Guidance for evaluating laboratory and field dissipation studies to obtain DegT50 values of plant protection products in soil

Scientific guidance on soil phototransformation products in groundwater - consideration, parameterisation and simulation in the exposure assessment of plant protection products

This Guidance Document gives recommendations how to consider transformation products from soil photolysis ('phototransformation products') when modelling the predicted environmental concentrations in groundwater. It describes possible parameterisations of the photolytic pathway (i.e. the photolytic half-life and the corresponding reference irradiation) in a tiered approach using the FOCUS-PELMO model. Following the recommendations of the EFSA guidance (2014), separate half-lives can be derived for the surface processes (kfast) and the biodegradation in the soil matrix (kslow) from field dissipation studies by using biphasic models. From field dissipation studies evaluated with biphasic kinetics, the kfast value can be considered representative for the photolytic degradation on soil surface for non-volatile substances. This value should be determined after a time-step normalisation according to irradiance data for the location and period of the field trial, to a reference irradiance of 100 W m-2. In case irradiance values are not available in the study, these values can be derived from databases such as AGRI4CAST or NASA, freely available in the Internet.

Scientific report of EFSA on the 'repair action' of the FOCUS surface water scenarios

The European Commission asked EFSA to undertake a 'repair action' of the FOCUS surface water report after the EFSA Pesticide Steering Network had been consulted. The main request was to introduce into all FOCUS surface water scenarios (both run-off and drainage) a 20-year assessment period instead of the current 12- or 16-month assessment period. Because of the 20-year assessment period, the way application dates are defined needed to be reviewed, reconsidering the functionality of the pesticide application timing currently used. Guidance on how substance parameters should be handled when correlated with soil properties has been provided. Foliar wash-off calculated in MACRO and Pesticide Root Zone Model was aligned and the appropriateness of including rotational crop aspects was discussed. Processing time and how to use the results of the exposure assessment were considered.

Quantifying soil surface photolysis under conditions simulating water movement in the field: a new laboratory test design

Soil surface photolysis can be a significant dissipation pathway for agrochemicals under field conditions, although it is assumed that such degradation ceases once the agrochemical is transported away from the surface following rainfall or irrigation and subsequent drainage of soil porewater. However, as both downward and upward water movements occur under field conditions, relatively mobile compounds may return to the surface, prolonging exposure to ultraviolet light and increasing the potential for degradation by photolysis. To test this hypothesis, a novel experimental system was used to quantify the contribution of photolysis to the overall dissipation of a new herbicide, bicyclopyrone, under conditions that mimicked field studies more closely than the standard laboratory test guidance. Soil cores were taken from 3 US field study sites, and the surfaces were treated with [(14) C]-bicyclopyrone. The radioactivity was redistributed throughout the cores using a simulated rainfall event, following which the cores were incubated under a xenon-arc lamp with continuous provision of moisture from below and a wind simulator to induce evaporation. After only 2 d, most of the test compound had returned to the soil surface. Significantly more degradation was observed in the irradiated samples than in a parallel dark control sample. Degradation rates were very similar to those observed in both the thin layer photolysis study and the field dissipation studies and significantly faster than in the soil metabolism studies conducted in the dark. Thus, for highly soluble, mobile agrochemicals, such as bicyclopyrone, photolysis is not terminated permanently by rainfall or irrigation but can resume following transport to the surface in evaporating water.