Programa e Resumos - I Congresso Ibérico de Ciência do Solo 2004

I Congresso Ibérico da Ciência do Solo – 15 a 18 de Junho de 2004, Bragança, Portugal
Heavy metals soil degradation in an area affected by mining wastes of
Murcia (Southeastern Spain)
Joaquin A. Hernández Bastida, Mª Teresa Fernández Tapia, Armando Ortuño Castellano
& Francisco Garcia-Villalba Hernández
1 University of Murcia, Dpt. of Agricultural Chemistry, Geology and Pedology, Campus
Espinardo, 30100 Espinardo, Murcia, Spain. Phone: 34- 968 - 367450 – Fax: 34- 968 - 364148
E-mail: hbastida@um.es
Summary
Communication: Poster
The mining wastes are a very important source of environmental contamination, mainly
by heavy metals anywhere they are located. Several areas of Murcia (SE Spain) have
been mining along 2500 years nearly for various metals (silver, lead, zinc, copper, iron,
etc.). The wastes of this activity are accumulated in a lot of silt ponds distributed on
several places. These acid mine spoils present high amounts of heavy metals most of
them are persistent in soil or have been transported by different watercourses to adjacent
places causing a strong environmental degradation. To know the most important soil
characteristics of this area and subsequently to establish the contamination level by
heavy metals and their availability is the aim of present paper.
The studied zone, with an area of about 20 km 2 , is located between Los Urrutias and
Los Nietos villages, very close to Mar Menor (Murcia, SE Spain) and shows an arid
climate with a strong water deficit along the year; the average temperature is about 18ºC
and the rainfall is never higher than 300 mm. According to Alías et al. (1999) the main
soils are Haplic Calcisols, Calcic Luvisols, Calcaric Arenosols and Gleyic Solontchaks
(FAO-ISRIC-ISSS, 1998). Twenty-one sampling points from the arable layer (0-30 cm)
were taken according to a regular sampling grid of 1 km 2 , besides a soil profile of
Gleyic Solontchak. Van Rieuwjk analysis methods (1995) are used to determine soil
properties. The total metal content was determined on acid microwave digestions while
DTPA-extractable metals were determined on adequate soil extracts (Lindsay and
Norvell, 1969), by Atomic Absorption Spectrometry using electrothermal (ETAAS) or
flame atomization (FAAS).
The results show for these samples, in a general way, a low organic carbon content (1-
18 g kg -1 ). There is a wide pH differences (5.5-8,2) because of the oxidation of
sulphides provokes a strong pH decreasing in some points. Variable amounts of CaCO 3
(40-250 g kg -1 ) appear in the samples with alkaline pH values. Most of the samples have
high electrolytic conductivity (2-130 dS m -1 ) in the saturation extract. On the other hand
these the total content of heavy metals present in these soils are in a wide rank of
values: Cr (25-100 µg g -1 ), Cu (15-300 µg g -1 ), Mn (600-7000 µg g -1 ), Ni (20-40 µg g -1 ),
Pb (500-20000 µg g -1 ) and Zn (500–11000 µg g -1 ). However the DTPA-extractable
metal contents are much lower and within levels considered non-toxic except in those
zones with acid pH values that show a more high content. Therefore it is necessary to
control pH values in those points so that these metals are kept in a low availability for
the crops and, consequently they do not cause a toxic effect.
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