ISO standardization

With its technical and methodological characteristics and its application to concrete problems in the field, it proved possible to launch an ISO (International Organization for Standardization) procedure for the RHIZOtest on an international scale.

International consensus was recently obtained on defining the concept of contaminant bioavailability in soils, thereby making it possible to fix the guidelines for the selection and application of bioavailability assessment methods [1]. More particularly for the assessment of trace element phytoavailability, a certain number of chemical and biological methods have already been standardized on an international scale.

Although chemical methods are currently the most tried and tested methods for estimating the phytoavailability of trace elements, their validation through correlation with biological measurements nonetheless remains partial. In addition, these chemical methods cannot, by definition, take into account the biological diversity of the responses observed in higher plants. In terms of biological methods, while there are currently four biotests standardized on an international scale [2–5], they have only been developed to assess the phyotoxicity (i.e. toxicological phytoavailability) of trace elements.

There is therefore currently no standardized  biological method for assessing soil-plant transfers (i.e. environmental phytoavailability) of trace elements in contaminated soils. It was notably to plug this methodological gap that the RHIZOtest was developed with a view to obtaining ISO standardization.

The project to standardize the RHIZOtest was launched in 2010 culminating in the publication of standard ISO 16198 in 2014 [6]. The content of the standard was presented, revised then validated by experts from the different national standards agencies making up ISO, during 5 successive votes.  Standard ISO 16198 thus specifies:

  • The equipment to be used and the experimental protocol for implementing the RHIZOtest
  • The three species to be used as a priority in the standardized protocol which tend to maximize the phytoavailability of trace elements, in line with the principle of precaution
  • The analytical procedure enabling determination of the three phytoavailability parameters, i.e. trace element concentrations in the aerial and root sections, and the flow of trace element take-up by plants
  • A statistical procedure enabling an analysis of the experimental results
  • The criteria used to validate a RHIZOtest experiment
  • The main results of the international round robin test that determined the robustness, repeatability and reproducibility of the RHIZOtest.
  1. ISO 17402 - 2008 - Soil quality - Requirements and guidance for the selection and application of methods for the assessment of bioavailability of contaminants in soil and soil materials
  2. ISO 17126 -2005a - Soil quality - Determination of the effects of pollutants on soil flora -- Screening test for emergence of lettuce seedlings (Lactuca sativa L.)
  3. ISO 22030:2005b - Soil quality - Biological methods - Chronic toxicity in higher plants
  4. ISO 11269-1:2012a - Soil quality - Determination of the effects of pollutants on soil flora - Part 1: Method for the measurement of inhibition of root growth
  5.  ISO 11269-2:2012b - Soil quality - Determination of the effects of pollutants on soil flora - Part 2: Effects of contaminated soil on the emergence and early growth of higher plants
  6. ISO 16198 - Soil quality -- Plant-based test to assess the environmental bioavailability of trace elements to plants