EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Heavy Metal City-Zen. Exploring the potential risk of heavy metal contamination of food crop plants in urban gardening contexts using a citizen science approach.

Elisabeth Ziss, Wolfgang Friesl-Hanl, Christoph Noller, Andrea Watzinger, and Rebecca Hood-Nowotny
Elisabeth Ziss et al.
  • Institute of Soil Research, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria (

Urban Gardening has become increasingly popular globally in the past two decades as urbanites begin to recognise the benefits of growing their own food and the sense of community these gardening activities engender. These activities grow as citizens reclaim derelict land and are increasingly using roof top gardens and novel containers, providing much needed green oases in the city, concepts which are particularly popular with the “share” generation. However, many such sites are in areas of high traffic density, on brown field sites or on sites overlying landfill, as a result of their urban location. The proximity to such sites may lead to worries about the food safety and reduction of the adoption of such healthy urban gardening practices. One of the main concerns is the transfer of urban pollutants into the consumer’s food chain. Trace metals are one of the contaminants frequently found in urban crops and soils. Perceived concerns about the effects of these heavy metal contaminants on human health often outweigh the true risk; part of the problem is the lack of data in the urban production context. Moreover, collection of city-wide data on the health of the soil is often difficult and expensive to collect. In this project we intend to attempt to overcome these issues by recruiting citizens to conduct simple common collaborative experiments in their urban gardens, from these data we will create a city map of soil health status and providing information on potential risk of heavy metal contaminants and ways in which to mitigate those risks in an Urban Gardening context. We chose a citizen science approach in this project, not only as it will allow us to gather a wealth of data but also it will empower us to jointly generate useful information for the greater public good which can contribute towards creating green sustainable cities.

This project will place the citizen at the heart of the experimental process in contrast to more traditional observational data collection. Using an experimental approach really exposes the citizens to the scientific process and enables them to gain tacit knowledge of how scientists overcome variance, bias and arrives at scientifically sound evidence based conclusions. As a result, citizen science can provide reassurance to the public about the rigour and process of scientific enquiry. In doing so it can inspire confidence and understanding of the nuances of political bias; putting contextual knowledge together, in learning by doing.

How to cite: Ziss, E., Friesl-Hanl, W., Noller, C., Watzinger, A., and Hood-Nowotny, R.: Heavy Metal City-Zen. Exploring the potential risk of heavy metal contamination of food crop plants in urban gardening contexts using a citizen science approach., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2380,, 2020


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  • CC1: Alice Badin, FOEN, attendee, Alice Badin, 04 May 2020

    Thank you very much for this very interesting project!

    Could you tell me:

    - how many samples are planned to be measured, their costs and who will ensure the costs

    - what will you do with the data: it will apparently be public. Did all owners easily agree to it? The gardens are maybe not "private"?

    - on what basis do you choose which acid you use?

    - what is exactly the difference between native (which might contain HM) and treatment (compost might be another source of HM) or why do you differenciate them?

    - did you choose the plants for their different HM uptake capacities? Or is it based on what people mostly plant...?

    - In which steps are the citizens involved? (sampling, measuring pH...?)

    Thank you in advance for your answers!

  • AC1: Comment on EGU2020-2380, Rebecca Hood-Nowotny, 04 May 2020

    We think we will get a maximum of 20 experimental sets. (2 treatments, 4 reps)

    The analysis costs are covered by the project.

    The idea is that the native soil is that is what is there they are (worst case) and the ammended is the soils the growers have improved using compost etc.

    We have tried to involve the gardeners in all aspects of looking at the soil, pH etc.

    We will use the standard digestion procedure if I remember rightly it is a nitric acid digestion. Here you go...

    Well mixed and subsampled dry plant tissue will be acid digested, 0.2g of finely ground plant material will be carefully weighed in to pre-weighed digestion vessels.  5 ml 65 % HNO3, 1 ml H2O2 and a drop of iso-octanol will be added to prevent foaming. Microwave or conventional digestion (3 h@150 °C), will be carried out. When cool samples will be quantitively, filtered and accurately made up to 200 ml with deionized distilled water. Soils will be prepared for metal analysis using an aqua regia digestion (4.5 ml 37% HCl and 1.5 ml 65 % HNO3, one drop of iso-octanol) and conventionally digested (3 h at 150 °C) and filtered and diluted as above.  A full range of metal standards and blanks will be run to bracket the un-known values.

    I hope this helps

    We chose two varieties that had been shown to be accumulators, spinach and radish. We supplied them to the citizens.

    But feel free to contact us if you want any other information.


    And see our great website that Elisabeth

    All the best


    • CC2: Reply to AC1, Alice Badin, 04 May 2020

      Great, thank you for the answers! Have a nice day, Alice