Pyrethrum: Nature's Pesticide (this paper has not been reviewed for technical content)

Transcription

1 Pyrethrum: Nature's Pesticide Paper # 908 (this paper has not been reviewed for technical content) Robert F. Ryan and Simon Bishop BOC Australia PO Box 280 Chatswood NSW 2057 Australia Brian Chung and Ian Folder Botanical Resources Australia, PO Box 852 Sandy Bay, Tasmania 7005 Australia Hari Krishna and Alex Lemon Crop & Food Research Palmerston North, New Zealand ABSTRACT Pyrethrum is derived from the dried flowers of the plant Tanacetum cinerariifolium. The name given to the active insecticidal components of the dried flowers is "pyrethrins". Tasmanian pyrethrum production is among the most innovative, high-tech agricultural industries in the world. With an output that nearly quadrupled since 1996, Botanical Resources Australia (BRA) now supplies more then 30% of the global pyrethrum markets. Developments such as vacuum precision direct seeding allowed dramatic expansion in the total area planted to pyrethrum which is now ~ 3,000 ha. Using new generation cutter rower the flower is dried, pelletised and extracted. Initially the hexane extracted dark, treacly crude pyrethrum extract was exported to be refined overseas. BRA designed, built and commissioned a refinery in Tasmania during This environmental friendly process involving carbon dioxide was cutting edge technology. BRA is currently commissioning a new large-scale multi-purpose hexane extraction plant. The unique solvent-propellant properties of liquid carbon dioxide (CO 2 ) were the basis for the BOC global patent. This patent described Pestigas as a non-flammable, high-pressure (5,000kPa) aerosol spray (droplets range 2-20µ) with natural pyrethrins as the quick knockdown, wide spectrum, non-residual and low mammalian toxicity insecticide. The non-flammable, liquid CO 2 solvent-propellant is recycled from by-product industrial processes. The small droplet size range (2-20µ) of the particles formed results in the pyrethrins being suspended for ~ one hour. The Pestigas system treats the total space with low ppm levels of insecticide and the reformulated product is now being developed by Crop & Food Research, NZ for "organic" quarantine treatment of NZ export fruit & vegetables. 1

2 INTRODUCTION Pyrethrum, a natural insecticide, is derived from the dried flowers of the "pyrethrum daisy". The outstanding properties of pyrethrum are: Rapid Action (contact insecticide attacking the nervous system of insects almost immediately and causing knockdown and flushing out effects followed by kill). Low Mammalian Toxicity (proven safety towards humans and other warm blooded animals) Lack of Insect Immunity (insect resistance is not a practical concern) Broad Spectrum of Activity (consist of a group of insecticidal compounds and has activity against a wide spectrum insect species) Lack of persistence (degraded by UV in sunlight and other light sources). Repellency (very effective insect repellant) It is by far the most widely used natural insecticide The term pyrethrins is used collectively for the six insecticidal constituents present in extracts of the flowers Tanacetum cinerariifolium. They comprise esters of the natural sterioisomers of Chrysanthemic acid commonly known as Pyrethrins 1(pyrethrin 1, cinerin 1 and jasmolin 1) and the corresponding esters of pyrethric acid commonly known as Pyrethrins 2 (pyrethrin 2, cinerin 2 and jasmolin 2). The ratio of Pyrethrins 1 / Pyrethrins 2 is commonly within the range and most commercial Refined pyrethrum extracts contain 20-50% pyrethrins. The dried flower heads of Tanacetum cinerariifolium (once known as the Dalmatian Insect Flower/Dust) were introduced into Europe from western Asia c.1820, but their use is now replaced by that of refined extracts of crops grown in Kenya, Tanzania and Tasmania. This paper report on the high technology used by BRA to plant, harvest, extract and refine this historical, botanical, low mammalian toxicity and quick acting pesticide. The innovative formulation based on liquid carbon dioxide will be reviewed, as will modifications to adapt to "organic", "biodynamic" and associated requirement. The applications of liquid carbon dioxide formulations in horticulture (greenhouse etc) and quarantine treatments will be reported. 2

3 Pyrethrum Harvesting, Extraction & Refining: This section reports on the high technology agricultural practice now used to plant, harvest, extract and refine this historical, botanical, low mammalian toxicity and quick acting pesticide. Pyrethrum is a member of the daisy and chrysanthemum plant family and has been grown for many years for its insecticidal properties. Pyrethrum has been used for more then 160 years as a major pest control agent. It is recognised for its effectiveness against a wide range of insects, but has very low toxicity when ingested by mammals and is non-pollutant and non-residual because of the fast breakdown in light. In all respects, pyrethrum is the ideal pest control agent for the enlightened 21 Century and is expected to have a bright future. Uses such as in domestic home insect control, commercial building fumigation, hospitals, food processing factories, domestic pet products, high value agricultural uses and public health uses such as head lice and malaria control is expected to grow in the near future. Natural pyrethrum is produced by the pyrethrum plant Tanacetum cinerariifolium and is found in oil glands located on the surface of the achenes. The achenes are a true fruit, but it is commonly referred to as the seed because it looks and has the size of a seed and it is found at the base of the flowers. Pyrethrum has been very successfully incorporated into the high value cropping program of the fertile north-west coast of Tasmania, a island state world famous for the production of high quality agricultural products such as vegetables, cheese, wine, apple and medicinal poppy. The success of the pyrethrum industry is the cumulating of research initiated by the local state government, university and far-sighted private companies some 20 years ago. BRA is now one of the two most significant producers of pyrethrum products in the world and is the most technologically advanced producer in the world. The strong focus on innovations via R&D and the adoption of these outcomes by all segments of the industry is perhaps the most outstanding feature of this success story. BRA currently has 220 contract growers and some 3,000 ha of pyrethrum crops in Tasmania. This crop has proven to be an ideal rotational crop for the intensive vegetable growing areas. The advantages of having a perennial crop of some 4-5 years duration in an annual cropping environment lies with the resting of the soil from annual cultivation for the 4-5 year period. This resting period will allow the soil structure, organic matter and microflora to regenerate and recover from heavy disturbance from annual vegetable cropping. At the end of a productive pyrethrum cropping program, these valuable soil resources can be utilised again for intensive vegetable cropping with improved results. A competitive payment schedule has been made 3

4 available to the growers such that a long-term rotation program consisting of 4 years of pyrethrum and 4 years of vegetable cropping becomes a very attractive financial package. BRA and growers have achieved very high and consistent yields in recent years and this trend of increasing yield and operational efficiency is expected to continue to increase in the foreseeable future. Highly focussed and industry funded R&D and BRA crop management advice has provided much of the impetus for this yield improvement and on-going R&D in crop agronomy, mechanical harvesting and processing will ensure that the BRA industry will continue to be a leading world class producer of pyrethrum products. The BRA industry contracts R&D projects to suitable consultants, the University of Tasmania as well as experimentation conducted by BRA staff. At present, BRA is supporting two Post Doctoral Fellows, four PhD students, one Honours student and five University Scholarship students. BRA has developed a fully mechanical process that allows very timely and efficient harvesting of the mature pyrethrum flowers. In recent years, BRA has utilised a fleet of 30 large combine harvesters to harvest the crop in the most efficient manner. The flowers are harvested field dried and are delivered into the receival store, weighed and sampled for the pyrethrum assay. The sample is mixed, sub sampled and analysed by HPLC at the BRA laboratory for the pyrethrin assay. This BRA laboratory has achieved the nationally recognised NATA accreditation. This initial pyrethrin analysis provides the measure of the total pyrethrum yield at harvest. BRA uses a two step process to extract the pyrethrins from the harvested crop, an initial hexane extraction followed by a refining process with carbon dioxide as the partitioning fluid. Initially, the harvested material is pelletised as soon as possible and a small amount of the antioxidant butylated hydroxy toluene (BHT) is added at this stage to help stabilise the active pyrethrins. The pelletised material is extracted using hexane as the extracting solvent. Currently BRA use a counter current batch process extraction, but a new and much larger capacity continuous counter current extraction plant is being commissioned during early 2002 and both extraction plants are expected to be used in the future. During this hexane extraction process, there is a very efficient recovery of the hexane solvent and this recovered hexane is recycled for use with the next batch 4

5 of pellets. The crude pyrethrum extract obtained following hexane extraction is a dark brown, viscous oleoresin that is semi-solid at room temperature, but flows readily with a little warming. This crude pyrethrum extract commonly contains about 30% pyrethrins and 3% BHT with the balance being an assortment of vegetable extractables such as waxes, colours and fragrants. Crude pyrethrum extract can be sold to specific customers for further refining or for direct use in some formulations. However, the vast majority of the crude pyrethrum extract is further refined by BRA into Refined pyrethrum extract using the very sophisticated BRA developed carbon dioxide refining process. During the refining process, the crude pyrethrum extract is treated in a counter current of carbon dioxide. By selecting the appropriate temperature and pressure combination, BRA can very efficiently separate the natural pyrethrins into solution with the carbon dioxide and the bulk of the coloured plant vegetable matter and plant waxes, commonly called the raffinate, are collected for other commercial outlets. The carbon dioxide is removed from the pyrethrins in carbon dioxide solution under mild conditions to give the final Refined pyrethrum extract, a light amber/yellow clear liquid with a faint flowery fragrant note. Recovery of the carbon dioxide is very efficient and this carbon dioxide is then recycled for use in the refining process. The Refined pyrethrum extract is commonly diluted with the paraffinic solvent Vista LPA to give a 50% Refined pyrethrum extract called PY-T-50. The PY-T-50 has 50% pyrethrins with a Pyrethrins 1 / Pyrethrins 2 ratio commonly between 0.95 to 1.15, % of Vista LPA, 3-5% BHT and the balance (approximately 20%) consisting of miscellaneous plant extractables such as triglycerides, terpenoids, waxes and natural colours such as luteins. There are no metals or alkaloids in the PY-T-50. Epoxy lined steel drums are commonly used to store and transport the PY-T 50 to customers. The efficiency of the various processes during the production of Refined Pyrethrum Extract is very closely monitored by sampling at all stages for laboratory analysis of the pyrethrins content. This sampling and analysis is undertaken by the BRA at the onsite NATA accredited laboratory and is based on the HPLC method of analysis. BRA is one of the members of the task forces called Pyrethrum Joint Venture (PJV) and Non- Dietary Exposure Task Force (NDETF). These task forces consist of the major world producers and formulators of pyrethrum and were formed to support the Data Call-in for pyrethrum by the USA EPA. PJV and NDETF commissioned many high quality scientific studies based on EPA protocols (including GLP for most studies) and good quality data was produced to support pyrethrum. PJV and NDETF had invested in excess of $US30 million to date to generate this data package and this data package is proprietary information. As a member of the PJV and NDETF, BRA is a joint owner of this data package and is able to use this information to support customers with their registration requirements. This data package includes studies on the environmental fate and pathways for pyrethrum, ecotoxicity studies such as impact on aquatic organisms and acute and chronic toxicity to mammals. Crop and animal residue analysis from typical agricultural use patterns have also been collated. This data package is currently being used to support the Data cal-in by the USA EPA and is also used for the Nomination of pyrethrum to the European Biocide Directive. 5

6 Liquid Carbon Dioxide - Solvent / Propellant The unique solvent-propellant properties of liquid carbon dioxide (CO 2 ) was the basis for the international patent, Ryan and others (1978). This patent described Pestigas a high-pressure aerosol spray with natural Pyrethrins as the quick knockdown, non-residual and low mammalian toxicity insecticide. The high-pressure (5,000 kpa) liquid CO 2 solvent-propellant, recycled from by-product industrial processes, is a low cost liquid with fire retardant properties which enables the formulation of non-flammable products. Pestigas is available in industrial high-pressure gas cylinders fitted with an eductor tube (dip tube) to enable the liquid mixture to be withdrawn and dispensed as an aerosol fog. The small droplet size range (2-20µ) of the particles formed results in the Pyrethrins being suspended for ~ one (1) hour. The Pestigas system treats the total space with low ppm levels of insecticide (spray travels ~30 metres), minimises the occupational health & safety hazards of handling chemicals and the process is clean, fast and biologically efficient. The product can be dispensed manually using portable equipment or automatically using programmable time release systems. The active components in Pestigas are the naturally occurring insecticidal active esters called Pyrethrins which are extracted from the pyrethrum daisy (Tanacetum cinerariifolium). The six active constituents of Pyrethrins are: * Pyrethrin I [C 21 H 28 O 3 ] Molecular weight: * Cinerin I [C 20 H 28 O 3 ] Molecular weight: * Jasmolin I [C 21 H 30 O 3 ] Molecular weight: * Pyrethrin II [C 22 H 28 O 5 ] Molecular weight: * Cinerin II [C 21 H 28 O 5 ] Molecular weight: * Jasmolin II [C 22 H 30 O 5 ] Molecular weight: Pestigas which contains 4 g/kg of Pyrethrins, the naturally occurring low toxicity botanical insecticide, 20 g/kg piperonyl butoxide a synergist made from sassafras oil, 100 g/kg paraffin hydrocarbon dissolved in the liquid solvent-propellant carbon dioxide. Pyrethrum is one of the oldest organic insecticide and its continued popularity is attributed to its high toxicity to insects and its remarkable low toxicity to mammals. Other features of pyrethrin are its broad-spectrum activity, rapid action, excellent flushing activity, powerful insect repellency and lack of insect immunity. The unique features of the Envirosol range (liquid CO 2 based products), which has resulted in its continued acceptance, include; * Non-flammability (carbon dioxide solvent-propellant) * Ultra-fine particle size (range from 2 to 20 microns) * Sized for commercial and industrial needs (6 kg and 31 kg cylinders) * Automatic, Fixed or Portable space spray systems.) The development of the liquid carbon dioxide technology has resulted in the investigation of the physical behaviour of these products, the evolution of analytical techniques for product development, quality control and fundamental research. In order to facilitate the application of these products, Nieass & Ryan (1983) researched automatic dispensing and distribution systems. To compensate for the lack of information concerning the behaviour of the liquid carbon dioxide system during isothermal product discharge, Nieass and others (1981) developed a mathematical model to describe this phenomenon. The Envirosol method of space spraying has advantages over conventional techniques as insecticide concentrates do not have to be handled as the cylinders are provided ready to use. Because of this and the rapid rate of output of the system, the time spent carrying out a treatment is relatively short and the spray is produced comparatively noiselessly and is both nonflammable and non-tainting. 6

7 Measurement on particle size of a Pestigas product by Slatter and others (1981) at the Wellcome Research Laboratories proved the very efficient atomisation of the insecticide with a spray cloud average particle size of ~3 microns that remained airborne for long period (half life of ~30 minutes). The researchers concluded that the Pestigas produced a very efficient and effective spray cloud that provided excellent control of flying insects at low dosages, and useful control of crawling insects. A peculiar property of the high pressure (~5000 kpa) carbon dioxide Envirosol system is the relative large mass of gas remaining in the cylinder when all the liquid active ingredient and liquid carbon dioxide has been dispensed. This amount of gas could represent as much as 20% of the original contents, however, the active ingredient is only dissolved in the liquid carbon dioxide propellant has already been dispensed from the cylinder. This effect also exists in household aerosols, although it is not as noticeable as the vapour pressure of the propellant (fluorocarbon / hydrocarbon) is at a much lower pressure (~300 kpa). Applications of Liquid Carbon Dioxide Formulations: Pestigas is used to control insect pest in dwelling, hotels, restaurants, warehouses, factories, retail stores, nurseries, tobacco storage, commercial office buildings, communications centres, museums, herbariums, archives, mushroom houses, grain handling equipment, animal houses, sewer mains, and in horticultural applications. Crop & Food Research, New Zealand are developing the horticulture application with particular emphasis on modified formulations to suit the sophisticated modern "greenhouse" and with specific emphasis on "organic" approved treatment of fruit and vegetables. A typical new generation greenhouse is built in 5 hectares modules and total area under glass is often greater than 10 hectares. With an increased height of 5m, this represents a volume of 500,000 m 3. Treatment with Pestigas using the recommended rate of 0.5g/m 3 requires 250 kg of product. Selecting spray time at dusk allows for longer half-life for the "quick knockdown / non-residual" Pyrethrins in the absence of Ultra Violet (UV) light. The next day the UV quickly degrades the pyrethrum residual and pesticide residues are not a issue. The use of natural pesticides adds value to commodities, as there is a market demand for "organic" produce. CONCLUSIONS Pyrethrins, one the oldest organic insecticides being first commercialised in 1828, continues to enjoy widespread acceptance because of its natural product status and low toxicity. Pestigas enables the effective and efficient dispensing of this environmental acceptable insect control agent. The control of insect pests continues to be a difficult task and the industry needs to take advantage of all available technology to win this battle. REFERENCES 1. Nieass, C.S. & Ryan, R.F. (1983) Proc. 3rd Pac. Chem. Eng. Congress, Seoul, Korea, May, p Nieass, C.S., Wainwright, M.S., Chaplin, R.P. and Ryan, R.F. (1981) Proc. 9th Australasian Conference on Chemical Engineering, Christchurch, New Zealand, August, p Ryan, R.F., Shervington, E.A. and Catchpoole, D.J (1978) Aust.Pat. 494, Slatter, R., Stewart D.C., Martin R., White A.W.C. (1981) An Evaluation of Pestigas BB a New System for Applying Synthetic Pyrethroids as Space Sprays Using Pressurised Carbon Dioxide International Pest Control, Nov/Dec. 7