Detalles: La conferencia inaugural del Programa de Doctorado de Recursos Naturales y Medio Ambiente de la Universidad de Sevilla será impartida por la profesora de la Universidad de Nápoles, Paola Adamo, el 29 de octubre a las 12.00 horas en el salón de actos del Pabellón de Méjico. Cuenta con la colaboración de Real Academia Sevillana de Ciencias y del CNA (Unidad ACOMETA).
La Doctora Adamo versará su ponencia sobre el tema"Chemical speciation, bioavailability and geochemical forms of toxic metals in polluted soils”.
MICAL SPECIATION, BIOAVALABILITY AND GEOCHEMICAL FORMS
OF TOXIC METALS IN POLLUTED SOILS
Paola Adamo
Dipartimento di Agraria, Università di Napoli Federico II, Portici, 80055, Italy
e-mail address: paola.adamo@unina.it
The term potentially toxic metals (PTMs) includes essential (e.g., Cu, Mn, Se, Zn, Co) and
nonessential (e.g., Hg, Cd, Pb) elements. The elements essential for plants and animals are
required in low concentrations and are termed micronutrients, but at high concentrations
they may be toxic for plants, animals, and humans. In the soil environment potentially toxic
metals (PTMs) are persistent contaminants and it is generally accepted that their
distribution, mobility, biological availability and toxicity depend not simply on their total
concentrations but, critically, on their forms. These may be soluble, readily exchangeable,
complexed with organic matter, or hydrous oxides, substituted in stoichiometric
compounds, or occluded in mineral structures. Any changes in in environmental conditions,
whether natural or anthropogenic, can alter the forms of PTMs, thereby affecting their
behaviour in soil. The main controlling factors include pH, redox potential, sorption–
desorption reactions, chemical complexation with inorganic and organic ligands, and time.
Metal bioavailability is the fraction of the total metal occurring in the soil matrix, which can
be taken up by an organism and can react with its metabolic system. Metals can be plantbioavailable,
if they come in contact with plants (physical accessibility) and have a form
which can be uptaken by plant roots (chemical accessibility). Soil metals become accessible
for humans by ingestion, inhalation and dermal contact. Available forms of PTMs are not
necessarily associated with one particular chemical species or a specific soil component.
Plant roots absorb nutrients from the soil solution, but rarely availability is equated with
solubility.
The common determination of PTMs total or “pseudototal” content in soil might minimize
the risks for biota and human health, assuming that contaminants transferring to water
resources or biota are basically correlated with contamination level. In contrast, relevant
paradigms in environmental monitoring, risk assessment and remediation feasibility are the
PTMs mobility and availability to microorganisms, plants, animals and humans. For a
proper assessment of risk/toxicity (according to PTMs content and availability) of a
polluted soil and to predict its attenuation after application of remediation techniques it is
crucial to establish the speciation, mobility, and biogeochemistry of the contaminants. In
this sense, a requirement exists for analytical methodologies and strategies providing
information on the dynamics and behaviour of PTMs in soil.
Speciation science seeks to characterise the diverse forms or, at least, the main metal pools
in which PTMs are present in soil. It can be achieved using either direct, mainly nondestructive,
or indirect analytical methods. The lecture describes the fundamental principles
of soil pollution by PTMs and provides a critical review of the single and sequential
chemical extraction procedures that have been widely applied to determine the plant
bioavailability and the main geochemical forms of PTMs from contaminated soil. Examples
of complementary use of chemical and instrumental techniques and applications of PTMs
speciation for risk and remediation assessment will be illustrated.
Key words: soil pollution, bioavailability, speciation, chemical extractions, risk assessment