CS2 blinds in Brassica crops: False positive results in the dithiocarbamate residue analysis by the acid digestion method

Various members of the Brassicaceae family (cauliflower, savoy cabbage, red cabbage, turnip-rooted cabbage) grown without any application of pesticides were analyzed according to the acid digestion method commonly used for the determination of dithiocarbamate fungicide residues. Depending on postharvest treatments, high non-anthropogenic CS2 values up to 4 mg/kg were found in some cases, especially in frozen raw cabbage samples, exceeding maximum residue limits. To explore phytogenic CS2 occurrences, two model substances (phenylisothiocyanate and methyl tryptaminedithiocarbamate) representing natural mustard oils and brassinines, respectively were analyzed for their acid hydrolysis decomposition products. In both cases, COS was found generally, but CS2 was readily formed during acid digestion, too, when sulfides were present. The results obtained clearly demonstrate that CS2 values determined by using the acid digestion method of crops rich in secondary metabolism sulfur compounds have to be interpreted carefully.