4 research outputs found
Spatial variability in heavy metal concentration in urban pavement joints â a case study
Heavy metals are known to be among one of the major environmental pollutants, especially in urban
areas, and, as generally known, can pose environmental risks and direct risks to humans. This study deals with
the spatial distribution of heavy metals in different pavement joints in the inner city area of Marburg (Hesse,
Germany). Pavement joints, defined as the joint between paving stones and filled with different materials, have
so far hardly been considered as anthropogenic materials and potential pollution sources in urban areas. Nevertheless, they have an important role as possible sites of infiltration for surface run-off accumulation areas and
are therefore a key feature of urban water regimes. In order to investigate the spatial variability in heavy metals
in pavement joints, a geospatial sampling approach was carried out on six inner city sampling sites, followed
by heavy metal analyses via inductively coupled plasmaâmass spectrometry (ICPâMS) and additional pH and
organic matter analyses. A first risk assessment of heavy metal pollution from pavement joints was performed.
Pavement joints examined consist mainly of basaltic gravel, sands, organic material and anthropogenic artefacts (e.g. glass and plastics), with an average joint size of 0.89 cm and a vertical depth of 2â10 cm. In general,
the pavement joint material shows high organic matter loads (average 11.0 % by mass) and neutral to alkaline pH
values. Besides high Al and Fe content, the heavy metals Cr, Ni, Cd and Pb are mainly responsible for the contamination of pavement joints. The identified spatial pattern of maximum heavy metal loads in pavement joints
could not be attributed solely to traffic emissions, as commonly reported for urban areas. Higher concentrations
were detected at run-off accumulation areas (e.g. drainage gutters) and at the lowest sampling points with high
drainage accumulation tendencies. Additional Spearman correlation analyses show a clear positive correlation
between the run-off accumulation value and calculated exposure factor (ExF; Spearman correlation coefficients
(rSP) â 0.80; p<0.00). Further correlation analyses revealed different accumulation and mobility tendencies of
heavy metals in pavement joints. Based on sorption processes with humic substances and an overall alkaline
pH milieu, especially Cu, Cd and Pb showed a low potential mobility and strong adsorption tendency, which
could lead to an accumulation and fixation of heavy metals in pavement joints. The presence of heavy metals in
pavement joints poses a direct risk for urban environments and may also affect environments out of urban areas
if drainage transports accumulated heavy metals. Finally, we encourage further research to give more attention
to this special field of urban anthropogenic materials and potential risks for urban environments. Overall urban
geochemical background values, and the consideration of run-off-related transport processes on pavements, are
needed to develop effective management strategies of urban pavement soil pollution
Investigating the dispersal of macro- and microplastics on agricultural fields 30 years after sewage sludge application
Plastic contamination of terrestrial ecosystems and arable soils pose potentially negative impacts on
several soil functions. Whereas substantial plastic contamination is now traceable in agro-landscapes,
often internal-caused by the application of fertilizers such as sewage sludge, questions remain
unanswered concerning what happens to the plastic after incorporation. Based on a combined surface
and depth sampling approach, including density separation, fuorescence staining and ATR-FTIR or
”FTIR analyses, we quantifed macro- and microplastic abundance on two agricultural feldsâ34 years
after the last sewage sludge application. By sub-dividing the study area around sludge application
sites, we were able to determine spatial distribution and spreading of plastics. Past sewage sludge
application led to a still high density of macroplastics (637.12 items per hectare) on agricultural soil
surfaces. Microplastic concentration, measured down to 90 cm depth, ranged from 0.00 to 56.18
particles per kg of dry soil weight. Maximum microplastic concentrations were found in regularly
ploughed topsoils. After 34 years without sewage sludge application, macro- and microplastic loads
were signifcantly higher on former application areas, compared to surrounding areas without history
of direct sewage application. We found that anthropogenic ploughing was mainly responsible for
plastic spread, as opposed to natural transport processes like erosion. Furthermore, small-scale lateral
to vertical heterogeneous distribution of macro- and microplastics highlights the need to determine
appropriate sampling strategies and the modelling of macro- and microplastic transport in soils
Disilane cleavage with selected alkali and alkaline earth metal salts
The industryâscale production of methylchloromonosilanes in the MĂŒllerâRochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes MenSi2Cl6ân (n=1â6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into monoâ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride
Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts
The industryâscale production of methylchloromonosilanes in the MĂŒllerâRochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes MenSi2Cl6ân (n=1â6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into monoâ and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride