Micro plastic particles have been found in 15 brands of common table salt. Sea salt has over 1200 particles of plastic per pound, the highest quantity measured.

Sea salt is extracted from evaporation of ocean water. The process leaves the plastic particles in the salt as the ocean water evaporates. The source of plastic includes water bottles, cellophane, exfoliate micro-beads and several other plastics. (Environ. Sci. Technol., 2015.) Dumping is the main source of plastics, although  Mother Nature has developed enzymes to break down these particles.

There is a possibility of some plastic contamination during packaging, especially since China has the most adulterated salt.

Chemical & Engineering News, Nov. 2, 2015