D. Michael Revitt

INCIDENCE OF HEAVY METALS IN STREET SURFACE SEDIMENTS: SOLUBILITY AND GRAIN SIZE STUDIES

Samples of surface and gutter sediment from roads within N.W. London have been analyzed for levels of Cd, Cu, Fe, Mn, Pb, and Zn. Sediment and associated metal grading curves are presented and apart from Mn and Fe which reflect natural background levels, the remaining metals show distributions which relate to road type and traffic conditions. For highways carrying the highest traffic densities the concentrations of Cd and Pb are greatest for grain sizes between 100 and 500 µm and an aggregation process is postulated. Residential side street samples show a marked affinity of Cd, Fe, and Zn for the coarsest grain fractions.Laboratory sorption and desorption studies are described and solution concentrations are obtained for Cd, Cu, Mn, Pb, and Zn over 1 to 30 day time periods. Solubility curves are typically variable with time. The relationship of leachate patterns to particle size and sample site location is discussed and its relative importance to Stormwater loadings is considered. Extraction efficiencies for the five metals are found to be independent of road type and in the order Cd > Zn, Cu > Mn > Pb. The relevance of this hierarchy to Stormwater toxicity is discussed.

Ecotoxicity of carbamazepine and its UV photolysis transformation products

Carbamazepine, an anti-epileptic pharmaceutical agent commonly found in wastewater, is highly recalcitrant to standard wastewater treatment practices. This study investigated the mixture toxicity of carbamazepine transformation products formed during ultraviolet (UV) photolysis using three standard ecotoxicity assays (representing bacteria, algae and crustaceans). UV-treatment of 6 mg L(-1) carbamazepine solution was carried out over a 120 min period and samples were removed periodically over the course of the experiment. Quantification results confirmed the degradation of carbamazepine throughout the treatment period, together with concurrent increases in acridine and acridone concentrations. Ecotoxicity was shown to increase in parallel with carbamazepine degradation indicating that the mixture of degradation products formed was more toxic than the parent compound, and all three ecotoxicity endpoints were still inhibited >60% relative to control populations upon dosing with 90+min UV-treated carbamazepine solution. Single compound toxicity testing also confirmed the higher toxicity of measured degradation products relative to the parent compound. These results show that transformation products considerably more toxic than carbamazepine itself may be produced during UV-treatment of wastewater effluents and/or photo-induced degradation of carbamazepine in natural waters. This study highlights the need to consider mixture toxicity and the formation and persistence of toxicologically relevant transformation products when assessing the environmental risks posed by pharmaceutical compounds.

Hydrological controls of pollutant removal from highway surfaces

Abstract Sediment and metal loadings to roadside gully-pots (weight/area of catchment/runoff depth) are calculated for two defined sites within a highway catchment and compared with data from other urban studies. The higher metal loadings associated with the more active site are particularly noticeable for Cu but at both sites the relative sizes of the metal loadings reflect the expected metal availabilities. The measured total surface runoff volumes represent between 34 and 83% of the total incoming rainfall volume for the catchment. The possible reasons for these water losses are assessed in terms of surface characteristics, seasonal variations and instrument limitations. Stepwise linear regression analysis of pollutant loadings against five selected hydrological parameters indicates that total runoff volume and storm duration together explain over 90% of the observed variance in Pb, Cd, Mn and sediment loadings. The results demonstrate the lack of importance of antecedent dry period and rainfall intensity in controlling the removal of particulate associated pollutants from this catchment. The derived model is used to predict temporal pollutant removal rates and these are shown to be consistent with those reported in other urban catchment studies.

The impacts of urban discharges on the hydrology and water quality of an urban watercourse

Abstract This paper presents the findings of a study which has investigated the effects of urban discharges upon the hydrology and water quality of a small urban watercourse located in north London. A variety of hydrological variables and water quality parameters were monitored at a site downstream of two surface water outfalls (SWOs) and two combined sewer overflows (CSOs). Precipitation volume was found to be highly correlated with the total storm discharge ( r 2 = 0.91) and the duration of storm flow ( r 2 = 0.93). Precipitation intensity displayed a 0.67 level of correlation with peak discharge volume. Aqueous loadings of biochemical oxygen demand (BOD), nitrate, chloride, total ammonia, suspended solids and total and dissolved zinc, copper, cadmium and lead, increased during the five monitored storm events. The highest increases in pollutant loadings compared with dry weather values were associated with BOD and suspended solids.

Transport mechanisms and processes for metal species in a gullypot system

Abstract The measurement of soluble and solid associated Cd, Cu, Pb and Zn species within the immediate environment of a gullypot during storm events has enabled the identification of six major processes which affect metal mobilisation and transport through the gullypot system. These processes are described under the headings: (a) Atmospheric Fallout, (b) Acid Rain Mobilisation from Road Dusts, (c) Constant Metal Concentration Time Zones, (d) pH/Surface Area Dependent Suspended Solid Metal Transport, (e) Metal Increase in the Gullypot Liquor between Storm Events and (f) Contribution of Gullypot Liquor and Sediment to Metals in the Gullypot Outflow. The contribution of each of these processes towards controlling the form of the metal in the gullypot outflow is discussed and a number of theoretical concepts are established.

The implications of household greywater treatment and reuse for municipal wastewater flows and micropollutant loads

An increasing worldwide interest in water recycling technologies such as greywater treatment and reuse suggests that additional research to elucidate the fate of xenobiotics during such practices would be beneficial. In this paper, scenario analyses supported by empirical data are used for highlighting the potential fate of a selection of xenobiotic micropollutants in decentralised greywater treatment systems, and for investigation of the possible implications of greywater recycling for the wider urban water cycle. Potential potable water savings of up to 43% are predicted for greywater recycling based on Danish water use statistics and priority substance monitoring at a greywater treatment plant in Denmark. Adsorption represents an important mechanism for the removal of cadmium, nickel, lead and nonylphenol from influent greywater and therefore the disposal route adopted for the generated sludge can exert a major impact on the overall efficiency and environmental sustainability of greywater treatment.

Seasonal removal of herbicides in urban runoff

The occurrence of two herbicides (diuron and simazine) in receiving surface waters is related to their seasonal applications within an urban catchment. Comparisons of herbicide concentrations within baseflow and during rainfall conditions provide an insight into pollutant transport processes following application to urban surfaces. Two storm events, with different hydrological characteristics, are described. The maximum recorded herbicide concentrations reached 238.4 and 2.23 μg/l for diuron and simazine, respectively, with the former corresponding to an application loss of 45.1% with respect to the diuron recently applied to the urban catchment. The factors influencing the extent of application losses to receiving waters of herbicides applied to urban substrates are discussed.

The sources, impact and management of car park runoff pollution: a review

Traffic emissions contribute significantly to the build-up of diffuse pollution loads on urban surfaces with their subsequent mobilisation and direct discharge posing problems for receiving water quality. This review focuses on the impact and mitigation of solids, metals, nutrients and organic pollutants in the runoff deriving from car parks. Variabilities in the discharged pollutant levels and in the potentials for pollutant mitigation complicate an impact assessment of car park runoff. The different available stormwater best management practices and proprietary devices are reported to be capable of reductions of between 20% and almost 100% for both suspended solids and a range of metals. This review contributes to prioritising the treatment options which can achieve the appropriate pollutant reductions whilst conforming to the site requirements of a typical car park. By applying different treatment scenarios to the runoff from a hypothetical car park, it is shown that optimal performance, in terms of ecological benefits for the receiving water, can be achieved using a treatment train incorporating permeable paving and bioretention systems. The review identifies existing research gaps and emphasises the pertinent management practices as well as design issues which are relevant to the mitigation of car park pollution.

An impact assessment methodology for urban surface runoff quality following best practice treatment.

The paper develops an easy to apply desk-based semi-quantitative approach for the assessment of residual receiving water quality risks associated with urban surface runoff following its conveyance through best practice sustainable drainage systems (SUDS). The innovative procedure utilises an integrated geographical information system (GIS)-based pollution index approach based on surface area impermeability, runoff concentrations/loadings and individual SUDS treatment performance potential to evaluate the level of risk mitigation achievable by SUDS drainage infrastructure. The residual impact is assessed through comparison of the determined pollution index with regulatory receiving water quality standards and objectives. The methodology provides an original theoretically based procedure which complements the current acute risk assessment approaches being widely applied within pluvial flood risk management.

A pollutant removal prediction tool for stormwater derived diffuse pollution

This report describes the development of a methodology to theoretically assess the effectiveness of structural BMPs with regard to their treatment of selected stormwater pollutants (metals, polyaromatic hydrocarbons and herbicides). The result is a prioritisation, in terms of pollutant removal efficiency, of 15 different BMPs which can inform stormwater managers and other stakeholders of the best available options for the treatment of urban runoff pollutants of particular environmental concern. Regardless of the selected pollutant, infiltration basins and sub-surface flow constructed wetlands are predicted to perform most efficiently with lagoons, porous asphalt and sedimentation tanks being the least effective systems for the removal of pollutants. The limitations of the approach in terms of the variabilities in BMP designs and applications are considered.