2008-03-25

"The mercury in one CFL bulb can contaminate 1000 gallons of water"
Recently, in an internal company bulletin board, someone posted this link, citing the title and asking "Is it true?"

My answer was, let's do the math.

How much mercury is in a bulb? According to wikipedia, anywhere between 1 and 12 mg. The best models seem to have limited it to 1mg but there is a limit in place of no more than 6 mg, so let's assume that we're talking about 6mg.

1000 US Gallons of water is 3890 L, 1000 Imperial Gallons of water is 4540L. Typically gallons nowadays refers to US gallons, but let's make it 4000, just in case (makes the later math easier, even if it's not a fair mid-point).

4000L has a mass of 4000kg. 6mg in 4000kg is 1.5 parts per billion by mass.
According to this link, the American FDA's "Maximum Contaminant Level Goal" for mercury, a cumulative neurotoxin, in drinking water is 2 parts per billion.

So, as usual, this kind of a headline looks like a little late-breaking hysteria. Mind you, if enough of the bulbs have 12 mg, that would be 3ppb which would fail the (arbitrary?) MCLG. Where the "safety line" actually is is probably a matter for debate that gets very political very quickly. Like, did you know that crematoria are a prime source of airborne mercury pollution? Years of dental fillings, all going up in smoke...

All that said, ever since the fad of CFL bulbs started taking hold, aside from my complaint that they don't emit enough light and what light they emit tends to be too cold, I have wondered aloud quite often where the infrastructure for safe disposal of expired bulbs was. A rhetorical question, I know. But then, such infrastructure must grow fast enough to take up the slack. Given the likelihood that "incorrect recycling" of CFLs is going to mean concentrations of mercury in landfills, I wonder how the neighbours of the various dumps in the western world are going to feel about those dumps becoming mercury magnets, alongside all the other wonderful things they've taken in over the years?

This stuff has all got to be solved a different way. Wish I knew what that way was...

1 comment:

Greg said...

Reminds me of a hospital announcing that it had gone "mercury free" (meaning that the blood pressure cuffs no longer held mercury) thinking nothing of the thousands and thousands of flourescent light bulbs hanging over people's heads...