Evaluating the environmental soil quality: a case study of the city of Seville
In urban areas, although soils acquire properties and functions different than their agricultural equivalents, they maintain a fundamental role in the preservation of local and regional environmental quality. Besides esthetical and recreational functions in parks and gardens, they contribute to the preservation of urban natural riches while influencing citizens' quality of life. Attending to the high percentage of people inhabiting urban areas it became crucial to understand the status of urban soil quality and define quality indicators and guidelines in order to generate tools for sustainable soil management. To achieve this objective URBSOIL project adapted current methods for studying soils to urban settings. Sophisticated analytical techniques as well as easy-to-handle rapid tests were used for the measurement of soil parameters for various cities in Europe. A unique data set was generated which covered a wide range of quality indicators from simple bulk parameters such as pH and cation exchange capacity to specific analytes such as heavy metals. Two different methods were used to determine the metal contents of soil samples taken from parks and allotments in the urban area of Seville. Using a strong acid digestion, aqua regia, the metal pollution evaluation was conducted based on "pseudo" total metal concentrations without taking into consideration mobility and bioavailability of metals in different forms. Metals of higher availability were extracted with EDTA solution. Additionally, Standard Measurement and Testing programme's sequential extraction scheme was performed in order to obtain information about metals fractionation. Moderate pollution was revealed in soils from public-access areas and a common pattern was found in the distribution of the concentrations of some particular metals. Concentrations of copper, lead and zinc at several localized sites, often ornamental gardens, exceeded limits established as acceptable in residential areas. However, in most parks the values of these metals considered of urban origin were less than those considered as normal in literature. These findings can be further refined when considering additional data obtained from other cities in order to provide a more realistic environmental situation. Resultant datasets will serve as input parameters for state-of-the-art modelling of changes in soil quality and build-up of decision support system.
