Radioisotopes in Weed Research

Kassio Mendes, Kassio Ferreira Mendes, Kassio Mendes, Kassio Ferreira Mendes

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9781000282870
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Herbicides are of great importance in weed management and are one of the most widely used pesticide groups for weed control across the globe. Concerns around the residual effects of these intensively used chemicals are equally widespread. Offering a new direction for research that focuses on herbicide behavior and its impacts on the environment, this book covers the use of radioisotopes in weed research and the detoxification of herbicides.

Applying technological advances in radiation detection, Radioisotopes in Weed Research explains how isotopic techniques can be used to identify degradation products and trace the fate of herbicides applied to crop plants. This book provides essential information on the historical use and recent advances of radioisotopes in weed research. It demonstrates the potential these methods offer the field of weed science in gaining a better understanding of the behavior of herbicides in plants and soil and working to ensure the continuous, effective, and safe use of herbicides, minimizing harmful impacts on ecosystems.

Features:

• 
  
  

• Explains the radiometric method with studies of radiolabelled herbicides and includes case studies as examples

• 
  
  

• Describes radiometric methods to study the behavior of herbicides in soil from transport and transformation to retention

• 
  
  

• Elucidates the absorption, translocation, and metabolism studies of herbicides in plants

Authored by a team of leading scientists, this book is written for professors, researchers, extensionists, graduate and undergraduate students, rural producers, and other professionals involved in weed science.

chapter one

Historical use of radioisotopes in weed research

Ziming Yue and Te-Ming Tseng

Mississippi State University

Contents

• 1.0Introduction
• 1.1Traditional radioactive isotope application in weed research
  • 1.1.1Liquid scintillation counting
    • 1.1.1.1Equipment
    • 1.1.1.2Cocktail
    • 1.1.1.3Sample preparation: oxidizer vs. solubilization
  • 1.1.2Absorption, translocation, and distribution
  • 1.1.3Plant carbon metabolism
  • 1.1.4The fate of ¹⁴C-labeled herbicide in plants and environments
  • 1.1.5Determination of crop domestication time and biofuel analysis
• 1.2Recent progress
  • 1.2.1Root exudate and allelopoathy
  • 1.2.2Application of other radioactive nuclides in weed research
  • 1.2.3Glyphosate resistance
  • 1.2.4Progress in techniques
    • 1.2.4.1Autoradiographic imaging
    • 1.2.4.2Heavy metal radionuclides and gamma counting
    • 1.2.4.3Oxidizer-free liquid scintillation
• 1.3Concluding remarks
• References

1.0 Introduction

An atom consists of a certain number of protons and different numbers of neutrons. The former determines its chemical property, and the latter determines its atomic weight. An atom with an unstable number of protons or neutrons tends to disintegrate to release different particles (such as β-particles) or photons (such as γ-rays). The discovery of radioactivity was attributed to the pioneering work of Röntgen (1895) and Becquerel (1896). Further investigation by Curie and Curie (1898), and Rutherford (1911) established that radioactivity is exhibited by heavy elements such as uranium, thorium, and radium. Large-scale application of radioactivity began at the end of World War II in the Manhattan Project, during which the scintillation counter was invented by Sir Samuel Curran in 1944 (Curran, 1949). The liquid scintillation counter (LSC) was first commercialized by Packard as TriCarb 314 in 1953.

Coincidently, modern synthetic herbicides such as 2,4-D and MCPA were commercialized as “Weedone” by the American Chemical Paint Company in the US in 1945, and as “Agroxone” by Imperial Chemical Industries (ICI) in the UK in 1946, respectively. Their independent discoveries could be traced back to 1941 when Templeman (ICI), and Nutman and collaborators (Rothamsted Experimental Station) first demonstrated the herbicidal activity of MCPA in the UK. Pokorny in 1941 synthesized 2,4-D, while Zimmerman and Hitchcock in 1942 characterized its growth regulatory properties in the US. The herbicide technology, combined with the availability of the radioactivity detection technology, especially LSC, led to the application of radioisotopes in weed research. Such a combination soon contributed to weed physiology and ultimately weed control. The invention of the autoradiography technique to detect radioisotope translocation in plants was attributed to Crafts (Yamaguchi and Crafts, 1958; Zsweep, 1961). This technique allowed ¹⁴C-labeled herbicide or other organic compounds to be applied on the surface of the leaf, stem, or root. After allowing some time for the ¹⁴C compound to be absorbed and translocated in the plant, the plant is then heated to 60°C for 10 minutes to kill the plant, and then mounted to press and dry for 1 week (ideally freeze-dried to avoid any movement of the herbicide during drying). The dried plant (part) is then pressed on an x-ray film for 3−6 weeks to collect sufficient radiation for exposure (excessive pressure avoided), after which a film is developed to capture an image. This technique had a low detection limit and allowed the study of herbicide translocation in plants at physiological ranges. Because of the simplicity and reliability of the technique, it soon spread more widely throughout the academic community than LSC in the 1960s and lasted 60 years until now, where it is still widely used.

Another milestone was the symposium on the Use of Isotopes in Weed Research, which was convened jointly by the Food and Agriculture Organization of the United Nations and the International Atomic Energy Agency (IAEA) and was held in Vienna at the Headquarters of IAEA in October 1965. The symposium collected six papers on herbicide absorption and translocation, six papers on herbicide metabolism, and eight papers on practical techniques on the subject, with almost all the topics in the field being covered. Since then, 55 years ago, more progress has been achieved in this field. Recently, Nandula and Vencill (2015) and Mendes et al. (2017) reviewed the general methods, procedure, and equipment for absorption and translocation of ¹⁴C-labeled herbicide in weeds excellently. This paper aimed at reviewing broader topics and focusing on the contributions of radioisotopes to weed research by following the historical development in the field. During the selection of references, personal judgment was applied, and complete coverage was not sought. In addition, following the tradition of IAEA (1966) and journal articles in this field, crop species were also covered in the review.

1.1 Traditional radioactive isotope application in weed research

1.1.1 Liquid scintillation counting

1.1.1.1Equipment

In weed research, the two dominant ways to detect radioactivity were through LSC and autoradiography, although early authors used a Geiger tube (Leonard and Hull, 1966). While the latter is simple and visual, the former requires at least one piece of equipment, which has gone through several generations. The LSC mixes a liquid sample with a cocktail (usually includes a solvent, emulsifier, and scintillator), and the scintillator absorbs the radiation energy and emits light, which is detected by photomultipliers (PMT) (two or three, depending on the equipment) (Figure 1.1). The early PMT was subject to high noise (background) and had to cool down to around 5°C to reduce noise. Later improvements in PMT technology allowed it to work at room temperature. Since the first commercialized LSC by Packard Instrument Company (TriCarb 314) in 1953, many manufacturers entered the market during the 1960s−1970s including the Nuclear Chicago (later Searle-Analytic), USA; Beckman Instruments, USA; Intertechnique, France; Wallac, Finland; Phillips, Holland; and Hitachi AccuFLEX (later Hitachi Aloka), Japan. In the 1980s, the TriCarb series introduced time-resolved (TR) counting technique, which significantly lowered background noise (1987). Wallac Oy of Finland introduced Quantulus, which used a guard detection system to reduce background (1985). Perkin Elmer entered the field by acquiring Wallac and Packard Bioscience from the 1990s to 2001, and it kept their fundamental designs unchanged except the software. Hidex, Finland entered the field by launching Hidex Triathler in 1993, which was the first portable LSC with a single PMT. There was no significant improvement in technology since the 1980s until the launch of the Hidex 300 SL in 2008 (Eikenberg et al., 2014). The Hidex 300 SL is a new-generation automatic counter with a different design than the conventional coincidence counter based on two PMTs. It utilized three PMTs aligned at 120° from each other. This detection geometry yielded exceptionally high counting efficiency and counting of samples in triple mode with no risk of luminescence interference from the background. The three-PMT design also enabled triple to double coincidence ratio counting (TDCR), which is an absolute counting method for obtaining the counting efficiency of the samples without external or internal standard sources (Temple, 2015). The TDCR was established as a unique technique by Hidex. The major commercial LS manufacturers that remain at present are PerkinElmer (TriCarb and Quantulus), Hidex, and Aloka.

Figure 1.1Principle of liquid scintillation counting (https:/​/​www.perkinelmer.com/​lab-products-and-services/​application-support-knowledgebase/​radiometric/...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Editor Biography
• Contributors
• Chapter 1 Historical use of radioisotopes in weed research
• Chapter 2 Sorption and desorption studies of herbicides in the soil by batch equilibrium and stirred flow methods
• Chapter 3 Mobility studies of herbicides in the soil: soil thin-layer chromatography, leaching columns, and lysimeters
• Chapter 4 Anaerobic and aerobic degradation studies of herbicides and radiorespirometry of microbial activity in soil
• Chapter 5 Absorption, translocation, and metabolism studies of herbicides in weeds and crops
• Chapter 6 Radiological protection for the use of radiation and radioisotopes in agricultural research
• Index