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

• Distribution of metal(loid)s in particle size fraction in urban soil and street dust: influence of population density 2020-01-18

### Abstract

Assessment of street dust is an invaluable approach for monitoring atmospheric pollution. Little information is available on the size distribution of contaminants in street dusts and urban soils, and it is not known how the population density would influence them. This research was carried out to assess the size distribution of trace metal(loid)s in street dust and urban soil, and to understand how population density might influence the size-resolved concentration of metal(loid)s. Three urban areas with a high, medium and low population density and a natural area were selected and urban soil and street dust sampled. They were fractionated into 8 size fractions: 2000–850, 850–180, 180–106, 106–50, 50–20, 20–10, 10–2, and < 2 µm. The concentration of Pb, Zn, Cu, Cd, Cr, Ni, As, and Fe was determined, and enrichment factor and grain size fraction loadings were computed. The results indicated that the concentration of Pb, Zn, Cu, Cd, and Cr was highly size dependent, particularly for particles < 100 µm, especially for street dust. Low concentrations of Ni and As in street dust and urban soil were size and population density independent. Higher size dependency of the metals concentration and the higher degree of elemental enrichment in the street dust fractions than the urban soils indicate higher contribution of human-induced pollution to the dust. Findings also confirm the inevitability of size fractionation when soils or dusts are environmentally assessed, particularly in moderately to highly polluted areas. Otherwise, higher concentrations of certain pollutants in fine-sized particles might be overlooked leading to inappropriate decisions for environmental remediation.

• Soil–plant system and potential human health risk of Chinese cabbage and oregano growing in soils from Mn- and Fe-abandoned mines: microcosm assay 2020-01-17

### Abstract

In Portugal, many abandoned mines are often close to agricultural areas and might be used for plant food cultivation. Soils in the vicinity of two Mn- and Fe-abandoned mines (Ferragudo and Rosalgar, SW of Portugal) were collected to cultivate two different food species (Brassica rapa subsp. pekinensis (Lour.) Hanelt and Origanum vulgare L.). Chemical characterization of the soil–plant system and potential risk of adverse effects for human health posed by plants associated with soil contamination, based on the estimation of hazard quotient (HQ), were assessed in a microcosm assay under greenhouse conditions. In both soils, the average total concentrations of Fe and Mn were above the normal values for soils in the region and their concentration in shoots of both species was very high. Brassica rapa subsp. pekinensis grew better in Ferragudo than in Rosalgar soils, and it behaved as an excluder of Cu, Mn, Fe, S and Zn in both soils. The HQ for Cu, Fe, Mn and Zn in the studied species grown on both soils was lower than unit indicating that its consumption is safe. The high Mn tolerance found in both species might be due in part to the high contents of Fe in the soil available fraction that might contribute to an antagonism effect in the uptake and translocation of Mn. The obtained results emphasize the need of further studies with different food crops before cultivation in the studied soils to assess health risks associated with high metal intake.

• Concentration, fractionation, and ecological risk assessment of heavy metals and phosphorus in surface sediments from lakes in N. Greece 2020-01-13

### Abstract

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, were investigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index Igeo values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as “unpolluted,” while many sediments in lakes Volvi and Kerkini were characterized as “moderately to heavily polluted” with regard to Cd. The descending order of potential ecological risk $$E_{\text{r}}^{i}$$ was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.