My background is in mass spectrometry and analytical chemistry. I had a long-standing interest in halogenated and aromatic compounds—PCBs, for instance. The concentrations of these compounds in the environment are going down, in some cases rather dramatically. So I was at a meeting in Stockholm in 1998, sitting in the audience in a darkened room, when this Swedish student presented a paper about PBDEs in human milk in Sweden as a function of time.

The Swedes had the foresight to actually keep an archive of human milk samples for at least the last 30 years—maybe longer. This student went back and analyzed many of those samples, and the concentrations of PBDEs were not only increasing, they were doing so exponentially, doubling in concentration about every five years. Well, I woke up.

“I don’t want to leave anyone with the impression that these brominated compounds are inherently bad. They’re persistent, and they do move around in the environment. On the other hand, they do prevent fires.”

I had been a little worried before that the compounds I was studying would disappear from the environment before I retired. Here was something that was increasing—dramatically—which meant it was something out of control. The data were very striking. I put my hand up, and asked, "Can you tell me why the concentration is going up?" She looked up at me and replied, "I’m not as old as you are, so I really couldn’t tell you." After that, I came back to the US and assigned one of my students to look into it.

I had been collaborating with a colleague in the medical school here at Indiana University, in the department of obstetrics and gynecology, so I asked him about PBDEs in people. The first thing he said was that it would be really interesting to look at babies. If the PBDE concentrations in human milk were going up, these concentrations were probably going up in babies too. Eventually, we were able to get delivery room nurses, after the delivery, to drain some blood out of the umbilical cord—blood that minutes ago had been in the baby. We analyzed those samples and found relatively high levels of PBDEs. In fact, the levels were 10 to 20 times higher than they were in the human milk samples from Sweden.

In the meantime, we actually went through the human subjects committee and got permission to sample the mothers’ blood, as well. The concentrations in the mothers and in the babies were very similar, again 20 times higher than in Europe. That was a striking finding.

Then my students went on to do a variety of other studies, mostly related to PBDE concentrations in the Great Lakes.

Well, it was published in Environmental Health Perspectives, a journal with a pretty good citation index, so I really don’t know. Reviews always get a lot of citations, which basically explains why my 2004 paper in Environmental Science and Technology ("Polybrominated diphenyl ethers in the environment and in people: A meta-analysis of concentrations," 38[4]: 945-56, 15 February 2004) has been cited a lot.

When I did that review, I got together all the concentration data that existed at that time. The interesting thing is that I was able to get human tissue, blood, and milk data from pretty much all around the world. There was not much data from China, but in Japan, Europe, and the US. When I plotted all that data as a function of time, I saw a significant concentration increase starting in the 1970s. After that, these concentrations doubled every three to five years. In addition, the US concentrations were well above the regression line by a factor of at least 10 or 20.

I’m an associate editor of ES&T, which is the number-one rated journal, by any number of measures, in environmental chemistry. The only topic ES&T doesn’t fully cover is the ecology side of environmental science, but the chemistry, physics, and engineering sides are all covered well. ES&T has the highest rating for science in Journal Citation Reports® in the field of Environmental Engineering. It’s very highly rated, and people read this journal. It’s the one journal you can publish in and know that everybody in the environmental chemistry community will see it.

I put the human baby data in Environmental Health Perspectives because I thought that audience was a little more attuned to environmental pollutants in people than ES&T, although ES&T would probably have taken it as well. On the other hand, ES&T has a 65% rejection rate, so it’s even getting tough for me, an associate editor, to get my papers in there.

As you might expect, everybody has been measuring PBDEs in everything. There are probably another 200 papers on PBDE concentrations in this, that, or the other thing. In fact, those papers are getting increasingly difficult to publish because we know PBDEs are in everything.

What’s now going on is a little more on the side of mechanistic interests. How do PBDEs get from the place where they are used—namely in polyurethane foam or plastic or carpet padding—into people and out into the environment? How are these compounds transported through the environment? As they move through the air, do they undergo any reactions with light or with hydroxyl radicals? How do these compounds partition to particles? How far does this atmospheric transport take these compounds? In addition, research interests have moved on to include decabrominated diphenyl ether—the jargon is BDE-209.

Initially, people had been finding tetra- through hexabrominated PBDEs in the environment, and these had come from two commercial products: one was called the penta product, and it was a mixture of brominated diphenyl ethers with four to six bromines, and the other was called the octa product, which was a mixture of brominated diphenyl ethers with six to nine bromines. Given these early results, there was enough public pressure and enough interest from the press that these two products were withdrawn from the marketplace.

The other major PBDE product consisted almost exclusively of decabrominated diphenyl ether, and there was about 10 times more of this being manufactured than of the penta and octa products. The deca PBDE product was not removed from the market, and the companies that make it maintained that it "is like a rock," and it is probably going to stay on the market.

Around 2004, the analytical technology for decabrominated diphenyl ether got better, and now everybody is interested in measuring it in animals like polar bears and penguins. If you went to conferences in 2004 on brominated flame retardants, there wouldn’t have been much discussion about deca PBDE, but at the last conference I went to in April of 2007, at least half the talks were about it.

The issue is two-fold. One question is, does the deca degrade to lower homologues—say, to penta or tetra PBDEs? It does under some conditions, and doesn’t under others. So that’s an open issue. The other question is more straightforward: is deca persistent and bio-accumulative? If it can be shown that this is the case, then that’s a presumption for it to be considered an environmental problem in Europe. This argument will not work in the US, though. In the US, you have to show a compound is toxic before its use can be restricted. It seems to me that finding deca in the Arctic is a pretty good indication that it’s persistent.

I’m still working on brominated ethers. I just had a student graduate about a month ago, who looked very carefully at some chemistry questions. He measured gas-phase rate constants for the reaction of PBDEs with the hydroxyl radical in a fundamental study. Then he put together a mass balance model to show why the different PBDE homologues accumulate in lake sediment differently. I also have a long-term study going on, in which we are measuring the atmospheric concentrations of brominated diphenyl ethers every 12 days at five different sites around the Great Lakes.

A big challenge has been lack of funding. The EPA actually funded the student I was just telling you about through one of their STAR fellowships, which are very hard to come by. I was really impressed that he was able to get one. The measurements around the Great Lakes that we’re doing are funded by the Great Lakes National Program Office of the EPA. But the national EPA is not putting any money into PBDEs at all. My guess is that this is for two reasons: one, why do any research? It’s crossed off the EPA’s list; PBDEs are not made any more. The other reason is that the EPA doesn’t have much money to be doing research of any sort.

The fact that US environmental and human levels of these compounds are 20 times higher than those in Europe was striking to me. But once you go back and look at where brominated flame retardants are sold and what kind of material is sold in different places, it makes sense. I gave a talk on this once and there were a bunch of Europeans in the audience. I said the average US PBDE concentration in people is about 30 nanograms per gram of lipids and in Europe it’s about two. A Swiss guy shouted out from the back of the room, "Once again, the US wins by 28 points."

An interesting finding is that the Japanese levels are a lot lower than those in Europe, which was a surprise. The Japanese eat a lot of fish—about 300 grams of fish a day, and we eat maybe 10 grams here. That means the Japanese diet is very much more closely connected to the environment than ours. Most environmental pollutants would be expected to be higher in the Japanese. Mercury levels, for example, are a lot higher in Japan than here. So it was a surprise that the Japanese levels were so low. This result probably means the Japanese don’t use as much of these diphenyl ethers to flame-retard their household goods as we do.

Yes. I don’t want to leave anyone with the impression that these brominated compounds are inherently bad. They’re persistent, and they do move around in the environment. On the other hand, they do prevent fires. You and I are probably sitting on polyurethane foam right now. Without flame retardants in that foam, if you dropped a cigarette on it, you’d have a pretty good fire. That’s also true of mattresses, which have to be flame-retarded because of people who smoke in bed. Without brominated flame retardants, there would be a lot more deaths by fire.

I talk to the manufacturers about their products; we all go to the same conferences and we heckle each other. These guys believe that they’re doing good work preventing fires, which could kill thousands of people if they didn’t manufacture these compounds and that we are just alarmist environmentalists who can detect these compounds at levels that don’t mean anything. I ask why don’t they find a product that doesn’t get out into the environment and accumulate in people and animals, such as polar bears? They do respond to bad press, and they do take some of their products off the market. I assume they are now marketing new brominated flame retardants that are not as environmentally persistent and transportable. That’s all anyone can ultimately ask from the flame-retardant industry: they should keep making flame retardants, but they should figure out a way to make them stay put in the polyurethane foam.

Ronald Hites, Ph.D.
Distinguished Professor
School of Public and Environmental Affairs
Indiana University
Bloomington, IN, USA