Here's hoping that Australian soylent (Aussie soylent I think it was) is alright, as with all the other DIY soylents...
If I understand correctly the main source of these heavy metals is the brown rice protein, thus anything containing it may potentially have the same issue as Soylent.
A bit of googling shows up that there have been recent concerns about heavy metals contamination in rice grown in various Asian countries which is then traded worldwide.
Press Release
Edit: Soylent's Reply, provided by Trevor_Blake