A graphical technique for distinguishing soil and atmospheric deposition in biomonitors from the plant material

This paper explores the limits to which a new graphical technique based on log-log plots of selected elemental ratios can distinguish the various hierarchical levels of sources of trace elements within biomonitors. When applied to a large suite of samples from Portuguese lichens that had been analyzed by neutron activation and proton-induced X-ray emission, the technique appears to be able to resolve four levels of sources, including plant material, local soils, the three major components of atmospheric deposition (crustal, marine, pollution), and individual types of pollution such as oil and possibly incineration and nonferrous smelters. Careful factor analysis with the new Positive Matrix Factorization produces seven or eight defensible factors, including lichens, marine, oil, industry, coal, and two to three crustal factors (lighter elements, heavier elements, and resistate elements). Proportions of key elements in these factors fell within 30–50% of proportions determined graphically and sometimes were indistinguishable from them. Thus, it now seems possible to determine sources for elements in lichens with considerably more detail, precision, and reliability than were available previously.