Environmental Fate of Synthetic Pyrethroids: A Study on the Loss Pathways and Processes of Termiticides in Tropical climates

Amanda Strachan (2008). Environmental Fate of Synthetic Pyrethroids: A Study on the Loss Pathways and Processes of Termiticides in Tropical climates PhD Thesis, School of Medicine, The University of Queensland.

       
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Author Amanda Strachan
Thesis Title Environmental Fate of Synthetic Pyrethroids: A Study on the Loss Pathways and Processes of Termiticides in Tropical climates
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2008-12
Thesis type PhD Thesis
Supervisor Dr Caroline Gaus
Prof Des Connell
Dr Ross Sadler
Dr Andrew Hewitt
Total pages 118
Total colour pages 7
Total black and white pages 111
Subjects 03 Chemical Sciences
Abstract/Summary Synthetic pyrethroids are popular insecticides which have commercial applications in agriculture, forestry, horticulture, public health and residential pest control, and represent some of the most frequently used insecticides on the global market today. The success of synthetic pyrethroids is due to their high toxic potency to target species at low concentrations, their moderate persistence and low mobility in the environment. However, relatively little information has been published on the environmental fate of synthetic pyrethroids, in particular regarding their loss from pesticide products and the influence of environmental and application specific parameters on loss pathways and processes. Such information is important for evaluating both the longevity of pesticide products, as well as their potential impact on the environment. In recent years, the detection of synthetic pyrethroids has increasingly been reported from both environmental and biological samples, indicating that synthetic pyrethroids are transported from the site of application to the environment. This may be a concern as synthetic pyrethroids are highly toxic to insects and aquatic life and have been shown to have sub lethal effects on mammals (e.g. carcinogenic, reproductive and developmental effects). The objective of this study was to identify major knowledge gaps in the current understanding on the environmental fate of synthetic pyrethroids. The research investigates the fate of termiticides from pesticide products under long-term application scenarios. Specifically, this study aimed to identify the key loss pathways and determine the loss rates of bifenthrin from a commercial pesticide product, and to evaluate the influence of environmental and application specific parameters on the fate of synthetic pyrethroids in the environment. This was achieved using controlled field and laboratory studies, with particular focus on tropical climatic conditions. Information on chemical fate, including loss processes and transport pathways, is required for pesticide risk assessments to determine the potential for adverse effects on humans and/or the environment. A review of the literature revealed that there are few published data available on the environmental fate of synthetic pyrethroids. In particular, information on the effects of application methods, formulations and environmental conditions (i.e. effect of rainfall, humidity and temperature) on the fate of synthetic pyrethroids is limited. Due to a general lack of field studies, the fate of synthetic pyrethroids is often assessed based solely on their physico-chemical properties, however, the review also highlighted that the available physico-chemical data for synthetic pyrethroids are highly variable and may be unreliable. To determine key loss processes and loss rates of bifenthrin under a commercial application scenario, a prototype of a commercially available plastic termite barrier (BF-plastic) was deployed for a 2-year field study. The BF-plastic was deployed in the wall spaces of houses and under concrete slabs on soil, simulating two common application methods. Although the loss rate of bifenthrin from plastic was relatively slow, there was a significant loss of bifenthrin from the plastic over the 2 years (average 20 %) and no significant difference was observed between the two application types. The incorporation of bifenthrin into the plastic greatly increased its half-life (estimated 12 to 21 years) compared to its half-life in soils (78 to 249 days). The loss pathways of bifenthrin from the BF-plastic were investigated by evaluating the potential for loss via partitioning to air, soil and water using a combination of calculated partition coefficients and laboratory studies. The calculated partition coefficients suggest that under equilibrium conditions bifenthrin partitioning to organic carbon represents the most important loss pathway for bifenthrin from BF-plastic, followed by partitioning to water and air. However, the laboratory volatilisation studies suggest that volatilisation may represent a significant loss pathway and that temperature played a significant role in the loss of bifenthrin from BF-plastic. To observe the effect of formulation and several environmental parameters on the fate of synthetic pyrethroids, the leaching of seven synthetic pyrethroids through soil columns was tested on different soil types under simulated tropical climatic regimes, and in the absence/presence of formulation. Several environmental parameters were observed to influence the leaching potential of the pesticides through soil. Among these, temperature showed the most influential role on the leaching of the pesticides. Soil parameters were found to also influence the leaching potential of the pesticides through the soil, and increased leaching of the pesticides was observed with increased simulated rainfall. It was found that the specific commercial formulation tested (Biflex lo-odour) retarded the leaching of the pesticides. The laboratory and field experiments conducted indicated that environmental and application specific parameters may have significant influence on the fate of synthetic pyrethroids in the environment. Environmental parameters such as increased temperature and rainfall were found to increase the mobility of synthetic pyrethroids (i.e. increased volatilization and leaching), suggesting that the fate synthetic pyrethroids may differ in non-temperate climates i.e. tropical and arid climates. Due to the high toxicity of synthetic pyrethroids non-target species, their enhanced mobility under some climatic regimes may have adverse implications for wildlife and/or humans in these areas. Therefore better quality data is required for risk assessments on the use of synthetic pyrethroid pesticides in climates other than temperate.
Keyword Agrochemicals
Synthetic Pyrethroid
Bifenthrin
Volatilisation
Leaching
Low density polyethylene
Tropical Climates
Temperature
Rainfall
Formulation
Additional Notes Colour pages: 50, 51, 54, 87, 90, 92, 94. Landscape Pages: 26, 27, 28, 84, 85.

 
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