Fluoridation: putting chemical contamination in context

Anti-fluoridation activists often claim fluoridating chemicals used for water treatment are contaminated with heavy metals and radionuclides. I have written about this before in Fluoridation – are we dumping toxic metals into our water supplies?, Water treatment chemicals – why pick on fluoride? and Hamilton – the water is the problem, not the fluoride!  The issue was also discussed in my exchange with Paul Connett (see Fluoride debate).

Trouble is, many people have difficulty putting measured levels of contamination into context. After all, if there is a sufficiently sensitive analytical method available just about any contaminant will be detected and measured in our food and water. The important issue is the magnitude of the contamination (which is often natural anyway). That is why measured levels of contaminants must be compared with the maximum allowable values defined in regulations for food and water safety.

I have seen anti-fluoridation activists presenting submissions to councils who will flash on the screen a copy of a certificate of analysis as “evidence” of heavy metal contamination without any reference to the measured values at all! Their logic seems to be that the fact contaminant levels have been measured at all is some sort of “proof” of dangerous contamination.

Arsenic in Hamilton City water

It may help to consider the possible levels of contamination with the contamination from natural sources. In the graph below I have plotted the relative contribution of arsenic from natural and fluoridating chemicals in the treated Hamilton City (NZ) water. Arsenic is commonly mentioned by opponents of fluoridation.

The source water for Hamilton (Waikato River) contains arsenic from natural sources usually 2 or 3 times the maximum acceptable value (MAV) for drinking water (10 ppb As) (McLaren and Kim 1995). (ppb = parts per billion). In the figure the first bar represents river water arsenic content just under 30 ppb. After treatment up to 90% of the arsenic is removed so that it does not exceed the  MAV  (here 3 ppb) – red horizontal line. However, the contribution from fluoridation chemicals used (assuming about 2 ppm As in the FSA – the last batch used in Hamilton had 0.4 ppm As) is miniscule (about 0.01 ppb) compared with that from natural sources. Too small to show in the above graph.

Seems to me rather silly to argue against treating Hamilton water with fluoridating chemicals because they are “contaminated” with arsenic while ignoring the much large contribution of arsenic from the source Waikato River water.

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