A Monitor's Guide to Water Quality


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National guidelines recommend less than 0.026 µg/L of mercury in water for the protection of aquatic life. The guideline for methylmercury is even lower, at 0.004 µg/L.

How is it measured?

Mercury and methylmercury samples are collected in the field in glass or specially coated plastic bottles, which are then sent to a lab for analysis. Specific procedures are used when collecting the sample to prevent contamination, which can easily occur.

A field-blank sample is also often taken, where a bottle filled with clean distilled water will go through all the steps as the others but will not be used to collect an actual sample. Analysis of this blank sample helps the lab determine if mercury contamination was present apart from the water samples taken. Mercury and methylmercury concentrations are often reported in very small units, such as nanograms per litre (ng/L).