The argument was that the risk model assumptions about safe doses to the public were “an Arbitrary and Capricious standard as applied to rulemaking” and thus challengeable in US law.

Source: https://www.counterpunch.org/2023/03/16/uranium-weapons-residues-in-uk-air-samples-have-been-measured-since-the-ukraine-war-why-is-google-suppressing-the-evidence/