
What are your dissipation studies telling you? Part 1: Alligators and Rice and Aquatics, Oh My!
In this 2-part article series, we explore the various aspects of dissipation studies and how they are used in risk assessment.
Used to collect field data on a pesticide's behavior within a real-world environment, dissipation studies are an important part of environmental exposure and the regulatory process. Aquatic dissipation studies, as the name suggests, focus on pesticide behavior when present in water-based environments that could range from rivers and lakes to rice paddies or cranberry bogs.
Waterborne’s long history of managing aquatic field dissipation studies has led us to develop sampling procedures that apply to a broad range of environments and their respective challenges, such as aggressive alligators. The variables within study environments themselves often need innovative solutions for atypical sampling requirements. We've learned that, while these studies can be quite complex with a number of environmental variables to monitor, our focus remains on the extent of potential degradation and mobility of pesticide active ingredients and their degradates in the natural aquatic landscape under typical use conditions.
Aquatic dissipation studies are particularly useful in the agriculture industry where crops like rice have relied heavily on the resulting data. Using pesticides in rice paddies as an example, small-scale outdoor flooded soil studies and/or full-scale aquatic dissipation studies may need to be conducted. Samples of soil from the paddy field and water from the field and outflow are also collected then analyzed with the objective of determining DT50-field and DT90-field values for soil and water.
Field study design at full-scale should use rice paddies at two locations following normal agricultural practices. As part of our aquatic field dissipation studies for rice, we will often design different applications (i.e., seed treatment, foliar application, incorporation, etc.) and agricultural practices (wet seeding and dry seeding), and may also consider if the pesticide is applied to a saturated, dry or flooded paddy.
The study doesn't end in the field! Depending on the crop, geographic location, and regulatory entity, data derived from these studies may then be used by Waterborne modelers to further evaluate the pesticide’s exposure. For example, DT50 values from flooded soil studies may be used directly in EU rice models such as MedRice1,2 and Waterborne’s model, RICEWQ3, to calculate concentrations in surface water and groundwater. In the US, data from these studies may be used as weight of evidence support in overall risk characterization for a pesticide or a particular use scenario.
Waterborne has also conducted aquatic dissipation studies for pesticides used on aquatic weeds. In one pesticide study, the objective was to determine how far the pesticide may move off-target for labeling a distance from drinking water intakes. These studies were conducted on rivers and lakes on emerged and submerged aquatic weeds. The use of dye during application aided in the sampling regime as assays were conducted at the site. In addition, some of the studies included a mesocosm component to determine a DT50 value (in situ degradation) when the pesticide was not influenced by dispersion. This work is not without its challenges! Over the years, we’ve had to deal with a bevy of wildlife aggressors, variable weather, and once we had to reset up the sampling grid on the day of application because the aquatic weeds floated away overnight.

Application to aquatic weeds. Dye shows potential movement of chemical
No matter the challenges, our teams of expert engineers, scientists, analysts and modelers can assist in any or all phases of a study from initial design planning and development, working closely via remote or in-field with research farms and cooperators during field phase setup and execution to post data collection analysis, modeling and risk predication.
1MedRice (2003). Guidance Document for Environmental Risk Assessments of Active Substances used on Rice in the EU for Annex I Inclusion. Document prepared by Working Group on MEDRICE, EU Document Reference SANCO/1090/2000 – rev. 1, Brussels, June 2003, 108 pp.
2ICPS proposal (2019). Update and harmonization of rice pesticide risk assessment and revision of European guidelines. Via G.B Grassi, 74; 20157 Milano; tel. 02.3904.1; www.asst-fbf-sacco.it; CF e PI: 09319690963.
3Williams, W.M., Cheplick, J.M., and Ritter, A.M. (2014): RICEWQ: Pesticide runoff model for rice crops. Users manual and program documentation: Version 1.92. Waterborne Environmental, Inc., Leesburg, Virginia.

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