The rise and fall of bromided flame retardants
A drilling core tells a poisonous tale
Empa has coaxed the life story of bromided flame retardants from a drilling core cut from the bed of the Greifensee lake their rapid ascendancy following their market launch, their subsequent fall from grace once their toxicity had been recognized and the explosion in popularity of their successor. The drilling core will be on display at Empa's Open Day in Dübendorf on Saturday 25 June 2005.
Bromided flame retardants are an effective way of preventing plastics and textiles from burning. But protection comes at the cost of undesirable side effects, and several of these industrial chemicals are hazardous. For this reason they have not been used in Europe for several years. Empa, in conjunction with Eawag, the Swiss Federal Institute of Aquatic Science and Tecnology, recently confirmed this using a drilling core from the bed of the Greifensee lake. Following rapid growth in the 1980s, volumes of this flame retardant started to fall slightly again as of 1995. However, Empa has also established that concentrations of one of its successors are rising worryingly.
Bromided flamed retardants decompose only very slowly. Year by year they are deposited in lake bed sediment, thereby recording their own history. In 2003 Empa and Eawag decided to unearth this history. Eawag drilled a 150 cm core out of the bed of the Greifensee lake and dated its "rings" by measuring the isotope caesium 137. Large quantities of this isotope were released during the Soviet atom bomb tests in 1961/62 and following the explosion of the Chernobyl reactor in 1987, and it is to be found in the appropriate layers of the core.
After being cut into slices and freeze dried, the top 42 cm of the drilling core finally arrived in Empa's laboratories. Here scientists are conducting in-depth research into bromided flame retardants. As part of National Research Programme 50 Endocrine Disruptors: Relevance to Humans, Animals and Ecosystems they are studying their environmental characteristics and developing methods for detecting them chemically.
POPs a long-term hazard
Researchers extracted the substances from the sediment, cleaned them and examined three types of bromided flame retardants, each with a different number of bromine atoms in the molecule. The molecules in question are pentaBDE (five bromine atoms), octaBDE (eight bromine atoms) and decaBDE (ten bromine atoms). PentaBDE and octaBDE are POPs or persistent organic pollutants. POPs are toxic substances that do not biodegrade easily and are bioaccumulatable in other words they amass in the food chain.
PentaBDE and octaBDE both possess these properties. They are hormonally active, affect hormone levels and are suspected of disrupting the development of people and animals. They are also extremely long-lived. Wind and water have carried them to all corners of the globe; they can even be found in the polar bears of the Arctic. And they are transmitted along the food chain, from the tiniest organisms through to the top consumers people and carnivorous animals. By contrast decaBDE is unlikely to be a POP because research to date has not produced any evidence that it is bioaccumulatable. Furthermore it is less toxic.
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The drilling core cut from the bed of the Greifensee lake impressively documents the history of bromided flame retardants. However, it also recounts the rise and fall of other pollutants: PCB, an insulator used in electrical applications; dioxins, the substances that are released when chemicals are incinerated; and DDT an insecticide. All these substances are highly toxic and were banned as soon as their hazards were recognized.
The results of the analysis of the drilling core have recently been published. PentaBDE and octaBDE first appear in the sediment of the Greifensee in 1960. Concentrations peak in 1995 and since then have been falling slightly. By contrast, concentrations of decaBDE have shot up in the last 20 years, doubling every nine years.
The reasons for this trend are political. With a ban on pentaBDE and octaBDE looming in the mid-1990s, European industry voluntarily stopped using the substances. The EU ban took effect in June 2004. Since then decaBDE has been used as a less harmful substitute and in increasing quantities.
The scientific community is alarmed at this trend. Empa's initial investigations show that decaBDE biodegrades into substances similar to the toxic pentaBDE and octBDE. In other words, the "less harmful" substitute in fact harbours hazards of its own. It is planned to conduct further research projects to establish which decomposition products are formed and how they are carried into lakes and food chains. Empa and Eawag are also planning to take further drilling cores from Alpine lakes.