They are a portion of the total residue retained by a standard glass fiber filter. A major contribution to these constituents is the natural contact with rocks and soil. Chloride is one of the major inorganic anions in water. Chloride originates from natural minerals, seawater intrusion, improperly capped drilling wells and industrial pollution. Wastewater usually has high chloride content caused by the presence of dietary sodium chloride in domestic wastewater.
Most sulfates originate from the oxidation of sulfate ores such as gypsum, anhydrite and pyrite.
Groundwater or sedimentary rocks may contain magnesium sulfate and sodium sulfate. Bacterial reduction of sulfate produces hydrogen sulfide as a byproduct which has the odor of rotten eggs. Sulfate is one of the major dissolved constituents in rain and may be derived from dust particles, oxidation of sulfur dioxide and hydrogen sulfide. High concentrations of ammonia in the form of ammonium hydroxide are toxic. Seventy eight percent of the atmosphere consists of nitrogen.