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If some clever party has found a way to get the Po210 OUT of the anti-static brushes, then this would mean the security they designed to prevent this had been breached by whoever killed Litvinenko.
If these safegiards can be easily breached by one party then they can be easily breached by another.
And so that would mean governments would have to ban the sale of these brushes IMMEDIATELY, because now they're a major risk to public safety.