Sue Charlesworth

A review of the distribution of particulate trace elements in urban terrestrial environments and its application to considerations of risk

We review the evolution, state of the art and future lines of research on the sources, transport pathways, and sinks of particulate trace elements in urban terrestrial environments to include the atmosphere, soils, and street and indoor dusts. Such studies reveal reductions in the emissions of some elements of historical concern such as Pb, with interest consequently focusing on other toxic trace elements such as As, Cd, Hg, Zn, and Cu. While establishment of levels of these elements is important in assessing the potential impacts of human society on the urban environment, it is also necessary to apply this knowledge in conjunction with information on the toxicity of those trace elements and the degree of exposure of human receptors to an assessment of whether such contamination represents a real risk to the city’s inhabitants and therefore how this risk can be addressed.

Particulate-associated heavy metals in the urban environment: their transport from source to deposit, Coventry, UK.

A sequential digest was used to examine the speciation of particulate-associated heavy metal pollutants in a holistic approach to the study of the movement of sediment within the urban environment. Sediments were classified according to whether they mainly acted as sources, were mostly transported, or had become deposited and were fractionated into two particle sizes to reflect sediment deposited in lakes (< 63 microns) and transported in rivers (< 2 mm). Results showed that the two particle size fractions yielded the same data, but that trends were found in terms of dominant heavy metal species as the sediment moved through the source-transport-deposit cascade. Whilst the results highlighted the complexity of the urban environment, a sequential digestion of the samples enabled comments to be made in terms of risk which could subsequently feed in to a management strategy for polluted urban sediments.

Laboratory-based experiments to investigate the impact of glyphosate-containing herbicide on pollution attenuation and biodegradation in a model pervious paving system.

An experimental investigation was carried out to determine the effect of glyphosate-containing herbicides (GCHs) on the hydrocarbon retention and biodegradation processes known to occur in pervious pavement systems (PPSs). The PPS test rigs were based on the four-layered design detailed in CIRIA C582. This enabled the pollutant retention capacity of the PPS and biodegradation of retained pollutants by microorganisms to be investigated. The use of test rigs also enabled the impact of GCH on PPS eukaryotic organisms to be studied, by the monitoring of protist bioindicators. Results showed that GCH disrupted hydrocarbon retention by the geotextiles relative to rigs with mineral oil only added, as 9.3% and 24.5% of added hydrocarbon were found in herbicide only rigs and herbicide plus oil rigs respectively. In previous studies, PPS contaminated by mineral oil had been shown to retain 98.7% of added oils and over several weeks, biodegrade this oil in situ. Where GCH was added to experimental models, much higher concentrations of heavy metals, including Pb, Cu, and Zn, were released from the PPS in effluent, particularly where GCH and mineral oil were added together. The source of the majority of the metal contamination was thought to be the used engine oil. The herbicide generally increased the total activity of microbial communities in rig systems and had a stimulating effect on bacterial and fungal population numbers. Although the protists, which are part of the microbial community directly or indirectly responsible for biodegradation, were initially strongly affected by the herbicide, they showed resilience by quickly recovering and increasing their population compared with rigs without added herbicide, including the rigs with mineral oil added to them. However, the presence of herbicide was associated with a decrease in the species richness of recorded protist taxa and a predominance of robust, cosmopolitan or ubiquitous protist genera.

Laboratory based experiments to assess the use of green and food based compost to improve water quality in a Sustainable Drainage (SUDS) device such as a swale.

Many tonnes of compost are generated per year due to door step composting of both garden and kitchen waste. Whilst there are commercial outlets for the finer grade of compost (<10mm) in plant nurseries, there is little demand for the coarser material (>25 mm). This paper reports part of a WRAP-sponsored (Waste Resources Action Programme) study which investigated the potential for green (GC) and mixed green and food (MC) composts to be incorporated into Sustainable Drainage (SUDS) devices such as swales, and replace the topsoil (TS) onto which turf is laid or grass seed distributed. However, it is not known whether compost can replace TS in terms of pollutant remediation, both the trapping of polluted particulates and in dealing with hydrocarbons such as oil, but also from a biofilm development and activity perspective. Using laboratory based experiments utilising leaching columns and an investigation of microbiological development in the composts studied, it was found that many of the differences in performance between MC and GC were insignificant, whilst both composts performed better in terms of pollutant retention than TS. Mixed compost in particular could be used in devices where there may be oil spillages, such as the lorry park of a Motorway Service Area due to its efficiency in degrading oil. Samples of GC and MC were found to contain many of the bacteria and fungi necessary for an active and efficient biofilm which would be an argument in their favour for replacement of TS and incorporation in swales.

An evaluation of the use of individual grass species in retaining polluted soil and dust particulates in vegetated sustainable drainage devices

Abstract A sustainable means of preventing polluted particulates carried in urban storm water entering rivers, groundwater and lakes is by employing vegetated sustainable drainage system (SUDS) devices, or best management practices to trap or biodegrade them. In the UK, a mixture of grass species is recommended for use in devices such as swales or filter strips. However, there is little evidence in support of the efficiency of the individual grasses or mixtures to deal with such contaminated material. A pot-based pollutant retention study was conducted using processed street dust from central Coventry, UK, as a simulated pollutant to be applied in different quantities to a variety of recommended grasses for vegetated SUDS devices. Analysis was conducted on compost cores, roots and shoots for heavy metals (Cd, Cu, Ni, Pb and Zn). Street dust mainly concentrated in the top compost layer for all grasses with only the finer material migrating down the profile. Analysis of roots indicated little accumulation, with ANOVA statistical tests indicating significant differences in heavy metal concentrations, with less in the compost and more in the shoots. Development of root systems on or near the surface possibly explains increased uptake of heavy metals by some species. Overall Agrostis canina and Poa pratensis showed the greatest accumulations compared to their controls although Agrostis capillaris syn.tenuis and Agrostis stolonifera also demonstrated accumulation potential. On ranking, Agrostis canina and Poa pratensis were highest overall. These rankings will assist in selecting the best grasses to address pollution of the urban environment by contaminated particulates.