SEGH Articles

# Urban sediments: Geochemistry and mineralogy towards improved risk assessments

07 November 2012
Raquel was a joint oral presentation winner at the ISEG meeting in Aveiro in July 2012. The main aim of Raquel’s present research is to characterize the presence of PHE in soils and urban sediments, exploring the spatial, geochemical and mineralogical linkages within and between these media.

Raquel Cardoso is currently a final year PhD student at Manchester Metropolitan University, UK in collaboration with the British Geological Survey, studying urban environmental geochemistry. Raquel was a joint oral presentation winner at the ISEG meeting in Aveiro in July 2012. The main aim of Raquel’s present research is to characterize the presence of PHE in soils and urban sediments, exploring the spatial, geochemical and mineralogical linkages within and between these media.

Road deposited sediments (RDS), the accumulation of particles on pavements and road surfaces, have been documented to carry a high loading of contaminant species, including trace metals. These potentially harmful elements (PHE) may cause deleterious health effects to urban residents and commuters due to RDS high susceptibility to remobilisation and transport - RDS is spatially and temporally highly variable. Furthermore, urban agglomerations tend to grow and so does the importance of RDS characterization and monitoring: 50% of the world population currently lives in urban centres, a figure which is set to increase in the next decades.

With the purpose of better understanding RDS compositional variations across Manchester, UK, and its relationship to soil geochemistry, 144 RDS samples were collected in two seasons  across 75Km2 of Manchester urban centre. Samples underwent elemental analysis by X-ray fluorescence spectrometry (XRF), organic matter determination, grain size analysis by laser diffractrometry, and grain-specific microanalysis by scanning electron microscopy (SEM-EDS).

The amount of RDS collected in summer was generally larger than in winter and grain size was also coarser in summer for most samples. Nevertheless, PHE content remained similar between seasons for each location. GIS (geographic information system) spatial interpolation analysis  allowed the detection of contamination hotspots present in both winter and summer datasets, where PHE concentrations (namely Cr, Ni, Cu, Zn, Pb and Cd) were above the 90th percentile. Further GIS data analysis pointed proximity to main roads and industrial areas as the main influential factors on RDS composition, which can vary considerably over short distances.

Grain size analysis evidenced that among the most contaminated samples are those with highest contents in grain size fractions below 63µm. However, correlation and principal component analysis showed that PHE tend to be associated to the 63-125µm, suggesting that these might act as hosts for PHE rather than the finest fractions of the sediment (<63µm). Elements correlated to the 63-125µm fraction include Zn, Pb and Cd for both seasons, as well as Co, Ba, Ni and Cu only for the summer dataset. Further SEM-EDS analysis revealed grains between ~90-130µm composed by combinations of the above elements, either in crystalline forms or aggregates. The source of these grains still needs further investigation.

Future sequential extraction analysis of trace metals will clarify the availability of these PHE, providing essential information for the risk assessment to human populations. With the aid of geostatistical models, PHE associations will be defined, as well as the spatial, geochemical and mineralogical linkages between RDS and other environmental media, namely soils - for which similar research is being undertaken presently. This will lead to a better understanding of PHE dynamics in urban systems and add vital knowledge on the risks posed to human populations by RDS exposure.

Raquel Cardoso

Manchester Metropolitan University

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## Science in theNews

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Fertilizer usage and cadmium in soils, crops and food 2018-06-23

### Abstract

Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent $$\hbox {Cd}^{2+}$$ , $$\hbox {Mg}^{2+}$$ and $$\hbox {F}^-$$ ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

• Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

### Abstract

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

• Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

### Abstract

Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.