The concentrations of nitrite-nitrogen in sea water varies from 0.000 to 2.00 microgram atoms (µg. atoms) per liter of sea water at 20° C. In the open ocean nitrites are seldom found in depths below 100 meters, and even at these depths the water may be completely devoid of nitrites. When occurring in waters near the surface, the concentration is generally less than 0.10 µg. atom of nitrite-nitrogen per liter. The higher values are obtained at times in the waters on the continental shelf and in sounds, straits, fjords and estuaries.