Release and flows of metals from building materials due to corrosion and degradation

Transcription

1 Release and flows of metals from building materials due to corrosion and degradation D. Persson and V. Kucera Swedish Corrosion Institute, Stockholm, Sweden Abstract Runoff measurements of heavy metals from different material surfaces used in buildings and other materials were conducted to identify potential sources of heavy metal emissions due to corrosion and degradation. The runoff was collected from different metal containing materials during two runoff periods with a total duration between one to two weeks. Elevated concentrations were found for zinc in runoff from galvanized steel, aluzink and paint containing zinc compounds, for lead from PVC surfaces and red lead based painted surfaces, for chromium from new concrete tiles and chemically passivated aluzink surfaces, for nickel from asphalt roofing felt and older concrete tiles and for copper from older concrete tiles. This study was performed on relatively small samples, with a single orientation and during short exposure periods and further research is needed to establish realistic runoff rates from materials exposed on buildings and other constructions during longer exposure periods and with different orientations and inclination of the surfaces. Keywords: Heavy metals, runoff, corrosion, degradation, building materials.

2 1 Introduction Metals are important components in the modern society and are used in large amounts in buildings, in constructions and in vehicles. In the ongoing accumulation of metals in urban environments an increased risk of detrimental effects due to emissions of heavy metals to the environment can be suspected in the long-term perspective. Metals runoff from materials on buildings and other constructions can give a significant contribution to metal emissions in urban enviroments. In recent studies [I] the aqueous emissions of metals such as zinc, cadmium and lead -have to a large extent been attributed to emissions from diffuse sources, to which corrosion and degradation of materials containing metals belong. Although the rates of corrosion and degradation of different materials have been studied extensively investigations of runoff from metals are rare. However, realistic values of metal emission rates are essential in order to estimate the contributions from different materials and products to the total flow of metals to the environment. Metals are used in a wide range of materials and components used in buildings and other constructions and many of these materials are exposed to environments where they can be subjected to corrosion and degradation, for instance roofs and facings, poles and barriers, plumbing installations and motor vehicles. Examples of building materials which are composed of metals or contain significant amounts of metals are shown in Table 1. As shown in this table a wide range of materials are possible sources of metals emission when they are subjected to corrosive environments. Metal coatings and metallic materials are obvious candidates, but other materials such as paints, plastics and concrete which are used in large amounts on buildings and constructions may also be potentially important sources of metal emissions. In a research programme initiated by the Swedish Environmental Protection Agency [2] the flow of different metals from buildings, constructions, vehicles and other products to the environment is evaluated for the greater Stockholm urban environment. As a part of this programme, investigations of metal emissions and runoff rates of different materials are conducted, in the first place to identify materials which significantly contribute to emissions of heavy metals, and secondly to determine realistic values of metal emissions from common building materials. This paper presents results of a study of metal emission from a wide range of these materials containing metals in order to provide a basis for further investigations of metal emission rates from important materials. 2 Experimental 2.1 Performance of field exposures The samples were exposed at a test site close to the Swedish Corrosion Institute which is located at the outskirt of central Stockholm. There are no local sources of metal emission close to the exposure site except a road with dense traffic approximately 100 m from the exposure site. The metal samples, the coil coated samples, the asphalt roofing felt and the concrete samples were exposed from the end of April until the middle of May and the PVC samples and the painted samples in September The materials were exposed 19 days in total, but runoff from the first rain events was not collected. Runoff from three

3 samples of each material was sampled during two periods, each about one week long. The samples were mounted on polycarbonate holders and the runoff was collected quantitively from the samples in containers of the same material. The surfaces were oriented with 45 inclination facing south except for the concrete surfaces which were exposed at 60. Table 1. Important applications of materials containing heavy metals in buildings and other constructions. Metal Materials Applications Chemical form Zinc rolled zinc sheets, galvanized steel roofs, faces, gutters, barriers, poles, pipes paints (pigments) barriers, poles roofs, faces, windows brass plumbing, fittings rubber tyres zinc zinc, zinc phosphate zinc oxide zinc zinc oxide Cadmium polymers (stabilizers,pigments), glass coated steel PVC gutters traffic signals fasteners cadmium compounds 11 cadmium Lead lead pipes fittings PVC pipes (stabilizers anti rust paint plumbing installations lead 11 lead II lead stearate,.... steel constructions lead oxide ChrOIIliUIn stainless steel concrete surface protection of metals paints wood impregnation roofs, faces constructions, roofs steel constructions, fasteners, roofs roofs, facings buildings, constructions chromium Cr3+ -,Cr?-compounds II II II Nickel stainless steel asphalt tar felt roofs, faces roofs nickel nickel compounds Copper rolled copper sheet brass wood impregnation roofs, faces, gutters, copper plumbing, fittings copper buildings, constructions Cu +-compounds 2.2 Materials The materials used in the field study were chosen from common building materials used on roofs, facings and other components in buildings and other constructions. Most of the materials used were new but a few samples have been exposed to atmospheric environments before the start of the runoff experiments. The following materials were exposed in the investigation: - Galvanized steel (new) - Aluzink steel with a coating of 55% Al, 43% Zn, 1.8% Si (new)

4 Coil-coated steel, PVC-plastisol coating (new) Stainless steel (new) Asphalt roofing felt, coated with gravel (new) Concrete tiles, pigmented with iron oxide (both new and old) PVC gutter (old) red lead paintcoated steel (new) linseed oil based paint on steel containing zinc oxide (new) alkyd paint, anticorrosive paint containing zinc phosphate (new) Polyethylene, new, applied as inert surface (new) The Aluzink is protected with a passivating solution which creates a thin layer containing chromium on the surface; the coil-coated material is chromium rinsed and has a chromium containing primer and a PVC plastisol topcoat which does not contain any heavy metals. The lead content of the PVC gutter was analysed with atomic absorption spectroscopy after dissolving the material. The sample contained 0.6 weight % lead, originating probably from heat stabilizers added to the material during manufacture. 2.3 Analysis of runoff After collection, the runoff water was acidified with HN03 corresponding to 1 ml acid in 100 ml solution and stored in polyethylene bottles. The analysis of the runoff was performed with ICP-AES or ICP-MS (plasma emission spectrometry or plasma mass spectrometry) for all surfaces except the runoff from painted materials and the PVC material which were analysed by atomic absorption spectrometry. 3 Results and Discussion Concentrations in runoff from different materials are presented in Figures 1 to 8. The concentrations of metals in the runoff from two periods when runoff was collected are presented as mean values and standard deviations of the three samples from the two runoff periods. For the painted materials and the PVC material are the concentrations in the runoff for the two runoff peroids presented separately because of the lrge difference in concentrations between exposure periods. 3.1 Zinc Significantly higher concentrations of zinc in the runoff compared to the inert polyethylene surface were observed for galvanized steel and Aluzink, see Figure 1 and 2. Zinc concentrations in the runoff from the paints which contain zinc were considerably higher compared to the inert surface and were of the same magnitude as the runoff from the galvanized steel and Aluzink surfaces. However, the differences are considerable between the runoff periods which indicates that the values may not be representative for average concentrations in the runoff from surfaces exposed for longer periods. It should be noted that the concentration in the runoff from the inert surfaces during the runoff period in April-May 1997 are remarkably high, however, similar values have been reported in rainwater in industrial environments [3] and in roof runoff from residential houses [4]. During the runoff period in September the zinc concentration in

5 the runoff from the inert surface was lower, mg/l which is similar to the concentrations found in other studies [5,6]. An explanation of the high zinc concentrations from the inert surfaces in this study is deposition of zinc containing particles. A possible emission source could be the dense traffic on the road close to the exposure site, which give rise to abrasion of tires containing zinc oxide s 23 a inert surface galvanized steel Aluzink stainless coil-coated asphalt concrete, concrete, steel steel roofing felt new old Figure 1. Concentration of zinc in runoff from different materials, exposure April-May From materials such as the asphalt roofing felt and the concrete the concentrations of zinc in the runoff lower compared to the inert surface. This is probably due to adsorption of the deposited zinc ions on these surfaces, which is to a large extent influenced by the ph in the runoff and the acid-base properties of the surfaces and the metal ions [7]. In the study mentioned above, the ph in the runoff from surfaces of asbestos cement [5] was slightly alkaline, which is probably true also for the concrete surfaces in this study. The sorption of metal ions on the materials is also influenced by the roughness of the surfaces and the porosity of the materials. This can account for a part of the capability of concrete surfaces and the asphalt roofing felt to retain metal ions. The fact that lowering in concentrations in runoff was not observed for the other metals in this study can probably be explained by the differences in ph-dependence of the adsorption of the cations of the metals. The amount of zinc released from the galvanized steel during the exposure period 2. was estimated at 120 mglm if the amount of zinc in the runoff from the inert surface is subtracted. This corresponds to 5.5 g/m2, year which should be compared with the corrosion rates in Stockholm measured by the Swedish Corrosion Institute which are approximately 3.6 g/m2, year during The values of metal runoff obtained under the present conditions, i.e. 45 inclination, facing south, is probably representative of a higher value of runoff compared to surfaces with other orientation and inclinations. Other studies [S] have shown that the corrosion rates can differ up to five times for surfaces with different inclination, orientation and degree of sheltering.

6 2,5 - inert surface oil paint 1 oil paint 2 alkyd 1 alkyd 2 Figure 2. Concentration of zinc in runoff from inert surfaces and materials painted with oil paint and alkyd paint for two runoff periods (denoted as 1 and 2), exposure September Cadmium As seen in Figure 3 increased concentrations in runoff were not observed for any of the materials investigated in this study. However, in an analogous way as for zinc runoff from asphalt roofing felt and concrete surfaces, also lower concentrations of cadmium were found compared to the inert surface and the other surfaces. The chemical behaviour of cadmium is in many respects similar to zinc and the lower concentrations can be explained by the adsorption of cadmium ions on the surfaces of the materials. The cadmium concentrations are similar to the values reported in the study by Quek and Fijrster [5], where the effect of lowering of cadmium concentrations in runoff was observed for surfaces of asbestos cement and gravel T inert galvanized Aluzink stainless coil-coated asphalt concrete, concrete, surface steel steel steel roofing felt new old Figure 3. Concentration of cadmium in runoff from different materials, exposure April- May Lead The concentrations of lead in the runoff given in Figure 4 and 5 show that elevated concentrations compared to the inert surface were only observed for the lead containing PVC materials and the red lead based oil paint. For the PVC material and the painted material significant differences were observed between the first and second runoff period, possibly because of a decreased content of lead compounds in the outer

7 layers of the materials due to the rapid dissolution in the beginning of the exposure period. The lead concentrations for the inert surface were similar to the values in rain bbtained in the studies mentioned above [3,5] c 2o bn x inert galvanized Aluzink stainless coil-coated asphalt concrete, concrete, surface steel steel steel roofing felt new old Figure 4. Concentration of lead in runoff from different materials, exposure April-May ??I z$ inert surface PVC 1 PVC 2 red red lead lead paint1 paint2 Figure 5. Concentration of lead in runoff from inert surfaces and materials painted with red lead based oil paint and from PVC for two runoff periods (denoted as 1 and 2), exposure September Chromium For chromium, higher concentrations in the runoff were found for the Aluzink material, which is chemically passivated and for the new concrete tiles. The natural chromium con&t of cement is about the same as in the earth crust and are depending on raw materials used, usually in the range of 10 to 100 ppm. The older concrete tiles did not exhibit elevated emissions of chromium probabaly.because of the lower content of soluble material in the outer layers of the material. The chromium released from the concrete is both in the form of dissolved ions and as particles, probably most in the latter form, but these are not discriminated in the analysis performed in this work. Very low concentration of chromium were found in the runoff from stainless steel.

8 inert galvanized Aluzink stainless coil-coated asphalt concrete, concrete, steel steel steel roofing felt new old Figure 6. Concentration of chromium in runoff from different materials, exposure April-May Nickel Nickel was found in higher concentrations compared to the inert surfaces in runoff from asphalt roofing felt and from the older concrete tiles. Nickel concentrations in asphalt higher than 1000 ppm have been reported [9] and nickel emissions from the asphalt roofing felt arise probably from the natural content of the material. The source of nickel in the runoff from the older concrete tiles is unknown, but the nickel may origin from raw materials, from contamination in the iron oxide pigments or from added metal slag used as filler. This illustrates the fact that concrete constructions and products in this respect can not be treated as materials with uniform composition and content of metals. inert galvanized Afuzink stainless coil-coated asphalt concrete, concrete, surface steel steel steel roofing felt new old Figure 7. Concentration of nickel in runoff from different materials, exposure April- May Copper The copper concentrations were all quite similar for the different materials except for the concrete tiles for which significantly higher concentrations in runoff were observed for the older concrete tiles. The copper concentrations from the inert surfaces were similar to the values in rain obtained in the study by Quek and Fijrster [S]. Further studies are currently performed on copper surfaces on buildings in order to determine metal emission rates from copper roofing materials during longer exposure periods.

9 inert galvanized Aluzink stainless coil-coated asphalt concrete, concrete, surface steel steel steel roofing felt new old Figure 8. Concentration of copper in runoff from different materials, exposure April- May Conclusions Investigations of runoff from different building materials have been performed and elevated concentrations in runoff were obtained for zinc from galvanized steel, Aluzink and zinc containing paints, for lead from PVC surfaces and red lead based painted surfaces, for chromium from new concrete tiles and chemically passivated Aluzink surfaces and for nickel from asphalt roofing felt and older concrete tiles and for copper from older concrete tiles. The concentrations of zinc and cadmium in runoff from concrete surfaces and asphalt roofing felt were lower compared to the concentration in runoff from inert reference surfaces of polyethylene, probably as a result of adsorption of zinc and cadmium ions on the former surfaces. The emission of heavy metals due to corrosion and degradation of materials is a complicated process and is dependent on severals factors such as levels of air pollution, rain chemistry and intensity, inclination and orientation of the surfaces and the age of the material which can lead to build-up of protective layers or depletion of the surface layer of the material. The data collected in this work were obtained during relatively short runoff periods and thus does not permit any conclusions about the rates of metal emissions over longer periods of exposure. Further studies will be performed on materials surfaces on buildings and other constructions over longer exposure periods in order to determine metal emission rates that can be used for- estimation of metal flows from materials to the environment 5 References 1. Stigliani, W.M., Jaffd P. R. and Anderberg S. (1993) Heavy Metal Pollution in the Rhine Basin,. Environ. Sci. Technol. Vol. 27, No. 5, pp Naturvardsverket, (1994) Metaller i stad och land - kretslopp och kritisk belastning, forskningsprogram 1994/ /99 (in Swedish) 3. Thomas, P. R. and Greene, G. R. (1993) Rain Water Quality from Different Roof Catchrnents. Vat. Sci. Tech., Vol. 28, No. 3-5, pp Chang, M. and Crowley, C. M. (1993) Preliminary Observations on Water Quality of Storm Runoff from Four Selected Residential Roofs. Water Resources Bulletin, Vol. 29, pp

10 * Quek, U. and Forster, J. (1993) Trace Metals in Roof Runoff. Water, Air and Soil Pollution, Vol. 68, pp Verbiest P., Waeterschoot, H., Racek, R. and Leclerq M. (1997) Zinc and the Environment: A Study of Run-Off and Corrosion of Rolled Zinc Sheet in Different Exposures, Protective Coatings Europe, pp Stumm, W. (1992) Chemistry of the Solid Water Interface. John Wiley & Sons, New York. Rendahl, B., Kucera, V., Vlckova, J., Knotkova, D., Norberg, P. and Sjostrom, C., (1996) The Microenvironment and Corrosivity in Different Positions on the Royal Palace in Sockholm and on Prague Castle. Durability of Building Materials and Components, 7 (volume one), Ed. Sjostrijm, C., E & FN Spon, London, pp Malmquist, P. -A., (1983) Urban Stormwater Pollutant Sources, Thesis, Dept. of Sanitary Engineering, Chalmers University if Technology, Gothenburg, Sweden.