In this 2-part article series, we explore the various aspects of dissipation studies and how they are used in risk assessment. Part 1 was published in October and examined Aquatic Dissipation studies.

Today, we move away from water to take a closer look at Terrestrial Field Dissipation (TFD) studies. Unlike their wetter counterparts, Terrestrial Studies, as their name implies, focus on pesticide behavior under typical use conditions when a product is applied to the landscape. These studies help qualify and quantify where and what happens to active ingredients and their degradation products over time. While laboratory studies provide valuable data for specific individual process such as with leaching or microbial degradation, observations and results can differ when multiple processes, like drift, plant uptake, runoff, or volatilization, occur in parallel. If the differences are significant, they can potentially change the timing and magnitude of a chemical’s fate. 

In the US, TFD studies are a key data requirement in two situations: the registration of new agrochemical products or when existing products seek changes to their labels such as rates and geographical application areas. To conduct these studies, entities must follow US Environmental Protection Agency (USEPA) and North American Free Trade Agreement (NAFTA) guidance (835.6100) along with Good Laboratory Practice Standards to ensure that quality data and testing are completed. This rule is in place so that comparisons to models of pesticide behaviors from laboratory studies can be confirmed.

Since TFD design and the parameters monitored and collected can vary, samples from soils in the field are typically taken over a 1-2 year period across a replicate block to determine the DT50, DT75 and DT90 field values for soil along with a representative half-life of each parent and major metabolite. Other critical parameters like volatilization or plant uptake may require air samples, plant tissue, or even nectar extraction sampled at different timepoints throughout the study timeline. The data needs drive the TFD’s chosen site selection, design, instrumentation, and field cooperators and specialists.

Over the last three decades and hundreds of TFDs covering a broad array of study designs, geographical locations, pesticide application methods, sampling techniques, and crops, Wateborne has learned that smaller integrated systems work best—and to expect the unexpected. By leaning into our strengths in instrumentation design and data collection crossed with the latest technology in air and soil monitoring equipment, we have learned to re-engineer and re-use systems for fast and reliable data collection needed to conduct these studies as well as shrink the footprint of the use area. 

We’ve also learned that sometimes “the unexpected" can become a study asset. In one study, wild pigs frequently ran through the fields at similar times through the week. After a few instances of seeing the data outage, repairing the data connections, and discussions with the field scientist about daily operations, we determined that the pattern of data absence matched routine wildlife runs. Our team was able to restore continuous data output by quickly relocating the station boxes. 

From wild pigs to snakes sheltering themselves under equipment or furry mammals chewing through wire, wildlife can play havoc on a TFD. We’ve learned to keep the instrumentation footprint as tight as possible within the study area. In addition, our teams work closely with research farm scientists and cooperators to ensure data are looked after continuously via remote connections or direct in-field access. It’s vital to the integrity of the study to be able to have secure, resilient, and repairable systems in place, no matter the wildlife neighbors.

TFDs don’t stop in the field! Kinetic models are used by Waterborne modelers to further evaluate the pesticide's exposure. DT50, DT75, and DT90 values from the terrestrial studies are reported in the studies and data from the field trials are reviewed by regulators as part of the risk assessment process to confirm the predicted behavior determined from the derived conceptual models for the pesticide.