INTEGRATED METHODS FOR ASSESSING HEALTH POTENTIAL RISK AND BENEFITS OF CLAY SEDIMENTS. A CASE STUDY

In this contribution to the 5^th IMGA conference, we report the data resulting from a multidisciplinary study aimed to assess potential health risks of clay sediments outcropping in Basilicata, Italy. We collected 25 samples of marine clay sediments from outcrops having different age, stratigraphic position, and diagenetic degree. The samples were characterized for their mineralogical, geochemical, microbiological and rheological characteristics.

Mineralogical compositions were determined by XRD. Morphological and microchemical observations were carried out by SEM. Major elements were measured by XRF. Clay fraction was submitted to a selective sequential chemical dissolution by the BCR procedure. Concentrations of a set of 17 trace elements (As, Be, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Se, Sn, Te, Tl, V, Zn), relevant in the Italian legislation, and Fe, Mn and K were measured by ICPMS.

Major elements chemical composition, specific surface and cation exchange capacity are in agreement with the mineralogical composition.

Trace elements (TR) distributions in the extracting solutions vary largely. The amount of TR associated with the most mobile fraction is low and higher amounts were measured for Mn (8%) and Cd (5%). Mn (21%), Co and Te (15%) and Cu (13%) are significantly associated with the oxidisable fraction. A surprisingly high amount of Cd (17%) is associated with organic fraction.

The sum of the average values of the 3 steps led to calculate the following elemental mobility: Cd>Co>Cu>Te>Ni>Se>Be>Pb>Mo>Zn>As>Fe>V>K>Cr>Tl>Sb>Sn

Although high elemental mobility has been measured for hazardous chemical elements, their concentrations are low and do not constitute a risk for health and the environment. This conclusion is supported by microbiological investigations and cytotoxicity tests carried out using both animal and human cell lines that gave negative results thus confirming that the examined clays are “safe” sediments.

The high mobility of some potentially harmful trace elements should push to measure their concentrations and mobility in clays before their industrial applications and human uses.