The use of lithium heteropolytungstate in the heavy liquid separation of samples which are sparse in pollen

We experimented with the use of lithium heteropolytungstate (LST) as a heavy liquid to concentrate pollen in sediments from a desert paleolake with low pollen abundance. LST is one of several non-toxic heavy liquids based on inorganic tungsten that are replacing an older generation of heavy liquids that are harmful to human health, such as zinc bromide, zinc chloride, and bromoform. Several researchers have reported on the use of sodium heteropolytungstate (SPT) in processing pollen samples, but we found no previous reports on using LST in pollen preparation. For our low pollen desert samples, we developed a palynological preparation procedure with LST heavy liquid separation that entails fewer chemical treatments and washes than standard protocols, to minimize laboratory destruction or loss of pollen. In the heavy liquid step, we varied centrifuge times and the specific gravity of the LST solution in an effort to extract the most pollen possible. In the end, our samples proved too pollen-poor to yield countable residues, even under the best circumstances. But our protocols and results can serve as models for experimenting with this new heavy liquid with other sediments.