This is almost impossible to find out. There is no requirement for ships to declare via AIS tracking exactly what cargo is being carried, although ships are required to inform VTS/ports of hazardous goods.
Furthermore, whatever cargo is being transported is usually a private matter between the parties involved in shipment. Some bulk cargoes might be publicly reported in fixture lists published by the Baltic Exchange, but this would represent only a small fraction of the global fleet.
Brgds
Phil