U.S.EPA
Methyl Bromide Alternative Case Study
Part of EPA 430-R-97-030, 10 Case Studies, Volume 3
September 1997
Use of Controlled Atmospheres As A Quarantine Treatment for Table Grapes
Controlled atmosphere technology with elevated carbon dioxide and/or reduced oxygen concentrations can be a viable alternative to methyl bromide as a post harvest quarantine treatment for table grapes. It is effective against insect pests and pathogens (Carpenter and Potter 1994) and has the added benefit of improving the quality of grapes and extending their shelf life by lowering respiration rates (Mitcham et al. 1994). Other benefits include the prevention of color change and softening and the maintenance of fruit composition and nutritional value. Furthermore, the gas used in this technology are chemically inert and will not corrode handling equipment (Ke and Kader 1992, Calderon and Barkai-Golan 1990). Unlike some other fumigants, controlled atmosphere treatments (with carbon dioxide and/or nitrogen) do not leave toxic residues on grapes. The treatment also penetrates more easily than most fumigants because of its small molecular size (Smith and Newton 1992). Furthermore, grapes are ideally suited for this treatment technique because they produce very little ethylene (a compound emitted from fruit which stimulates ripening) and are highly resistant to its effects (Lamb 1996).
Technological advances have led to the development of refrigerated controlled atmosphere sea transport shipping containers used by commercial exporters for storage treatment. These containers can be equipped with controlled atmosphere units that control insects and other pathogens. As a result, controlled atmosphere technologies could be used as quarantine treatments. By maintaining low oxygen levels and refrigerated temperatures, decreased commodity spoilage and pest control can be accomplished (Gay 1995). Furthermore, because of the demonstrated benefits of sulfur dioxide in combination with carbon dioxide in the control of black widow spiders (Shorey and Wood 1993), omnivorous leafrollers, and other grape pests, it may be possible to combine these two treatments to achieve even more effective control of grape pests (Mitcham et al. 1994).
Controlled Atmosphere Technologies
Controlled atmosphere technology has been used to control a variety of economically important pest species including thrips, aphids, and beetles infesting a wide variety of fruits and vegetables, including grapes (Anonymous 1993b). Controlled atmosphere technology works by reducing the respiration of grapes, inhibiting pathogen reproduction, and killing insects and pathogens. The greatest impact on insects is achieved by maintaining low oxygen levels for an extended period of time, leading to oxygen depravation in insect body tissues (Gay 1995). Controlled atmospheres are most effective at preserving grapes when they exhibit no signs of senescence or damage from handling; therefore field packaging, purchase of physiologically younger, less ripe commodities, and installation of ripening rooms may reduce difficulties in using controlled atmosphere technologies for grapes (Anonymous 1993b).
The effectiveness of controlled atmospheres varies depending on the insect species and developmental stage, temperature, oxygen and carbon dioxide levels, and relative humidity. Likewise, factors influencing the grapes treated with controlled atmosphere technology include storage temperature, oxygen concentration, respiration rate, resistance of gas diffusion, soluble solids content, and ethanol accumulation rate of the commodity under a low oxygen treatment (Ke and Kader 1992, Calderon and Barkai-Golan 1990).
Current Research
Current research on the use of controlled atmospheres on grapes is being conducted at the University of California at Davis. The main focus of this research is the development of a quarantine treatment technique for export of grapes from California to Australia (although the same research may later be applied to U.S. imported grapes from Chile). Currently, U.S. grapes are not exported to Australia; however, a proposal for use of controlled atmospheres as a quarantine commodity treatment for grapes shipped to Australia is currently under review (Kader 1996, Christie 1996). Pests of quarantine concern to Australia include the omnivorous leaf roller (Platynota stultana), western flower thrips (Frankliniella occidentalis), spider mites, and grape mealy bug (Pseudococcus maritimus) (Mitcham et al. 1994).
Initial studies indicate that table grapes can tolerate and are effectively disinfested by carbon dioxide. For example, Mitcham et al. (1995) demonstrated that by increasing the carbon dioxide levels and lowering temperatures to 45 percent and 0°C to 5°C, respectively, over an 8 to 10 day period results in 100 percent mortality of all life stages in the pests of economic concern. Research is still pending for the Grape Mealy Bug. Grapes have also been evaluated for firmness, soluble solids, berry shatter, browning, and weight loss of the cluster. In general, controlled atmospheres have only minimal effects on grape quality. The most notable difference between treated and non-treated grapes was a decrease in titratable acidity in treated grapes; however, there was not consistent effect on berry shatter, weight loss, or soluble solids. Future research will include consumer taste tests (Mitcham et al. 1994 and 1995).
Potential to Use Controlled Atmospheres as Quarantine Control Technology in Grapes
Current U.S. regulation requires that grapes be fumigated with methyl bromide as a condition of entry (i.e., Chilean grapes--which undergo treatment because of a mite). Furthermore, grapes exported by the United States must be fumigated with methyl bromide in order to comply with the quarantine requirements of recipient countries (i.e., Japan). Finding alternatives to methyl bromide as a quarantine commodity treatment is critical because large quantities of grapes are both imported to and exported from the United States and may carry non-indigenous insects and pathogens. In 1989 to 1990, for example, the United States imported an annual average of approximately 372,135 tonnes of grapes of which 302,502 tonnes (92 percent) were fumigated with methyl bromide. In fact, grapes fumigated with methyl bromide represented 34 percent of the annual U.S. fresh grape supplies in that same year (Anonymous 1993a). By comparison, currently 80 percent (1,488,540 tonnes) of table grapes are consumed domestically, while 20 percent (372,135 tonnes) are shipped overseas; therefore, the use of controlled atmospheres could increase trade by lowering costs and extending shelf life (Wineman 1996, Anonymous 1993a).
After a disinfestation treatment, the majority of controlled atmosphere shipments do not require methyl bromide fumigation for quarantine control of pests (Gay 1995b). However, controlled atmospheres are not currently recognized by USDA's Animal and Plant Health Inspection Service (APHIS) as a quarantine treatment, and therefore if a quarantine pest was found on the shipment, fumigation with methyl bromide would be required for quarantine purposes (Gay 1995b). Industry, government, and academic partnerships are currently compiling data on pest control efficacy required to secure quarantine approval. If successful, controlled atmosphere technology for grapes may become an important quarantine treatment technology. Continued research is expected to lead to effective methods to achieve insect control that will satisfy strict international quarantine regulations (Gay 1995, Mueller 1994, Delate and Brecht 1989).
Costs
Although controlled atmosphere technologies require significant operating, labor, and capital investments in hardware required to customize containers, the benefits in these investments far outweigh the costs, making it an economically viable alternative to methyl bromide (Anonymous 1993b). Estimating costs for application of controlled atmosphere technology compared to methyl bromide use is presented in Table 1 below. Two standard methods used to conduct controlled atmosphere treatments are presented independently. Although capital, labor, and operating costs vary between these two methods, their total costs are similar. The first method has low capital costs but high labor and operating costs, while the opposite is true for the second method.
In the first treatment method, the controlled atmosphere unit partially displaces air in the container by purging the container with carbon dioxide (usually supplied via a compressor) and closing the system until the container has reached its final destination. The second method is believed to be more effective because it is more automated. The process generates nitrogen from surrounding air, which is then pumped into the chamber. Gas concentrations in the containers are then monitored and maintained throughout transport in an open system which vents gases to the atmosphere (Lamb 1996, Calderon and Barkai-Golan 1990). In general, the cost to adapt a shipping container for controlled atmosphere treatments cost between $800 to $7,000 per container, depending on which type of treatment method is used, the number of containers shipped, the type of commodity, destination, place of origin, and pests of concern (Cea 1996, Gay 1995). Typically controlled atmosphere equipment has a useful life of about 10 years and is used between 6 and 12 times a year. Currently commercial facilities only use controlled atmospheres to improve grape quality and extend shelf life; however, it was assumed that storage treatment costs (operating and labor costs) would be comparable to the costs of disinfestation treatments with controlled atmospheres. As a result, treatment costs range from $800 to $1,200 per container. Fumigating grapes with methyl bromide, on the other hand, costs nearly twice as much as controlled atmosphere treatments. Specifically, operating/labor costs for methyl bromide fumigation represents a large percentage of the total costs, while capital and chemical costs are relatively minor.
If controlled atmosphere technology becomes an approved quarantine treatment, shippers will quickly recover their initial investment as expensive methyl bromide treatments will no longer be required. Furthermore, methyl bromide can often damage, destroy, or shorten the shelf life of grapes. Therefore, the risks associated with reduced inventory due to fumigation can partially offset the costs of using controlled atmosphere technology (Murphy 1995). Lastly, controlled atmosphere treatments add significant value to grapes by extending and improving both their quality and shelf life and enabling them to be shipped using surface transport where aircraft or airlift transport was required previously (Gay 1995).
Table 1. Costs Comparison for Controlled Atmospheres vs. Methyl Bromide.
| Cost Factors
|
Controlled Atmospheres
Case #1 and #2
($/tonne) |
Methyl bromide
($/tonne) |
| Annualized Capital |
<1 |
8 |
5 |
| Labor & Operating |
45-58 |
66 |
100-150 |
| Chemical |
N/A |
N/A |
<1 |
| Total |
46-59 |
74 |
106-156 |
Notes: N/A = Not applicable.
Sources: Rodde 1996, Lamb 1996, Cea 1996, Folwell 1996.