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Soil Biology & Biochemistry 33 (2001) 227±234
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De¯uorination of sodium mono¯uoroacetate by soil microorganisms from
central Australia
L.E. Twigg*, L.V. Socha
Scienti®c Services Division, Parks & Wildlife Commission, Northern Territory, P.O. Box 1046, Alice Springs, NT 0871, Australia
Received 13 October 1999; received in revised form 11 April 2000; accepted 22 June 2000

Abstract
Sodium mono¯uoroacetate (1080) is a commonly used vertebrate pesticide throughout Australia and New Zealand. However, little is
known about the persistence of 1080 in arid environments, or whether soil microorganisms capable of de¯uorinating 1080 are present in soils
from arid Australia. Soil samples (3 replicates) from central Australia were collected on seven occasions over an 8-month period, and the
microorganisms capable of de¯uorinating 1080 were isolated. When grown in an inorganic medium containing 20 mM 1080 as the sole C
source, 24 species were able to de¯uorinate 1080: 13 bacteria and 11 fungi. The abundance of these microorganisms appeared to be
in¯uenced by climatic conditions with the relative abundance of many species increasing after rain. The fungus Fusarium oxysporum
had by far the greatest de¯uorinating ability, and de¯uorinated approximately 45% of added 1080 within 12 d. De¯uorination of 1080 added
to soil was signi®cantly greater at pH 5.6 compared to pH 6.8, suggesting that the fungal species were important de¯uorinators in these soils.
In a 28-d time course trial, de¯uorination of added 1080 by soil microorganisms appeared to asymptote after 21±28 d. The presence of these
microorganisms in soil from central Australia indicates that 1080 can be used safely even in arid environments. 1080 is unlikely to persist in
these soils, or to contaminate ground water. The implications of these ®ndings with respect to the environmental safety of 1080 in other

regions where 1080 baits are used are also discussed. q 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Microbial de¯uorination; Pest control; Sodium mono¯uoroacetate; Soil persistence

1. Introduction
Sodium mono¯uoroacetate (Compound 1080) is highly
toxic to most endothermic vertebrates and many invertebrates except where individual species have had evolutionary exposure to naturally occurring ¯uoroacetate-bearing
vegetation (Twigg and King, 1991). Most of the plants in
Australia which produce ¯uoroacetate belong to a single
genus (34 species of Gastrolobium), and most are con®ned
to the southwest of Western Australia although three species
do occur in parts of northern and central Australia (two
species of Gastrolobium plus Acacia georginae; Aplin,
1971; Oelrichs and McEwan, 1961; Twigg and King, 1991).
1080 poison is also an important vertebrate pesticide
in Australia where, under strict guidelines, 1080
impregnated baits are commonly used for controlling
rabbits (Oryctolagus cuniculus), foxes (Vulpes vulpes) and
dingoes (Canis familiaris dingo) (Thomson, 1986; McIlroy
* Corresponding author. Present Address: Vertebrate Pest Research
Services, Agriculture Western Australia, Bougainvillea Avenue, Forrest®eld, WA 6058 Australia. Tel.: 161-8-9366-2330; fax: 161-8-9366-2342.

E-mail address: ltwigg@argic.wa.gov.au (L.E. Twigg).

et al., 1988; Saunders et al., 1995; Williams et al., 1995).
Because 1080 is highly water soluble and readily leached
from baits (Wheeler and Oliver, 1978; McIlroy et al., 1988),
there has been some concern regarding the persistence of the
¯uoroacetate entering the environment both from the toxic
baits, and from ¯uoroacetate-bearing plants (Par®t et al.,
1994; Walker 1994; Twigg et al., 1996). However, this
concern has not been realised as 1080 does not persist in
soil or waterways at least, in areas with ¯uoroacetate-bearing vegetation in southwestern Western Australia (Twigg et
al., 1996). In fact several genera of soil fungi (e.g. Fusarium, Penicillium) and bacteria (e.g. Pseudomonas, Bacillus)
from these soils are now known to degrade 1080 (Wong et
al., 1992). While some of these microorganisms are ubiquitous and commonly occur in a variety of moist soils (Kelly,
1965; Bong et al., 1979), little is known about the ability of
soil microorganisms from arid and semi-arid regions to
degrade 1080.
Here we report on the ability of soil microorganisms from
arid central Australia to de¯uorinate 1080. We also examine
the relative abundance of these microorganisms both before

and after rainfall events, and make some comments as to the
likely persistence of 1080 in this environment.

0038-0717/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S 0038-071 7(00)00134-6

228

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234

2. Materials and methods
2.1. Study area and collection of soil samples
Soil samples were collected from Palm Paddock within
the Finke Gorge National Park (248 10 0 S; 1328 50 0 E) which
is approximately 150 km west of Alice Springs. To the best
of our knowledge, none of the soils tested had any known
previous exposure to 1080. Soil substrates in this region are
generally calcerous stony rises with some red clays/sandy
loam's in the low lying areas, but they also include areas of
sandstone. The dominant vegetation is hummock (Triodia)/

Acacia grasslands. Landforms include undulating plains,
steep hillsides, dissected plateaus, watercourses, and the
Finke river (dominant feature). The ®ne red sandy loam
soil within Palm Paddock has a 20% crust of cryptogam
(micro¯ora). Mean soil pH was 6.6 (SEM 0.12, …n ˆ 3†:
Average annual rainfall, which can be highly variable, is
260 mm (monthly maxima range from 0±496 mm).
Temperatures can be extreme with recorded maxima of
108C in July (mean, 208C) to over 448C in January
(mean, 378C) (Bureau of Meteorology Records, Northern
Territory).
Our current study was part of a larger investigation examining the longevity of 1080 meat baits in central Australia
(Twigg et al., 2000). To examine what micro¯ora were
present in the soil in Palm Paddock where these trials
were carried out, and to determine temporal variation in
the relative abundance of these microorganisms, 30±40 g
soil samples (1±8 cm depth) were collected from undisturbed soil at permanently marked locations over a 32
week period commencing in March 1998. There were 7
sampling periods: Day 0, then 0.5, 1, 2, 4, 6 and 8 months
after the 1080 baits were placed into the predator-proof

cages. The ®ve cages used in the longevity trials were in a
circular pattern with approximately 20 m between each cage
(i.e. soil collection site). The soil samples were collected
within 1 m of three of these cages. Thus there were three
replicate soil collections for each sample period. All soil
samples were placed into individual resealable plastic
containers and kept at 78C until analysis. Rainfall, and
ambient and soil temperature (depth 5 cm), were monitored
daily at the site using a ENVIRODATA AUSTRALIA
EASIDATA data logger.
2.2. De¯uorinating activity of soil microorganisms
Methods used for determining the de¯uorinating activity
of soil microorganisms were similar to those described by
Wong et al. (1992). All water was deionised and autoclaved
at 1218C and 15 kPa for 15 min. To avoid heat degradation,
the 1080 solution was sterilised using a 0.22 um Millipore
®lter membrane. An enriched, autoclaved broth containing
2 g l 21 KH2PO4, and 1 g l 21 (NH4)2SO4 adjusted to pH 6.8
with a few drops of 0.1 M NaOH was used for the bacterial
incubations. For fungi, the broth contained traces of CaCl2

(0.2 mg l 21) and FeSO47H2O (10 mg l 21), and was adjusted
to pH 5.6 with a few drops of 0.1 M NaOH. Ten ml aliquots
of these broths were dispensed into sterile 120 ml polycarbonate bottles. After cooling to 508C, 20 mM of 1080 and
1 g of air-dried soil were added to each bottle. The bottles
were incubated at 278C on an orbital shaker (180 rev.
min 21). There was one bottle per replicate with three replicates per soil collection period. After 12 d incubation, the
concentration of F 2 in the culture broths was determined
using an Orion ¯uoride electrode (model 94-09-00), an
Orion EA 940 expandable ion analyser, an Orion single
junction reference electrode 90-01 and an Orion automatic
temperature compensation probe.
A time-course experiment was used to determine the
de¯uorination activity of the microorganisms present in
the soil samples. One ml of 20 mM 1080 was added to 5 g
of soil (®nal moisture content about 15% w/w) in 120 ml
sterile polycarbonate bottles, and the bottles incubated at
288C. (12 h day) and 158C (12 h night). Five bottles were
established for the soil from each collection period for each
site and the amount of de¯uorination of 1080 was

measured at 7 d intervals from 0 to 28 d (i.e. 5 timecourse periods £ 3 sites £ 7 soil collection periods, n ˆ
105†: At each time- course collection period, one of the
bottles was removed from the incubator, 10 ml of sterile
water was added, and after 30 min, the F 2 concentration
measured using the F 2 electrode (see above).
Background levels of F 2 in each soil type, and water used
during the trials was determined by mixing 5 g soil in 10 ml
deionised water. This mixture was allowed to stand for
30 min in polycarbonate bottles and the concentration of
F 2 was then measured using the F 2 electrode. Background
levels for the 1080 solution were also determined using the
F 2 electrode. Because ¯uoride ions can bind to soil particles
(Barrow and Shaw, 1977), the recovery of added F 2 from
both 1 g and 5 g sterile soil samples was also determined.
The amount of F 2 binding to the soil was measured by
adding a known amount of F 2 to 5 or 1 g of sterile soil in
a known amount of the standard fungi culture broth without
1080. This was then allowed to stand for 24 h. Deionised
water (10 ml) was added to the 5 g sample containers, the
containers allowed to stand for 30 min, and the recovery rate

of added F 2 determined using the F 2 electrode. This was
compared to the measurement of F 2 in solutions with
identical F 2 concentrations without soil. There were two
replicates for each soil type. This approach simulated the
two main incubation methods used. All trials were corrected
for background levels before determining de¯uorination
rates.
2.3. Isolation of 1080 microorganisms
After 12 d incubation, for bacteria, a 100-fold dilution
using deionised water was made from each of the enriched
culture broths and then plated onto nutrient agar (NA).
Enriched culture broths for fungi were plated undiluted

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234

onto potato-dextrose agar (PDA). NA plates were incubated
at 308C and PDA plates at 258C. Single colonies of different
microbial species were subcultured onto NA or PDA and
subsequently identi®ed. Bacterial colonies were identi®ed
to genera or species using the Analytical Pro®le Index (API)

strips (bioMerieus sa) and associated software (APILAB).
Fungal colonies were identi®ed using known morphological
characteristics described by Raper and Fennell (1965),
Booth (1971), Pitt (1979), and Burgess et al. (1988).
2.4. De¯uorinating activity of microbial isolates
The de¯uorinating ability of each isolate was determined
in the presence of 20 mM 1080 with trace elements
(bacteria: 2 g l 21 KH2PO4, and 1 g l 21 (NH4)2SO4 at pH
6.8; fungi: 0.2 mg l 21 CaCl2 and 10 mg l 21 FeSO47H2O
adjusted to pH 5.6), and with and without 5 g of sterile
soil. Bacterial suspensions (1.5 £ 10 9 cells ml 21) were
prepared in sterile 0.85% NaCl w/v for the 1080 only
inoculum, and in a 20 mM 1080 solution for the sterile
soil inoculum. Fungal suspensions were prepared by scraping off aerial mycelium from 48 h-old cultures into 5 ml
sterile 0.85% NaCl w/v and sterile 20 mM 1080. As appropriate, the samples were inoculated with either 1 ml of
inoculum to 10 ml of sterile 20 mM 1080 solution or 1 ml
inoculum to 5 g of sterile soil. There were two independent
broth cultures for each isolate for each soil treatment.
The broths were kept at 278C for 12 d in sterile 120 ml
polycarbonate bottles.

2.5. Statistical analysis
Statistical analyses were undertaken using Statistica
(StatSoft 1994). The decay curve for added 1080 was determined using nonlinear regression. The effect of pH and time
on the de¯uorination of 1080 by soil was assessed using a
®xed effects ANOVA with the individual cage locations
…n ˆ 3† acting as a blocking factor (Winer et al., 1991).
Differences in the de¯uorination ability between microbial
isolates were tested using log-transformed de¯uorination
rates, and a ®xed effects ANOVA with the Tukey HSD
post-hoc test (Winer et al., 1991). Data for Streptomyctes
sp. 1 (Actinomycetes) were presented separately, and were
exclude from the `bacteria' category during the analyses,
because this species had marked differences in their isolation and growth requirements (e.g. aerial mycelium)
compared to that of the other bacteria.
3. Results
3.1. Recovery of added F 2
Little F 2 was found to bind to the soil. Mean recovery rates
for 1.25±5.0 and 10.0±40.0 mg of added F 2 were 95.5 ^ 0.8
% (SEM, n ˆ 3†; and 98.5 ^ 4.4% (SEM, n ˆ 4†;
respectively. Little free F 2 occurred naturally in the soil

229

(1.14 mg g 21, n ˆ 4†; deionised water (0.16 mg ml21, n ˆ 5†
or the 20 mM 1080 solution (2.5 mg ml 21, n ˆ 5†: Because
of the high recovery rates of added F 2, our data are
presented as unadjusted values. The recovery of F 2 ion
from known amounts of 1080 as determined by the amount
of inorganic ¯uoride subsequently released following degradation by oxygen combustion can range from 90±97.5%
(Peters and Baxter, 1974). However, for our purposes, we
assumed that all added 1080 could be de¯uorinated such
that 1 ml of 20 mM 1080 would yield 380 mg of F 2. This
value was used for all the percentage calculations of the
amount of added 1080 de¯uorinated.
3.2. De¯uorination ability of soil
Soil samples from central Australia de¯uorinated 23% of
added 1080 within 28 d; however, de¯uorinating activity of
these soils appeared to asymptote after 21±28 d (Fig. 1a).
The model decay curve used was: mg F 2 d 21 g
soil 21 ˆ A 1 B1 £ time 1 B2 £ time 2, where time is in
days, and A (0.928), B1 (1.050) and B2 (20.017) are
nonlinear regression constants …n ˆ 105; r ˆ 0:654†
However, soil samples appeared to have greater de¯uorinating ability after signi®cant rainfall events, as the highest
rates were observed for the November, May and March
soil samples and these collection periods were preceded
by moderate rainfall (Fig. 1b; Table 1).
De¯uorination by soil samples (1 g) incubated in the
enriched medium with added 1080 (Fig. 2) was greater at
pH 5.6 than at pH 6.8 …F ˆ 19:27; df ˆ 1, 26, P ˆ 0:0002†:
The ability of soil to de¯uorinate 1080 was also in¯uenced
by time of year …F ˆ 3:42; df ˆ 6, 26, P ˆ 0:013† with the
highest de¯uorination occurring in early November after
54 mm of rainfall (Table 1). The interaction was also significant …F ˆ 2:78; df ˆ 6, 26, P ˆ 0:032† indicating the
effects of pH varied between time periods. The pH of the
soil at the ®eld sites was 6.6 …n ˆ 3†: Approximately
223 mm of rainfall occurred during the trial, with a weekly
mean of 6.95 mm (range 0±60 mm). Rainfall was greatest in
early April and early November, and the highest temperatures occurred during November to March (Table 1).
3.3. Relative abundance of soil microorganisms
Twenty-four species of microorganisms capable of
de¯uorinating 1080 were isolated from the central Australian soil. Microorganisms were least abundant during, or
following, periods of low rainfall (Table 1). Fusarium was
the most abundant fungi, with species of this genus present
in most months. The presence and abundance of bacteria
was more varied with some species totally absent for consecutive collection periods. Two species of bacteria were not
identi®ed (Table 1).
3.4. De¯uorination by microbial isolates
All 24 isolates were capable of de¯uorinating 1080 when

230

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234
20

9.1 mg F 2 g sterile soil 21) and 19.5 mg F 2 ml 21 inoculant
…n ˆ 11 £ 2†; and Streptomycessp.1, 58.5 mg F 2 ml 21
inoculant
(or
6.3 mg F 2 g
sterile
soil 21)
and
2
21
15.4 mg F ml inoculant …n ˆ 1 £ 2†:

(a)

Fluoride released (µg F-/g soil)

15

10

4. Discussion
5

0
0
30

7

14

21

28

14

21

28

(b)

25
20
15
10
5
0
0

7

Days of incubation
Fig. 1. Mean de¯uorination of added 1080 (i.e. 380 mg F 2) by 5 g soil
samples incubated at 288C (day) and 158C (night) over 28 d. (a) The
mean of repeated incubations of soil from each site …n ˆ 3† for each collection period …n ˆ 7†; and the curvilinear line ®t for all sites is shown …r ˆ
0:99; n ˆ 21†: Symbols represent the different sites. (b) Mean of the three
sites for soils collected in March (A), April (P), May (W), July (X),
September (K) and November (V). Except for April …n ˆ 6† n ˆ 3:

1080 was their sole source of carbon (Fig. 3a). In the
absence of soil, the fungal isolates had greater de¯uorinating ability than the bacteria …F ˆ 5:09; df ˆ 1, 44, P ˆ
0:03†: Within the fungi, de¯uorination by F. oxysporum
was greater than for any other species …F ˆ 9:30; df ˆ 10,
11, P , 0:001†; but de¯uorination by bacterial species was
similar …F ˆ 5:09; df ˆ 11, 12, P ˆ 0:10†: However, the
amount of 1080 de¯uorinated increased considerably
when isolates were provided with an additional carbon
source in the form of added sterile soil (Fig. 3b). The fungal
isolates again had greater de¯uorinating ability than the
bacteria …F ˆ 10:03; df ˆ 1, 44, P , 0:003†; with F.
oxysporum better than all other fungal species …F ˆ 21:48;
df ˆ 10, 11, P , 0:001†: However, de¯uorination by
bacteria now differed between species with B. megaterium
and C. albidus having the highest rates (Fig. 3b; F ˆ 7:76;
df ˆ 11, 12, P ˆ 0:001†: Fungal de¯uorination in the
presence of sterile soil increased approximately four-fold
with F. oxysporum having by far the greatest de¯uorinating
ability of any microbial isolate. Bacterial de¯uorination
increased only two-fold (Fig. 3). Mean de¯uorination rates
after 12 d incubation with 1080, and with and without
sterile soil, were: bacteria, 32.7 mg F 2 ml 21 inoculant (or
3.5 mg F 2 g sterile soil 21) and 15.1 mg F 2 ml 21 inoculant
…n ˆ 12 £ 2†; fungi, 82.6 mg F 2 ml 21 inoculant (or

Twenty-four species of microorganisms, which were
capable of growing in the presence of 1080 were isolated
from soil in arid Australia. Although not all microorganisms
could be identi®ed, species of Bacillus, Pseudomonas,
Aspergillus, Penicillium and Streptomyces capable of
de¯uorinating 1080 are known to occur in soil in temperate
climates in Australia (Wong et al., 1991, 1992; Kirkpatrick,
1999) and New Zealand (Bong et al., 1979; Walker, 1994).
In fact, F. oxysporum, F. solani and B. subtilis are widespread occurring in both countries. F. oxysporum is the most
ef®cient and proli®c de¯uorinator of 1080 of all the microorganisms capable of detoxifying 1080 identi®ed to date
(Wong et al., 1991, 1992; Walker, 1994; Kirkpatrick,
1999; our study). However, the ability of Acinetobacter,
Arthrobacter, Aureobacterium, Cryptococcus and Weeksella to de¯uorinate 1080 has not been recorded previously.
Our ®ndings are also in contrast with those of Wong et al.
(1992) who were unable to isolate any soil microorganisms
capable of de¯uorinating 1080 from four arid/semi-arid
sites in Australia. There are several possible reasons for
this. Their sandy soil from the Tanami Desert site in central
Australia may not have had such organisms. However, in
sandy loams in New Zealand, 50% of 1080 (6.1 mg added)
was detoxi®ed within 38 d at 218C with 9±20% soil moisture (Par®t et al., 1994). The more likely cause of Wong et al.
(1992) ®ndings is that the initial isolation of soil microorganisms was undertaken at a temperature (45±508C) which
inhibited microbial growth. Our incubation and isolation
procedures were undertaken using a temperature range of
15±308C. Furthermore, in New Zealand silt loams, 50% of
added 1080 was degraded within 10 d at 238C, 30 d at 108C,
and 80 d at 58C (Par®t et al., 1994). This is similar to the
rates we observed where about 10±50% of added 1080 was
de¯uorinated within 12 d at 278C.
The rate of de¯uorination for similar species of microorganism often differed between our study and studies by
Wong et al. (1991, 1992). The latter found de¯uorination
rates ranging from 4±78% of added 1080 within 12 d at
278C. The high level of F 2 binding to the soil may have
been a confounding factor during Wong et al.'s (1992) trials
(.60% by back calculation of data presented). The binding
of F 2 to soil in their trials was only determined for one soil
type and then extrapolated to all soils tested. The correction
factor used to overcome this binding may have led to an
over estimation of the amount of 1080 de¯uorinated in some
instances. Although not measured, our soils contained little
obvious organic matter and hence the amount of binding of
F 2 was low, ranging from 2±5%, depending upon the

Table 1
The relative abundance of microorganisms isolated from soil in central Australia over an eight month period and which were capable of growing in an enriched media containing 10 ml of 20 mM 1080. Weather
variables for the corresponding periods are also shown over two week intervals. Tot, Total number of colonies for all three sites; Mn, Mean number of colonies from the three sites; NS, Number of sites …n ˆ 3†
containing that isolate for that collection period, ND, data not collected
March
Microorganism

April #1

Tot

Mn

NS

0
100
0
1600
400
500
900
0
1500
1100
500
0

0
33
0
533
133
167
300
0
500
367
167
0

800

267

April #2

Tot

Mn

NS

0
1
0
3
2
2
1
0
1
3
2
0

0
1300
0
200
0
0
100
0
1000
0
200
0

0
433
0
67
0
0
33
0
333
0
67
0

2

0

0

May

Tot

Mn

NS

0
1
0
1
0
0
1
0
1
0
1
0

1200
1100
0
0
0
3800
1900
0
2300
2600
2600
800

400
367
0
0
0
1267
633
0
767
867
867
267

0

600

200

July

Tot

Mn

NS

1
1
0
0
0
3
1
0
1
2
3
1

1200
0
0
600
500
0
0
500
0
900
1100
1100

400
0
0
200
167
0
0
167
0
300
367
367

1

2200

733

September

Tot

Mn

NS

2
0
0
1
1
0
0
2
0
1
2
1

0
300
100
400
0
0
300
0
200
1200
900
0

0
100
33
133
0
0
100
0
67
400
300
0

3

1100

367

November

Tot

Mn

NS

Tot

Mn

NS

0
1
1
1
0
0
1
0
1
3
1
0

500
0
2300
0
800
0
0
200
0
0
1300
600

167
0
767
0
267
0
0
67
0
0
433
200

1
0
3
0
1
0
0
1
0
0
2
1

2500
0
2900
1200
200
200
0
0
0
0
1000
0

833
0
967
400
67
67
0
0
0
0
333
0

2
0
2
2
1
1
0
0
0
0
2
0

2

600

200

1

700

233

2

Bacteria

Total number of species

9

5

9

8

8

7

7

Fungi
Aspergillus ¯avus
Aspergillus fumigatus
Aspergillus sp. 1
Fusarium avenaceum
Fusarium compactum
Fusarium equiseti
Fusarium oxysporum
Fusarium proliferatum
Fusarium semitectum?
Fusarium solani
Penicillium spinulosum

3
2
0
2
1
17
6
14
6
6
0

1.0
0.7
0
0.7
0.3
5.7
2.0
4.7
2.0
2.0
0

Total number of species
All species

1
2
0
1
1
2
2
2
1
2
0

10
0
9
0
10
1
0
0
4
3
0

9
18

3.3
0
3.0
0
3.3
0.3
0
0
0.7
1.0
0

1
0
1
0
1
1
0
0
2
1
0

15
3
0
4
9
0
0
0
0
22
0

5.0
1.0
0
1.3
3.0
0
0
0
0
7.3
0

6
11 a

2
1
0
1
3
0
0
0
0
2
0

0
0
0
3
2
4
5
5
12
3
5

0
0
0
1.0
0.7
1.3
1.7
1.7
4.0
1.0
1.7

5
14 a

0
0
0
2
1
2
3
2
3
1
1

0
1
2
2
1
0
1
1
4
0
0

0
0.3
0.7
0.7
0.3
0
0.3
0.3
1.3
0
0

8
16

0
1
1
2
1
0
1
1
1
0
0

0
0
5
7
11
3
11
0
4
3
0

0
0
1.7
2.3
3.7
1.0
3.7
0
1.3
1.0
0

7
15

0
0
2
3
2
2
3
0
1
1
0

0
4
3
13
9
33
22
1
16
6
10

0
1.3
1.0
4.3
3.0
11.0
7.3
0.3
5.3
2.0
3.3

7
14

0
2
1
2
2
3
3
1
3
2
2

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234

Acinetobacter sp. 1
Arthrobacter sp. 1
Arthrobacter sp. 2
Aureobacterium sp. 1
Aureobacterium sp. 2
Bacillus megaterium
Bacillus subtilis
Cryptococcus albidus
Pseudomonas alcaligenes
Weeksella virosa
Unknown, gram 1 bacillus
Unknown, gram 1 coccus
Actinomycetes
Streptomyces sp. 1

10
17

Weather (two week periods)?
Total Rainfall (mm)
Mean Max Temperature (8C)
Mean Min Temperature (8C)

Total unique species for April ˆ 18.

1.5
28.8
17.3

59.7
33.1
14.7

0.1
24.4
13.4

0.0
26.2
10.4

0.0
24.0
8.4

0.0
24.4
6.6

35.6
25.0
7.2

0.0
28.3
10.0

21.0
29.1
12.8

53.8
37.4
16.8

ND
ND
ND
231

a

9.0
30.3
20.7

232

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234
pH 5.6

Fluoride released (µgF-/g soil)

800

pH 6.8

600

400

200

0
Mar

Apr

Apr

May

Ju l

Sep

N ov

Month
Fig. 2. The effect of pH on the mean (^SEM, n ˆ 3† de¯uorination of
added 1080 (i.e. 3800 mg F 2) by 1 g soil samples grown in 10 ml of
20 mM 1080 solution at 278C for 12 d. Soil was collected from each site
for each collection period …n ˆ 7†:

amount added. Kirkpatrick (1999) also reported rapid
de¯uorination of 1080 in factory waste by F. oxysporum
and species of Pseudomonas, with de¯uorination rates
ranging from 10 to 100% of added 1080 within 5 d at
308C. While Wong et al. (1991, 1992) also provided an
additional nitrogen source (peptone) to many of their broths,
which could account for their greater levels of de¯uorination, the low levels of organic matter in our soil samples
suggest that alternative sources of carbon, or available nitrogen, may be limited in arid zone soils. Such a response is
supported by our time course experiment, where de¯uorination of added 1080 appeared to asymptote after 21±28 d.
Wong et al. (1992) also used 12 g of soil (more carbon?)
compared to the 5 g of soil used in our trials; the amount of
added 1080 in the two studies was the same.
The abundance of microorganisms capable of de¯uorinating 1080 in central Australian soils generally increased
following periods of rain. Adequate soil moisture is required
to enable metabolism of substrates for vegetative and
reproductive growth. The existence of a complex soil

Fluoride released (µgF-/ml)

500

(a) Broth only

11

400
Bacteria

9
Fungi

300
7
200
5

FA c Degraded (%)

13

100
3
Acin sp1
Ar th sp1
Ar th sp2
Aure sp1
Aure sp2
Baci meg
Baci sub
Cryp alb
Pseu alc
Week vir
Unkn bac
Unkn coc
Asp flav
Asp fum
Asp sp1
F u s av e
Fus com
Fus equ
Fus oxy
Fus pro
Fus sem
Fus sol
Pen spi
Str sp1
All Bac
All Fungi

0

50

35
30
20
Bacteria

Fungi

25
20
15

10

10
5
0

0
Acin sp1
Ar th sp1
Ar th sp2
Aure sp1
Aure sp2
Baci meg
Baci sub
Cryp alb
Pseu alc
Week vir
Unkn bac
Unkn coc
Asp flav
Asp fum
Asp sp1
F u s av e
Fus com
Fus equ
Fus oxy
Fus pro
Fus sem
Fus sol
Pen spi
Str sp1
All Bac
All Fungi

Fluoride released (µgF-/g soil)

40

FA c Degraded (%)

45

(b) Broth & sterile soil

30

Fig. 3. Mean (^SEM, n ˆ 2) de¯uorination of added 1080 by soil microorganisms from central Australia after 12 d incubation at 278C in enriched media (see
methods). (a) By microbial isolates grown in 10 ml of 20 mM 1080 solution (sole carbon source, with 3800 mg added F 2), and (b) microbial isolates grown in
1 ml of 20 mM 1080 solution (i.e. 380 mg F 2) plus 5 g of sterile soil at 278C for 12 d.

L.E. Twigg, L.V. Socha / Soil Biology & Biochemistry 33 (2001) 227±234

micro¯ora is also dependent upon the presence of adequate
food and energy sources (Gray and Williams, 1971). Similar
to our ®ndings, the degradation of 1080 in sandy loams in
New Zealand appears to be slower when soil moisture is
reduced (,9%; Par®t et al., 1994), suggesting the longevity
of 1080 in soil may be increased in some arid environments.
In our trials, little de¯uorination …1:28 ^ 0:05 mg F2 ml21 ;
n ˆ 2† occurred in sterile soil incubations in the absence of
microorganisms. Thus we are con®dent that the de¯uorination of 1080 in the presence of non-sterile soil was the result
of microbial isolate activity. However, as both the spatial
distribution and the abundance of these microbial isolates
appeared to change over time, we recommend that soil
samples need to be collected from a wide area in both
space and time to be sure whether an individual species is
present or not Ð or at least, soil moisture conditions need to
be recorded. De¯uorination of 1080 was greater in our soil
samples at pH 5.6 (Fig. 2), which is the preferred pH for
many fungi. Although the pH of our soil was 6.6, we believe
that, because of the regular occurrence of Fusarium and the
exceptional ability of F. oxysporum to de¯uorinate 1080,
fungi are probably the most important de¯uorinators of
1080 in central Australian soils. However, de¯uorinating
activity seems to be dependent upon both the type and
number of microorganisms present (Table 1).
The presence of numerous species of microorganisms,
some with considerable ability to detoxify 1080, suggests
that the half-life of 1080 in soils in many arid regions may
be less than 40 d, particularly after signi®cant rainfall
events. However, this will depend upon the species of
microorganisms present, their abundance, their ability to
de¯uorinate 1080, and the soil moisture conditions. 1080
can bind to cellulose (Hilton et al., 1969), and is readily
leached through the soil pro®le (Par®t et al., 1994), thus
pest control operations which utilise 1080 are extremely
unlikely to result in any long term environmental contamination. 1080 is also readily degraded in waterways (Par®t et
al., 1994; Twigg et al., 1996). The 1080-baits used in pest
control operations can contain up to 6 mg bait 21 (or
approximately 25 mg 1080 g 21). This amount is well within
the observed de¯uorinating ability of the soil micro¯ora in
Australia and New Zealand (Wong et al., 1991,1992; Par®t
et al., 1994; our study). Furthermore, baits containing these
high concentrations are usually well spaced (.200 m apart),
which also helps with biosafety. Pseudomonas spp. and F.
oxysporum are also capable of degrading factory waste
products containing 1080 (Kirkpatrick, 1999). The bacteria,
P. cepacia has been isolated from the seed of ¯uoroacetateproducing plants in South Africa, and this bacteria is
capable of substantial de¯uorination of 1080 (Meyer,
1994). Consequently, both the target speci®city and rapid
biodegradation of 1080, ensure that 1080 can be safely used
in pest control programs in most areas of Australia and New
Zealand. Despite this, some caution is required in arid
Australia because dried meat baits (6 mg 1080 bait 21) can
remain toxic for over 12 months (Twigg et al., 2000).

233

Acknowledgements
We thank Dennis Matthews, Steve Eldridge, Lester
Burgess and Win Kirkpatrick for their advice and help
with parts of this project. Ian Arthur, and Max AravenaRoman helped identify the bacteria. Dennis King and
Glenn Edwards commented on earlier drafts.

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