Due to its location at the air-sea interface, the sea surface microlayer is prone to accumulating anthropogenic pollutants. We analyzed the presence of antibiotic compounds, including ciprofloxacin, in this area using ultra-performance liquid chromatography—triple quadrupole mass spectrometry in tandem with ionization spray (UPLC-QqQMS/MS) (Bruker EVOQ Elite system, Billerica MA). We compared the numbers and concentrations of these compounds in the microlayer to those found in the underlying water column.

The value <0.001 in the data table refers to 'below the detection limit'. The specific limit of quantification for each antibiotic compound can be found in the supplementary information.