Who would think that an incorrect color change in a routine water chemistry test could have a serious ripple effect? Field-testing for Molybdate and Dissolved Iron both share a common chemistry and a common interference. When a test is performed incorrectly, it could promote the growth Legionella bacteria.
There has been a great deal of research since the first cases of Legionnaire’s Disease were identified back in 1976. Some of that research has been in the area of Dissolved Iron as a nutrient source for the Legionella bacteria. It has now been proven that if you can starve Legionella bacteria of available iron, you limit the bacteria’s ability to multiply and therefore reduce the potential to cause illness.
When field testing for Molybdate, standard test procedures uses a reagent called Thioglycolate, which is also the active ingredient to test for Dissolved Iron. Since Thioglycolate reacts with both parameters in a sample, it can be difficult to know what you are really testing for.
We will discuss the cause and effects of an incorrect color change related to these common water quality tests and how to overcome this interference so that operators better understand the nature of their sample to make better decisions regarding the treatment in a water system.