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In an effort to reduce the occurrence of chlorine derived residues such as chlorate and trichloromethane (TCM) in milk and ultimately in dairy products, ‘chlorine-free’ cleaning of milking equipment became compulsory in the Republic of Ireland (ROI) from January 2021. While data exists on TCM levels in bulk tank milk, little is known about the prominence and typical levels (mg/kg) of chlorate residue in bulk tank milk. To address this, 3625 bulk milk samples were collected from six milk processors and were analysed for chlorate and TCM residues across 2020 and 2021, with 2020 representing a period before chlorine-free cleaning was introduced and 2021 being the period after chlorine removal. In 2020, 15% of the samples analysed had detectable levels of chlorate (0.0020–1.6 mg/kg), but this reduced to 8% in 2021 (0.0020–3.9 mg/kg), following the introduction of ‘chlorine-free’ cleaning. Chlorate and TCM residues have not been totally eliminated because sources of residue other than cleaning chemicals exist, i.e., chlorinated water.