U.S.EPA
Methyl Bromide Alternative Case Study
Part of EPA 430-R-97-030, 10 Case Studies, Volume 3
September 1997
Fumigation with Carbonyl Sulfide for Controlling Pests on Perishable and Non-Perishable Commodities
Carbonyl sulfide (CAS Number 463-58-1) has traditionally been used as a chemical feedstock; however, recent studies suggest that carbonyl sulfide may be a technically and economically viable alternative to methyl bromide for use as a non-perishable and perishable commodity fumigant to control insects (e.g., termites, beetles, and moths) and mites, and possibly as a soil fumigant for control of nematodes. The first research performed on the efficacy of carbonyl sulfide was conducted by the Commonwealth Scientific and Industrial Research Organization (CSIRO), which lodged a patent for carbonyl sulfide as a fumigant in July 1993 (CSIRO 1993). Further, the potential to use carbonyl sulfide to control stored product insects in fruits and nuts is being evaluated through laboratory studies conducted by the United States Department of Agriculture/Agricultural Research Service (USDA/ARS) Horticultural Research Laboratory located in Fresno, California. Additional research needed to complete applications for registering carbonyl sulfide as a pesticide in the U.S. and elsewhere in the world is currently underway (Zettler et al. 1997, Banks 1996).
Based on initial research efforts, carbonyl sulfide has been found to be an effective method of disinfesting non-perishable commodities such as timber products. Studies also indicate that it can be used to control pests on perishable commodities (research is being conducted to determine potential effects on commodities and to determine residue characteristics). Research is also being conducted to determine how to use carbonyl sulfide to control soil pests, especially nematodes. Finally, carbonyl sulfide has been found to be efficacious against termites, indicating that structural treatments may be another potential use area. (Banks 1993, Desmarchelier 1993, Zettler et al. 1997, Desmarchelier 1994, Plarre and Reichmuth 1996).
Research to Support Registration
CSIRO's Stored Grain Research Laboratory in Australia and the USDA/ARS are conducting research to examine the development of carbonyl sulfide as a replacement for methyl bromide. As noted above, research data generated by CSIRO indicate that carbonyl sulfide will be useful as a non-perishable commodity fumigant. Recent data generated by USDA/ARS suggest that carbonyl sulfide could also be useful as a perishable commodity fumigant. Studies are on-going to determine its potential for use as a soil treatment and to determine potential effects on commodity quality, if any. (Desmarchelier 1993, Banks 1996).
A number of tests have been conducted to determine the likelihood that carbonyl sulfide could be used in commodity applications. First, Plarre and Reichmuth (1996) found that a concentration (C) of 32 mg/liter for 72 hours (T) (CxT value of 2,304 mg/hr/liter) effectively controlled all life stages of the granary weevil (Sitophilus granarius (L.)). Another study found that with application rates of 25 mg/L combined with exposure periods of 24 hours (CxT value of 600 mg/hr/liter), over 99.8 percent efficacy could be achieved against some immature stages of insects, including the rice weevil and lesser grain borer (Rhyzopertha dominica). It was also determined that application rates could be lowered to 8 mg/L while still obtaining a high efficacy (98.1 percent) if exposure periods were increased to 48 hours. It was suggested that the shorter exposure periods with the higher application rates could potentially be used for treating perishable commodities that require rapid fumigations prior to shipment (Desmarchelier 1993).
In addition to studies on grain pests, a recent USDA/ARS study evaluated carbonyl sulfide for use on stored product insects affecting dried fruits and nuts (Zettler et al. 1997). The toxicity of carbonyl sulfide for five economically important pest species was determined. The insects tested included larval navel orangeworm, Amyelois transitella (Walker); adult sawtooth grain beetle, Oryzaephilus surinamensis (L.); adult driedfruit beetle, Carpophilus hemipterus (L.); adult cigarette beetle, Lasioderma serricorne (F.); and adult confused flour beetle, Tribolum confusum (Jacquelin duVal). Each pest had different susceptibilities to fumigation with carbonyl sulfide, with LC90 toxicities ranging from 2.66 to 15.4 mg/liter. The CxT value which resulted in complete mortality for the most resistant life stage of the least susceptible insect tested (i.e., the egg and pupal stage of the adult confused flour beetle) ranged from 750 to 1,008 mg/hr/liter for a 24 hour exposure. Based on these results, it was concluded that carbonyl sulfide could be an effective fumigant for dried fruits and nuts.
The CSIRO Stored Grain Research Laboratory has also conducted tests to identify the effects of carbonyl sulfide treatment on the quality of malting barley, wheat (various types), sultanas, chickpeas, and canola (Desmarchelier 1993). The results of these tests are as follows:
- Barley displayed no significant loss of malting quality when treated with carbonyl sulfide. Similarly, no significant effects have been found on wheat or flour properties with the exception of marginal effects on dough properties. None of these commodities displayed a foreign odor.
- Although research on canola and chickpeas is still underway, researchers found little or no sorption after 24 hour exposures and no detectable odor after 24 hours airing.
- Sultanas fumigated with carbonyl sulfide were assessed for quality by taste, odor, and color change. Fumigated fruit had a distinctive odor, which diminished over time. There were no taste or color changes detected.
Additional research (Desmarchelier 1993) on wheat fumigated with carbonyl sulfide has revealed the following:
- Studies of the sorption of carbonyl sulfide by wheat have been conducted, with the detection of very low levels of possibly naturally occurring carbonyl sulfide in untreated controls. As carbonyl sulfide concentrations in fumigated wheat decline, it becomes increasingly difficult to distinguish carbonyl sulfide in fumigated wheat from that in untreated wheat.
- A comparative study on the effects of carbonyl sulfide and hydrogen cyanide (HCN) on germination and plumule length of wheat indicates that carbonyl sulfide can be used to control insect infestation in wheat without affecting seed viability or plumule length (i.e., it has no effect on seedling vigor and thus potentially is a valuable treatment for seed for planting).
- Additional studies being conducted to support carbonyl sulfide registration as a fumigant are evaluations of soil and commodity residue potential, flammability, and the potential for worker exposure. Many of the toxicity, emission, and environmental fate studies needed to complete registration have been completed (Banks 1996, Desmarchelier 1993). Studies to more accurately determine the efficacy of carbonyl sulfide for controlling specific insect species are also being initiated (Zettler et al. 1997).
Performance Characteristics
With regard to its potential as a commodity fumigant, carbonyl sulfide has what is considered to be excellent physical and chemical characteristics (Banks 1994, Desmarchelier 1993, Kluczewski et al. 1985). Its spectrum of activity, mobility and penetration, efficacy, and environmental fate characteristics are briefly discussed below.
- Spectrum of activity – Carbonyl sulfide effectively controls insect pests and mites. It may also be useful for controlling soil borne pests such as nematodes; additional research is pending.
- Mobility and penetration – Carbonyl sulfide has a high penetration and mobility rate; thereby increasing distribution and efficacy. This characteristic may be particularly useful for fumigation of logs and lumber, where its penetration is much superior to methyl bromide.
- Efficacy – In ten comparative efficacy studies using the rice weevil and lesser grain borer, carbonyl sulfide consistently out-performed carbon disulfide at application rates ranging from 8 mg/L to 24 mg/L and exposure periods of up to two days. Data on direct efficacy comparisons with methyl bromide generally are not available. Efficacy comparisons for treatment of logs indicate that carbonyl sulfide may be comparable to methyl bromide. Further, studies evaluating the efficacy of carbonyl sulfide for controlling stored product insects in dried fruits and nuts indicate the potential for carbonyl sulfide to replace methyl bromide in these applications.
- Environmental fate – Carbonyl sulfide is biodegradable, is a natural part of the sulfur-cycle, and has low water solubility.
Cost Comparison Data
Although cost data for the use of carbonyl sulfide are not currently available because research and development is still in the early stages, it is believed that carbonyl sulfide will be both a technically and economically viable alternative to methyl bromide (Banks 1996 and 1994, Desmarchelier 1993).
References
Banks, H.J., Commonwealth Scientific and Industrial Research Organization (CSIRO), Stored Grain Research Laboratory, Canberra, Australia, personal communication, 1996.
Banks, H.J. Presented at the International CFC and Halon Alternatives Conference, Washington, D.C., October 1994; notes on presentation.
Commonwealth Scientific and Industrial Research Organization (CSIRO). "Carbonyl Sulphide as a Fumigant for Control of Insects and Mites"; CSIRO report, p 1; CISRO: Canberra, Australia, 1993.
Desmarchelier, J.M. "Carbonyl Sulphide as a Fumigant for Control of Insects and Mites"; Commonwealth Scientific and Industrial Research Organization (CSIRO); CISRO report; CISRO: Canberra, Australia, 1993.
Desmarchelier, J.M. Presented at the 6th International Working Conference, Canberra, Australia, 1994; pp 78-82.
Kluczewski, S.M.; Brown, K.A.; Bell, J.N.B. Deposition of carbonyl sulphide to soils; Atmospheric Environment 1985, 19(8).
Plarre, R.; Reichmuth, C. Effects of carbonyl sulfide (COS) on Sitophilus granarius, Fusarium avenaceum, and Fusarium culmorum, and possible corrosion on copper. Nachrichtenblatt des Deutschen Pflanzenschutzdienstes 1996, 48(5), 105-112.
Zettler, L.; Leesch, J.G.; Gill, R.F.; Mackey, B.E. Toxicity of carbonyl sulfide to stored product insects. Journal of Economic Entomology, submitted for publication.
Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.
Visits since 1/1/98: