New Zealand Journal of Agricultural Research Persistence of sodium ...

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Persistence of sodium monofluoroacetate (1080) in baits under simulated rainfall a

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L. H. Bowen , D. R. Morgan & C. T. Eason

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Manaaki Whenua—Landcare Research , P.O. Box 31 011, Christchurch, New Zealand Published online: 17 Mar 2010.

To cite this article: L. H. Bowen , D. R. Morgan & C. T. Eason (1995) Persistence of sodium monofluoroacetate (1080) in baits under simulated rainfall, New Zealand Journal of Agricultural Research, 38:4, 529-531, DOI: 10.1080/00288233.1995.9513155 To link to this article: http://dx.doi.org/10.1080/00288233.1995.9513155

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New Zealand Journal of Agricultural Research, 1995, Vol. 38: 529-531 0028-8233/95/3804-0529 $2.50/0 © The Royal Society of New Zealand 1995

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Persistence of sodium monofluoroacetate (1080) in baits under simulated rainfall

L. H. BOWEN D. R. MORGAN C. T. EASON Manaaki Whenua—Landcare Research P.O. Box 31 011 Christchurch, New Zealand Abstract The rate of leaching of sodium monofluoroacetate (1080) by simulated rainfall was determined for carrot and possum pellet baits containing 0.08 and 0.15% 1080. Carrot baits were highly water-resistant and showed no decline in 1080 concentration after 200 mm of rain. It is therefore inadvisable to use carrot bait in arid areas when rapid restocking of land is required after a control operation, but they may be particularly suitable for forest habitats. Of the two types of pellet (Wanganui No. 7 and RS5) tested, RS5 pellets were the less water-resistant and started to disintegrate after only 5 mm of rain. The 1080 concentration also declined more rapidly in these pellets. So that toxicity is retained for the maximum length of time, RS5 pellets should be used in arid areas and Wanganui No. 7 pellets in wetter environments, when pellets are the bait of choice. RS5 pellets should be used if rapid return of stock to the land is required,. Keywords sodium monofluoroacetate (1080); bait leaching; pellets; carrot bait

INTRODUCTION Poisoning by 1080-impregnated carrot and cereal baits has proved an efficient method for controlling

rabbits (Oryctolagus cuniculus) and possums (Trichosurus vulpecula) and has been used extensively in Australia and New Zealand for many years. Understanding the amount of rainfall required to render baits non-toxic is essential for pest management and for determining how long stock and the general public should be excluded from areas after control operations. The available data on 1080 pellet and carrot baits are limited and partly conflicting. Leaching of 1080 has been monitored for two types of cereal pellets, RS5 and Wanganui No. 7, indicating that the toxin is rapidly leached after 5 mm of rain, but the rates of leaching could not be compared as the pellet types contained different initial concentrations of 1080 (Morgan 1988; unpubl. FRI contract report). Corr & Martire (1971) found that only 12.5 mm of rain was required to reduce the 1080 concentration in carrot bait by 90%, but Staples (1967) found that over 100 mm was required to reduce the 1080 content by the same amount. Data are therefore required to enable comparison of bait types and to resolve the conflicting data for carrot bait. Furthermore, a reevaluation of the rate of 1080 leaching is required as the quality of bait used in possum control has improved greatly since these earlier studies, through development of manufacturing specifications and better processing equipment (Morgan 1994). This study therefore aimed to provide reliable data on the persistence of 1080 in commonly used cereal pellets and carrot baits at both 0.08 and 0.15% toxin concentrations.

MATERIALS AND METHODS

A95029 Received 31 May 1995; accepted 21 July 1995

No. 7 pellets of mean weight 6 g that contained either 0.08 or 0.15% 1080 were obtained from Animal Control Products Ltd, Wanganui. RS5 6 g pellets with 0.15% 1080 and 5 g pellets with 0.08% 1080 were obtained from Animal Control Products

New Zealand Journal of Agricultural Research, 1995, Vol. 38

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Fig. 1 Leaching of 1080 in 0.08% cereal bait.

Fig. 2 Leaching of 1080 in 0.15% cereal bait.

Ltd, Waimate. RS5 pellets at 0.08% 1080 concentration with a mean weight of 6 g are not available. These four types of pellets have the same concentrations and sizes as those used in possum control operations. Carrot baits were prepared at Landcare Research Ltd by chopping carrot into 6 + 0.5 g pieces and tumbling 180 g of carrot pieces with 2.25 ml of 12% 1080 stock solution for the 0.15% baits and 2.25 ml of 6.4% 1080 stock solution for the 0.08% baits. This method is a laboratory simulation of the Regional Council method, which uses a cutting machine (e.g., Reliance or Gibson Cutter) to cut the carrot to the appropriate size before the baits are sprayed with stock solution at a rate of 12.5 litre/t. Samples of 30 baits of each type were placed on turf under the central 50 cm swath of "rainfall" produced by a common garden rotary sprinkler. The sprinkler had a water output of 20 mm/h which would be consistent with field conditions, and was operated over 48 h. Two rainfall gauges were placed at opposite points of the sprinkler "sweep" to assess the consistency of rainfall. A subsample of two baits for each bait type was randomly removed at 0 mm of rainfall and then after 5, 10, 20, 50, 100, 150, and 200 mm, and stored at -20°C for later analysis. The bait samples were thawed, crushed in a mortar and pestle, and mixed until homogenous. A subsample was mixed with hydrochloric acid, and the 1080 was extracted by repeated shaking with ethyl acetate. An aliquot of the extract was derivatised with pentafluorobenzyl bromide and

quantified by gas chromatography with electroncapture detection. The method is based on Method 8B of the Denver Wildlife Center (1989). RESULTS Rainfall collected by the two rain gauges was the same throughout the study, indicating that baits were uniformly exposed to rainfall. There was a noticeable difference in texture for the two types of pellets even before the experiment began, the RS5 pellets being more crumbly than the No. 7 pellets. The RS5 pellets started to disintegrate after 5 mm of rain, but the No. 7 baits retained their shape throughout the experiment. The concentration of 1080 in the RS5 and No. 7 pellets started to decline rapidly after only 5 mm of rainfall (Fig. 1 & 2). The decrease in 1080 concentration was more rapid in the RS5 pellets. The toxin had largely been leached out after 50 mm of rain, and completely leached after 150 mm at both 1080 concentrations. A relatively high concentration of 1080 was retained for both the 0.08% (0.007%) and 0.15% (0.02%) No. 7 pellets even after 200 mm of rain. The carrot bait showed no decrease in 1080 content after 200 mm of rain (Fig. 3). DISCUSSION The expected field life of bait is an important consideration when planning a control operation. Our data indicate likely differences in the leaching

Bowen et al.—Persistence of sodium monofluoroacetate (1080) in baits 0.160.140.15% bait

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Fig. 3 Leaching of 1080 in carrot bait.

rate of 1080 from different bait types under rainfall. The study has also shown that bait type is a more important determinant of 1080 persistence in baits than the initial 1080 concentration. The observed decline of 1080 in cereal pellets after only 5 mm of rainfall is consistent with previous field data (Morgan 1988; unpubl. FRI contract report). RS5 pellets were not as waterproof as No. 7 pellets and the 1080 concentration declined much more rapidly. The 0.08% RS5 pellets were small (5 g), which may have affected their leaching characteristics slightly. However, both 0.08 and 0.15% RS5 pellets lost 1080 more quickly than equivalent No. 7 pellets. Pellet baits may therefore be a safer option than carrot baits for use on open farmland. For early return of livestock, RS5 pellets should be used. No. 7 pellets withstand more rain than RS5, both in retaining shape and 1080, and would therefore be a better option for use in forest operations if pellets were desired. The water resistance data for the carrot baits contrasts with the data produced by Corr & Martire (1971), but agrees with the results produced by Staples (1967). Carrot baits may be unsuitable for use on arid, open farmland where rapid restocking of the land is required as the baits may persist in the environment for prolonged periods. However, carrot baits are rapidly dehydrated when exposed to sunlight and may become unpalatable to pests

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and livestock. Therefore carrot baits may be particularly suitable for use in wetter forest where prolonged retention of 1080 is required to eradicate all pests present. In these environments, the carrot will not dehydrate and become unpalatable to animals. Although our results indicate relative differences in leaching of 1080 toxin from different bait types, we caution against using rainfall alone as the primary basis for determining the "withholding" period for operation sites. Under field conditions, loss of 1080 may be influenced by other factors such as pattern and intensity of rainfall, humidity, temperature, and sun, in addition to the total amount of rainfall. Furthermore, biodegradation may be expected to contribute to the decline of 1080 in baits in the field, particularly under warm conditions in between periods of rain. Field studies are planned that will develop a greater understanding of leaching of 1080 pellets and carrot baits in different conditions in the environment. ACKNOWLEDGMENTS We thank the Animal Health Board for funding this work; Mr G. R. Wright for technical assistance; Shaun Ogilvie for refereeing this paper; and Joanna Orwin for editing it. REFERENCES Compound 1080 grain bait assay. Denver Wildlife Center Method No. 8B May 1989. Corr P. V.; Martire, P. 1971 : Leaching by rain of sodium fluoroacetate (" 1080") from baits used for rabbit control. Australian journal of experimental agriculture and animal husbandry 11: 278-281. Morgan, D. R. 1994: Improved cost-effectiveness and safety of sodium monofluoroacetate (1080) possum control operations. Pp. 144-150 in: Proceedings of the science workshop on 1080, Seawright A. A.; Eason C. T. ed. The Royal Society of New Zealand miscellaneous series 28: 144-150. Staples, E. L. J. 1967: The reduction of the sodium monofluoroacetate ("1080") content of carrot baits of various thicknesses by weathering. New Zealand journal of agricultural research 11: 319-329.