of the danger created by the nuisance.
- Wisconsin applies a “substantial factor” test for causation; a plaintiff need not show a defendant’s conduct was the sole cause, only that it was a substantial factor in producing the harm.
- When the claim is that the defendant created (rather than maintained) a nuisance, proof that the defendant had notice of the hazardous condition that later developed is not required in the same way it may be for a maintenance theory.
- Summary judgment is improper when, viewing the evidence and reasonable inferences in the nonmoving party’s favor, a reasonable jury could find causation and the other required elements.
- Even when factual causation is shown, Wisconsin courts may limit liability on public-policy grounds (e.g., remoteness or lack of a sensible stopping point), but those limits did not justify ending this case as a matter of law on the summary-judgment record.

## Conclusion

The Court of Appeals held that Milwaukee’s lack of house-by-house product identification did not require dismissal at summary judgment where the City offered evidence that defendants sold substantial amounts of lead-based paint/pigments into Milwaukee’s residential market and that this conduct could be found a substantial factor in creating a community-wide hazard; accordingly, the court reversed the dismissal in substantial part and remanded, reinstating the nuisance claim and allowing related conspiracy and restitution theories to proceed past summary judgment.


City of Milwaukee v. NL Industries, 691 N.W.2d 888 (2004)