Phosphorus in archaeological soil: comparison of different extraction methods

Abstract

Phosphorus is one of the most widely studied chemical elements to identify paleoanthropogenic activity. Various methods have been used to analyse phosphorus in archaeological soil, however, general recomendations for the adequate choice of the research method are yet to be formulated. The search for a reliable and efficient method to estimate phosphorus of anthropogenic origin in soil is important from the applied point of view, especially in the case of a large series of samples.
The aim of these studies was to test different P extraction methods with samples of the known archaelogical context. The sample texture, elemental composition (XRF), pH, loss on ignition at temperatures of 550 and 1000 °C have been determined. The P extraction methods using aqua regia, 1 and 5M HCl, citric acid, Mehlich 2 and Mehlich 3 extractants, as well as sample ignition at 550 ir 800 °C have been tested. It has been determined that the proportion of total P (XRF) extracted by nearly all the methods was higher and in a better agreement with the total P in sand soil samples than that in loamy sand samples. The extraction of sieved/unmilled and ignited at 550 °C soil with 1M HCl appeared to be a reliable and sustainable method and therefore was best suited for the samples of the series studied.