"A Little Extra Arsenic at No Charge"
In a letter from Chemifloc Ltd., a chemical manufacturer, they clearly state there are two sources of chemicals used for water fluoridation: 1) specially manufactured for fluoridation and 2) derived from fertilizer waste products - which contains much higher levels of arsenic.
Here's a letter from them. [quoting..]
I would like to inform you that Chemifloc does not supply Fluosilicic Acid which is derived from the fertilizer industry - we supply a manufactured product which is of high quality. Typically, manufactured Fluosilicic Acid contains only 5-10% of the arsenic levels which are found in the fertilizer derived material.
..it didn't matter if ours had substantially less arsenic.
In any event you can be happy that not only is the Eastern Health Board ensuring that your water is fluoridated, they're also seeing you get a little extra arsenic at no charge. Personally I would prefer to do without the arsenic.