Assessment of 34 dissolved and particulate organic and metallic micropollutants discharged at the outlet of two contrasted urban catchments

The assessment of micropollutants in urban wet weather discharges is essential to improve the knowledge of the impact of such discharges on receiving waters. This study assessed the quality of combined sewer overflows (CSOs) in Ecully (residential catchment) and stormwater runoff in Chassieu (industrial catchment) during rain events by providing data on occurrence and total event mean concentrations (EMC_t) of 34 priority substances (PS) (9 metals, 13 pesticides, 6 PAHs, 4 alkylphenols and 2 chlorobenzenes) in dissolved and particulate fractions. Over 34 substances monitored, 23 were quantified in urban wet weather discharges of both catchments. For both catchments, 9 metals and 6 PAHs monitored were always quantified, reflecting their ubiquitous presence. For other organic pollutants, only 5 pesticides were quantified and only 2 alkyphenols were measured solely in dissolved fraction. A significant site-to-site difference was observed for metals, PAHs and alkylphenols. The highest concentrations were measured in stormwater runoff in Chassieu vs. Ecully. On the contrary, the diuron concentrations were highest in CSO discharges in Ecully. Distribution of the PS between particulate and dissolved fractions provides information for urban stormwater practitioners. Most PS in urban wet weather discharges were mainly linked to particles (PAHs, Pb, Ti for example). The comparison between daily flows of wastewater treatment plants during dry weather and CSOs daily flows in Ecully showed that stormwater was the most important source of contamination for fluoranthene, benzo(b)fluoranthene and benzo(k)fluoranthene and 7 metals (As, Cr, Co, Cu, Pb, Ti and Zn) in receiving water bodies, but not for pesticides and alkylphenols.

Dynamics of toxicity within different compartments of a peri-urban river subject to combined sewer overflow discharges

Combined Sewer Overflows (CSO) in small peri-urban streams and rivers are potentially toxic for their biocenosis. Improving the management of CSO discharges requires better knowledge of their dynamics and toxicity. In view to characterizing this toxicity, we sampled the different compartments (benthic and hyporheic zone) of a peri-urban stream located near the city of Lyon in France. The samples were taken at different distances from a CSO and at three period characteristic of different hydrological conditions. Their toxic effects were assessed by bioassays on the dissolved fraction (D. magna, V. fisheri and B. calyciflorus bioassays) and on the particle fraction (V. fisheri and H. incongruens bioassays). The results highlighted significant toxicity of the particulate fraction for the benthic and hyporheic samples, in particular downstream of the CSO, but with high spatio-temporal variability. This variability can first be attributed to the variability of CSO discharge sampling as a function of season and rainfall, and the dynamics of polluted particles (trapping of transported particles in infiltration zones, mobilization during floods). These parameters play a fundamental role in the distribution of pollutants according to the geomorphology of stream facies. Regarding dissolved pollutants, the chemical exchanges taking place at the "water-sediment" interface trigger the transfer of pollutants from one phase to another, after which the dispersion of these pollutants is governed by hydraulic flows. Finally, critical zones and periods are identified for the peri-urban river toxicity studied: benthic sediments under mean flow downstream; hyporheic sediments after a storm event downstream, close to the CSO. Recommendations are made on the basis of the knowledge obtained to optimize the management of these discharges.

Event-based quantification of emerging pollutant removal for an open stormwater retention basin - loads, efficiency and importance of uncertainties

Up to now, emerging contaminants have not been further-studied in in-situ stormwater best management practices and especially in detention basins. In this article, the efficiency of a dry stormwater detention basin was investigated regarding the removal of 7 alkylphenols and alkylphenol ethoxylates, 9 polybrominated diphenyl ethers, 45 pesticides and bisphenol A. Concentrations of contaminants were obtained by chemical analysis on dissolved and particulate phase distinctly. The removal efficiency was assessed on total, dissolved and particulate phase accounting for the global chain of uncertainty with a 95% confidence interval. Results showed that pesticides (rather hydrophilic) are not trapped in the detention basin but are released contrarily to B209 which is mostly in particulate phase. Alkylphenols and alkylphenol ethoxylates are present in both phases and the efficiency is storm event-dependent. Uncertainty consideration in efficiency determination revealed efficiency data, usually presented by raw values are not relevant to conclude on the performance of a detention basin. In this case study, efficiency data with a 95% confidence interval indicate that only 35%, 50% and 41% of campaigns showed an impact (in trapping or releasing) of the detention basin on alkylphenols and ethoxylates, polybrominated diphenyl ethers and pesticides respectively.

Accumulated sediments in a detention basin: chemical and microbial hazard assessment linked to hydrological processes

Accumulated sediments in a 32,000-m(3) detention basin linked to a separate stormwater system were characterized in order to infer their health hazards. A sampling scheme of 15 points was defined according to the hydrological behaviour of the basin. Physical parameters (particle size and volatile organic matter content) were in the range of those previously reported for stormwater sediments. Chemical analyses on hydrocarbons, PAHs, PCBs and heavy metals showed high pollutant concentrations. Microbiological analyses of these points highlighted the presence of faecal indicator bacteria (Escherichia coli and intestinal enterococci) and actinomycetes of the genus Nocardia. These are indicative of the presence of human pathogens. E. coli and enterococcal numbers in the sediments were higher at the proximity of the low-flow gutter receiving waters from the catchment. These bacteria appeared to persist over time among urban sediments. Samples highly contaminated by hydrocarbons were also shown to be heavily contaminated by these bacteria. These results demonstrated for the first time the presence of Nocardial actinomycetes in such an urban context with concentrations as high as 11,400 cfu g(-1).