Threshold determination for the dense cloud environments for 3 different flat continua (1, 0.1 and 0.04 mJy), the synthetic ice spectrum in teal is the ice composition containing sulphur (and noise added), with in black the synthetic ice spectrum without sulphur and without noise. Molecular parameters used in these spectra are listed in Table A.1. Each panel shows the 5σ threshold for one of the S-bearing species considered (on the left, top to bottom: H₂S, OCS; on the right, top to bottom: CS₂, SO₂).