Zinc is considered an essential element in human and animal nutrition . IT can be naturally occurring , the most significant source being zinc ores : sphalerite (ZnS) and smithsonite (ZnC03). These compounds end up in water on locations where zinc ores are found .
It may come from industrial contamination such as wastewaters containing zinc stem from galvanic industries and battery production . Zinc compounds are applied for many different purposes including parchment production . Zinc oxide is a constituent of salves , paints and catalysers, zinc vitriol is applied as a fertilizer , and zinc bacitracine is applied as a growth stimulant in animal husbandry. Zinc can also be the result of corrosion of fixtures mostly brass, of which zinc is a major component.
In concentrations over 5 mg/I, zinc produces an objectionable taste and may cause water to appear milky, or upon boiling, to seem to have a greasy surface scum. Cases of zinc poisoning have been reported from prolonged consumption of water at concentrations of 40 mg/I.
What do the results mean? Is it regulated?
The average zinc concentration in seawater is 0.6-5 ppb. Rivers generally contain between 5 and 10 ppb zinc. Algae contain 20-700 ppm, sea fish and shells contain 3-25 ppm, oysters contain 100-900 ppm and lobsters contain 7-50 ppm.
Zinc is regulated as a secondary contaminant under the Safe Drinking Water Act. This means it is regulated based upon the aesthetic effects it may produce . The EPA has established a secondary MCL of 5 mg/L. The World Health Organization stated a legal limit of 5 mg Zn2+/L.
How can you test for zinc?
You can analyze for zinc using 3500-Zn B. Zincon Method, which is a Standard Method utilizing a colorimeter. This can be an accurate analysis for field measurements .Laboratories analyzing drinking water samples can utilize various methods including EPA method 200 .7 and 200 .8 which utilize an Inductively Coupled Plasma (ICP) or the Standards Method 31138 which uses Graphite Furnace
Water Treatment Options:
If the presence of zinc is due to corrosion , it is best to treat the source of the problem by using a soda ash feed . You can also successfully remove zinc using distillation or reverse osmosis.