PLoS One. 2015; 10(9): e0139191.
Published online 2015 Sep 29. doi: 10.1371/journal.pone.0139191
PMCID: PMC4587841
Pieter Spanoghe, Editor
1Julius Kühn Institute,
Federal Research Centre for Cultivated Plants, Institute for Plant
Protection in Horticulture and Forests, Vertebrate Research, Münster,
North Rhine-Westphalia, Germany
2University of Münster, Institute of Landscape Ecology, Münster, North Rhine-Westphalia, Germany
3Julius
Kühn Institute, Federal Research Centre for Cultivated Plants,
Institute for Ecological Chemistry, Plant Analysis and Stored Product
Protection, Berlin, Germany
4Food
and Veterinary Institute Braunschweig/Hannover, Lower Saxony State
Office for Consumer Protection and Food Safety, Hannover, Lower Saxony,
Germany
Ghent University, BELGIUM
Competing Interests: The authors have declared that no competing interests exist.
Conceived
and designed the experiments: AG AE JJ. Analyzed the data: AG.
Contributed reagents/materials/analysis tools: AG DS BK SK. Wrote the
paper: AG AE JJ DS.
Abstract
Anticoagulant
rodenticides (ARs) are commonly used to control rodent infestations for
biocidal and plant protection purposes. This can lead to AR exposure of
non-target small mammals and their predators, which is known from
several regions of the world. However, drivers of exposure variation are
usually not known. To identify environmental drivers of AR exposure in
non-targets we analyzed 331 liver samples of red foxes (Vulpes vulpes)
for residues of eight ARs and used local parameters (percentage of
urban area and livestock density) to test for associations to residue
occurrence. 59.8% of samples collected across Germany contained at least
one rodenticide, in 20.2% of cases at levels at which biological
effects are suspected. Second generation anticoagulants (mainly
brodifacoum and bromadiolone) occurred more often than first generation
anticoagulants. Local livestock density and the percentage of urban area
were good indicators for AR residue occurrence. There was a positive
association between pooled ARs and brodifacoum occurrence with livestock
density as well as of pooled ARs, brodifacoum and difenacoum occurrence
with the percentage of urban area on administrative district level. Pig
holding drove associations of livestock density to AR residue
occurrence in foxes. Therefore, risk mitigation strategies should focus
on areas of high pig density and on highly urbanized areas to minimize
non-target risk.
Introduction
Commensal rodent populations are mainly regulated by anticoagulant rodenticides (ARs) [1]
in plant protection as well as for the protection of hygiene,
environmental health and to prevent damage to stored food and materials.
ARs inhibit the blood clotting of all vertebrates [2,3],
which causes a risk for non-target animals to ARs. Direct bait intake
by non-target animals results in primary poisoning, which has been shown
for several non-target rodent and shrew species [4–6], whereas secondary poisoning happens when predators ingest poisoned prey [7]. A reduction of red fox (Vulpes vulpes) population density has been shown in France after bromadiolone applications in open areas against water voles (Arvicola terrestris) [8,9]. In Canada, fox density was significantly lower in areas where ARs were used to control Richardson’s ground squirrels (Spermophilus richardsonii) than in control areas [10].
Such decreases of predator densities can be due to poisoning (primary
or secondary) of predators or to poisoning of prey or a combination
thereof.
Liver samples of carcasses are often used to
screen for AR poisoning in wildlife because AR active substances
accumulate in animal tissue—mainly in the liver [11], whereas plasma retention times are considerably shorter [12].
Worldwide, many studies investigated diurnal birds of prey and owls to
assess secondary non target exposure to ARs (e.g. Scotland [13], Great Britain [14], USA [15], Canada [16], Spain [17], New Zealand [18], France [19]). Common buzzards (Buteo buteo) [20,21], red kites (Milvus milvus) [13,19,21] and barn owls (Tyto alba) [22,23] are regularly exposed to ARs and mainly prey on small mammals [24,25]. Wildlife poisoning or exposure to ARs has also been shown in terrestrial predators like polecats (Mustela putorius) [26], stoats (Mustela erminea) and weasels (Mustela nivalis) [27,28].
AR residues had been quantified in feces of red foxes [29] and liver samples (e.g. France [20], USA [30,31], Spain [17]). Field application of ARs can be a source of secondary poisoning in predators [20]. An association of AR exposure to urban area has been shown in bobcats (Lynx rufus) [32] and some predatory bird species in Spain [33]. Nevertheless, most studies monitored ARs in predator carcasses without consideration of environmental drivers of exposure.
Regulation
of rodenticide usage varies among countries. In Germany, only
difenacoum was authorized in plant protection products during the period
in which foxes were collected for the present study, but only for use
in and around buildings to protect stored products, whereas eight ARs
(see below) were authorized for biocidal use. Therefore, exposure of
predators to ARs via field application for plant protection should not
have occurred. Three registered substances are first generation ARs
(FGARs: chlorophacinone, coumatetralyl and warfarine) and five are
second generation ARs (SGARs: brodifacoum, bromadiolone, difenacoum,
difethialone and flocoumafen). SGARs have a higher toxicity to
vertebrates and persist longer in tissues than FGARs [18,34].
This could lead to an enhanced risk of secondary poisoning for
predators from SGAR, which has been demonstrated for several species [18,35].
ARs are used as biocides in and around buildings at farms when rodents
occur, to prevent contact to livestock, animal food and stored products.
In urban areas Norway rats (Rattus norvegicus) are often controlled in sewage systems. Furthermore, Norway rat and house mice (M. musculus)
infestations can be found for instance in all sectors of the food
industry (including restaurants and supermarkets), living quarters and
public parks.
Red foxes are carnivores with a wide distribution [36]. They inhabit urban environments [37,38] as well as farmlands [37,39]. In farmland areas red foxes mainly prey on small mammals and birds [39,40]. When animal food is stored on the ground it is easily accessible to rodents [41],
suggesting more intense AR usage on farms with many open food
resources. The diet of urban foxes is dominated by scavenged meat, but
commensal rodents are hunted as well [42].
Therefore, red foxes could be at risk to ingest poisoned prey during
rodent baiting with ARs in urban and rural situations and seem a
suitable study species for analyzing the effect of environmental drivers
(i.e. urban area and livestock) of exposure of predators to ARs.
The
aim of our study was to identify factors that influence the exposure of
foxes to ARs. We analyzed residue occurrence of ARs in fox liver
samples in relation to the intensity of livestock holding and the
percentage of urban area. We hypothesized that increased livestock
density and increased urban area result in higher AR usage, due to
increased rodent manifestations and common AR application resulting in
high exposure of foxes to ARs. Furthermore we expected livestock species
that are kept in indoor feedlots on a farm to be more associated with
increased AR application than species kept outdoors. Information about
environmental factors that are associated with FGAR and SGAR exposure in
predators can aid optimizing risk assessment and developing risk
mitigation strategies.
Materials and Methods
Sample sources
Liver
samples from 331 red foxes derived from 35 administrative districts
were mainly provided by veterinary institutes of the German federal
states Brandenburg, Baden-Wuerttemberg, Lower Saxony and North
Rhine-Westphalia in 2012 and 2013. 301 foxes were individuals found dead
or shot in the states’ rabies monitoring scheme. An additional 30 foxes
originated from the Warendorf district (North Rhine-Westphalia) were
provided by a taxidermist. These foxes were dissected at Julius Kühn
Institute. No information was available on age or sex of foxes. For
pathogen disinfection (e.g. Echinococcus multilocularis) liver
samples were frozen for at least one week at -80°C and stored afterwards
at -20°C. Samples (N = 303) from districts (N = 14) that provided at
least 5 liver samples (Fig 1) were used to determine associations between AR residue occurrence and local parameters of the districts.
Anticoagulant rodenticide residue analysis
The analysis of liver samples is described in detail by Geduhn et al. [5].
Shortly summarized, subsamples of about 1.5 g liver were taken from
defrosted liver samples and spiked with a surrogate mixture and
homogenized into an ice bath with methanol/water. Interfering substances
were removed by solid supported liquid extraction on a diatomaceous
earth column. The quantification of the eight ARs (brodifacoum,
bromadiolone, chlorophacinone, coumatetralyl, difenacoum, difethialone,
flocoumafen and warfarin) were realised by LC-MS/MS in electrospray
ionization negative mode. The calibration standards including internal
standards (chlorophacinone-d4 and warfarin-d5) and surrogates (acenocoumarol, phenprocoumon, diphacinone-d4 and coumachlor; 0.1 to 100 ng/ml; r2
> 0.99) were solved in methanol:water (1:1). The limits of detection
with a signal to noise ratio of > 3:1 were between 0.001 μg/g for
coumatetralyl, 0.002 μg/g for warfarin, difenacoum, 0.003 μg/g for
brodifacoum, bromadiolone and 0.005 μg/g for difethialone, flocoumafen
and chlorophacinone. Spectra comparison between sample and references
based on Enhanced Product Ion-spectra was done additionally. Recovery
rates based on spiking clean turkey (Meleagris gallopavo) liver
(0.2 μg/g, N = 4) ± standard deviation were for chlorophacinone 83%
±14%, warfarin 118% ±4%, coumatetralyl 100% ±6%, difenacoum 78% ±7%,
bromadiolone 77% ±4%, brodifacoum 58% ±6%, flocoumafen 65% ±4% and
difethialone 41% ±7% and for the surrogate acenocoumarol 112% ±5%,
diphacinone-d4 106% ±9%, phenprocoumon 101% ±1% and
coumachlor 91% ±2%. Concentrations are μg AR active substance per g
liver wet weight throughout and were extrapolated to 100% based on
recovery rates in clean liver samples.
Data preparation and statistical analysis
To
compare the occurrence of FGARs and SGARs in fox liver samples, the
percentage of residue occurrence and the median concentration in
individuals that carried a residue for each active substance was
calculated (Table 1).
Two sided Welch t-tests were used to test for differences in occurrence
and concentrations of ARs between FGAR and SGAR because values were
normally distributed but variances and sample sizes were unequal.
Residue concentrations were classed in five groups (0, >0<0.2,
≥0.2<0.8, ≥0.8<2.0, ≥2.0 μg/g) according to biological effects
from concentrations that are known from the literature [20,29] and are discussed.
Livestock parameters and the percentage of urban area were obtained from GENESIS-online-database [43]. Livestock units (1 livestock unit = 500 kg body weight) from a survey in 2010 [43]
were used to calculate livestock density as livestock units per area
(100 ha) for each relevant district. Data were pooled for all livestock
larger than chickens in one model. Furthermore, the number of livestock
individuals per 100 ha for cattle, pigs and sheep (from a survey in
2010) and the number of laying hens per 100 ha (from a survey in 2007,
because no more recent data were available) were analyzed for
associations to residue occurrence of pooled ARs and brodifacoum.
The
first aim was to investigate if livestock density and the percentage of
urban area within German districts affect the occurrence of residues of
pooled ARs and the four most prevalent AR substances found in red foxes
(brodifacoum, bromadiolone, difenacoum and flocoumafen). We used
binomial linear mixed models to screen data for associations between AR
occurrence with livestock density and the percentage of urban area of 14
German districts (shaded in Fig 1)
with one model per AR substance and one where we pooled all ARs. There
were at least 5 liver samples from red foxes per district. The depending
variable was a combined vector of the number of foxes that contained
and did not contain residues (cbind function) per German district (N =
14). We added the federal state as random factor in both models
(presence/absence of AR ~ livestock density + urban area + (1|federal
state)). For modeling we used the lme4 package [44].
The variance inflation factor (VIF) was calculated using the vif.mer
function for the fixed factors of each model, but no multi-collinearity
occurred between livestock density and urban area in any model
(VIF<3, referring to [45]).
As
livestock density was associated to the residue occurrence of pooled
ARs and of brodifacoum, the second aim was to test if specific livestock
species drive these associations. Therefore, we designed two models
containing cattle, pig, sheep and laying hen density as explanatory
variables and pooled ARs and brodifacoum residue occurrence (combined
counts of AR positive and negative individuals per district) as
depending variable. The variable with the highest VIF (at least >3)
was excluded from the model. VIFs of factors from adapted models were
all <3. The final model was selected stepwise by AIC (Akaike
information criterion) comparison and resulted in: 1) presence/absence
of pooled ARs ~ pig density + (1|federal state) and 2) presence/absence
of brodifacoum ~ pig density + (1|federal state).
All
covariates were standardized before modeling by subtracting the mean
and dividing by the standard deviation to reduce associations between
parameter estimates. R² values are not provided by lme4. We calculated
pseudo r-square values from linear regression of observed vs. predicted
values to derive power of the mixed models. All statistical analyses
were conducted with R 3.1.3 [46]. Level for significance was p≤0.05.
Results
AR residues in fox liver on animal level
198
of 331 liver samples (59.8%) from red foxes contained residues of at
least one AR. 128 samples (38.7%) contained more than one active
substance, 70 samples (21.1%) contained two active substances, 44 three
(13.3%), 6 four (1.8%), 7 five (2.1%) and one sample (0.3%) contained
six different AR active substances. Chlorophacinone was detected only
once (0.3%) while 151 individuals (45.6%) contained residues of
brodifacoum (Table 1).
Median values of residue concentrations of AR positive samples varied
between 0.010 μg/g for warfarin and 0.091 μg/g of brodifacoum (Table 1).
Brodifacoum
and bromadiolone residues were found most often and residue
concentrations were highest for these active substances (Table 1 and Fig 2).
Two individuals contained brodifacoum residue concentrations >2.0
μg/g, whereas all active substances occurred as least once with a
concentration >0.2 μg/g except chlorophacinone and warfarin. Residue
concentrations >0.2μg/g occurred in 51 samples (15.4%) containing
brodifacoum and in 25 samples (7.6%) containing bromadiolone. Residues
>0.8 μg/g (including concentrations >2.0 μg/g) almost exclusively
occurred in samples with brodifacoum (N = 12; 3.6%) or bromadiolone (N =
10; 3.0%) residues (Fig 2).
Residues of flocoumafen and difenacoum rarely occurred in all
concentration classes and only sporadically at concentrations >0.2
μg/g (Fig 2).
SGARs
(brodifacoum, bromadiolone, difenacoum, difethialone, flocoumafen)
residues occurred more often than FGARs (chlorophacinone, coumatetralyl
and warfarin) (Table 1, Fig 3 (left); N FGARs = 3, N SGARs = 5, t = -2.67, p = 0.05). Median concentrations were lower in FGARs than in SGARs (Fig 3 (right): median: N FGARs = 3, N SGARs = 5, t = -3.82, p = 0.011).
Spatial distribution of AR residues
The occurrence of AR residues was determined in 14 German districts (Table 2, Fig 1).
Residue occurrence of brodifacoum varied from 13 to 100% and was the
lowest in districts of the federal state Baden-Wuerttemberg (mean: 34%)
and the highest in North Rhine-Westphalia (mean: 79%) compared to all
other federal states. Occurrence of bromadiolone residues varied between
0 and 80% and was the lowest again in districts of Baden-Wuerttemberg
(mean: 16%) and the highest in North Rhine-Westphalia (mean: 52%).
Median concentration of brodifacoum was remarkably high in the district
of Minden-Luebbecke and low in the Rhein-Neckar district, whereas the
concentration of bromadiolone was the highest in Rhein-Neckar (Table 2) compared to all other districts.
Effects of local parameters on AR residue occurrence
Livestock
density was positively associated with the occurrence of pooled ARs and
the occurrence of brodifacoum in the 14 districts (Table 3, Fig 4).
AR occurrence ranged from 79 to 100% in samples from districts with a
livestock density above 0.45, whereas below 0.45 AR occurrence varied
between 17 and 86% but mostly between 40 and 65% (Fig 4).
Brodifacoum occurrence in foxes from districts with livestock densities
above 0.45 varied from 55 to 100% whereas below that threshold
brodifacoum occurred in 13 to 76% of samples per district (Fig 4).
The percentage of urban area was positively associated with pooled ARs, brodifacoum and difenacoum occurrence (Table 3, Fig 4).
In districts with urban areas <13%, AR residues occurred in 17 to
83% of samples, whereas AR residue occurrence varied from 71 to 100% in
samples from districts with urban area >13% (Fig 4).
In
a second step, density (No. individuals per area) of cattle, pig, sheep
and laying hens were tested for associations with pooled AR residues
and brodifacoum. Cattle density was highly collinear to other livestock
density (verified by the variance inflation factors VIF >3) in both
models and was therefore excluded from the analysis. Pig density was
positively associated to residue occurrence of pooled ARs and
brodifacoum residues (Table 3). Sheep and laying hen densities were excluded by model simplification through AIC.
Discussion
Our
large-scale study provides clear evidence for AR exposure in red foxes
across Germany. Residues of brodifacoum and bromadiolone were most
common and at the highest concentration. ARs occurred in foxes from all
German districts; therefore, wildlife contamination with ARs is not a
local problem. All ARs authorized in the EU/Germany for use in either
biocidal products or plant protection products could be found in at
least one liver sample. Residues of SGARs were considerably more common
than those of FGARs and were detected at higher residue concentrations.
Accumulation could explain those differences because SGARs have a remarkably longer persistence in animal tissues than FGARs [12].
Another possible explanation is a more common usage of SGARs than
FGARs, which is indicated by the fact, that more SGAR than FGAR products
(425 versus 82) are authorized in Germany [47]. Resistance to FGARs [48–50]
has led to the development and use of SGARs. For example SGARs are
known to be applied much more frequently than FGARs in Scotland [13].
In a farmer survey in the Münsterland (Germany), brodifacoum was the
active substance used most often for biocidal rodent management [5],
most likely due to the fact that resistances against FGARS as well as
some SGARS have been reported for this region. Additionally, brodifacoum
is a rodenticide active substance with a long persistence in liver
tissue [34]
resulting in a longer time window when residues can be detected. This
could explain the highest occurrence and concentration of brodifacoum
residues in foxes in the present study. The rare occurrence of FGARs in
fox liver samples (5.4% of all residues) suggests that these active
substances do not play an important role in secondary poisoning with ARs
in red foxes in Germany. In contrast, the occurrence of SGARs (94.6% of
all residues) indicates high exposure of predators and increased risk
of poisoning due to high toxicity and persistence.
AR
usage is common at livestock farms, because often livestock food is
easily accessible to commensal rodents and there are plentiful places to
hide and rest [51], resulting in high population densities of rodents. Red foxes in farmland mainly prey on rodents [39]
and are therefore at risk of secondary poisoning in these areas, which
could explain the positive association between AR and brodifacoum
residue occurrence and livestock density we found. The results show a
clear association of livestock density and AR residues in foxes
suggesting pronounced AR usage associated with livestock production. The
latter seems plausible but cannot be confirmed because no detailed data
are available about AR application in animal husbandry. There are
almost no publications that investigate the effect of local parameters
such as landscape and land use on residues of ARs in red foxes, except
Tosh et al. [52],
who demonstrated higher exposure of red foxes to ARs in lowlands than
in “less favourable areas” suggesting more intense AR application in
agriculturally used lowlands.
Pig density was
positively associated with AR and brodifacoum residue occurrence whereas
sheep density and laying hen density were not associated to pooled AR
or brodifacoum occurrence. In Germany management of commensal rodents is
mandatory in pig husbandry [53]
but not in cattle, laying hen or sheep holding, suggesting more intense
AR usage on pig farms. This is in line with the positive associations
of pig density and residue occurrence. Nevertheless, rats regularly
occur on cattle farms as well, because of easy access to food and nest
sites. Density of cattle was collinear to other livestock species and
was removed from both models (pooled AR and brodifacoum) before model
selection by AIC. Therefore, cattle density could also explain the
association of pig density and residue occurrence of pooled ARs and
brodifacoum. In contrast to cattle and pigs that are often kept indoors
in feedlots sheep are commonly kept free-range on pastures. AR
application in sheep husbandry therefore could be less common, because
the application of biocidal ARs is often restricted to the use in and
around buildings and less food is available for commensal rodents on
pastures. This is reflected in the lack of an association between sheep
livestock density and AR occurrence. Chicken holding was also expected
to represent a source of ARs, but no association was found for laying
hens. The lack of an association may be due to the restriction of the
available data to laying hens, which represent only a subset of chicken
holding.
Beside agricultural usage of ARs they are
regularly applied in urban areas to control commensal rodents. Commensal
rodents occur in a wide range of habitats in urban areas such as sewage
systems, waste dumps, in parks and gardens, within the food industry
(supermarkets, bakeries, restaurants etc.) and in apartment buildings
and houses, where waste and food is accessible to rodents [54,55].
Our results suggest a risk for foxes to ingest ARs in these areas.
Pooled ARs, brodifacoum and difenacoum residue occurrence in German
districts associated positively with the percentage of urban area. The
diet of red foxes in urban and periurban areas of Zurich consists of 11%
rodents and 10% of them are commensal rodents [42],
which could explain the uptake of ARs by urban foxes. In Eastern
Germany urban foxes mainly prey on waste, but commensal rodents are
taken also and in higher frequencies than in rural areas, where Microtus species are the predominant rodent taxa [37].
Brodifacoum and difenacoum were the main ARs detected in foxes in urban
areas, which is similar to results observed in bobcats in California [32] and predatory birds in Spain [33].
The
high variation of AR occurrence among German districts suggests that
also other factors than livestock density and urbanization influence AR
distribution in predators. Further research is needed for a better
understanding of the pathways of AR exposure in predators.
In
other studies residues of ARs were found in red foxes, but active
substances and concentrations differ greatly. In the UK, France and
Spain bromadiolone residues are most commonly found in foxes but liver
concentrations vary extremely [17,20,52].
Bromadiolone concentrations we found (median: 0.061 μg/g and a range
from 0.0004 to 1.574 μg/g) were remarkably lower than those in France
(0.800 to 6.900 μg/g [20]), but similar to those found in the UK (0.004 to 1.781 μg/g [52]) and Spain (mean 0.155 μg/g [17]). High concentrations found in France could result from extensive field usage there [20], which is prohibited in Germany. Brodifacoum residues occur less often than bromadiolone residues in Spain and the UK [17,52], whereas brodifacoum residues occurred in all of 5 red fox samples in the US [22,56]. Brodifacoum concentrations in the present study were higher than those found in the UK (0.003 to 0.654 μg/g [52])
suggesting higher risk for predators in the German environment.
However, the comparative assessment of results among studies concerning
secondary poisoning of non-target predators is difficult due to
different usage patterns of AR, local situations and AR residue analysis
methods. Furthermore, residues in our study were corrected for recovery
rates, making concentrations comparable between active substances but
this was not done in all previous studies (e.g. [17], [52]).
If residue concentrations of brodifacoum are not corrected for recovery
rates, our findings are similar to those reported by Tosh et al. [52].
Nevertheless, residue concentrations may provide rough information on biological effects in non-target animals. Sage et al. [29]
found liver residues of about 2.0 μg/g in red foxes 24 to 26 days after
feeding them with bromadiolone poisoned rodents. Two out of four foxes
were suspected to have died without an injection of the antidote vitamin
k. Concentrations of bromadiolone in livers of red fox carcasses in
France ranged from 0.8 to 6.9 μg/g in individuals with clinically
confirmed poisoning signs, but a threshold of 0.2 μg/g was suspected for
biological effects [20].
We found 7.6% red foxes containing bromadiolone concentrations ≥0.2
μg/g and 3.0% carried bromadiolone residues ≥0.8 μg/g suspecting
toxicological effects for these individuals. No fox had bromadiolone
residues above 2.0 μg/g. To our knowledge there are no studies
concerning biologic effects of brodifacoum residues in fox livers.
Brodifacoum is more toxic to mammals than bromadiolone [30,57].
Therefore, using the thresholds for bromadiolone for brodifacoum should
underestimate effects. 15.4% of tested red foxes had brodifacoum
residues ≥0.2 μg/g, 3.6% at concentrations ≥0.8 μg/g and 0.6% at >2.0
μg/g. Therefore, biological effects of ARs were most likely through
brodifacoum, although we could not screen fox carcasses for
haemorrhaging to confirm this suggestion. 27.5% of foxes had pooled SGAR
residue concentrations above 0.2 μg/g, including 35 samples (10.6%)
with residues higher than 0.8 μg/g and 5 (1.5%) samples with even more
than 2.0 μg/g. Accumulation of different AR active substances could
enhance biological effects, but effects of interactions between
substances are unknown.
In total 20.2%
of samples contained a particular SGAR with a concentration higher than
0.2 μg/g. Residues of flocoumafen and difenacoum occurred considerably
less often than brodifacoum and bromadiolone and concentrations above
0.2 μg/g occurred in only 6 and 4 samples respectively, a concentration
>0.8 μg/g was measured once for flocoumafen. LD50 values of flocoumafen and difenacoum for house mice are between the values of brodifacoum and bromadiolone [12].
Therefore, biological effects on red foxes seem less common but
possible. Residue concentrations >0.2 μg/g were even rarer for all
other active substances and a concentration >0.8 μg/g of AR occurred
in only one sample (coumatetralyl), which demonstrates that the
biological relevance for non-target predators especially of brodifacoum
and bromadiolone is higher than the relevance of flocoumafen and
difenacoum. Concentrations of other AR substance were even lower. Based
on such low residue concentration and occurrence it is suggested that
there was low risk imposed on non-target predators by these ARs in the
system considered here.
Conclusion
Residues
of ARs such as brodifacoum and bromadiolone in red foxes are widespread
in Germany, which reflects the widespread use of these active
substances as biocidal rodenticides in Germany. Our study highlighted
that foxes carry residues of SGARs more frequently and in higher
concentrations than FGARs. Therefore, risk mitigation strategies should
consider especially SGARs when these compounds are used in the biocide
sector. The occurrence of AR residues associated positively with
livestock density in general and with that of pigs in particular,
indicating that ARs do not affect non-target terrestrial predators
similarly in all land use types. This is especially the case for the
highly persistent SGAR brodifacoum that is commonly used in animal
holding. Our results are consistent to the hypothesis that indoor
livestock feedlots are a source for AR exposure to non-target predators,
in our case mainly from pig (or cattle) production. As a conclusion,
risk mitigation strategies are needed for AR application in farmland. In
contrast to brodifacoum residues that were associated to livestock
density as well as to the percentage of urban area difenacoum residues
seemed mainly to originate from urban areas. 7.6% of red foxes in our
study may have been biologically affected by bromadiolone, based on the
results of Sage et al. [29] and Berny et al. [20]
and possibly even more by brodifacoum. More detailed information about
the relation of AR uptake and liver concentrations are required to make
precise assessments also for other AR substances. Research on risk
mitigation strategies should focus on application methods in areas with
high livestock density as well as on urban areas.
Supporting Information
S1 Table
Residues of anticoagulant rodenticides [μg/g] (recovery corrected) of 331 analyzed red fox (Vulpes vulpes) liver samples from administrative districts in Germany.
(PDF)
Click here for additional data file.(118K, pdf)
Acknowledgments
We
thank all veterinary institutes for providing fox liver samples.
Further thanks go to Ramazan Koç, Martina Hoffmann and Ina
Stachewicz-Voigt for residue analysis. We thank Doreen Gabriel for
statistical assistance and Erik Schmolz and Sarah Gerhardt for helpful
comments on the manuscript.
Funding Statement
This study was funded by the Federal Environment Agency (http://www.umweltbundesamt.de/en) within the Environment Research Plan of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (grant number 3710 63 401). The funders had no role in study design, data collection and analysis, or decision to publish. An employee of the Federal Environment Agency provided comments and authorised the manuscript.Data Availability
Local parameters on German administrative district level are available from "The Regional Database Germany" (https://www.regionalstatistik.de/genesis/online). Data of the rodenticide residue analysis are provided in the Supporting Information file.
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