2015 IMPEL Soil Conference -“Many Soil Functions, many reasons to protect it”
ASSESSING BACKGROUND VALUES OF METALS AND METALLOIDS
IN SOILS OF THE VENETO REGION
Paolo Giandon, Adriano Garlato and Francesca Ragazzi
(1) ARPAV – Environmental Protection Agency of Veneto Region – Soil Unit, via S. Barbara 5/A, 31100 Treviso, [email protected]
During soil field description for the realization of the regional soil map, throughout several years, ARPAV has
measured the concentration of some metals and metalloids in soil, with the aim of defining a basic information level
for the regional territory.
Determination of metal background values in soil was carried out as specified by ISO 19258:2005 (Soil Quality Guidance on the determination of background values), the international reference for sampling, analysis and data
elaboration.
The choice of sampling sites was carried out following the "typological approach" of ISO 19258:2005, i.e.
depending on the parent material, soil types and land use. Homogeneous areas were defined by parent material
composition.
2393 samples were totally analyzed, of which 1363 taken from upper layer and 1030 taken from deeper. In the
plain 1119 samples from upper layer and 835 from deeper, while in mountain areas 244 from upper and 195 from
deeper.
The analytical determination of the "pseudo-total" fraction of antimony, arsenic, beryllium, cadmium, cobalt,
chromium, copper, mercury, nickel, lead, selenium, tin, vanadium and zinc was performed through aqua regia
extraction and ICP-AES detection.
Statistical analysis of data was worked out for the whole dataset and for each homogeneus unit. Some descriptive
statistics were performed, keeping separate values of upper horizons from the ones of deeper; for each variable
many parameters were determined mean, median, minimum, maximum, percentiles (5th, 25th, 75th, 90th and
95th), standard deviation, standard error, skewness and kurtosis, normality tests. Once outliers were removed,
background value for each metal was determined by means of 95th percentile value within each
depositional/physiographic units. Background values were then compared to threshold limits for residential sites
stated by Italian environmental act (D. Lgs. 152/2006).
If compared to the limits of Italian law for gardens and residential sites, 24% of analyzed samples (in upper layer)
overcomes screening values for arsenic, 12% for vanadium and 8% for cobalt and zinc; in the deeper layer 27% of
samples exceeds screening values for arsenic and 12% for vanadium.
For antimony, mercury, lead, copper and selenium pedo-geochemical background values no exceeding of
screening values for residential sites in any depositional or physiographic units occurs. For lead and copper 2 units
exceed it.
For cadmium both for pedo-geochemical and background screening values exceeding occurs only in prealpine
area on hard limestone also if values next to them are observed in all Prealpine units on soils developed from marly
limestones.
Arsenic, beryllium, cobalt, chromium, nickel, vanadium and zinc values exceed screening values in many units both
in upper and deeper layers, involving a significant area within the region.
The units with the highest number of both pedo-geochemical and background values exceeding the screening
values are the Prealps on basalts and Prealps on limestones units in mountain area and the Agno-Guà and the
Leogra-Timonchio river fan units in the plain, which receive alluvial deposits from the alteration of basalts, in which
concentration of zinc, nickel, chromium, cobalt, arsenic, tin and vanadium is significantly higher than in sedimentary
rocks (Alloway, 1995; Kabata Pendias, 2001). Exceeding of chromium, nickel, cobalt and vanadium often occurs in
the same unit.
Milan, Italy - 7th and 8th October, 2015