Federal agents fired tear gas and pepper spray at multiple standoff sites across the Twin Cities during Operation Metro Surge, the immigration enforcement operation that ran from December 2025 through February 2026. Now a team of researchers at the University of Minnesota is trying to find out whether that chemical residue left heavy metals behind in the ground, with effects that could outlast the operation itself.
The operation, described by the Department of Homeland Security as the largest immigration enforcement action ever carried out, led to nearly 3,800 arrests, most of them people from Ecuador and Mexico. It also drew heavy use of crowd-control weapons: a national study by Physicians for Human Rights and UC Berkeley's Human Rights Center logged 94 incidents of misused chemical irritants in Minnesota, out of 412 documented nationwide. The most common weapon was MK-9 pepper spray, meant to be deployed from at least 6 feet away — officers were found to have often used it closer than that.
That heavy use is what put soil on researchers' radar. Chemical irritants can settle into dust and dirt at the site of a standoff and, depending on their composition, leave behind metallic residues that don't break down quickly. The UMN team is sampling soil from sites where standoffs took place to see whether that's happened here, and what it could mean for people who live, garden or let kids play nearby for years to come.
It's the latest research effort to tally the operation's lingering toll.
But it adds an environmental dimension to a growing body of Twin Cities research trying to measure what an operation this size leaves behind long after the agents are gone.
