Leif (PhD, Organic Chemistry, 1997) has measured and detected biogenic organic compounds, like semiochemicals and secondary metabolites, in trace amounts from animals and plants using mass spectrometry and other organic spectroscopies for twenty years. He has studied how these chemicals interact in ecosystems like the North American Sonoran Desert, Biosphere 2, the Amazonian tropical forest, and in plant-insect relationships. He has also investigated chemical interactions amongst marine microorganism assemblies, mammalian ligand receptors, and in the interstellar media. Most recently he is developing methods for analysis of trace, organic contaminants (e.g. endocrine disrupting compounds, PFAS, insensitive munitions) in complex environmental matrices like breastmilk and treated wastewater.