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Urban soils as a source and sink for pollution : towards a common european methodology for the evaluation of their environmental quality as a tool for sustainable resource management

Exploitable results

General guidelines for the sampling of soils from different types of land surface within the urban environmental have been drawn up. Sampling regimes appropriate to large, visually homogeneous areas of land, roadsides, riverbanks, and sealed surfaces are proposed. Recommendations are also provided for sample pre-treatment and storage. Protocols must be selected on the basis of the analytes of interest and purpose of the urban soil study.
The user-oriented standardised report on urban soil status has been developed. Standard report delivers the comprehensive and accurate information on investigation of soils including the end-user (non-expert) oriented interpretation of analytical results. The standard soil report was defined to: -Produce the exact information on soil analytical data. -Interpretation of the state of the soil pollution in the location. -Interpret the analytical results for non-experts. -Give the overview of the analytical information in the context of the legislation on soil pollution. -Information on sampling location, land-use, possible sources of pollution and additional information important for the interpretation. -Comments and suggestions on possible remediation measures. The Report is composed of three, optionally four pages. Page 1: Sampling site geographical information, coordinates, location name, aero-photo picture of the sampling location including neighbourhood area, picture from the ground, soil type, land use, details on sampling campaign. Comments on soil pollution and general soil quality interpretation or remediation suggestions can be given. Page 2 contains the standard soil analytical information (texture, pH, organic matter, CEC, base saturation) and it's graphical presentations for non-experts. Page 3: Inorganic substances in soil (predominantly heavy metals which are listed in the legislation), analytical information and the graphic interpretation regarding to the legislation. Page 4 is optional and contains information on organic substances. A set of the possible organic pollutants is site specific and differs from town to town.
Potentially toxic elements have been measured and fractionated in soil samples from public-access areas in Glasgow, UK. The spatial variability of analyte concentrations has been studied (a) within two urban parks and (b) across 94 sites (including parks, roadsides, riverbanks and ornamental gardens) within the city. Levels of analytes were broadly similar to those reported in previous studies of large, industrial cities. A few soils contained chromium, nickel or lead concentrations in excess of the UK CLEA soil guideline values. Distribution profiles, and variability in analyte concentrations, were assessed in order to distinguish elements arising mainly from natural sources from those influenced more strongly by Man. Aluminium, iron, lithium, magnesium and manganese levels were least variable and more frequently normally distributed, indicating that these elements are predominantly natural in origin. Barium, calcium, copper, chromium, lead and zinc were characterised by higher variability and non-normal concentration distributions, suggesting anthropogenic sources are important. Principal component analysis confirmed these relationships, grouping the "natural" elements separately from the "urban" metals, and revealed that chromium behaved differently from either group. PCA scores constitute a potentially useful tool for Local Authorities attempting to identify particularly contaminated sites. When applied to soils from Glasgow, the four-step sequential extraction protocol developed under the auspices of the EU BCR, revealed no differences between analyte fractionation patterns in park and roadside soils, nor between samples with markedly different pseudototal (aqua-regia soluble) metal concentrations. Chromium and nickel were found predominantly in associated with the residual phase of the soils, but ~ 73% of the lead content was released in step 2, indicating this elements has high potential mobility. The work illustrates the need to consider lability, as well as total concentrations of potential toxic elements in both contaminated site risk assessment and the setting of legislative limits.
Experience gained in the urbsoil project suggests that, although proper quality control is vital for the production of valid analytical data, not all expert soil science laboratories have detailed knowledge about its role and implementation. The inclusion of suitable quality assurance measures should be a pre-requisite for future collaborative studies on urban soils in Europe. Specific recommendations: 1. Partners should review their current practices and methodology against international standards and agree on harmonised procedures before practical work commences. 2. ISO methods should be used wherever possible. 3. Even where common methodology is agreed, partners should conduct appropriate inter-laboratory tests to ensure results obtained are comparable. 4. Partners should include analysis of appropriate reference materials in their work to ensure analytical methods remain under control for the duration of the study. At least one CRM (or RM) should be included in every batch of analysis. 5. Partners should appoint a Quality Manager from amongst the group (preferably with experience in analytical science) to oversee the implementation of the QA scheme.
In view of the difficulties of sampling and monitoring the environmental quality of urban soils we propose the implementation of one or more PERMANENT MONITORING AREA (PMA) within cities. These are areas devoted to the periodic measurement of soil properties and contaminants according to a defined spatial and temporal scheme. The establishment of PMAs has the following advantages: a) Costs are significantly lower than extensive monitoring; b) Allows analytical synergies as many parameters can be measured for the same site and correlated; c) Allows for temporal variability of parameters to be more easily detected; d) Reduces problems of spatial variability (which would be known); e) Allows for links between environmental compartments to be better investigated (PM10 from soil, contaminant leaching, diffuse contamination,¿); f) Allows for investigation of the effects of environmental measures GUIDELINES FOR THE ESTABLISHMENT OF A PERMANENT MONITORING AREA a) Size and shape It is recommended that a PMA has a surface of about 40-50000m2. This would correspond approximately to a 200 x 200m square but the no precise indication can be given about the shape, as it has to adapt to the available space. An example of a possible Permanent Monitoring Area is presented in the figure below. The proximity with Air Quality and Traffic monitoring stations make this site particularly suitable for this type of installation. b) Number and location The number and location of PMAs depends on the limitation of available space, as describe above. However they should be conveniently located (centre/suburb, industrial/residential, etc) according to the main features of the urban ecosystem and to the parameters to be kept under control. Whenever possible the location should be far from known point source of pollutions. Ideally PMAs should be coupled with other ecosystem monitoring operations such as: - traffic intensity - climate (air temperature, precipitation) - air quality (gases, airborne particulate, etc.) The number would also depend on the size of the city. In small towns like Aveiro or Uppsala one PMA could be sufficient while in a large city like Glasgow 4-5 could give a reasonable quality of information. Once established, the PMAs should be included in the Land Use Plan so that their use is not changed. c) Parameters to be measured A tentative list of parameters that can be measured in a permanent monitoring area is provided together with sampling indications and frequency of measurement. It is intended that, a part from the parameters indicated in the Soil Quality Indicators list, all others characteristics are optional and can be selected according to specific situation of the city. Similarly, the number of samples and the frequency has to be established on the basis of local requirements. These can also be changed in time when the results of previous analyses become available. The indications provided here are based on the results of the URBSOIL project and on current soil knowledge.
A definite representation of the environmental quality of the soils of the city of Torino is offered. Soil environmental quality was expressed through measurement of a large set of very effective general and specific indicators. This can be of use for Local Administrator to set future monitoring strategies, environmental thresholds or remediation goals. All the methodologies produced can be easily incorporated in Environmental Monitoring and Auditing Schemes (EMAS) in Strategic Environmental Impact Assessment protocols and would be of crucial importance for those actions, such as the Local Agenda 21, that include citizen's participation to the environmental management procedures. Urban soils from the city of Torino, Italy were investigated. The soils were chosen among roadsides, parks and open spaces, riverbanks and ornamental gardens. Soils were sampled at a depth of 0-10cm and 10-20cm, giving a total of >300 samples. Samples were analysed for some general physico-chemical properties (pH, Organic Matter, Particle size distributions etc) and for their metal content. Five metals were investigated: Pb, Zn, Ni, Cu and Cr. Their pseudototal content was measured on all the samples and their bio-available content on a part of them. A subset of twenty samples was chosen for some specific analyses such as distribution of metals in the different soil particle size fractions and release of metals under reducing conditions. Some biological soil quality indicators and the speciation of metals were also investigated. Results show that urban soils of a large city like Torino are largely polluted, often exceeding legislative limits. Soils show a high variability, both horizontal and vertical, reflecting the anthropogenic influence on urban soils' formation and development. The accumulation of metals in the finest particles highlight the role urban soils could play in contributing to the air Particulate Matter. The high amount of metals that were found to be bound to the reducible fraction (according to the BCR-speciation method) do not seem to be actually released from urban soils if reducing conditions occur. The incorporation of soil data in a GIS system allows to spatially manage results and to easily produce urban soils maps, particularly useful in the case of contaminants. Results from this extensive campaign should be incorporated into decision-making processes where urban soil is an issue. Monitoring of some specific areas and remediation of some highly accessed sites should be carefully considered by local authorities to improve and protect citizen's health.
To maximise practical utility, soil information systems (SIS) can be embodied into a decision support framework. Providing decision support for optimum planning and sustainable management of the urban soil resource at local, national and European levels necessitate an acceptance of differing value sets among stakeholders. Environmental justification is a key need. This demands transparency, flexibility and inclusion as a foundation to an appropriate spatial decision support system (SDSS) geared to appraise the urban soil resource and its valuable functions within a wide range of urban environments. The URBSOIL DST facilitates the ongoing and continuous capture of heuristic urban soil knowledge within an online computer mediated decision support (OCMDS) framework. Its methodologies have generated extremely significant participation levels, recorded each stage of the decision making process and have generated iterative statistical group response. Such methodologies have been shown to aid consensus building among a broad peer group of expertise, separated throughout the geographical extremes of Europe, with little opportunity for face-to-face discussion. The framework has allowed the development of urban soil quality methodologies that are transparent in construction. Each stage of the decision making process is transferable to an appropriate knowledge base. Integration of OCMDS with an online geographic information system (GIS) and appropriately flexible SIS, with options to include models, provides a Web-based spatial decision support system. It allows end users the ability and flexibility to reason a problem "as a soil scientist". In addition, the combined SDSS framework allows added opportunity for stakeholders to participate in the decision making process and to do so in an asynchronous manner. Together with the added transparency of knowledge, the framework thus increases the probability of consensus building and environmental justification for sustainable urban soil management. Data access and knowledge or possession of information is key barrier to delivering harmonised approaches to environmental management and planning decisions. Therefore the URBSOIL DST is flexible to maximise utility. It tries to bridge the gap between a highly specific tool, which has limited flexibility to adapt to changes in requirements and consequently limited application and a highly general tool that is of very little scenario specific use without considerable development. The tool needs to take into account the significance of transient data, released by data owners. To manage this process, we have created a software framework within which soil data can be entered by members of the project teams working at different locations and that data viewed by all members online as html tables, on GIS maps as well as through downloads as excel spreadsheets. The data is stored in a general format and the data management strategies may then be discusses and progressed using a component of the toolkit which allows an iterative set of questionnaires to be constructed and analysed, each questionnaire based on the previous. Data harmonization (e.g. both soil and climate etc.) is achieved through storage in a standardized yet flexible format that is converted to Excel (for upload/download) and Access (for GIS presentation) and is suitable for conversion to other formats for future development/applications. Automatic calculations of statistical properties and summaries of data are immediately available online whenever soil data is uploaded or edited online using the tool. Data can be compared online, using box plots for instance, between cities and sites within cities and within arbitrary subcategories, representing current land uses or some other characteristic, which can easily be defined and modified, and in which data can be assigned and reassigned to multiple categories. The soil properties, localities or cities and even sites within these cities are not fixed at any stage and the tool contains the functionality to add new these to the database at any stage in the process even to add new properties as the need for them arises (i.e. are not constrained). The software currently allows for new properties to be added, analysed and can be viewed at any stage even after data collection and site investigations have begun. We employ a 3-stage approach involving remote data input, data viewing and analysis, and collaborative decision making/knowledge management. External validation with a range of stakeholder groups has provided feedback confirming the information and communication issues in decision-making relating to urban soils. Use of the URBSOIL DST has significantly increased participation levels in debate and consultation and provided information/knowledge capture detailing the process. Future development provides opportunities for application in any resource/decision-making context for sustainable urban management.
Urban soils were analysed in 77 sites and 2 depths. Several parameters considered as general indicators of soil quality of the soils were measured: soil pH, organic C, total N, H, S, size distribution analysis (sand, silt, clay), cation exchange capacity, and contents of several metals that are considered as potential pollutants: Cd, Cr, Cu, Ni, Pb and Zn, and also Fe and Mn as metals that can be considered to be unlikely to be influenced by human intervention. The metal contents were determined by digestion with aqua regia and analysed by ICP-OES. This represents the metal forms of greater environmental interest ("pseudo totals").
It is proposed that the original role of the soil as an element of the environment is adopted as the reference use. Consequently, its environmental quality would be defined as "the mode and capacity of an urban soil to interact with other environmental compartments such as water, air and the biosphere. Any use of the soil by the humans would degrade its environmental quality, at least because it would move it away from its climax. It is well known that agriculture itself that can improve some soil properties in the short term could, in the long run, degrade the environmental significance of the soil. Loss of organic matter (desertification) and salinization are but two of the current threats to European soils that descend from agricultural misuse of the soil resource. Such degradation is even more evident in urban settings where human intervention on soil is dramatic. Diffuse- and point source contamination is the most obvious but mixing with foreign materials, removing and replacing of the soil also contribute heavily to the present status of urban soils. A priority list should be produced of the possible soil uses having the Environmental Quality - and the properties that define the soil in this role - as a top, reference use. The preparation of a city specific list would help to establish limits for contaminated site remediation. Also, it could certainly help in defining the value of the soils as a commodity in environmental terms: - the value of traded land could based on its current EQ and on the envisaged EQ after trade; - damage to the soil could be quantified in terms of EQ loss; - criteria for protection of the soil would use its EQ as a guiding principle leading to more consistent and stable results. This systems appears to have the following advantages: - It can easily be integrated into our DST - Only 3 classes: easy to understand and adopt. - Each city can define its top and bottom classes and can define subclasses - The system can be made to work with minimal amount of information and does not necessarily require harmonization of data and procedures to be implemented. Synthetical grades can in fact carry the same amount of information, even though it is originally expressed through different measurements or units. - It can be easily upgraded with some expert support The Minimum Data Set for the evaluation of urban soils quality The MDS is based on the measurement of a set of parameters, important for the evaluation of urban soil quality, and on the ranking of soils in different soil quality classes in function of the results obtained. Using data from analytical results and from the general descriptors of the urban environment, the MDS allows ranking urban soils on a scale based on their environmental quality. Three different sets of parameters are considered: 1) Soil parameters. 2) Degradation parameters 3) Descriptors of the urban environment The two first classes directly use analytical results, giving a quantitative classification of urban soils. This quantification is obtained by attributing to each parameter a score from 1 (worst) to 3 (best conditions). In the first ("Soil") class, the parameters are considered that directly relate to the soil and have a strong influence on its quality, especially for what concerns fertility and mobility of contaminants. The second ("Degradation") class takes into account the parameters that could lead to a depletion of soil functions, with special reference to contaminants. The same conceptual scheme than the table above is applied: a score from 1 (worst) to 3 (best) is assigned to each class of parameters. The presence of extraneous materials and the evidence of mixing processes are also considered as they represent an important visual evidence of man¿s influence on urban soils. The sum of the points obtained in the first two tables ("Soil" and "Degradation") gives an overall score that allows to fit the soils in one of the following classes of environmental quality: A) Overall score from 24 to 36: best environmental quality. Soils in this class show characteristics close to the natural ones. No remediation is required and these soils can be safely used for all the purposes, particularly as parks and gardens. B) Overall score from 12 to 24: average environmental quality. These soils reflect the anthropogenic influence, reflected by a depletion in their environmental quality. These soils are likely to be suitable for construction but should be avoided from being used as parks, especially for children. If this would be the case, the opportunity of a remediation should be carefully considered C) Overall score from 0 to 12. Worst environmental quality. These soils strongly reflect man's influence; their quality is reduced to the minimum. Data about the city ecosystem can be incorporated in the classification mostly as correction factors whose value needs to be established according to the specific case and use.
Urban soils were analysed in 154 sites and 2 depths. Several parameters considered as general indicators of soil quality of the soils were measured: soil pH, contents of carbonate, organic C, N, P, and K, size distribution analysis (sand, silt, clay), electrical conductivity, cation exchange capacity, and contents of several metals that are considered as potential pollutants: Cd, Cr, Cu, Ni, Pb and Zn, and also Fe and Mn as metals that can be considered to be unlikely to be influenced by human intervention. The metal contents were determined by two different methods, digestion with aqua regia and extraction with EDTA solution. The former includes those metal forms of greater environmental interest ("pseudo totals") and the latter represents an estimate of the most "available" contents. Fractions of different availability were estimated by a sequential extraction protocol proposed by the European Commission through the Standards, Measurement and Testing Programme. The soils in Sevilla are moderately polluted with some metals (copper, lead and zinc) in some localized sites, often-ornamental gardens. However, most large parks do not show especially high contents of these metals, except in some particular spots. These 3 metals are some of those considered as of urban origin in the literature. Other metals considered as pollutants in other cities (chromium, nickel) are present in low concentrations and thus are not cause for concern. The quality of any amendments added to the city soils by the Parks & Gardens Service should be observed concerning their contents of pollutants, and possible practices for decreasing metal availability should be studied.