SHE-Net - Outcome of the first workshop

Transfer of organic pollutants from soils to plants

The first workshop was held at the University of Reading on the 25th and 26th September 2007, with the aim of addressing the key components of this process. The attendees came from six different countries with expertise in plant physiology, risk assessment, plant metabolism and modelling plant uptake processes.

Session 1

The first session of the meeting was devoted to keynote speakers who presented the latest findings from their research:

  • Uptake and translocation of non-ionised pollutants by plants. Richard H. Bromilow. 
  • Xtrafood: Chain model for the impact analysis of contaminants in primary food products. Katleen De Brouwere, Christa Cornelis and Mirja Van Holderbeke (Integral Environmental)
  • Challenges in the modelling of plant uptake of organic pollutants: Modelling the exposure of children and adults to chemicals in the environment. Charlotte Legind, Stefan Trapp.
  • Plants & Organics: A Global Perspective. Edward Wild, Matteo Dalla Valle, Jon Barber, John Dent, Kevin Jones, Lancaster University, Luca Nizzetto and Antonio Di Guardo, Jordi Dachs and Ana Cabrerizo.
  • Plant uptake data for risk assessments: laboratory and field experiments. Bill Doucette. 
  • Plant uptake and the CLEA model. Ian Martin.

Session 2

The second session discussed and determined the important processes which determined the transfer of organic pollutants from soils to plants. These were:

  • How good do models have to be?
  • Do we need to focus on a particular set of chemicals?
  • Which are the critical pathways?
  • Can crops be placed into groups? E.g. all herbaceous crops together.
  • How do we address data variability?

Initially regulators need to know if there is a potential risk or not. A simple screening model to determine if there is any possible chemical transfer to crops may be enough at the stage. One order of magnitude was deemed a reasonable margin of error for a model; although two orders of magnitude maybe useful because of the high uncertainty associated with some plant processes.

The modelling approach needs to be able to address the whole suite of organic pollutants and transport of these from soils to plants and within the plant will be controlled by physical-chemical properties of the pollutant. It was recognised that some ionisable compounds such as the perfluorooctane sulponates may need further experimentation for us to understand their behaviour. The uptake processes should be modelled dynamically, but steady state solutions maybe reasonable. The workshop believed that developing one core model with crop groups would be the most efficient, but a screening matrix was developed at the workshop to determine which chemicals would be transferred by which transport processes and hence to what plant organ.

Metabolism of chemicals within the plant is known to occur in a number of cases, but there is insufficient data to include this in a model and so at present this process should be excluded. Modelling will therefore be conservative for those compounds where metabolism does occur.

The data variability encountered across experiments was a considerable problem recognised by the workshop. It was proposed that guidelines are required before data can be used in the validation and calibration of models. Plant and chemical specialists will be required to draw up such guidelines.

Conclusion

In conclusion the workshop was a success with two days of energetic discussion with some tangible outcomes. The most visible of these is the screening matrix which will allow regulators to quickly establish if a pollution scenario poses a potential risk to human health via crop ingestion. We also now have some clear pointers for the subsequent workshops on how the modelling of plant uptake should be undertaken before it is included in broader contaminated land risk assessments.

Participants

Organising Committee

Chris Collins

University of Reading

George Shaw

University of Nottingham

Tanja Ples-Mulloli

Newcastle University

Ian Martin

Environment Agency

David Mortimer

Food Standards Agency

Invited Experts

Rob Edwards

Durham University

Ross Cameron

University of Reading

Anne Verhoef

University of Reading

Kevin Jones

Lancaster University

Raquel Duarte-Davison

Health Protection Agency

Richard Bromilow

BBSRC Rothamsted

Ross Brown

Astra Zeneca Brixham

Melinda Evans

Worley Parsons Komex

Michael Moore

Plymouth Marine Laboratory

Peter Schroeder

GSF, Munich

Charlotte Legrind

Technical University of Denmark

Katleen De Brouwere

VITO, Belgium

Michael McLachlan

Stockholm University, Sweden

William Doucette

Utah State University, USA

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