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Heavy metal contamination in soils of urban highways (comparision between runoff and soil concentration
HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS: COMPARISON BETWEEN RUNOFF AND SOIL CONCENTRATIONS AT CINCINNATI, OHIO DILEK TURER 1 , J. BARRY MAYNARD 1∗ and J. JOHN SANSALONE 2 1 University of Cincinnati, Department of Geology, ML 0013, Cincinnati, OH 45221-0013, Ohio, U.S.A.; 2 Louisiana State University, Department of Civil and Environmental Engineering, Rm. 3510 CEBA Bldg, Baton Rouge, LA 70803-6405, U.S.A. ( ∗ author for correspondence, e-mail: maynarjb@email.UC.Edu) (Received 17 March 2000; accepted 15 November 2000) Abstract. Rainfall runoff from urban roadways often contains elevated amounts of heavy metals in both particulate and dissolved forms (Sansalone and Buchberger, 1997). Because metals do not degrade naturally, high concentrations of them in runoff can result in accumulation in the roadside soil at levels that are toxic to organisms in surrounding environments. This study investigated the accumulation of metals in roadside soils at a site for which extensive runoff data were also available. For this study, 58 soil samples, collected from I-75 near Cincinnati, Ohio, were examined using X-ray fluorescence, C-S analyzer, inductively coupled plasma spectroscopy, atomic absorption spec- trometry and X-ray diffraction. The results demonstrated that heavy metal contamination in the top 15 cm of the soil samples is very high compared to local background levels. The maximum measured amount for Pb is 1980 ppm (at 10–15 cm depth) and for Zn is 1430 ppm (at 0–1 cm depth). Metal content in the soil falls off rapidly with depth, and metal content decreases as organic C decreases. The correlation to organic C is stronger than the correlation to depth. The results of sequential soil extraction, however, showed lower amounts of Pb and Zn associated with organic matter than was expected based on the correlation of metals to % organic C in the whole soil. Measurement of organic C in the residues of the sequential extraction steps revealed that much of the carbon was not removed and hence is of a more refractory nature than is usual in uncontaminated soils. Cluster analysis of the heavy metal data showed that Pb, Zn and Cu are closely associated to one another, but that Ni and Cr do not show an association with each other or with either organic C or depth. ICP spectroscopy of exchanged cations showed that only 4.5% of Pb, 8.3% of Zn, 6.9% of Cu and 3.7% of Cr in the soil is exchangeable. Combined with the small amounts of metals bound to soluble organic matter, this result shows that it is unlikely that these contaminants can be remobilized into water. At this site, clays are not an important agent in holding the metals in place because of low amounts of swelling clays. Instead, insoluble organic matter is more important. Mass balance calculations for Pb in soil showed that most of the Pb came from exhausts of vehicles when leaded gasoline was in use, and that about 40% of this Pb is retained in the soil. This study shows that, highway environments being a relatively constant source of anthropogenic organic matter as well as heavy metals, heavy metals will continue to remain bound to organic matter in-situ unless they are re-mobilized mechanically. Removal of these heavy metals as wind-blown dust is the most likely mechanism. Another possibility is surface run-off carrying the metals into surface drainages, bypassing the soil. This study also shows that for those countries still using leaded gasoline, important reductions in Pb contamination of soils can be achieved by restricting the use of Pb additives. Keywords: copper, flux, highway soils, lead, organic carbon, pavement runoff, zinc Water, Air, and Soil Pollution 132: 293–314, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 294 D. TURER ET AL. Abbreviations: AAS, Atomic Absorption Spectrometry; CEC, Cation Exchange Capacity; EMC, Event Mean Concentration; ICP, Inductively Coupled Plasma; LECO, C-S Analyzer; meq, milli- equivalent; XRD, X-ray diffraction; XRF, X-ray fluorescence. 1. Introduction Adverse health effects of lead as an environmental contaminant have long been known (EPA, 1999). Consequently, there have been many studies on contamination of soils along highways, with the main emphasis on Pb. For example, Vandenabeele and Wood (1972), who worked on highway soil samples in Utah, found 180 to 215 ppm Pb in surface soil and 65 to 125 ppm Pb at 10 cm depth, 10 m away on the east and west sides of the highway. They interpreted the amounts of contamination at 10 cm as unusually high and they stated that although contamination is limited to a narrow zone along highways, it is not limited to surface soil. They further stated that Pb in soil can be leached and mobilized by solutions containing NaCl, for example from road salting. Ward and others (1975) investigated the lead content of soil and vegetation along a part of a state highway passing through an uninhabited area of New Zea- land. They observed an inverse relationship between Pb content of vegetation and distance from the road, as has been reported from other areas. Their analysis showed that washed vegetation samples contained 70–80% of the Pb levels of unwashed samples, indicating that the majority of the Pb is relatively immobile. They found the same fall-off of Pb levels in soil samples with distance from the road. The highest levels of soil Pb, reaching 160 ppm, were obtained from the top 5 cm of the soil (the background level of Pb was 40 ppm). To calculate total excess Pb in the soil, they plotted the values of excess lead for 1-m by 1-m by 6-cm volume increments as a function of distance and found an integrable function which fit the data: M(x) = M(0) exp [–k(x) 1/2 ] (where M(x) is the excess mass of lead in the increment at distance x). They estimated the total emitted lead from vehicles for that area using the known traffic flow of 6.0±1.0 × 10 6 vehicles since 1960. When they compared the total amount of emitted Pb (240 g along each meter of the road) with the calculated excess in the soil (140 g along each meter of the road) they concluded that the elevated levels of Pb in the top 6 cm of soil were primarily sourced from leaded gasoline. Their results suggest that about 60% of the Pb emitted is retained by the soils close to the highway. Wheeler and Rolfe (1979) found that lead from automotive sources in roadside soil and vegetation follows a double exponential function of the following form: Pb =A 1 e −k1D +A 2 e −k2D . The terms A 1 and A 2 are linear functions of average daily traffic volume and the exponents represent different particle sizes. Their studies showed that larger particles are deposited within 5 m of the roadside and are inert in the soil whereas small particles are deposited more slowly and are deposited within 100 m of the roadside. Also they suggested that 72–76% of historical lead HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS 295 deposited on the soil has been lost from the surface 10 cm of soil. The highest amount of lead found was 1225 ppm in soil and 196 ppm in vegetation at 0.3 m away from highways of central Illinois with 8100 vehicles day −1 traffic density. In this area, background levels, which were 16 ppm for soil and 10 ppm for vegetation, were reached at 50 m from the highways. Similar results come from Onyari and others (1992), who worked on roadside soils in Kenya where lead is still used as a gasoline additive. They found that lead concentrations within Nairobi City varied from 137 to 2196 ppm with a mean of 659 ppm. The highest value was measured in the Nairobi hill region, which they explained by acceleration of motor vehicles because of the steep nature of the hill. The amount of Pb emitted as a percentage of Pb consumed increases as vehicle speed increases. Gratani and others (1992) studied the accumulation of Pb in agricultural soil and vegetation along the Fiano-San Cesareo highway in Italy. They documented an increase of Pb values in the soil within the few years that had passed since the highway was opened. Agricultural soils were found to accumulate more Pb, because the organic matter causes it to be bound to organic exchange sites, reducing its availability for root uptake (Albasel and Cottenie, 1985). They also looked at oak leaves, which showed similar increases in Pb concentration with time. Teichman and others (1993) sampled yards within 1 mile of Interstate 880 in Alameda County, California. Surface samples contained an average of 570 ppm Pb with a maximum of 2030 ppm. Subsurface samples from the same sites showed an average of 620 and a maximum of 1400 ppm Pb. 63% of the subsurface Pb concentrations exceeded corresponding surface concentrations. They interpreted this pattern as indicating that as the use of leaded gasoline decreased, the Pb content of the upper layers of soil also decreased. There have been a few studies that included other heavy metals like zinc, cad- mium and copper with measurements of lead. Gibson and Farmer (1984) applied a six-step sequential leaching procedure to soil and street dirt in order to under- stand environmental mobility and bioavailability of Pb, Zn, Cu and Cd. The results of this study revealed that the exchangeable fraction was of significantly greater relative importance in street dust than in soil, especially for Pb, Zn and Cu. They reported exchangeable percentages of Pb dust : 13%, Pb soil :2%;Zn dust : 10%, Zn soil : 3%; Cu dust : 11%, Cu soil :2%;Cd dust : 27%, Cd soil : 19%. Hamilton and others (1984) investigated levels of Cd, Cu, Pb and Zn in road dust at three sites with different traffic usage and surface textures. The results showed that amount of contamina- tion increases as traffic density increases. They also applied sequential extraction procedure on size-fractionated dust samples. Cd is found as the highest proportion of total metal in the exchangeable fraction whereas Cu is mainly in the strongly bound organic and residual phases. Hewitt and Candy (1990), examined levels of Pb, Cd and Zn in soil and dust samples collected in and around the city of Cuenca, Ecuador. The metal concentrations for the urban environment were considerably elevated (Pb: 77–970 ppm, Cd: 0.23–0.42 ppm, Zn: 155–1018 ppm). The dominant 296 D. TURER ET AL. TABLE I Event mean concentration data for I-75 experimental site with EPA criteria (Sansalone and Buchberger, 1996) Total EMC (µgL −1 ) 8 April 30 April 5 July 8 September 3 October Discharge 1995 1995 1995 1995 1995 criteria Zn 459 628 15244 3612 1427 120 Cd 5 6115 8 5.6 Cu 43 70 325 166 71 18 Ni 9 23 91 83 11 1700 Pb 62 31 44 88 97 82 Cr 35 14 29 14 14 1400 Mn ∗ 120 175 820 337 166 None Fe ∗ 3477 932 4676 6415 5178 None Al ∗ 2224 1859 270 1621 5496 None Violations of EPA discharge criteria in bold. ∗ Not EPA priority pollutants. source for the Pb in urban street dust was shown to be emission of Pb aerosol from gasoline vehicles. Tyre rubber was shown to be the main source for Zn and also for Cd, plus some from metal platings on car parts. It was also suggested that the poor condition of road surfaces in Cuenca might have been enhancing tyre wear. Suburban samples taken from 5.5 km away from the city center had lower values of metals (Pb: 54–109 ppm, Cd: 0.20–0.27 ppm, Zn: 44–120 ppm). Samples taken from close to a rural track used by only 100 vehicles per day, had lower values of Pb: 0.6–15 ppm but not Cd and Zn: (0.29 ppm; 52–541 ppm). The background Pb obtained from Rio Mazan valley was very low: 0.02–9 ppm. The Cd levels however were not significantly different from those found in the other areas (0.05– 0.5 ppm). They suggested that the influence of vehicular emission of Cd was much more localized than it was for Pb, probably due to the emission of Cd as very large particles that are transported only short distances. In these studies, the main source for Pb in the soils was shown to be leaded gas- oline in highway vehicles. Also all the analyses showed that the amount of heavy metal contamination decreased with depth and with distance from the highway. Although some countries like the U.S. prohibit the use of leaded gasoline there are many other countries that continue using leaded gasoline in their transportation. Even for the U.S. the problem of heavy metal contamination has not been elimin- ated. Sansalone and Buchberger (1997) sampled lateral pavement sheet flow from a study area with an area of 15 × 20 m on I-75 in Cincinnati, during five rainfall events in 1995. Their results showed that the event mean concentrations (EMC) HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS 297 of Zn and Cu exceeded surface quality discharge standards for all rainfall events and that Pb had two and Cd had three excedences (Table I). They also investigated partitioning of metals and solids in storm water. Their results indicated that Zn, Cd, Cu were mostly in dissolved form whereas Pb, Fe and Al were particulate-bound in storm water. In the current study we use the same site as Sansalone and Buchberger (1997) to examine how much of this runoff of heavy metals gets transferred to the soil. We have also attempted to determine the mechanisms that control both the retention and remobilization of metals. To do so, we have included information about clay mineralogy and organic carbon content of the soil samples taken from the same site where Sansalone and Buchberger carried out their work. Also the work presented here goes one step further than previous studies in that it makes mass balance calculations for Zn, Cu, Ni and Cr in addition to Pb, calculations made possible by the availability of runoff data for the same site. 2. Methods 2.1. S AMPLING LOCATION The samples were collected along I-75, a heavily traveled north-south interstate in Cincinnati (Figure 1). 156 670 vehicles were counted per day in 1994 (ODOT, 1999). The soils are clay-rich and are visually uniform both laterally and with depth. Some 1961–1990 climate characteristics of Cincinnati (Climate Diagnostic Center, 1999) are Mean annual temperature 54 ◦ F Minimum temperature –15 ◦ F Mean annual precipitation 39.7 inches Mean annual snowfall 18.3 inches Winter conditions are such that road salting is commonly practiced. The soil samples were taken with Shelby tubes, one set (BH) in a N–S direction (parallel to the highway) and another (XS) in an E–W direction. Next, the soil samples were di- vided into sections with 5 cm increments down to 15 cm; at greater depths larger increments were used. 2.2. A NALYTICAL METHODS In this study five different types of analysis have been applied for different as- pects of the research: X-ray fluorescence (XRF, Rigaku 3070 spectrometer), C-S analyzer (LECO), Inductively coupled plasma spectroscopy (ICP, Perkin-Elmer Optima 3000), Atomic absorption spectrometry (AAS, Perkin-Elmer 3110) and X-ray diffraction (XRD, Siemens D-500). 298 D. TURER ET AL. Figure 1. Study area showing location of Cincinnati and the positions of sampling stations (After Sansalone et al., 1998). HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS 299 The first step in this research has been application of XRF to determine the bulk chemistry of the samples. For this, samples were dried at 100 ◦ C and ground using a steel ball mill. Pressed pellets for XRF were prepared with 5–6 g of sample pressed under 18 tons for 4–5 min. Samples were run against a set of U.S. Geological Survey rock standards combined with a set of roadside soil samples previously analyzed by XRAL, Inc. of Toronto, Canada by neutron activation. LECO analysis was applied in order to find percentages of organic C, total C and total S in the soils. Total C and total S were run on dried powders. Organic C was measured on acidified samples. The acidification was done using 50 mL of 1 N HCl to 0.5 g of sample on a hot plate at 60 ◦ C for 12 hr. Fifty mL of distilled water was then added to stop reaction. The solution was filtered through a glass fiber filter and the residue rinsed with distilled water to remove all acid. Samples were then dried at least four hours. ICP was used to determine the nature of the exchangeable ions. Fifteen mL of 1 molar NH 4 acetate at pH 7 was added to 0.2 g of sample. The suspension was left overnight and centrifuged the next day. Five mL of nitric acid was added to the liquid taken out from the centrifuged tubes to maintain metals in solution (Ulmschneider, 1977). Atomic absorption (AAS) was used to monitor sequential extraction of metals. 2 g of dry soil sample was placed into a labeled centrifuge tube. The extraction steps then are (Sposito et al., 1982): • 25 mL of 0.5 M KNO 3 was added and shaken for 16 hr (exchangeable fraction); • 25 mL of distilled H 2 O was added and shaken for 2 hr (absorbed fraction); • 25 mL of 0.5 M NaOH was added and shaken for 16–21 hr (organically bound fraction); • 25 mL of 0.05 M Na 2 EDTA was added and shaken for 6 hr (carbonate bound fraction); • 25 mL 4 M HNO 3 added and heated (70–80 ◦ C oven) for 16–21 hr (residual fraction). After each step the sample was centrifuged and filtered through a Whatman # 42 filter into a nalgene bottle. The solutions were refrigerated and saved for Atomic Absorption Spectrometric Analysis. XRD was used to determine sample mineralogy, especially the clay mineral types. Sample preparation started by putting 2–3 g of sample in a beaker filled with 200 mL of water. After stirring, the suspension was left for 45 min. The clay minerals, which were floating close the surface, were caught with a pipette and transferred onto a glass slide. The sample was left to air dry. For some samples it was not possible to collect the necessary amount of clay minerals by pipette. In that case, the top part of the water in the beakers was taken into centrifuge tubes. After centrifugation, the clay minerals separated at the bottom of the tubes were applied as a paste on glass slides. One set of slides was left air dried, a duplicate 300 D. TURER ET AL. set was glycolated, and another set was heated to 350 and to 550 ◦ C in order to differentiate clay minerals. 3. Results 3.1. B ULK SOIL COMPOSITION XRF data showed that heavy metal content is very high in the top 15 cm of the soil (Table II). The maximum measured amount for Pb is 1980 ppm, which was taken from 10–15 cm depth in core BH9. The highest value for Zn is 1426 ppm at XS1 from 0–1 cm depth. For comparison, background values, calculated as weighted averages of concentrations in samples taken from below 30 cm, were Pb 60 ppm; Zn 85 ppm; Cu 35 ppm; Ni 40 ppm; and Cr 35 ppm. Metal values decrease with depth (Figure 2). This inverse relationship is stronger for Zn and Cu (R 2 Zn :0.53and R 2 Cu :0.53)thanforPb,NiandCr(R 2 Pb : 0.33, R 2 Ni : 0.22, R 2 Cr : 0.16). From the LECO analysis, average organic C percent for these soil samples is 3.8 and total C is 6.8%. There is a positive correlation between organic C content and metal values: as the amount of organic C increases, the amount of heavy metal contamination also increases (Figure 3). In addition the correlation is stronger for organic C and metal content than for depth vs. metal content for each of the metals (R 2 Zn : 0.59, R 2 Cu : 0.77, R 2 Pb : 0.62, R 2 Ni : 0.40, R 2 Cr : 0.24). Note that the correlation coefficient for Pb is much higher for the Pb vs organic C relationship than for the Pb vs depth relationship, whereas both Ni and Cr show very weak relationships to both depth and to organic C. Cluster analysis was used to further illustrate which metals have close asso- ciations with each other, with depth and with organic C amount in the soil. The result showed that Pb, Zn and Cu are acting together and they are more closely associated with the amount of organic C in the soil than with depth. Ni and Cr, however, did not show any association with other metals, with organic C or with depth (Figure 4). The yields of exchangeable metals using NH + 4 as the exchange ion were low (except for Ca, which probably comes from dissolution of calcite as discussed by Tessier et al., 1979). For 12 samples analyzed by ICP (Table III), average exchange- able Pb was only 4.5%, Zn 8.3%, Cu 6.9%, and Cr 3.7% of the amount in the whole soil based on XRF. 3.2. S EQUENTIAL EXTRACTION The sequential soil extraction procedure was applied to 5 soil samples. The res- ults confirmed that the metal amounts in the exchangeable fraction are very low (Table IV). On average only 1.6% of Pb, 0.4% of Zn, 1.7% of Cu, 4% of Ni and 5% of Cr are exchanged with KNO 3 . Adsorbed metals were also very low. HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS 301 TABLE II Results of LECO and XRF Sample Depth LECO (%) XRF (ppm) (cm) Organic C Total C S Cr Cu Ni Rb Sr Zn Zr Pb BH1-01 0–1 2.65 5.11 0.16 71 125 50 70 233 598 245 670 BH2-01 0–1 4.76 8.81 0.15 67 230 58 77 168 329 230 566 BH2–612-818 36–46 0.16 1.98 0.06 36 30 47 84 172 107 293 47 BH3-01 0–1 3.50 8.09 0.14 72 131 55 64 204 224 203 358 BH3-1015-816 31–36 29.29 0.00 0.06 137 119 89 94 654 147 221 73 BH4-01 0–1 5.22 11.27 0.11 74 250 62 84 174 828 196 924 BH4-15 1–5 10.32 0.06 79 290 61 78 164 443 214 1001 BH4-510 5–10 1.55 3.86 0.06 79 90 53 180 328 BH4-1015 10–15 5.28 0.04 64 30 51 97 176 67 143 35 BH4-01-612 15–16 0.32 4.89 0.04 55 24 52 106 178 60 117 21 BH4-15-612 16–21 0.32 4.06 0.04 55 26 56 124 177 58 133 15 BH4-1219 30–48 0.20 4.35 0.04 –9 21 35 51 160 61 143 17 BH5-01 0–1 17.98 15.52 0.11 72 353 64 89 169 1207 148 942 BH5-15 1–5 4.98 10.53 0.08 82 389 64 68 192 578 218 1073 BH5-510 5–10 5.06 9.32 0.05 65 134 56 62 250 288 173 957 BH5-1015 10–15 1.87 5.29 0.05 78 124 60 266 600 BH5-611 15–28 0.96 5.16 0.03 6 34 40 60 184 104 95 75 BH6-01 0–1 7.92 10.82 0.13 75 249 53 62 211 380 196 368 BH6-15 1–5 4.36 9.65 0.13 69 233 54 344 314 BH6-510 5–10 2.72 8.38 0.20 84 106 47 192 469 BH61015 10–15 6.17 10.73 0.15 75 401 66 459 1298 BH6-612 15–30 1.13 4.62 0.09 64 61 50 86 212 96 195 117 BH6-1216 30–41 1.14 5.56 0.08 21 50 42 72 214 140 154 168 BH8-01 0–1 6.10 11.73 0.23 79 239 56 771 188 457 200 381 BH8–613 15–30 0.43 3.62 0.10 25 39 46 96 170 138 153 111 BH9-01 0–1 3.08 7.14 0.06 94 91 46 55 225 193 207 166 BH9-15 1–5 4.30 10.09 0.11 56 65 41 174 119 BH9-510 5–10 5.35 10.02 0.08 69 107 48 260 175 BH9-1015 10–15 6.60 11.77 0.10 73 275 54 49 195 619 266 1980 BH9-612 15–30 1.41 4.08 0.06 66 73 54 103 156 167 218 407 BH9-1218 30–46 0.77 2.69 0.10 68 30 59 130 132 71 198 27 BH9-1826 46–66 0.61 3.46 0.04 58 26 6 62 30 302 D. TURER ET AL. TABLE II (continued) Sample Depth LECO (%) XRF (ppm) (cm) Organic C Total C S Cr Cu Ni Rb Sr Zn Zr Pb XS1-01 0–1 14.69 0.24 79 170 48 41 214 1426 185 643 XS1-612 15–30 0.57 5.60 0.07 11 27 38 58 194 101 132 135 XS2-01 0–1 7.74 12.41 0.20 78 340 59 78 168 548 257 738 XS2-15 1–5 5.64 9.71 0.12 81 249 60 342 610 XS2-510 5–10 1.31 5.19 0.11 114 43 47 78 88 XS2–1015 10–15 0.58 2.05 0.06 92 29 53 63 24 XS2-714 15–36 0.26 1.47 0.07 37 26 44 93 166 92 252 41 XS3-01 0–1 6.16 12.14 0.16 957 270 XS3-15 1–5 1.14 5.69 0.08 55 50 45 98 59 XS3-510 5–10 6.40 11.22 0.17 125 444 57 466 1314 XS3-1015 10–15 3.34 7.03 0.14 44 145 50 70 176 529 165 1670 XS4-01 0–1 7.87 11.12 0.17 87 378 65 434 751 XS4-816.5 15–42 0.23 5.52 0.09 1 19 36 54 188 65 222 18 XS5-01 0–1 5.07 8.08 0.15 71 265 60 80 175 293 236 473 XS5-1215 30–38 0.14 0.53 0.12 44 27 47 112 104 101 268 29 XS6-01 0–1 6.01 10.62 0.18 74 236 63 438 402 XS6-15 1–5 6.09 10.24 0.19 77 404 67 523 828 XS6-510 5–10 4.36 7.59 0.11 86 150 58 216 421 XS6-513 12–33 0.20 1.19 0.07 48 33 56 132 110 134 223 33 XS6-1316 33–41 2.06 5.58 0.25 60 44 46 81 165 XS8-01 0–1 3.85 8.29 0.09 70 185 61 237 369 XS8-15 1–5 2.71 4.85 0.05 74 132 61 185 285 XS8-510 5–10 1.42 1.45 0.04 90 51 60 93 81 XS8-1015 10–15 1.48 4.53 0.04 130 53 50 79 67 XS8-612 15–30 1.42 3.90 0.06 75 54 52 108 73 XS8-1219.5 30–50 2.01 5.68 0.07 59 35 52 72 56 These analyses showed that only small amounts of metals in the soil can be easily remobilized In the next extraction step, which is designed to release metals bound to organic matter, significant Cu, Ni, and Cr were removed, but only very small amounts of Pb and Zn. Pb and Zn were found to be released dominantly in the carbonate step or to remain in the residual fraction. Because the low values of Pb and Zn in the organically bound fraction are contrary to the results of the correlation analysis, which indicated that these metals are strongly associated with organic C, we applied additional tests to this fraction. The first three steps of the procedure were reapplied to 5 g each of two samples with 100 mL of extractant solutions, with the objective of checking for any organic carbon left in the sample after application of NaOH. For XS3-1015 organic C after [...]... area of the southbound roadway, was calculated as 21 g yr−1 which makes ∼0.7 kg for the 34 yr that the highway has been in use This value includes only the amount of contamination coming from abrasion of brakes, tires of vehicles, etc In calculation 311 HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS TABLE VI Amount of metals in the runoff compared with soil Pb Amount of metal in the runoff Excess... along 15 m of the southbound roadway) The excess amount of Pb in a 15 × 20 × 0.3 m volume of the soil was calculated as 74 kg The amount of Pb contamination in runoff, which is 68 µg L−1 , was obtained by taking the average of the five runoff events of Sansalone and Buchberger (1997) (Table I) Knowing that the average rainfall in Cincinnati is 1.01 m yr−1 , the amount of Pb contamination in runoff from... resurfacing, will cause suspension of these heavily contaminated soils as small dust particles in the air Breathing these particles could be potentially harmful to the human body Secondly, discharge of metal- laden water to surface drainage could lead to elevated metal contents in water supplies HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS 313 5 Conclusions Heavy metal contamination in soils. .. for roadside soils is how much of the Pb present comes from former gasoline additives and how much from metal parts of vehicles, which is a continuing source Using the event mean concentrations of heavy metals in the runoff (Table I), which would represent the amount of heavy metal coming only from metal parts of vehicles (at the time of measurement, 1995, Pb was not an additive of gasoline in the U.S.),... reported in Wheeler and Rolfe (1979) and Teichmen HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS Figure 4 Cluster analysis Figure 5 XRD pattern of XS1 taken from 1–5 cm depth 309 310 D TURER ET AL and others (1993) for roadside soils Our results showed that these high levels of heavy metals are not confined to surface soils, which is consistent with the findings of Vandenabeele and Wood (1972) In fact... Ni and Cr (Table VI) These metals are assumed to come only from body parts and tyres of the vehicles The amount of Zn in the runoff is higher than the amount measured in the soil This could be because of discharge of some of the runoff waters into surface waters without any interaction with soil The amounts of Cu, Ni and Cr coming from runoff are, however, lower than the amounts measured in the soil. .. I-75, Cincinnati, Ohio, is very high in the top 15 cm when compared with background values The contamination decreases as depth increases and it increases as the amount of organic C increases in the soil The relationship between amount of contamination and amount of organic C is stronger than the one with depth Because of low amounts of swelling clay in the soil, in this particular case, clay mineralogy... proposed by Ward and others (1975) Another possibility is surface run-off carrying the metals into surface drainages, bypassing the soil Either of these last two possibilities points to potential health hazards A likely health problem for maintenance and construction workers along these highways exists from wind-blown dust Disruption of these soils during highway maintenance, including mowing, and excavation... analysis of clay minerals, 76% of the clay can be assigned to illite% (∼30% of which is smectite mixed layering) and the remainder is chlorite and kaolinite No changes in these proportions were found with depth or with position relative to the roadway HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS Figure 3a-c Organic C vs Pb, Zn, and Cu 307 308 D TURER ET AL Figure 3d-e Organic C vs Ni and Cr... constant source of anthropogenic organic matter as well as heavy metals, these metals will continue to remain bound to this insoluble organic matter in- situ unless the soils are remobilized mechanically Removal of these heavy metals as wind-blown dust is the most likely remobilization mechanism Another possibility is surface run-off carrying the metals into surface drainages, bypassing the soil Mass balance . HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS: COMPARISON BETWEEN RUNOFF AND SOIL CONCENTRATIONS AT CINCINNATI, OHIO DILEK TURER 1 ,. showing location of Cincinnati and the positions of sampling stations (After Sansalone et al., 1998). HEAVY METAL CONTAMINATION IN SOILS OF URBAN HIGHWAYS