Acid-free protocol for extracting pollen from Quaternary sediments

Abstract

Quaternary palynology commonly requires the use of acids such as hydrofluoric acid (HF), sulphuric acid (H2SO4), and hydrochloric acid (HCl) to extract pollen grains and spores. In some countries, restricted access to these acids makes fossil pollen studies challenging. Here, we propose an alternative pollen processing technique that does not require the use of acids. The methodology is mainly based on the use of potassium hydroxide (KOH) as a humic acid remover, sodium metaphosphate (NaPO3) and sodium pyrophosphate (Na4P2O7) as a deflocculant, and zinc chloride (ZnCl2) as a precursor for the flotation of the pollen grains. The techniques were tested and compared with a well-established and widely applied technique in palynology laboratories, which requires acids. For testing the techniques, 0.5 cm3 of samples from three different sedimentary environments (peat, lake, and swamp) in Brazil were used. The technique using sodium metaphosphate was successful because the structure of the fossil pollen grains and spores showed no retention of extraneous organic matter, thus facilitating their morphological identifications. The pollen grain concentrations for the sample were equivalent to the treatment with acids. This protocol was developed to allow broader, safer, and cheaper access to palynological research, as the impediments represented by restrictions on reagent controls do not apply. This protocol also respects environmental protection policies.