While it’s not a danger in and of itself, efflorescence can be linked to excess moisture, mold growth, or poor drainage.

Efflorescence is a white material that appears on brick as a powdery mass of mineral. Efflorescence occurs when moisture ...

White sand might be quartz ... the sand together and allows the mortar to bond to each brick (or concrete block, stone or other masonry unit). Common sense tells you if you just got sand wet ...