Chromium and nickel in stream sediments: comparing different methodologies for background level identification

Roberta Sauro Graziano (a), Stefano Menichetti (b), Stefano Tessitore (b) & Antonella Buccianti (a)
(a) Department of Earth Sciences, University of Florence, via G. La Pira 4, 50121, Florence, Italy. (b) ARPA Toscana, via N. Porpora 22, 50144, Florence, Italy. Corresponding author e-mail: roberta.saurograziano@unifi.it.

This research focuses on chromium and nickel behaviour in stream sediments, sampled in the Northern Apennines section interested from work on the new A1 highway segment, known as “Variante di Valico”. In order to verify possible relationships between anthropic activities and dispersion of metals during highway construction, we have characterized the background value. With this purpose, we have applied graphics and statistical surveys, since Italian law does not provide threshold parameters for stream sediments natural background, as in the case of other environmental matrices. The study area is featured by the presence of ophiolithic outcrops that represent a possible geogenic source of contamination, as they are known to be enriched in these elements. Frequency distribution analysis highlighted normal Gaussian model does not seem to be suitable as single mechanism of values generation and to identify the 95th percentile threshold. Therefore, it’s necessary to carry out indepth investigation.

background value, stream sediment, frequency distribution.