Is arsenic responsible for the toxicity of the Violet Crown Cup?

The Violet Crown Cup, Sarcosphaera coronaria, is a nicely coloured spring mushroom. In earlier days, the mushroom was considered edible, but several poisonings were reported in the early 20th century. The reason for the sporadic toxicity of S. coronaria is still unknown. The presence of arsenic could be a possible explanation, since Crown Cups can take up high amounts of this toxic element. Arsenic concentration and speciation were investigated in S. coronaria with inductively coupled plasma mass spectrometry (ICPMS) and HPLC coupled to ICPMS and revealed incredible maximum values of 0.9 % As (dry mass). Most of it was present in the form of methylarsonic acid (MA), a less toxic form of this element. However, low concentrations of the highly toxic methylarsonous acid (MA [III]) were also detected. The amounts were too low to pose an acute risk for consumers but the concentration of MA (III) significantly increased during simulated gastric digestion. We could not unambiguously identify arsenic as the toxic constituent of S. coronaria but we demonstrated that the extremely toxic MA (III) can be formed under certain circumstances, which should be carefully investigated in the future. This international research was conducted in co-operation of two Czech Academy of Sciences institutes (Institute of Geology, Nuclear Physics Institute) and the Austrian University of Graz.