Straight from our experts: Terrestrial Field Dissipation studies (TFD)

Emmanuel GRALL
GLP Study Director at Staphyt Spain

Trained as an agricultural engineer, Emmanuel began his career as a technician with CROs in Holland, France and Switzerland. Emmanuel joined Staphyt’s GLP team in 2014 and is now in charge of study management, i.e. developing the study plan, monitoring the different phases and drafting of the final report. He ensures a close link and optimal communication between the various study stakeholders and the sponsor, in compliance with GLP requirements for multi-site studies (OECD No. 13).

What are studies of phytosanitary substance residue dissipation in soil used for?

These studies make it possible to estimate the time needed to dissipate 50% and 90% (DisT50 field and DisT90field) of the active substance and/or one or more of its metabolites in the soil under natural conditions (in the field).

TFD tests cover a range of representative soils, usually at least 4, and should be performed until 90% of the active materials have been dissipated or degraded. European Commission Regulation (EU) No. 283/2013 laying down data requirements for active substances according to Regulation (EC) No. 1107/2009 requires that data from soil dissipation studies be presented in section 7 (“Fate and behavior in the environment”) when the 50% and 90% degradation half-lives (DegT50lab and DegT90lab) in soil in the laboratory are respectively greater than 60 d or 200 d.

Studies are conducted according to guidelines:

– OECD (OECD Environment, Health and Safety Publications, Series on Testing and Assessment, No. 232 “Guidance Document for Conducting Pesticide Terrestrial Field Dissipation Studies“), 

– EFSA (EFSA Guidance Document for evaluating laboratory and field dissipation studies to obtain DegT50 values of active substances of plant protection products and transformation products of these active substances in soil1), 

– NAFTA (Guidance Document for Conducting Terrestrial Field Dissipation Studies).

How is a soil dissipation study carried out?

Soil dissipation studies are complex, time-consuming and expensive.

1- Field phase

Site selection and soil preparation are important steps. The extensive Staphyt experimentation network allows sites to be selected with an appropriate soil type for the study and in an agricultural area of interest to the sponsor. Staphyt carries out multi-site studies on all types of crops, in all regulatory zones in the north and south of the European Union and beyond. Our teams are equipped with pneumatic drills allowing samples to be taken up to 1 meter deep, in France (North and South), Germany, Austria, Hungary, Spain, Italy, Greece, Australia and Morocco.

The treatment of the plot with the formulated product is carried out on bare, uncultivated, flat and homogeneous soil. Sand is incorporated or added to the treated surface to prevent photolysis of the applied product.

Soil samplings are taken between 0 and 30 cm before treatment and at intervals defined according to the study plan, for 1 to 2 years, at a depth of up to 1 meter.

A GLP soil analysis is carried out for each site. Each test site is equipped with a meteorological station, in order to collect the meteorological data necessary for the exploitation of the residue data (modeling).

2- Sample management

Storage and shipping: The total volume of soil taken from a TFD study is approximately 7 tons of soil (for a 4-trial study)! The preparation of soil cores, their storage and their shipping at -18°C are labor, time and energy consuming items therefore contributing to the high cost of such studies.

Preparation of samples for analysis: The samples are cold ground, very finely in order to prepare a homogeneous matrix for analysis.

3- The analytical phase

Our refrigerated transport network delivers samples to our partner laboratories throughout Europe. More than 400 residue analyzes may be required for a single study. The analyzes of the different sampling sections are made starting with the surface until the residue sought is no longer detectable.

Given that the time taken to carry out the studies and the arrival of the samples at the laboratory is rarely less than 30 days, the sponsor must ensure the storage stability of the active substance studied. For this, storage stability studies at -18°C are required.

4- Statistical analysis of data

After the field and analytical phases, comes the time for the statistical analysis phase of the data collected. The Focus Kinetics guide document is used to determine kinetics for persistence and modeling. The data is analyzed using software (e.g. CAKE) using SFO (Single First Order), FOMC (First Order Multi-Compartment) and DFOP (Dual First Order in Parallel) kinetics. The idea is to find the best degradation kinetic fit from the measured data. The estimated half-lives are then used to determine persistence in the field (if the DisT90field is greater than 1 year, accumulation studies are required) and to calculate the predicted concentrations over time in the soil, groundwater and water compartments of surface. This then makes it possible to assess the environmental risk according to the requirements of the regulatory files.

Our Study Directors, Principal and Regulatory Managers are at your disposal to design study plans with you in line with your registration objectives. Do not hesitate to contact us for more information.

Why choose Staphyt for your soil dissipation studies?

  • The experience of the teams: Studies carried out every year for more than 20 years
  • Trial sites equipped with irrigation systems and meteorological stations: Access to a wide choice of sites in Northern and Southern Europe, Australia, Morocco and Brazil
  • The efficient refrigerated transport network to laboratories
  • The latest generation pneumatic sampling equipment
  • A team of agronomist experienced in GLP field testing practices
  • An in-house study management team
  • The support of the Staphyt Regulatory Affairs team in the support, modeling, calculation of concentrations in the environment and risk assessments required by the authorities.