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Abstract: Soakaway sediment trapped in urban infiltration facilities exhibits high heavy metal content that makes it an important diffuse pollution source of groundwater contamination. In this study, heavy metal (Cu, Zn, Cd and Pb) content, speciation and stable isotopic variation of Pb in soakaway sediments were coupled and compared with soils (surface and underlying), and road dusts (residential and highway) to trace their contamination characteristics, mobility and source. Soakaway sediment and residential road dust were found to exhibit higher metallic content of anthropogenic origin with high mobility. Isotopic ratios in exchangeable fraction showed the least 206Pb/207Pb and 208Pb/207Pb ratios. Although there were significant differences in total metal content and speciation between two road dust samples, their isotopic signatures exhibited close resemblance and aligned with anthropogenic markers such as paint, petrol and aerosols. Heterogeneity of isotopic signature in different fractions of soakaway sediments seems to have originated from the mixing of multiple sources of heavy metals. Study concludes that mobility, source and contamination characteristics of metals in soakaway sediment were different from urban soil and road dust samples due to their complex environment and regular metal supply by road runoff. [Copyright &y& Elsevier]

Abstract: Artificial infiltration facilities (AIFs) that enhance groundwater recharge and regulate urban runoff are going to be an integral element of the urban infrastructure. However, AIFs provide a sink which trap pollutants that are likely to cause groundwater contamination. The current study aimed first to examine the mobility characteristics of Cu, Zn, and Pb through soil and soakaway sediment using an integrated analytical approach for column leaching with artificial road runoff (ARR) and then to differentiate the sorption patterns among different samples, (i.e., surface soil, underlying soil, and soakaway sediments) using mass balances. In addition, the study compares metal retention and release under continuous and intermittent flow conditions. Column leaching experiments were conducted using batches for 10 and 30d under continuous flow condition and for 20d of intermittent leaching. Heavy metal content and partitioning in soil and sediment used in columns were well characterized before and after leaching experiments. The results showed that a gradual increase in pH and decrease in dissolved organic carbon had pronounced effect on the mobilization of heavy metals. Pb showed the highest retention compared to Cu and Zn which implies that metal complexes play a pivotal role in metal transport. Labile fractions were found to be trapped by the solid materials for retention and their high concentration in ARR is a major concern from the pollution point of view through infiltration facilities. Results obtained in this study predict the risk associated with the release of retained heavy metal under changing environmental conditions in AIFs. [Copyright &y& Elsevier]

Lead (Pb) isotopic data were used in this study to first distinguish the partitioning of anthropogenic and natural lead in different fractions, obtained by BCR sequential extraction, and then to anticipate their mixing process in the soakaway sediment of artificial infiltration facilities (AIF). Total metal content was found higher in soakaway sediment samples than that of soil. The lowest 206Pb/207Pb ratios were mostly observed in exchangeable fractions of soil and sediment samples, while residual fractions mostly showed the highest 206Pb/207Pb and 208Pb/207Pb ratios than those of other fractions. In general, both ratios were higher in the soil than those of sediments. Further among soil samples, residual fraction of bottom soil exhibited higher ratios than surface soil indicating higher contribution of natural lead with depth. In addition, the difference in Pb content, partitioning and its isotope signature among four sediment samples were also investigated considering their sampling locations. The plot of 206Pb/207Pb versus 208Pb/207Pb showed two well demarcated cluster formations by soil and sediments samples that describe the partitioning between anthropogenic and natural lead; and some points falling in between soil and sediment samples pertinently illustrated the mixing processes between these two different pools of lead. [ABSTRACT FROM AUTHOR]

Isotope dilution techniques (IDT) and sequential extraction procedures (SEPs) were compared to apprehend the differences between two techniques in determining metal exchangeability and vulnerability to pollute the urban groundwater. For this purpose, soil (n = 2), "soakaway" sediment deposited in the artificial infiltration facilities (AIF) (n = 4), and road dust (n = 2) were sampled from Tokyo metropolitan. Sorption coefficients of four metals (Cu, Zn, Cd and Pb) were assessed through isotopic exchangeability (E-value) and potential mobile pool i.e. addition of exchangeable, reducible and oxidizable fraction obtained by Community Bureau of Reference (BCR)-procedures. The E-value for the three samples were found smaller than the potential mobile pool but were higher than BCR-exchangeable fractions. The use of strong extractants are likely to play an active role in the disagreement between SEPs and IDT. IDT accounts for the isotopic exchangeability while BCR provides information of vulnerability of metals associated with different fractions that can leach under different environmental conditions. Sorption coefficients measured in soakaway sediment was found comparable to soil thus likely to retain metals. However, as variability in environmental conditions is likely to affect Kd, the soakaway sediment may become an active metal source in future rather than acting as the permanent sink. The study concludes that there is the possibility of errors while predicting metal vulnerability to groundwater with both techniques and thus a model compliance integrating the virtue of both techniques will be a way forward. Image 1 • Better compliance amid isotope dilution and sequential extraction for high metal loading. • Isotopic exchangeability (E-value) was smaller than extracted potential mobile pool. • Coupling of IDT with BCR provide better estimate of leaching vulnerability for metals. • IDT accounts for actual exchangeability while SEPs provide leaching vulnerability. [ABSTRACT FROM AUTHOR]

Infiltration facilities are designed for both the retention of non-point pollutants and the replenishment of groundwater in urban areas. In this study, sorption tests were conducted to evaluate the speciation of heavy metals and their behaviour in infiltration facilities receiving urban road runoff containing high DOC concentrations and stable heavy metal organic complexes. Road dust and three soakaway sediments were collected from heavy traffic areas and a residential area with an infiltration-type sewerage system in Tokyo, Japan. Sequential multiple batch tests were conducted by adding prepared road dust leachate (artificial road runoff) or deionised water to soakaway sediment to obtain soakaway sediment leachate (artificial percolating water from soakaway sediment), which mimicked the sorption by sediments in soakaways receiving urban road runoff. Heavy metal speciation was assessed by means of a combination of anion-exchange resin measurements and MINTEQA2 model calculations, and further validated by chelating resin measurements. In road dust leachates and soakaway sediment leachates, Cu predominantly existed as organic complexes and carbonates, whereas most Mn, Zn and Cd were found to exist in the form of free ions and carbonate complexes. Stable organic complexes of Cu in road dust leachates were strongly adsorbed by soakaway sediments despite the limited adsorption of DOC. On the other hand, desorption of free Mn, Zn and Cd ions from the sediment receiving road dust leachates was observed, indicating that heavy metals such as Mn, Zn and Cd may ultimately reach groundwater as free ions. [Copyright &y& Elsevier]

Abstract: Stable nitrogen and oxygen isotope ratios of nitrate (δ15N–NO3 and δ18O–NO3) have recently been used to identify nitrogen sources in water environments. However, there have been no investigations designed to determine nitrate isotopes in non-point sources in urban areas for evaluating the impact of surface deposits on nitrogen in surface runoff. In this study, we collected rainwater, surface runoff and surface deposits (road dust, roof dust and soil) to evaluate the nitrogen sources in surface runoff using nitrate isotopes. There were no large differences in δ15N–NO3 among rainwater (−0.3‰ to 1.5‰), surface runoff (−2.7‰ to 0.4‰), leachates from road dust (−5.8‰ to 6.2‰) and soil (−11.5‰ to 0.6‰). In contrast, the δ18O–NO3 in surface runoff (28.5–47.9‰) was lower than that in rainwater (62.7–78.6‰), and higher than that in leachates from road dust (6.1–27.6‰) and soil (−1.1‰ to 6.6‰). δ18O–NO3 is a useful indicator for evaluating the NO3–N sources in surface runoff. Using this indicator, NO3–N from road dust was estimated to account for more than half of the NO3–N in surface runoff. This is consistent with a result based on a comparison of their loads per unit surface between rainwater and surface runoff, which also showed that most of the nitrogen in surface runoff was derived from surface deposits. [Copyright &y& Elsevier]