Urban geochemistry is a unique discipline that is distinguished from general geochemistry by the complex infrastructure and intense human activities associated with concentrated population centers. ...As stated by Thornton (1991) “This subject is concerned with the complex interactions and relationships between chemical elements and their compounds in the urban environment, the influence of past and present human and industrial activities on these, and the impacts or effects of geochemical parameters in urban areas on plant, animal and human health.” Urban areas present special challenges to geochemists attempting to understand geochemical states and fluxes. On the 5–6 of August, 2014, the first meeting of the reorganized Urban Geochemistry Working Group of the International Association of GeoChemistry (IAGC) was held in Columbus, Ohio, United States. Two goals of the meeting were to develop the overall scope, and a general definition of urban geochemistry. Five grand themes were developed: 1) recognizing the urban geochemical signature; 2) recognizing the legacy of altered hydrologic and geochemical cycles in urban environments; 3) measuring the urban geochemical signature; 4) understanding the urban influence on geochemical cycles from the continuous development and erosion of physical infrastructure and episodic perturbations; and 5) relating urban geochemistry to human and environmental health and policy. After synthesizing the discussion of these themes we offer the following perspective on the science of urban geochemistry building on the work of Thornton (1991): Urban geochemistry as a scientific discipline provides valuable information on the chemical composition of environments that support large populations and are critical to human health and well-being. Research into urban geochemistry seeks to 1) elucidate and quantify the sources, transport, transformations, and fate of chemicals in the urban environment, 2) recognize the spatial and temporal (including legacies) variability in these processes, and 3) integrate urban studies into global perspectives on climate change, biogeochemical cycles, and human and ecosystem health. We hope that this discussion will encourage other geochemists to engage in challenges unique to urban systems, as well as provide a framework for the future of urban geochemistry research.
•Urban geochemistry is a rapidly evolving discipline within the earth sciences.•Urban geochemistry contributes to geochemistry by treating urban environments as unique complex geochemical systems.•We review the discipline, propose five grand themes of study, a definition of urban geochemistry, and a unifying question.
The effect of rainfall on the behavior of Fe, Mn, Cu, Zn, Pb, and Ti in mature soils developed on same-age volcanic bedrock in Hawaii was studied. Concentrations of the mentioned metals in total ...digested and weak acid-leached soil and bedrock samples were analyzed. Mass transport calculations yielded the quantity of metal enrichment or depletion in the soils relative to the bedrock. In addition, elemental mobility and the distribution between the labile and the residual fraction were examined.
Based on mass transport calculations there is no significant effect of rainfall amount on the enrichment or depletion of any elements (except Cu) within soils receiving less than 570 mm/yr (4 sites). In the intermediate sites (4 sites, 930–1380 mm/yr) there is a variable effect of rainfall on all elements in the soil, but the extent of variation differs from one metal to the other. In the rainy site (2500 mm/yr) there is a large degree of enrichment or depletion of certain metals. Manganese and Zn are highly depleted and Pb is strongly enriched, whereas Fe and Cu do not show a significant mass change. Among all elements, Pb is the only one that has a continuous effect of rainfall throughout the transect. Lead is enriched in all the sites and this enrichment is well correlated with increasing rainfall. Iron is immobile in the soil, reflecting the relative stability of the Fe-rich phases and its high correlation with Ti. The mass change of Mn throughout the transect is remarkably correlated with Al (
R
2 = 0.87). The behavior of the trace metals Pb, Zn, and Cu in the Kohala soils is different because of the phases with which these metals are likely to be associated. Lead is probably adsorbed and coprecipitated mostly with Fe oxides and hydrous oxides. Zinc is presumably associated with Mn and Al oxides and hydrous oxides and with organic matter, whereas Cu is most likely complexed by organic matter.
Seven bulk chondrites, with
δ
57Fe/
54Fe values between −0.1‰ and 0‰ relative to IRMM-14, tend to be slightly lighter than 11 bulk iron meteorites, which have
δ
57Fe/
54Fe values ranging from 0.04‰ ...to 0.2‰. At the mineral scale, taenite from two iron meteorites, Cranbourne and Toluca, shows
δ
57Fe/
54Fe values heavier by up to 0.3‰ than their kamacite counterpart, thus calling into question the significance of bulk iron meteorite data. On three pallasites (Esquel, Marjalahti and Springwater) we measured a heavier iron isotope composition for the metal fractions compared to the coexisting olivines as previously observed on two other pallasites (Eagle Station and Imilac), but the range of
δ
57Fe/
54Fe differences (from 0.32‰ to 0.07‰) is larger than that originally found. Troilite from two pallasites appears to be even heavier than the metal fraction, whereas schreibersite is lighter than its olivine counterpart. There is thus a general tendency for minerals within a given rock to show a heavier Fe isotope composition as the coordination number of Fe increases, although troilite is an exception to this rule. Iron meteorites are classically considered as remnants of asteroid cores and pallasites as core–mantle interfaces. The simultaneous finding that the metal fractions of pallasites have a higher
δ
57Fe/
54Fe signature than the coexisting olivines, and that the iron meteorites are slightly heavier than chondrites could be taken as an indication that planetary core–mantle differentiation is accompanied by sizeable iron isotope fractionation. In this hypothesis, mass balance constraints imply that resultant planetary mantles should be isotopically lighter than the chondritic starting material. That is not observed, however, since all planetary mantles analyzed so far have
δ
57Fe/
54Fe values equivalent to or heavier than those of chondrites. It thus appears that the moderate temperature and pressure metal–silicate fractionation that occurred in pallasite and iron parent bodies is not readily transposable to planets as far as Fe isotopes are concerned. Instead, these mantle signatures could reflect equilibrium fractionation at a higher temperature, or the lack of a global core–mantle equilibration at the planetary scale. Overall, these new results show that the mass-dependent isotopic scatter observed among inner solar system bodies from the bulk-rock to the planetary scale (∼0.3‰
δ
57Fe/
54Fe) is more restricted than previously thought. This likely confirms a homogenization process that occurred in the protoplanetary accretion disk, between refractory inclusion condensation and chondrule formation.
Purpose
This paper aims to elucidate urban development-induced processes affecting the sediment and the distribution of contaminating metals in a seasonal pond located in the highly populated Israeli ...Coastal Plain. The paper demonstrates how an integrated approach, including geochemical, sedimentological, geochronological, mathematical, historical, and geographical analyses, may decipher a complicated and dynamic metal pollution history in a sedimentary environment controlled by anthropogenic activity.
Materials and methods
Three short sediment cores were collected from the margins and center of a small urban pond (Dora, Netanya), located within the Israeli Coastal Plain. Profiles of grain size, organic matter (OM), trace metals (Pb, Zn, V, Ni, Cu, Cr and Co), Pb isotopic ratios, and
210
Pb activities (center and southern cores) were determined and a geochemical mixing model was employed (southern core). The watershed contour was calculated, and aerial photos and satellite images were examined.
Results and discussion
Construction activities in the watershed were chronologically associated with coarse sediment transport and deposition in the margins of the pond. The upper sandy layers were superimposed on layers rich in fine particles and OM, high concentrations of trace metals, and with Pb isotopic composition of more recent petrol. In the
210
Pb-dated southern core, deep metal-rich layers with petrol-related Pb isotopic ratios were inconsistent with metal emissions history. These findings point to mobility and migration of recent contamination metals through the coarse upper sediment layers and into deeper denser layers, confirmed also by a geochemical mixing model. Conversely, in the center of the pond, homogeneous fine particles were deposited with metal profiles consistent with regional emissions.
Conclusions
A small urban pond was found to provide an important case study for understanding heavy metal pollution records in highly populated regions. The margins of the pond depicted the surrounding urban development and the induced coarse sediment erosion, accompanied with post-depositional metal mobility. Due to the proximate developing residential areas, high metal concentrations accumulated in the margins, overshadowing regional atmospheric pollution levels recorded by sediment at the center of the pond.
The influence of montmorillonite colloids on the mobility of
Pu,
U and
Cs through a chalk fracture was investigated to assess the transport potential for radioactive waste. Radioisotopes of each ...element, along with the conservative tracer tritium, were injected in the presence and absence of montmorillonite colloids into a naturally fractured chalk core. In parallel, batch experiments were conducted to obtain experimental sorption coefficients (K
, mL/g) for both montmorillonite colloids and the chalk fracture material. Breakthrough curves were modelled to determine diffusivity and sorption of each radionuclide to the chalk and the colloids under advective conditions. Uranium sorbed sparingly to chalk (log K
= 0.7 ± 0.2) in batch sorption experiments.
U(VI) breakthrough was controlled primarily by the matrix diffusion and sorption to chalk (15 and 25% recovery with and without colloids, respectively). Cesium, in contrast, sorbed strongly to both the montmorillonite colloids and chalk (batch log K
= 3.2 ± 0.01 and 3.9 ± 0.01, respectively). The high affinity to chalk and low colloid concentrations overwhelmed any colloidal Cs transport, resulting in very low
Cs breakthrough (1.1-5.5% mass recovery). Batch and fracture transport results, and the associated modelling revealed that Pu migrates both as Pu (IV) sorbed to montmorillonite colloids and as dissolved Pu(V) (7% recovery). Transport experiments revealed differences in Pu(IV) and Pu(V) transport behavior that could not be quantified in simple batch experiments but are critical to effectively predict transport behavior of redox-sensitive radionuclides. Finally, a brackish groundwater solution was injected after completion of the fracture flow experiments and resulted in remobilization and recovery of 2.2% of the total sorbed radionuclides which remained in the core from previous experiments. In general, our study demonstrates consistency in sorption behavior between batch and advective fracture transport. The results suggest that colloid-facilitated radionuclide transport will enhance radionuclide migration in fractured chalk for those radionuclides with exceedingly high affinity for colloids.
Iron partitioning data and whole soil
δ
57Fe values were combined to calculate the isotopic composition of Fe mixing end-members in profiles of a Czech forest soil and an Israeli semi-arid soil. A ...least-squares method was used to estimate the Fe isotopic composition of the end-members representing the three main Fe reservoirs in the Czech soil: (1) silicates (
δ
57Fe
=
−
0.02
±
0.17‰), (2) organically bound Fe (
δ
57Fe
=
−
0.48
±
0.27‰), and (3) pedogenic Fe-oxides (
δ
57Fe
=
−
1.07
±
1.02‰). A lack of variation in the isotopic and chemical partitioning patterns in the Israeli soil prevented the application of the least-squares technique, although an Fe-oxide end-member is proposed using a similar mixing model (
δ
57Fe
=
−
1.72
±
1.16‰). Combination of the isotopic values for the different reservoirs with published fractionation data from previous studies suggests that the isotopic signature of the silicate fraction in the Israeli soil is dominated by lithogenic sources, while the Fe-oxide pool is influenced mainly by pedogenic precipitation/dissolution processes. The results demonstrate the potential for Fe isotopes as a tool to quantify Fe cycling in soils.
