More Mercury Factoids: Compact Fluorescent Light Bulbs, Part 2

Note: part of a series. Other posts are here and here.

So, why aren’t you going to get mercury poisoning if you break a CFL bulb in your home? First, it’s going to release only a very tiny amount of mercury into the air for a fairly limited period of time (as was discussed in the previous post). Second, we’re comparing that tiny amount of mercury in air with a health-based level that is highly protective - the Reference Concentration (RfC).

From studies of exposed human populations, it’s been observed that the most sensitive effects of low level exposure to elemental mercury occur in the nervous system. The most sensitive neurobehavioral effects were observed at levels in air as low as 25 ug/m3 (that’s microgram per cubic meter of air) with exposure occurring over a period of several years, as confirmed in multiple studies of exposed workers. This lowest-observe-adverse-level (LOAEL) is further reduced with uncertainty factors to protect sensitive individuals and to address where we don’t know much about inhaling elemental mercury (such as effects to the fetus from exposure to pregnant women, or to young children). The value you then get as the RfC is 0.3 ug/m3, which is about 100-fold below the level at which the most sensitive adverse effects have been observed with long-term inhalation exposure to mercury.

In addition, the definition of the RfC further confirms it’s protective nature:

In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily inhalation exposure of the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. (see Note 1, below)

Recall that I had done some calculations of mercury concentrations in air that could result from the emissions from breaking a CFL bulb indoors. The modeled concentrations rose to 0.48 ug/m3 after a day, and drop below the RfC (i.e. below 0.3 ug/m3) after three days, and remain below it all times after that (see Note 2, below). After three days, the modeled concentrations in air continue to decrease. They won’t go to zero, because that’s the nature of a model with an exponential term in it. However, for the folks who believe they need to have zero exposure to be “safe”, the 5 milligram mass of mercury that’s been released will eventually volatilize completely, and at some point in the future, the mercury concentrations in air will become undetectable (which is a little different than “zero”; sorry about that). Things should remain that way until the next time you break a bulb, which should be fairly infrequently (for myself, I try to not break light bulbs because I don’t like taking the risk of stepping in the broken glass).

So what about those couple of days where exposures are over the RfC? There isn’t a published health effects level covering that situation According to the ATSDR as with EPA, the LOAEL for less serious effects (i.e., the most sensitive effects) in humans were neurobehavioral effects such as tremors and poor performance in neurological testing observed at exposures ranging from 14 to 25 ug/m3 over a period more than half a year to 41 years (sorry it can’t be more precise, but that’s the nature of observational data). There’s lot’s of information about neurological effects in humans with high-level short duration inhalation exposure, but no exposure information. However, the levels in air producing adverse neurological effects in lab animals such as rats or rabbits typically are around 1,000 ug/m3 in air or higher for a period of days or weeks. Taking these things into consideration, along with the underlying philosophy that occasional exposures above the RfC don’t imply adverse effects are going to occur, it doesn’t appear that a few days of slightly elevated exposure to mercury vapor from breaking a CFL bulb would produce the shakes. This isn’t really a reason to not buy CFL bulbs. (For more information about mercury-related health effects, here’s the ATSDR public health statement).

As mentioned before, the RfC includes uncertainty factors to address what we don’t know yet about developmental effects to a fetus. This is prudent – in the ATSDR profile, there is one study with laboratory animals in which pregnant rats were exposed to 50 ug/m3 in air for a few hours a day over seven days, where the offspring exhibited neurological impairment. This is different from the other developmental studies in animals, in which short term exposures of ranging from 500 to 1,800 ug/m3 in air were producing neurobehavioral effects in the offspring, which is a thousand-fold higher than the short-term levels potentially associated with breaking a CFL bulb. As before, it doesn’t seem that a few days with slightly elevated exposures constitutes “appreciable risk of deleterious effects”. Not enough to require hiring a cleanup contractor if a bulb breaks in your house, and not enough to deter a reasonable person from buying CFL bulbs.

Note 1: the RfC isn’t a fixed line – above it you’re risking your health, below it you’re safe. It doesn’t work that way. Levels below it are unlikely to be associated with adverse health effects, and are considered protective and of no concern to regulatory agencies. However, as the magnitude and frequency (both are important) of exposure to levels above the RfC increases, the probability of adverse effects occurring increases. However you can’t say categorically that all levels of exposure below the RfC are safe, and that all levels above the RfC are associated with adverse health effects. Welcome to the real world of toxicology.

Note 2: no, I don’t know why the Ellsworth American and Steven Milloy said that the Maine DEP finding was the mercury level was in excess of six times the "EPA standard" in Ms. Bridges home. As typically occurs with the media reporting environmental stories, they didn’t provide enough information. Maybe the inspector made the measurements at carpet-level, while the EPA’s study (and the model) evaluated general room air. Maybe it’s because the inspector was making a measurement with a real-time instrument, and the level represents a short-term peak concentration, while the EPA’s study (and the model) are calculations of time-weighted average concentrations. I won’t speculate about quality control, instrument calibration or operator experience because that’s pointless, but these are also factors that affect the reliability of the measurements.

More Mercury Factoids: Compact Fluorescent Light Bulbs

Note: part of a series. Other posts on CFLs are here and here.

So I’m online getting some consumer information about compact fluorescent light (CFL) bulbs, the latest weapon in the war on carbon dioxide, and I happen to run across this tidbit published last month from the Junkman himself, Steven Milloy. Mr. Milloy has used the misfortune of one Maine woman, who broke a mercury-containing CFL bulb in her home and got a raft of really bad advice for what to do about it, as a springboard for bashing all environmentalists about reducing greenhouse gas emissions.

The news media had taken up the chase on this issue, and from them we find that the facts in this matter were as follows: According to an article in the Ellsworth American, Brandy Bridges dropped one of about two CFL dozen bulbs she was installing in her home, which broke on a shag carpet. Alert to the potential hazards of mercury exposure, Ms. Bridges called Home Depot, where she had bought the bulbs. Home Depot warned her not to vacuum the glass and directed her to a poison control hotline, which in turn referred her to the Maine Center for Disease Control and Prevention and the Maine Department of Environmental Protection. The DEP sent a specialist to test the mercury vapor levels in her home.

Here’s where the story starts to become fact-free: In her daughter's room near the broken bulb the mercury level was in excess of six times the EPA standard. This is completely accurate as far as the journalist knows – but at the same time, an utterly useless piece of information for trying to understand if there is a real health risk associated with a release of mercury from a broken CFL. Mr. Milloy gratuitously adds that the “safe” level for mercury is 300 billionth of a gram per cubic meter of air, a framing that tells you he really isn’t that concerned about the mercury exposure, but this was just too good an opportunity to pass up to beat up again on the folks who are concerned about global warming. I guess he doesn’t own any Philips stock.

Back to our story. DEP specialist told Ms. Bridges not to clean up the glass herself, but to call an environmental clean-up firm. The firm gave Ms. Bridges an estimate of $2,000 to clean up the broken bulb. Keep in mind this advice was completely inconsistent with the recommendations that EPA and many other regulatory agencies provide for disposal of broken bulbs. If anyone should be scraping together the money to deal with this, it should be the state of Maine, not Brandy Bridges.

The final irony in this misfortunate episode is that there probably was no real risk to begin with. Think about it for a moment. Mercury is a substance that requires cumulative exposure over a period of months or years to produce its adverse effects. And, a CFL contains around 5 milligrams of mercury, scarcely a pinhead’s-worth. No doubt that it will volatilize into a room, but how much mercury could that produce in the air, and for how long?

Quite a number of investigators have examined the problem of indoor air pollution from elemental mercury resulting from breaking mercury-containing thermometers, ritualistic uses and just playing around with mercury beads. In 2005, EPA published a series of studies examining mercury emissions and indoor concentrations under controlled conditions. I used the empirical model published in that report to estimate the air concentrations potentially associated with emissions of the 5 mg of mercury that would be released from breaking a CFL light bulb in a small bedroom under “average” air exchange conditions. The modeled mercury concentrations slightly exceed the “EPA standard” (the Reference Concentration, or RfC – which is not a standard, but that’s a story for another day) for a couple of days, but then drop below it, and fall well below it within two weeks. I hear the objections now, “but that’s not what the news story said”, but the factoid “six times higher than the EPA standard” is so poorly described and poorly informed, as to not even qualify as a factoid, and scarcely the basis for making environmental health decisions around CFL light bulbs. It’s certainly not persuading me to avoid using them.

Part 2 of this post coming to a blog near you discusses why being exposed for a couple of days to mercury concentrations in air higher than the RfC isn’t a public health problem, certainly not one warranting scaring people off from using CFL light bulbs. In addition, we can further discuss the matter of the choices we make to optimize environmental health and climate protection. But until then, don’t be afraid of CFL light bulbs because of the mercury in them (particularly if you’re getting the news from the Junk Science guy himself; consider the source).