Characterization of a former dump site in the Lagoon of Venice contaminated by municipal solid waste incinerator bottom ash, and estimation of possible environmental risk
Introduction
Former disposal sites of hazardous materials may represent a long-term source of environmental contamination, since pollutants can be directly propagated to surface and ground waters and air. In particular, bottom and fly ashes, which are the main residues of MSWI (Municipal Solid Waste Incinerator) activity, contain high concentrations of potentially hazardous elements (such as heavy metals) (Chandler et al., 1997, Zevenbergen et al., 1998, Huang et al., 2006). There is evidence that bottom ash is unstable in atmospheric conditions, since weathering changes the mineralogical characteristics of bottom ash, mainly by reducing its chemical reactivity by carbonation and trapping of heavy metals in newly formed minerals (Piantone et al., 2004).
Although several studies have investigated weathered and unweathered MSWI bottom ash, to our knowledge there are no published data about bottom ash more than 12 years old (Zevenbergen et al., 1998, Meima and Comans, 1999). It is therefore of interest to study the 35-year-old MSWI bottom ash of a former disposal site located in the Lagoon of Venice.
In this study we examine the environmental risk related to ash stored on the island of Sacca San Biagio (SB in Fig. 1), near the city centre of Venice, over a period of about 10 years, during incinerating activity which started in 1973.
This paper provides data on metal contamination and the main mineralogical characteristics of MSWI bottom ash stored on the site. Mineralogical neoformations due to weathering processes are discussed with reference to data on younger bottom ash (Zevenbergen et al., 1998, Zevenbergen et al., 1999, Meima and Comans, 1999, Piantone et al., 2004). Comparisons of airborne particle collected from the nearby island of Sacca Fisola (SF in Fig. 1) is also discussed. Lastly, two single extractions with cold HCl and citric acid were carried out, to evaluate the potentially mobilizable and the directly exchangeable metal fractions, respectively, and to gain information on the risk associated with the diffusion of contaminants through the trophic chain.
The island of the former incinerator, called Sacca San Biagio (SB), is located in the middle of the Lagoon of Venice, at the western end of the island of Giudecca. The site covers about 45,000 m2 (Fig. 1). It was originally a natural deposit of sediments emerging at low tide, filled with inert materials and rubble in the post-war period. In 1970, a municipal solid waste incinerator was built, and operated from 1973 to 1984. During this time, approximately 60,000 m3 of bottom ash were collected and dumped on the site.
In 1994, the island was secured against erosion with walling made of reinforced concrete sheet piles, but total impermeabilization was not guaranteed.
The incinerator was demolished in summer 2003. Currently, the island is used as a temporary waste dump and is almost completely covered with spontaneous mainly herbaceous, pioneer vegetation.
Section snippets
Sampling and pre-treatment of bottom ash
Bottom ash samples were collected from various sub-areas of SB. In particular, as shown in Fig. 1, the island was divided into four sites, each containing three sampling points. A total of 12 samples was collected, from reciprocally distant points on the island for optimal representativity of the site itself. Samples were collected after a period of 72 h without rain. Primary samples (1 kg per sample) were collected between depths of 0 and 30 cm and were stored in polyethylene bags for transport
Total metal concentrations in bottom ash
Table 1 shows total element concentrations determined in the four sampling sites, and limits imposed by Italian regulations for various soil uses (mg kg−1 dry weight).
No significant statistical differences were noted between the average values of the four sites. This statement is supported by statistical analysis. The Wilks–Lambda and Fisher exact tests were combined to yield a significativity index (significativity level set at 0.05). Only As and Al turned out to discriminate between sites. As
Conclusions
Analyses carried out on bottom ash indicated the presence of secondary minerals. Carbonates (mainly calcite) and aluminosilicates, with heavy metal impurities, were extensively observed. Collected evidence supports other authors’ conclusions (Zevenbergen et al., 1999, Meima and Comans, 1999, Meima et al., 2002, Piantone et al., 2004) about adsorptive reacting bulks and the progressive decrease in pH values during weathering processes.
The study site is extensively contaminated by heavy metals.
Acknowledgements
The authors thank Lorena Gobbo for technical assistance and VESTA Spa for financial support.
References (28)
- et al.
Evaluation of microwave-assisted acid extraction procedures for the determination of metal content and potential bioavailability in sediments
Appl. Geochem.
(2008) Fluctuations in wind direction at Venice related to the origin of the air masses
Atmos. Environ.
(1981)- et al.
Bioavailability of heavy metals from polluted soils to plants
Sci. Total Environ.
(2005) - et al.
Comparison of a rhizosphere-based method with other one-step extraction methods for assessing the bioavailability of soil metals to wheat
Chemosphere
(2005) - et al.
Chemical changes and leachate mass balance of municipal solid waste bottom ash submitted to weathering
Waste Manage.
(2002) - et al.
The potential of recycling and reusing municipal solid waste incinerator ash in Taiwan
Waste Manage.
(2006) Soil–plant transfer of trace elements – an environmental issue
Geoderma
(2004)- et al.
Speciation and solubility of heavy metals in contaminated soil using X-ray microfluorescence, EXAFS spectroscopy, chemical extraction, and thermodynamic modeling
Geochim. Cosmochim. Acta
(2006) - et al.
Kinetic extractions to assess mobilization of Zn, Pb, Cu, and Cd in a metal-contaminated soil: EDTA vs. citrate
Environ. Pollut.
(2008) - et al.
The leaching of trace elements from municipal solid waste incinerator bottom ash at different stages of weathering
Appl. Geochem.
(1999)
Carbonation processes in municipal solid waste incinerator bottom ash and their effect on the leaching of copper and molybdenum
Appl. Geochem.
Mineralogical study of secondary mineral phases from weathered MSWI bottom ash: implications for the modelling and trapping of heavy metals
Appl. Geochem.
Comparison between non-residual Al, Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and a dilute hydrochloric acid leach for soil and road deposited sediment
Appl. Geochem.
Metal extraction from road-deposited sediments using nine partial decomposition procedures
Appl. Geochem.
Cited by (11)
Is incineration the terminator of plastics and microplastics?
2021, Journal of Hazardous MaterialsCitation Excerpt :Generally, for bottom ash, metal recovery and granulation take place after 4–12 weeks of aging, which may contribute to MPs being atmospherically transported. Similarities between bottom ash and atmospheric PM10 collected adjacent to bottom ash dump sites have been found (Rigo et al., 2009). In addition, unburned black fragment MPs have been collected from the marine atmosphere (Liu et al., 2019), and bottom ash reused in coastal areas might be the primary contributor to these.
Characterization of industrial secondary desulphurization slag by chemical fractionation with supportive X-ray diffraction and scanning electron microscopy
2015, International Journal of Mineral ProcessingCitation Excerpt :As industrial residue utilization or disposal involves materials which have been willingly removed from a unit process to minimize the effect of so-called non-process elements to the properties of the main product or stability of production, the respective potential environmental impacts should be investigated in detail. Single extractions can be used for estimating available element fractions through desorption and possible dissolution of easily soluble solid phases (Cappuyns and Swennen, 2008; Rigo et al., 2009) or in support of risk assessment concerning residue utilization or disposal (Fällman, 2000; Krüger et al., 2012; van der Sloot and Kosson, 2012). Sequential extractions can provide information for a more comprehensive evaluation of the effect of varying environmental conditions and lack the difficulties of, e.g., finding a single reagent effective in dissolving the non-residual trace element forms without attacking the residual matrix (Tessier et al., 1979).
Molecular characterization and glomalin production of arbuscular mycorrhizal fungi colonizing a heavy metal polluted ash disposal island, downtown Venice
2010, Soil Biology and BiochemistryCitation Excerpt :Bottom ashes contain high levels of toxic compounds and heavy metals, whose concentration during the incineration process represents a risk for the environment (Gau and Jeng, 1998). Besides, ashes can be easily transported to the surrounding areas by the action of wind and water (Rigo et al., 2009). Sacca San Biagio is an ash disposal island located downtown Venice (Italy).
XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca
2015, Journal of Synchrotron RadiationBiogenic iron-silver nanoparticles inhibit bacterial biofilm formation due to Ag<sup>+</sup> release as determined by a novel phycoerythrin-based assay
2020, Applied Microbiology and Biotechnology