I bought about 50 plastic bags of sand about a year ago and I keep them
outside for some small jobs.
Unfortunately, as I've only recently discovered, the sand inside some
of the bags have been affected by green mould.
The bags are loosely covered by a sheet of polythene and some wooden
planks.
Can I still use the sand for mortar and concrete mixes or shall I chuck
it away?

Any suggestion please,

Alex.