Jean-Marie Mouchel

Heavy metal concentrations in dry and wet atmospheric deposits in Paris district: comparison with urban runoff

In urban areas, dry and wet atmospheric deposits are more rarely sampled than atmospheric particles. Nevertheless, fallout data are needed in order to compare concentrations and fluxes with street deposits and with samples collected during rain periods at roof outlets, gullies or within the sewer system. Such comparisons represent key issues in the understanding of micropollutant transport and evolution in urban areas. Within the Paris conurbation, four sites have been studied for dry, wet and total atmospheric deposits: Chatou, a suburb west of the Paris conurbation, Creteil, suburb, south-east, Fontainebleau at 48 km south-east from the centre of Paris, and Le Marais within the centre of Paris. On each site, samples were continuously collected from 2 to 13 months. Comparison of median values of metal concentrations in various components of atmospheric fallout illustrates the influence of urban emissions: rain water contamination with trace metals is only slightly larger in the centre of Paris than at Fontainebleau which illustrates the occurrence of medium range transport of atmospheric contamination. Focusing on an experimental urban catchment equipped with combined sewers, situated inside the LeMarais district, within Paris, this paper compares metal concentrations of atmospheric deposits to dissolved and particulate ones in runoff from four roofs, three yards, six gullies, and at the catchment outlet. This comparison allows a better understanding of metal transport in urban areas and of the evolution of metal distribution between dissolved and particulate fractions.

Mass balance and decontamination times of Polycyclic Aromatic Hydrocarbons in rural nested catchments of an early industrialized region (Seine River basin, France)

Accumulation of Polycyclic Aromatic Hydrocarbons (PAHs) in soils and their subsequent release in rivers constitute a major environmental and public health problem in industrialized countries. In the Seine River basin (France), some PAHs exceed the target concentrations, and the objectives of good chemical status required by the European Water Framework Directive might not be achieved. This investigation was conducted in an upstream subcatchment where atmospheric fallout (n=42), soil (n=33), river water (n=26) and sediment (n=101) samples were collected during one entire hydrological year. PAH concentrations in atmospheric fallout appeared to vary seasonally and to depend on the distance to urban areas. They varied between 60 ng·L(-1) (in a remote site during autumn) and 2,380 ng·L(-1) (in a built-up area during winter). PAH stocks in soils of the catchment were estimated based on land use, as mean PAH concentrations varied between 110 ng·g(-1) under woodland and 2,120 ng·g(-1) in built-up areas. They ranged from 12 to 220 kg·km(-2). PAH contamination in the aqueous phase of rivers remained homogeneous across the catchment (72 ± 38 ng·L(-1)). In contrast, contamination of suspended solid was heterogeneous depending on hydrological conditions and population density in the drainage area. Moreover, PAH concentrations appeared to be higher in sediment (230-9,210 ng·g(-1)) than in the nearby soils. Annual mass balance calculation conducted at the catchment scale showed that current PAH losses were mainly due to dissipation (biodegradation, photo-oxidation and volatilization) within the catchments (about 80%) whereas exports due to soil erosion and riverine transport appeared to be of minor importance. Based on the calculated fluxes, PAHs appeared to have long decontamination times in soils (40 to 1,850 years) thereby compromising the achievement of legislative targets. Overall, the study highlighted the major role of legacy contamination that supplied the bulk of PAHs that are still found nowadays in the environment.

Impact of hydro-sedimentary processes on the dynamics of soluble reactive phosphorus in the Seine River

This paper focuses on soluble reactive phosphorus (SRP) dynamics along a 225xa0km stretch of the Seine River, including the Paris urban area, for the 2007–2011 period. The impact of hydro-sedimentary processes on SRP concentrations and fluxes is estimated under various hydrological conditions. Sorption interaction parameters between SRP and suspended matter are experimentally determined on river water samples and are included in a hydro-ecological model. Simulated concentrations are compared to weekly measurements at 11 monitoring stations. The introduction of sorption in the model reduces the root mean square error of simulated SRP concentrations by 20xa0% and allows the simulation of particulate inorganic P (PIP) accumulation in the system. With these ameliorations, the model constitutes a reliable management tool, which is compatible with the requirements of new regulations as the European Water Framework Directive. P mass balances are assessed upstream and downstream the major waste water treatment plant of the Paris urban area. P fluxes in the system are mainly driven by hydrological conditions and sediment-related processes. While SRP is the predominant P form during low flow, PIP accounts for more than 70xa0% of the total P during high flow. Moreover, SRP sorption fluxes are of the same order of magnitude as biotic fluxes affecting SRP concentrations. According to the model, and based on all the available data, 75xa0% of the SRP release by the river bed sediments occurs during high flow periods, and PIP exchanges at the sediment–water interface are more than 4 times higher during high flow periods than during low flow periods.

Combining measurements and modelling to quantify the contribution of atmospheric fallout, local industry and road traffic to \PAH\ stocks in contrasting catchments

Various sources supply PAHs that accumulate in soils. The methodology we developed provided an evaluation of the contribution of local sources (road traffic, local industries) versus remote sources (long range atmospheric transport, fallout and gaseous exchanges) to PAH stocks in two contrasting subcatchments (46-614 km²) of the Seine River basin (France). Soil samples (n = 336) were analysed to investigate the spatial pattern of soil contamination across the catchments and an original combination with radionuclide measurements provided new insights into the evolution of the contamination with depth. Relationships between PAH concentrations and the distance to the potential sources were modelled. Despite both subcatchments are mainly rural, roadside areas appeared to concentrate 20% of the contamination inside the catchment while a local industry was found to be responsible for up to 30% of the stocks. Those results have important implications for understanding and controlling PAH contamination in rural areas of early-industrialized regions.