Smithers Environmental Fate and Metabolism scientists will present at the 264th ACS National Meeting & Exposition, August 21 – 25, 2022, in Chicago, Illinois.

Presentations:

The Benefits of Data from Instrumentation with Higher Resolving Power in the Analysis of Some Radiolabeled Test Materials
Author: Dr. Jim Ferguson

Most compounds in environmental fate analyses are labeled with either ³H or ¹⁴C (making hydrogen and carbon so-called A+2 atoms in those molecules).  The radiolabeling allows for absolute quantification without having to develop compound-specific methods.  The ratio of labeled (hot) to unlabeled (cold) test compound in the application solution is maintained in any transformation products provided the label is retained.  In metabolism, hydrolysis, or photolysis studies on agricultural chemicals containing sulfur, chlorine, or bromine or other such A+2 atoms, the hot/cold ratio can be obscured by the presence of the other atoms when analyzed on instruments with lower resolving power.  Higher resolving power can help by separating the signals from the A+2 radioisotope from the other A+2 atoms in the test material.  This can also be of more help if the transformation product has a different number of stable A+2 atoms than the test material.

This presentation will show data from an aquatic metabolism (OECD 308) study that produced an unusual chlorination product.  Data from both a lower resolving power (ca. 30,000) instrument and from a higher resolution (variable resolution up to 500,000) instrument at various resolution setting will be compared.  The ease of confirming the identity of the transformation product with the higher resolution data, coupled with higher mass accuracy will show the applicability of these tools in these types of analyses.
 
Evaluating the effect of application solvent(s) used during a soil metabolism study with [¹⁴C]Glyphosate
Author: Xavier Poole

The OECD 307 Guideline ‘Aerobic and Anaerobic Transformation in Soil’ and the EPA Guideline OCSPP 835.4100 ‘Aerobic Soil Metabolism’ are both standard guidelines for defining the degradation rate of a test substance in a variety of soils.   These guidelines and preceding guidelines like them have been used successfully for years. However, questions often still remain concerning the solvent(s) used as a carrier for the test substance applied to the soil in the study and its effect on microbial biomass and the degradation rate of the test substance. 

A soil metabolism study was conducted by setting up treated samples with [¹⁴C]Glyphosate, a generic crop protection product, using two different carriers, i.e., aqueous and organic solvent, for the test substance application. Comparisons of the rate of degradation, rate of mineralization, and maintenance of microbial biomass have been made between the soil samples applied with two different solvents. The results of this study provide a justification to continue the use of an appropriate organic solvent as a carrier for the application of the test substance in soil metabolism studies performed with various soil types. 
 
Assessing the Impact of Soil Characteristics on the Rate of Chemical Degradation under Aerobic Conditions
Authors: Kayla M. Cabral, Sean McLaughlin, M.Sc., and Kalumbu Malekani, Ph.D.

The degradation rate of a test substance is one of the processes governing its persistence in the environment.  Degradation rate studies are performed in soils that are representative of agricultural fields, following the requirements and methods as specified in the test guidelines, such as those published by the U.S. EPA, OECD, JMAFF, and EU/EC. To briefly summarize, the aerobic transformation in soil study is intended to provide information on (1) the rate and route of degradation of the test substance in representative soils, (2) the patterns of formation and decline of transformation products, if possible, and (3) the identification of major transformation products formed during the incubation period.  Information gained from this study may be used for predicting the concentration of the parent compound and transformation products in aerobic soil environments.

These studies are conducted under controlled laboratory conditions, and not in an environment exposed to naturally-occurring weather conditions and other factors that could impact the degradation rate of the test substance.  The objective of this presentation is to assess the impact of soil characteristics on the degradation rate of pesticides and active pharmaceutical ingredients (APIs), utilizing historical data generated at Smithers within the past 8 years, which includes various soil types with different USDA texture classifications.  The presentation will demonstrate how persistence of chemicals (described as their DT50) may be influenced by soil characteristics, such as particle size and makeup (i.e., clay, silt, and sand content), organic matter content, microbial biomass, cation exchange capacity, and pH, which are inherent to the characterization of the soil type.  Correlations between the calculated DT50 and any of the soil characteristics, as well as their regulatory implications and impact on persistence will be discussed.

Our scientists will chair two symposiums at the conference:

Support of Agricultural Research & Development using LC-Mass Spectrometry or Extraction Efficiency Testing: New Trends & Best Practices
Organizers: Dr. Jim Ferguson and Rory Mumford
 
Climate Change and Sustainable Agriculture: Impacts on food security/trade, risk assessment and pesticide fate studies (Early Career Symposium)
Organizers: Aleksandra Dean and Xavier Poole
 
Contact us to learn more about these topics or schedule a meeting at ACS.