Interesting Chemistry in Seabird Eggs

Sheryl Tittlemier went to high school in Selkirk, Manitoba and decided to go into chemistry in university because she had fun in chemistry class in high school. When attending the University of Manitoba she worked summers in the chemistry research labs and at the Freshwater Institute before graduating with a B.Sc. in 1996. She is presently in the third year of her Ph.D. program in environmental analytical chemistry at Carleton University in Ottawa  Sheryl describes her Ph.D. research in the following way:

Many people associate pollution and toxic chemicals with human activities. Likewise, they may believe that since a substance is "natural" it somehow must be good. This fact is obvious when you walk down an aisle in a pharmacy or grocery store and see many products advertised as "naturally-produced" or "all-natural". Aside from being common, this way of thinking is also incorrect. In January 1999, as part of research for my Ph.D. thesis, our group published results that showed there may be naturally-produced chemicals in the environment that behave like industrially-produced toxic chemicals.

Back in 1988, Mary Simon, a mass spectrometrist at the National Wildlife Research Centre in Hull, Quebec, found a compound in a bird egg sample during routine pesticide testing that didn’t look familiar. Preliminary work suggested that the compound was organic, and that it contained both bromine and chlorine. This mixed halogenation was unusual for industrially produced pesticides.

Study on the compound stopped for a few years until Mary saw it again in a sample of a bald eagle liver from BC.  This time though, the compound was present at 5 parts per million, a high level for an organohalogen compound. She also found that there were other similar brominated and chlorinated compounds, but with different numbers of bromine and chlorine atoms.

Work on these mixed organohalogens stopped again until 1996 when I started my Ph.D. with Dr. Ross Norstrom, a research scientist also at the National Wildlife Research Centre. The first step in my work was to determine the molecular formula of the compounds. Using high resolution mass spectrometry, we determined the formulas of the four observed compounds to be C₁₀H₆N₂Br₃Cl₃ , C₁₀H₆N₂Br₄Cl₂, C₁₀H₆N₂Br₅Cl, and C₁₀H₆N₂Br₆ . A thorough literature search revealed no previous mention of compounds with any of these molecular formulas.

   Our next step involved finding out how widely distributed these compounds were. We took some liver from the highly contaminated bald eagle that Mary had previously worked on, and extracted out the organohalogens. We measured the amount of the major component, C₁₀H₆N₂Br₄Cl₂ , and then used the extract as a standard to measure C₁₀H₆N₂Br₄Cl₂ in bird eggs from the Pacific and Atlantic coasts of Canada, and from the Great Lakes.

    Surprisingly, we found that C₁₀H₆N₂Br₄Cl₂ was present only in the marine samples - it was not detected in any of the Great Lakes samples. Eggs from the Great Lakes contain relatively high amounts of a variety of man-made organohalogens, including PCBs and pesticides. The industries and communities present around the Lakes act as sources of these chemicals. The absence of C₁₀H₆N₂Br₄Cl₂ from the Great Lakes samples led us to believe that these mixed halogenated compounds were not man-made, but were naturally-produced.

    During the bird egg study we were also trying to figure out the molecular structure of these compounds. The structure of a molecule determines its function, and leads it to behave in certain ways. Molecular structure determines toxicity, distribution of a chemical in the environment, and whether a chemical will accumulate in wildlife or be metabolized. We had a breakthrough in the search for the structure when Dr. John Faulkner from the Scripps Institute for Oceanography in California told us about some of his previous work with marine natural products.

    It seemed that the mass spectrum of our compound was very similar to that of a compound produced by a marine bacterium that Dr. Faulkner’s group discovered.The structure of their compound was a hexabrominated bipyrrole (pyrrole is a five membered aromatic ring containing one nitrogen and four carbon atoms; bipyrrole is two connected pyrrole rings). We proposed that the structure of our compound was the same, except with a methyl group attached to each nitrogen atom.

    The dimethyl bipyrrole structure is similar to other toxic, persistent chemicals in that it is aromatic and contains a large number of halogen atoms. These two structural features also make it difficult for an animal to metabolize such compounds. Therefore, the compounds can accumulate in animals over time and up a food chain. This is consistent with the high levels which were found in the bald eagle liver sample.

At this point we are taking three different paths for our research. First, we are trying to find the exact molecular structure - we still don’t know the specific position of the bromine and chlorine atoms on the pyrrole rings. Second, we are going to study the worldwide distribution of the dimethyl bipyrroles in marine animals at the higher end of their food chains: seals, sea lions, dolphins, and porpoises. Finally, we are going to find out whether or not these compounds have any toxic activity. We expect that they do, since marine organisms are thought to make organohalogens as a chemical defense to protect themselves from predators.

    If the source of the halogenated dimethyl bipyrroles can be confirmed to be a marine organism, this will be the first instance of a naturally-produced organohalogen accumulating in wildlife. It will also be another piece of evidence showing that something "natural" does not necessarily mean that it’s "good".