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18/03/2015
Concept for modelling of chemicals

 

The availability of pan-continental datasets allows the development of spatially explicit GIS based models for assessment of fate and distribution of pollutants into different environmental media e.g. atmosphere, soil, freshwater and sea. In principle, spatial models predict chemical concentration at a given location when the emissions to different media at continental scale are known. This is a typical "direct" formulation of fate problem aiming to answer the question "where do pollutants go?"

Vice versa, when the emissions of chemicals are unknown, but their concentrations are widely spread monitored, then the "inverse" modelling approach answers the question "where do pollutants come from?" by back tracing of emissions from measured concentrations and identifing possible sources of contamination discharges.

Both approaches are used in our modeling-based assessment of pollutant fate and impacts at continental and regional scales.

 

Persistent Organic Pollutants (POPs) resist to degradation through chemical, biological, and photolytic processes.   Thus, POPs persist in the environment, are capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and have potential significant impacts on human health and the ecosystems. POPs are often halogenated and characterised by low water but high lipid solubility, leading to their bioaccumulation in fatty tissues. They are also semi-volatile, enabling them to move long distances in the atmosphere before deposition occurs.

POPs are used currently or in the past as pesticides, herbicides and insecticides. Others are applied in industrial processes and in the production of goods such as solvents, polyvinyl chloride, and pharmaceuticals. Though there are a few natural sources of POPs actually  most POPs are created by human activities, either intentionally or as byproducts.


Large scale screening modelling

 

The modelling conceptMAPPE (Multimedia Assessment of Pollutant Pathways in Environment) is a spatially explicit  fate and transport model of chemicals developed as a screening tool for the identification of hot-spots.

The basic idea of MAPPE is to generate maps of chemical emissions and maps of environmental removal rates.  Then, eventually to combine them using map algebra in order to obtain estimates of chemical mass and fluxes in different media.

Continental scale datasets

 

The model input consisits of data at European continental scale:

 

  • Landscape and Climate parameters
  • Chemical emissions to different environmental compartments
  • Physico-chemical properties of pollutants

 

Data are available at the following link. Follow "Read more" to see a short description to each dataset. 


MAPPE proved to be also very simple and quick from the computational point of view. On the contrary, models describing environmental processes in much finer detail result quite often in impractical computational burdens, lack of transparency and limited capability of error tracking.

MAPPE modelMAPPE overview scheme is shown in the Figure (click to the thumbnail to view a full size picture). The media concentrations and inter/intra media fluxes (deposition, volatilization, sedimentation, loadings to the coastal zone) computed by the model are meant to represent “average” conditions consequently  they reflect emissions assumed to be constant over the year (in the case of the atmosphere and inland water) or distributed monthly (in the case of soils). Moreover, environmental transfer rates are computed as annual or monthly averages based on the different environmental.

For atmosphere, a simplified approach has been employed equivalent to considering average contaminant concentration plumes from emissions supposed to be uniformly proportional to population density within a country. Therefore, the atmospheric module of MAPPE was adopted similarly to the ADEPT model [Roemer et al., 2005]. The latter has been extensively tested as documented in Pistocchi and Galmarini (2008). MAPPE was found to yield results in agreement with the traditional approaches used in risk assessment in Europe, but additionally giving spatial distribution of concentrations. 

Soil water and chemical budget are described directly through simple box models of steady state mass balance and handled using map algebra. The soil water budget is computed at monthly steps according to Pistocchi et al. (2008) and Pistocchi (2009).

Fate and transport in lakes and stream network, through sediment and water fluxes are described using the hydrologic functions of flow length and flow accumulation. The hydraulics of the stream network, including velocity and residence time in rivers and lakes, are specified according to Pistocchi and Pennington (2006) and Pistocchi (2008). 

Sea water compartment is also developed using a box model approach, neglecting lateral exchanges, but considering the atmospheric deposition, degradation, volatilization, and settling.

Atmosphere

The atmospheric parameters dataset contains information about: air temperature, OH concentration, Aerosol concentration in air, Organic carbon content in aerosol, 10 m height wind velocity, Atmospheric mixing height, Precipitation, Duration of the wet period, Atmospheric Source-receptor relations and Atmospheric Source-receptor time of travel. The different data subsets vary in time scales and spatial resolution.

 

Soil and vegetation

The soil and vegetation dataset contains information about: top soil organic carbon content, soil texture, runoff, evapotranspiration, infiltration, erosion rate, Leaf Area Index (LAI). The different data subsets vary in time scales and spatial resolution.

 

Surface water

The surface water dataset contains information about: river discharge, river slop, river water velocity, water depth, suspended sediment concentration, and surface water residence time. The different data subsets vary in time scales and spatial resolution.

 

Ocean and seas

The ocean and seas dataset contains information about: mixing depth, seawater velocity, seawater temperature, total suspended matter, wind speed at 10m height over ocean surface, and chlorophyll. The different data subsets vary in time scales and spatial resolution.

 

Modelling applications

Dioxins and Furans concentration in soil and seas

 

MAPPE, based on 'direct' modelling approach,  has been used to assess at continental scale the fate of:

  • POPs (PCBs and PCDD/Fs)
  • insecticides (Lindane).

Ibuprofen load

The environmental fate of other chemicals have been investigated using 'inverse' modelling approaches as applied to:

  • perfluorinated compounds (PFOS and PFOA)
  • pyrethroid insecticides
  • pesticides
  • household used chemicals including pharmaceuticals.

 

More details could be found in the 'publication' section.

 

 

Contact

Dimitar Marinov

Dimitar.Marinov(at)jrc.ec.europa.eu