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Creature Companion 2019; April: 44-45.
Anton C. Beynen
Arsenic in petfood
Online commentaries on detection of arsenic in pet and baby foods (cf. 1-6) probably stirred up
concern among some pet parents, especially when they know arsenic as poison used in older
detective stories. Arsenic is not intentionally added to petfood, but the pervasive earth element is
intrinsic to many ingredients. Possibly, arsenic is an essential nutrient for dogs and cats, albeit in
tiny amounts. Arsenic, often referred to as heavy metal, is toxic only in high quantities, but with its
chemical form as a co-definer.
European legislation has set upper limits for arsenic in complete food for dogs and cats (7). The
maximum is 2.3 mg total arsenic per kg canned or kibbled food when completely dried. However,
the maximum is 11.4 mg when the food contains (derivatives of) fish and/or seaweed. That higher
maximum unifies practical and health considerations (8): the two aquatic products are relatively
rich in arsenic, but in a form of low toxicity.
Chemical analysis of total arsenic in complete petfoods indicates typical compliance with European
legislation. Absorbed arsenic compounds are converted by the dog’s liver and/or kidneys and then
excreted with urine. Research data show that long-term intake of up to 20 mg total arsenic per kg
dry weight of food is not toxic for dogs. Thus, commercial dog foods are generally safe with regard
to their levels of total arsenic. In cats, the maximum tolerated dose of dietary arsenic is unknown.
Accidental ingestion of products containing a toxic amount of arsenic can cause acute poisoning in
dogs and cats. Such products used to be herbicides, insecticides and wood preservatives (9, 10), but
today ant and roach baits are major culprits (11, 12). Symptoms are vomiting, salivation,
abdominal pain, staggering gait and diarrhea. Affected pets should be taken to a veterinary
Concentrations of total arsenic (As) in dry and wet petfoods are mostly lower than 2.3 mg/kg dietary
dry matter (ddm) (13-19, Notes 1 and 2). Higher values are only found in foods containing fish
derivatives (8, 13, 18, 20, Note 3). Percent inclusion of fish and As in food were positively related
(20). Total As in fish-based dog and cat foods normally is well below 11.4 mg/kg ddm (8, 13, 18, 20),
but a higher level is sometimes found (8, 20). Thus, the European allowable limits are usually not
As is ubiquitous and thus may be found at detectable amounts in petfood ingredients. Moreover,
marine fish, seaweed and rice concentrate As from the environment. Fish meal and oil, hijiki
seaweed and rice may have total As contents of up to 20 and 14 (21), 34 (22) and 2 (23) mg/kg dry
weight. In finfish, As mainly occurs as arsenobetaine, whereas fatty fish and seaweed contain
arsenolipids (21, 24) and arsenosugars (22). Rice contains inorganic As, but speciation is variable
Three hours after a single oral dose of 74As as arsenic acid (H3AsO4), about 90% of the radioactivity
was present in dog’s blood (26), pointing to high absorption. In contrast, dogs poorly absorbed As
from arsenate bound to bog ore (27). Dogs excrete negligible amounts of As into bile (28). However,
the canine kidney reduces arsenate to arsenite for excretion (29, 30) and also excretes As as
dimethylarsinic acid (DMA) (26, 30-32).
As ingested in the form of arsenate or arsenic sulfide is converted into DMA by dogs (26, 30-32).
Biomethylation of inorganic As, which takes place in the dog’s liver (33), appears unreported for
cats. Interestingly, arsenic oxide was highly toxic for a feline kidney cell line, but DMA was not (34).
The results of five toxicity studies (35-39, Note 4), indicate that long-term intake of 20 mg total As/kg
ddm is not toxic in dogs. Inorganic As sources were tested, except for one study (36). The highest,
analysed value reported for commercial petfood was 18.9 mg/kg ddm, which concerned a fish-
based, wet food (20). Two-year toxicity studies in dogs (36, 37, 39) did not mention cancer
development. Toxicity feeding studies in cats are lacking. Intravenous administration of arsenic
trioxide, as uncorrected equivalent of 26 mg As/kg ddm for 6 days, was toxic in cats (40).
Toxicity of trivalent arsenicals, such as arsenite, relates to their reaction with thiol-containing
molecules. In dogs, administration of lipoic acid, a dithiol and co-factor of various enzymes,
prevented arsenite toxicity (41). Harm by pentavalent arsenate may result from replacing phosphate
in biochemical reactions. In rats, dietary inorganic phosphate partly counteracted arsenate toxicity
Oral toxicity of arsenicals in descending order, on the basis of acute LD50 values in rodents, is as
follows: arsenite, arsenate, DMA, arsenobetaine (43). Arsenobetaine is non-toxic due to readily
excretion in the urine intact. Arsenolipids and arsenosugars may be metabolized into di-methylated
arsenicals that could exert toxic effects (44, 45). Canine and feline metabolism and toxicity of those
dietary, organic arsenic forms are unknown.
Dogs that ingested sodium arsenite for four months, at three intake levels including zero, showed
dose-dependent As concentrations in urine, liver and hair (46). Urine may be an indicator of recent
dietary As exposure, whereas hair reflects the longer term. Hair As was very high in dogs from an
area with As-rich groundwater (47, 48). Liver As did not differ between dogs from rural and urban
Total arsenic in complete dog foods (mg/kg dietary dry matter)
Total arsenic in complete cat foods (mg/kg dietary dry matter)
Ref, Year = reference and year of publication; nr = not reported; *Dry and wet foods were assumed
to contain 90 and 20% dry matter; = results are expressed as mg arsenic/Mcal metabolizable energy;
it is assumed here that 1 Mcal equals 0.251 kg dietary dry matter; $ presumably complete foods; +
identical samples; ^middle of range; # mean of medians for three food groups each comprising 17
Analysis: a, samples were subjected to dry ashing, distillation of arsine and determination using the
silver diethyldithiocarbamate spectrophotometric method; b, food samples were ground in a
cryogenic freezer mill (dry samples) or blender (wet samples), digested with concentrated nitric acid,
and analyzed for arsenic by inductively coupled plasma-mass spectrometry (ICP-MS); c, instrumental
neutron activation analysis; d, microwave-assisted nitric acid digestion and ICP-MS
Other studies than those given in the table above also report arsenic levels in petfood, but they do
so without classifying the values according to nutritional completeness, moisture content and target
species. The Clean Label Project (50) reports arsenic values for 1,084 pet products from 80 brands,
but only disclosed the average values for dry dog and cat foods (17) as presented by the table above.
In addition, the average amounts for a certain brand were presented, which amounted to 1.18 (n= 3)
and 0.93 (n= 10) mg/kg ddm for dry cat and dog foods (17). A manufacturer reported the average
arsenic content of its dry foods, which was found to be 0.43 mg/kg ddm; further details are not
provided (51). The Alltech Heavy Metal Survey (52) includes petfood that is not specified while the
analysed arsenic concentrations are not given separately.
Squadrone et al. (8) have analysed arsenic in food samples during the period of 2007-2012. Arsenic
was quantified by using a wet digestion method and electro thermal atomic absorption. There were
133 samples of complete and 67 samples of complementary dog and cat foods, presumably dry
foods. The totals of fish-and meat-based products were 137 and 63. Only foods containing fish or
fish derivatives had detectable amounts of total arsenic. The mean, lowest and highest arsenic
concentrations were 2.05, 0.86 and 12.50 mg/kg food.
As mentioned, the paper by Squadrone et al. (8) clearly shows that fish-based foods are associated
with higher contents of total arsenic. The same observation was reported by Furr et al. (13) in 1976.
Two, more recent studies (18, 20) also indicate that fish is a major arsenic source.
Kim et al. (18) classified dry dog foods as fish, red meat (beef, pork, venison, bison) or poultry
(chicken, turkey, duck) based. There were 17 products from each category. The mean arsenic
contents were 0.15, 0.22 and 1.37 mg/kg ddm for the meat-, poultry- and fish-based foods. The
table above provides further information on the study.
Davies et al. (20) analysed total arsenic by ICP-MS in 113 complete cat foods (wet, n = 48; dry, n =
65) and 64 complete dog foods (wet, n = 49; dry, n = 15). The highest values were found in foods
with fish as main declared ingredient. For dry foods, the mean and highest values were 0.85 and 4.46
mg/kg ddm, while for wet foods these values were 3.15 and 18.85 mg. There was a positive
association between percentage fish and arsenic in food. Assessment of the percent of fish
derivatives in the foods is not described. Dry and wet foods without fish generally contained less
than 0.5 mg arsenic/kg ddm.
Overview of controlled experiments on arsenic intake and toxicity in dogs
mg As/kg dietary dry matter
Arsenic trioxide, As
0, 30, 119
Sodium arsenite, NaAsO
0, 6, 28, 56
Sodium arsenate, Na
0, 6, 28,
Sodium arsenite, NaAsO
85, 170, 340
1n = number of dogs per treatment; 2It was assumed that dry foods contained 90% dry matter
33-nitro-4-hydroxyphenyl arsonic acid: roxarsone, which has been used as growth enhancer and
coccidiostat in poultry; 4body weight was reduced; the dogs started with 64 mg As/kg ddm, which
caused loss of condition; after four weeks, the dogs were fed the unsupplemented diet and after
another four weeks they received an As level of 32 mg/kg ddm through the remainder of the two-
year testing period; 5all six dogs lost much weight and died; 6one of six dog lost weight and died;
7assumed dry food intake was 15 g/kg body weight per day; 8until day 59 of the experiment, half of
the dosages were fed; from days 59 to 183, the indicated dosages were fed; body weight was
unaffected by arsenic, but serum aspartate aminotransferase and alanine aminotransferase were
elevated in the two highest and all dose groups, respectively; 9dogs showed evidence of
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