Organic contaminants in urban soils: major inputs and potential risks

摘要

Urban soil quality may be severely affected by hydrophobic organiccontaminants (HOCs), impairing environmental quality and human health. Acomprehensive study was conducted in two contrasting Portuguese urbanareas (Lisbon and Viseu) in order to assess the levels and potential risks ofthese contaminants, to identify sources and study their behaviour in soils. Theconcentrations of HOCs were related to the size of the city, with much highercontamination levels observed in Lisbon urban area. Source apportionmentwas performed by studying the HOCs profiles, their relationship with potentiallytoxic elements and general characteristics of soil using multivariate statisticalmethods. Lisbon seems to be affected by nearby sources (traffic, industry andincineration processes) whereas in Viseu the atmospheric transport may beplaying an important role. In a first tier of risk assessment (RA) it was possibleto identify polycyclic aromatic hydrocarbons (PAHs) in Lisbon soils as apotential hazard. The levels of PAHs in street dusts were further studied andallowed to clarify that traffic, tire and pavement debris can be an importantsource of PAHs to urban soils. Street dusts were also identified as being apotential concern regarding human and environmental health, especially ifreaching the nearby aquatic bodies. Geostatistical tools were also used andtheir usefulness in a RA analysis and urban planning was discussed.In order to obtain a more realistic assessment of risks of HOCs to environmentand human health it is important to evaluate their available fraction, which isalso the most accessible for organisms. Therefore, a review of the processesinvolved on the availability of PAHs was performed and the outputs producedby the different chemical methods were evaluated. The suitability of chemicalmethods to predict bioavailability of PAHs in dissimilar naturally contaminatedsoils has not been demonstrated, being especially difficult for high molecularweight compounds. No clear relationship between chemical and biologicalavailability was found in this work. Yet, in spite of the very high totalconcentrations found in some Lisbon soils, both the water soluble fraction andthe body residues resulting from bioaccumulation assays were generally verylow, which may be due to aging phenomena. It was observed that thepercentage of soluble fraction of PAHs in soils was found to be different amongcompounds and mostly regulated by soil properties. Regardingbioaccumulation assays, although no significant relationship was foundbetween soil properties and bioavailability, it was verified that biota-to-soilbioaccumulation factors were sample dependent rather than compounddependent. In conclusion, once the compounds of potential concern aretargeted, then performing a chemical screening as a first tier can be a simpleand effective approach to start a RA. However, reliable data is still required toimprove the existing models for risk characterization.