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Description of key information

Read across approach

In the absence of substance-specific data, the repeated dose toxicity of diarsenic trioxide is assessed based on reviews and/or data for inorganic arsenic compounds.

Diarsenic trioxide is readily soluble in water (17.8 g/L at 20°C). Upon dissolution in water, it reacts acidically to trivalent arsenite ions which are not subject to any relevant degree of oxidation for up to 72 hours (Klawonn, 2010). Read-across from toxicological data on inorganic arsenites to diarsenic trioxide is justified without restrictions. However, it is also known that in the human body, inorganic arsenic compounds are converted apart from As(III) also to As(V). Upon becoming systemically available, As(V) is rapidly partly converted to As(III). As(III) species are considered to be more toxic and bioactive than As(V) species. The difference in toxicological potency between As(III) and As(V) cannot be quantified exactly and may vary between routes of exposure and/or type of toxicological effects. Generally, risk assessments are conducted for "inorganic arsenic compounds" as a group, and do not differentiate between various species. Following a conservative approach, the toxicity of diarsenic trioxide is therefore considered to be determined by the release of soluble inorganic species (trivalent arsenites and pentavalent arsenates) which do not differ substantially in potency and may be interconverted both in the environment and in the body. Consequently, it is justified to apply read across to soluble inorganic arsenic compounds to evaluate the systemic effects, including repeated dose toxicity, of diarsenic trioxide.

General remarks

A large number of investigations in animals and humans on the toxic effects of inorganic arsenic compounds following repeated exposure are available, and these have been reviewed on several occasions by renowned scientific organizations. Given the overwhelming volume of data, individual Robust Study Summaries (RSS) were not developed. Instead, an overview of available investigations is presented below.

When evaluating the results of the animal and human studies, it is important to remember that there are considerable differences in arsenic biotransformation between species and between individuals of a same species (see section on Toxicokinetics). Also, a number of aspects raise issues regarding the usefulness of some studies for quantifying, comparing and interpreting results, especially regarding relevance to humans and risk assessment. These include definition of the arsenic species analysed, concentrations/doses, types of cells, simulation of natural exposure for example (Cohen et al., 2013).

It is generally considered that trivalent arsenic compounds are more toxic than the pentavalent forms, at least at high doses. However, the difference is difficult to quantify since a conversion between trivalent and pentavalent arsenic can occur after the substance has entered the body (ATSDR, 2007).

Furthermore, exposure via the oral and inhalation routes is the most relevant for hazard and risk assessment of inorganic arsenic compounds. Dermal absorption is low (see section on Toxicokinetics), so that no significant systemic exposure is expected via this route.

The following paragraphs summarise the data available on the inhalation and oral toxicity of inorganic arsenic compounds. Data on humans is presented first, followed by studies conducted in animals.

Inhalation exposure

Effects in humans

Respiratory effects:

Workers exposed to arsenic dusts in air often experience irritation to the mucous membranes of the nose and throat, which may lead to laryngitis, bronchitis or rhinitis, and very high exposures characteristic of workplace exposures in the past can cause perforation of the nasal septum. However, there have been few systematic investigations of respiratory effects in humans exposed to arsenic. None are considered to be conclusive with regard to the relationship between inhaled inorganic arsenic and respiratory disease (ATSDR, 2007).

Cardiovascular effects:

There is some evidence from epidemiological studies that inhaled inorganic arsenic can produce effects on the cardiovascular system, but such effects resulting from oral exposure are better characterized (ATSDR, 2007).

Gastrointestinal effects:

Several case studies have reported nausea, vomiting and diarrhoea in workers with acute arsenic poisoning following occupational inhalation exposure. Such effects are a common feature of oral ingestion of high doses of arsenic but exposure levels have not been reliably estimated for any of these cases (ATSDR, 2007).

Neurological effects:

There is evidence from epidemiological studies that inhaled inorganic arsenic can produce neurological effects. Studies of workers at the ASARCO copper smelter (USA), a power station in Slovakia and the Ronnskar smelter (Sweden) demonstrated peripheral neurological effects in workers associated with arsenic trioxide exposure (ATSDR, 2007). However, the exposure levels were difficult to quantify.

Dermal effects:

Dermatitis has frequently been observed in industrial workers exposed to inorganic arsenic in the air, with the highest rates occurring in workers with the greatest arsenic exposure. However, limited quantitative information is available regarding the levels that produce such dermatitis and co-exposure to other substances in the workplace by the dermal route makes a dose-response analysis difficult. The highest arsenic exposures (0.384-0.034 mg As/m3) were associated with gross pigmentation, hyperkeratinisation and multiple warts. NOAEL values for dermal irritation have not been identified (ATSDR, 2007).

Other organ systems:

There is no reliable evidence in humans that inhaled inorganic arsenic produces effects on other important organ systems such as liver, kidneys or the haematological, immunological and musculoskeletal systems.

Effects in animals

Respiratory and gastrointestinal effects:

Respiratory symptoms such as rales (8 mg As/m3), laboured breathing and gasping (20 mg As/m3) were observed in a developmental study in rats with inhalation exposure to arsenic trioxide dust, with no symptoms at 2 mg As/m3. Since this sort of response is produced by a number of respirable particulate materials, it is likely that the inflammatory response was not specifically due to arsenic. Upon autopsy, some of the animals exposed to 20 mg As/m3 exhibited severe hyperaemia and plasma discharge into the intestinal lumen, whereas exposure to 8 mg As/m3 did not produce gross gastrointestinal lesions (Holson et al., 1999) (ATSDR, 2007).

Immunological effects:

Female mice exposed to arsenic trioxide aerosol for 3 hours showed a concentration-related decrease in pulmonary bactericidal activity, presumably as a result of injury to alveolar macrophages, and a corresponding concentration-related increase in susceptibility to introduced respiratory bacterial pathogens (Aranyi et al., 1985) (ATSDR, 2007).

Other organ systems:

There is no reliable evidence in animals that inhaled inorganic arsenic produces effects on other important organ systems such as liver, kidneys, skin or the haematological, immunological, cardiovascular and musculoskeletal systems (ATSDR, 2007).

Oral toxicity

Effects in humans

There is a large body of studies in humans and animals on the toxic effects of ingested arsenic. In humans, most cases result from accidental, suicidal, homicidal or medicinal ingestion of arsenic-containing powders or solutions, or from consumption of contaminated food and drinking water. In many cases, the exact chemical form of arsenic is not known; however, it is presumed that the most likely forms are either pentavalent arsenate, trivalent arsenite or a mixture of both.

Respiratory effects:

Bronchitis and sequelae (bronchiectasis, bronchopneumonia) have been observed in patients and at autopsy in some chronic poisoning cases (Guha Mazumder et al. 2005; Milton and Rahman, 2002; Rosenberg, 1974; Tsai, et al. 1999; Zaldívar, 1974; Zaldívar and Guillier, 1977). Bronchopneumonia secondary to arsenic-induced bronchitis was considered to be the cause of death in one young child after several years of exposure to an average dose of 0.08 mg As/kg/day (Zaldívar and Guillier 1977). Decrements in lung function, measured as decreased FEV1, FVC and FEF25–75 have also been reported in subjects exhibiting skin lesions exposed to 0.1–0.5 mg As/L in drinking water (von Ehrenstein et al., 2005). Although in general respiratory effects have not been widely associated with repeated oral ingestion of low arsenic doses, a few studies have reported minor respiratory symptoms, such as cough, sputum, rhinorrhoea and sore throat in people with repeated oral exposure to 0.03–0.05 mg As/kg/day (Ahmad et al., 1997; Mizuta et al., 1956) (ATSDR, 2007).

In a recent study, the respiratory effects of chronic low-level arsenic exposure from groundwater were evaluated in West Bengal, India, with the participants (834 non-smoking adult males) were subdivided in two groups: an arsenic-exposed group (n = 446, mean age 35.3 years) drinking arsenic-contaminated groundwater (11–50μg/L) and a control group of 388 age-matched men drinking water containing <10μg/L of arsenic. Arsenic in water samples was measured by atomic absorption spectroscopy. The prevalence of respiratory symptoms was documented via a structured, validated questionnaire. Pulmonary function test (PFT) was assessed by portable spirometer. Compared with controls, the arsenic-exposed subjects had a higher prevalence of upper and lower respiratory symptoms, dyspnoea, asthma, eye irritation and headache. Also, 20.6% of arsenic-exposed subjects had lung function deficits (predominantly restrictive and combined types) compared with 13.6% of control (p < 0.05). A positive association was observed between arsenic concentration in drinking water and the prevalence of respiratory symptoms, while a negative association existed between arsenic level and spirometric parameters. Based on the study results, the study author suggested that even low-level arsenic exposure has deleterious respiratory effects (Das et al., 2014).

To evaluate the chronic effects of arsenic poisoning due to consumption of contaminated groundwater, a non-randomized, controlled, cross-sectional, observational study was carried out in the Arsenic Clinic, Institute of Postgraduate Medical Education and Research, Kolkata, West Bengal, over a period of 1 year and 4 months. Seventy-three cases diagnosed clinically, consuming water containing arsenic ≥50μg/L and having arsenic levels in hair and nails >0.6μg/L, were included. Special investigations included routine parameters and organ-specific tests. Arsenic levels in drinking water, hair and nails were measured. Twenty-five non-smoking healthy controls were evaluated. Murshidabad and districts adjacent to Kolkata, West Bengal, were mostly affected. Middle-aged males were the main sufferers. Skin involvement was the most common manifestation (100%), followed by hepatomegaly [23 (31.5%)] with or without transaminitis [7 (9.58%)]/portal hypertension [9 (12.33%)]. Restrictive abnormality in spirometry [11 (15.06%)], bronchiectasis [4 (5.47%)], interstitial fibrosis [2 (2.73%)], bronchogenic carcinoma [2 (2.73%)], oromucosal plaque [7 (9.58%)], nail hypertrophy [10 (13.69%)], alopecia [8 (10.95%)], neuropathy [5 (6.84%)] and electrocardiography abnormalities [5 (6.84%)] were also observed. Based on the study results, the author concluded that mucocutaneous and nail lesions, hepatomegaly and restrictive change in spirometry were the common and significant findings in the study (Ghosh, 2013).

Cardiovascular effects:

A number of studies in humans indicate that arsenic ingestion may lead to serious effects on the cardiovascular system. Characteristic effects on the heart from both acute and long-term exposure include altered myocardial depolarization (prolonged QT interval, nonspecific ST segment changes) and cardiac arrhythmia (Cullen et al., 1995; Glazener et al., 1968; Goldsmith and From, 1986; Heyman et al., 1956; Little et al., 1990; Mizuta et al., 1956; Moore et al., 1994b; Mumford et al., 2007). A significant dose-related increase in the prevalence of cardiac electrophysiological abnormalities was observed in residents of Inner Mongolia, China; the incidences of QT prolongation were observed in 3.9, 11.1 and 20.6% of the residents with drinking water levels of <21, 110–300, and 430–690μg/L, respectively (Mumford et al., 2007). Long-term exposure to low to moderate arsenic levels was associated with cardiovascular disease and mortality in a population of American Indians men and women aged 47 to 74 in Arizona, Oklahoma and North/South Dakota (US) (Moon, 2013). Most dramatic is “Blackfoot Disease,” a condition that is endemic in an area of Taiwan where average drinking water levels of arsenic range from 0.17-0.80 ppm (Tseng, 1977), corresponding to doses of about 0.014–0.065 mg As/kg/day (IRIS, 2007). The disease is characterised by a progressive loss of circulation in the hands and feet, leading ultimately to necrosis and gangrene (Chen et al., 1988b; Ch’i and Blackwell, 1968; Tseng, 1977, 1989; Tseng et al., 1968, 1995, 1996). Despite other factors being suspected of playing a role in the etiology of this disease (Ko, 1986; Lu et al., 1990; Yu et al., 1984), the clear association between the occurrence of Blackfoot Disease and the intake of elevated arsenic levels indicates that arsenic is at least a contributing factor.

Arsenic exposure in Taiwan has also been associated with an increased incidence of cerebrovascular and microvascular diseases (Chiou et al., 1997; Wang et al., 2002, 2003) and ischemic heart disease (Chang et al., 2004; Chen et al., 1996; Hsueh et al., 1998b; Tsai et al., 1999; Tseng et al., 2003). Hypertension, defined as a systolic blood pressure of ≥140 mm Hg in combination with a diastolic blood pressure of ≥90 mm Hg, was associated with estimated lifetime doses of approximately 0.055 mg As/kg/day (0.25 mg/L in water) in a study of people in Bangladesh (Rahman et al., 1999), whereas no significant association was found with estimated doses of 0.018 mg As/kg/day (0.75 mg/L in water). Wang et al. (2003) found an increased incidence of microvascular and macrovascular disease among subjects in Taiwan living in an arseniasis-endemic area in which the water of artesian wells had arsenic concentrations >0.35 mg/L (estimated doses of >0.03 mg As/kg/day). An additional study of Taiwanese subjects reported a significant increase in incidence of hypertension associated with concentrations of arsenic in the water >0.7 mg/L (estimated doses of >0.06 mg As/kg/day) (Chen et al., 1995). Studies in Chile indicate that ingestion of 0.6–0.8 ppm arsenic in drinking water (corresponding to doses of 0.02-0.06 mg As/kg/day, depending on age) increases the incidence of Raynaud’s disease and of cyanosis of fingers and toes (Borgoño and Greiber, 1972; Zaldívar, 1974, 1977; Zaldívar and Guillier, 1977). Autopsy of five children from this region who died of apparent arsenic toxicity showed a marked thickening of small and medium sized arteries in tissues throughout the body, especially the heart (Rosenberg, 1974). In addition, cardiac failure, arterial hypotension, myocardial necrosis, and thrombosis have been observed in children who died from chronic arsenic ingestion (Zaldívar, 1974), as well as adults chronically exposed to arsenic (Dueñas et al., 1998). Likewise, thickening and vascular occlusion of blood vessels were noted in German vintners exposed to arsenical pesticides in wine and in adults who drank arsenic-contaminated drinking water (Roth 1957; Zaldívar and Guillier, 1977). A survey of Wisconsin residents using private wells for their drinking water found that residents exposed for at least 20 years to water concentrations of >10μg As/L had increased incidences of cardiac bypass surgery, high blood pressure, and circulatory problems as compared with residents exposed to lower arsenic concentrations (Zierold et al., 2004). Similarly, Lewis et al. (1999) reported increased mortality from hypertensive heart disease in both men and women among a cohort exposed to arsenic in their drinking water in Utah, as compared with the general population of Utah. Limitations in the study included lack of evaluation of smoking as a confounder and of other dietary sources of arsenic, and the lack of a dose-response for hypertensive heart disease. Another ecological study (Engel and Smith 1994) found significant increases in deaths from arteriosclerosis, aortic aneurysm, and all other diseases of the arteries, arterioles, and capillaries among U.S. residents with arsenic drinking waters of >20μg/L; the increase in deaths from congenital anomalies of the heart and other anomalies of the circulatory system also observed in this subpopulation limits the interpretation of the findings (ATSDR, 2007).

In a prospective cohort epidemiology study, the risk of young adult mortality due to high chronic exposure to arsenic through years of drinking arsenic-contaminated water was evaluated. 58,406 individuals of 4–18 years at baseline were enrolled and included using Matlab HDSS (Health and Demographic Surveillance System), an active surveillance system. Each individual’s arsenic exposure was calculated at (1) baseline As level as current exposure, (2) time-weighted lifetime exposure (average or lifetime average) and (3) cumulative arsenic exposure. Age, sex, educational attainment and SES were adjusted during the analysis. In this 13-year closed-cohort study (2003–2015), all young-adult deaths were captured through verbal autopsy using International Classification of Diseases (ICD-10) to define the causes. Girls had higher values of cumulative arsenic exposure via tube well water than boys (median: 1858.5 μg/year/L vs. 1798.8 μg/year/L) and higher mortality due to cancers, cardio-vascular disease and respiratory disease. There was a higher risk of death due to all cancers amongst young adults exposed to As > 138.7 µg/L compared to young adults exposed to As ≤ 1.1 μg/L. For cerebro-vascular disease, cardio-vascular disease and respiratory disease deaths, average arsenic in well water (>223.1 μg/L vs. ≤90.9 μg/L) and cumulative arsenic in well water (>2711.0 μg/year/L vs. ≤1013.3 μg/year/L) was linked to a 4.8 (1.8–12.8) and 5.1 (1.7–15.1) times higher risk of mortality than lower exposure. The study concluded that higher concentration of, and chronic exposure to, arsenic in drinking water, increased the mortality risk among the young adults, regardless of gender (Rahman et al., 2019).

Gastrointestinal effects:

Clinical signs such as gastrointestinal irritation, including nausea, vomiting, diarrhoea and abdominal pain are often observed in individuals with longer-term, low exposure to arsenic (e.g., Borgoño and Greiber, 1972; Cebrián et al., 1983; Franzblau and Lilis, 1989; Guha Mazumder et al., 1988, 1998a; Haupert et al. ,1996; Holland, 1904; Huang et al., 1985; Mizuta et al., 1956; Nagai et al., 1956; Silver and Wainman, 1952; Wagner et al., 1979; Zaldívar, 1974) but effects are usually not detectable at exposure levels below about 0.01 mg As/kg/day (Harrington et al., 1978; Valentine et al., 1985). These symptoms generally decline within a short time after exposure ceases. More severe symptoms (hematemesis, hemoperitoneum, gastrointestinal hemorrhage and necrosis) have been reported in individuals with long-term ingestion of 0.03–0.05 mg As/kg/day as a medicinal preparation (Lander et al., 1975; Morris et al., 1974) (ATSDR, 2007).

Haematological effects:

Anaemia and leukopenia are common effects of arsenic poisoning in humans and have been reported following intermediate (Franzblau and Lilis, 1989; Heyman et al., 1956; Nagai et al., 1956; Wagner et al., 1979) and chronic oral exposures (Chakraborti et al., 2003a; Glazener et al., 1968; Guha Mazumder et al., 1988; Hopenhayn et al., 2006; Kyle and Pease, 1965; Tay and Seah, 1975) at doses of 0.002 mg As/kg/day or more. These may be due to direct cytotoxic or haemolytic effect on blood cells (Armstrong et al., 1984; Fincher and Koerker, 1987; Goldsmith and From, 1986; Kyle and Pease, 1965; Lerman et al., 1980) and a suppression of erythropoiesis (Kyle and Pease, 1965; Lerman et al., 1980). However, haematological effects are not observed in all cases of arsenic exposure (EPA, 1981b; Harrington et al., 1978; Huang et al., 1985; Silver and Wainman, 1952) (ATSDR, 2007).

Hepatic effects:

A number of studies in humans exposed to inorganic arsenic by the oral route have noted signs or symptoms of hepatic injury. Clinical examination often revealed that the liver was swollen and tender (Chakraborty and Saha, 1987; Franklin et al., 1950; Guha Mazumder et al., 1988, 1998a; Liu et al., 2002; Mizuta et al., 1956; Silver and Wainman, 1952; Wade and Frazer, 1953; Zaldívar, 1974) and analysis of blood sometimes showed elevated levels of hepatic enzymes (Armstrong et al., 1984; Franzblau and Lilis, 1989; Guha Mazumder, 2005; Hernández-Zavala et al., 1998). These effects are most often observed after repeated exposure to doses of 0.01–0.1 mg As/kg/day (Chakraborty and Saha, 1987; Franklin et al., 1950; Franzblau and Lilis ,1989; Guha Mazumder et al., 1988; Mizuta et al., 1956; Silver and Wainman, 1952; Wade and Frazer, 1953), although doses as low as 0.006 mg As/kg/day have been reported to have an effect following chronic exposure (Hernández-Zavala et al., 1998). Histological examination of the livers of persons chronically exposed to arsenic revealed a consistent finding of portal tract fibrosis (Guha Mazumder, 2005; Guha Mazumder et al., 1988; Morris et al., 1974; Piontek et al., 1989; Szuler et al., 1979), leading in some cases to portal hypertension and bleeding from oesophageal varices (Szuler et al., 1979). Cirrhosis has also been reported at increased frequency in arsenic-exposed individuals (Tsai et al., 1999). Several researchers consider that these hepatic effects are secondary to damage to hepatic blood vessel damage (Morris et al., 1974; Rosenberg, 1974), but this is not directly established (ATSDR, 2007).

Dermal effects:

One of the most common, characteristic, effects of arsenic ingestion is a pattern of skin changes that include generalized hyperkeratosis and formation of hyperkeratotic warts or corns on the palms and soles, along with areas of hyperpigmentation interspersed with small areas of hypopigmentation on the face, neck and back. These and other dermal effects have been noted in a large majority of human studies involving repeated oral exposure (e.g., Ahmad et al., 1997, 1999b; Ahsan et al., 2000; Bickley and Papa, 1989; Borgoño and Greiber, 1972; Borgoño et al., 1980; Cebrián et al., 1983; Chakraborti et al., 2003a, 2003b; Chakraborty and Saha, 1987; Foyet al., 1992; Franklin et al., 1950; Franzblau and Lilis, 1989; Guha Mazumder et al., 1988, 1998a, 1998b, 1998c; Guo et al., 2001a; Haupert et al., 1996; Huang et al., 1985; Lander et al., 1975; Liu et al., 2002; Lüchtrath, 1983; Milton et al., 2004; Mizuta et al., 1956; Morris et al., 1974; Nagai et al., 1956; Piontek et al., 1989; Rosenberg, 1974; Saha and Poddar, 1986; Silver and Wainman, 1952; Szuler et al., 1979; Tay and Seah, 1975; Tseng et al., 1968; Wade and Frazer, 1953; Wagner et al., 1979; Wong et al., 1998a, 1998b; Zaldívar, 1974, 1977). In cases of low-level chronic exposure (usually from water), these skin lesions appear to be the most sensitive indication of exposure, so this endpoint is considered to be the most appropriate basis for establishing a chronic oral MRL. This is supported by the finding that other effects (hepatic injury, vascular disease and neurological changes) also appear to have similar thresholds. Numerous studies in humans have reported dermal effects at chronic dose levels generally ranging from about 0.01-0.1 mg As/kg/day (Ahmad et al., 1997; Bickley and Papa, 1989; Borgoño and Greiber, 1972; Borgoño et al., 1980; Cebrián et al., 1983; Chakraborty and Saha, 1987; Foy et al., 1992; Franklin et al., 1950; Guha Mazumder et al., 1988; Huang et al., 1985; Lüchtrath, 1983; Piontek et al., 1989; Silver and Wainman, 1952; Tseng et al., 1968; Zaldívar, 1974, 1977). However, in a study with detailed exposure assessment, all confirmed cases of skin lesions occurred following ingested water containing >100μg/L arsenic (approximately 0.0037 mg As/kg/day) and the lowest known peak arsenic concentration ingested by a case was 0.115μg/L (approximately 0.0043 mg As/kg/day) (Haque et al., 2003). Another large study reported increased incidence of skin lesions associated with estimated doses of 0.0012 mg As/kg/day (0.023 mg As/L drinking water) (Ahsan et al., 2006). Several epidemiological studies of moderately sized populations (20–200 people) exposed to arsenic through drinking water detected no dermal or other effects at average chronic doses of 0.0004–0.01 mg As/kg/day (Cebrián et al., 1983; EPA, 1981b; Guha Mazumder et al., 1988; Harrington et al., 1978; Valentine et al., 1985) and one very large study detected no effects at an average total daily intake (from water plus food) of 0.0008 mg As/kg/day (Tseng et al., 1968).

Neurological effects:

A large number of epidemiological studies and case reports indicate that ingestion of inorganic arsenic can cause injury to the nervous system. Repeated exposure to low levels (0.03–0.1 mg As/kg/day) is typically characterised by a symmetrical peripheral neuropathy (Chakraborti et al., 2003a, 2003b; Foy et al., 1992; Franzblau and Lilis, 1989; Guha Mazumder et al., 1988; Hindmarsh et al., 1977; Huang et al., 1985; Lewis et al., 1999; Mizuta et al., 1956; Muzi et al., 2001; Silver and Wainman, 1952; Szuler et al., 1979; Wagner et al., 1979). Neurological effects were not generally found in populations chronically exposed to doses of 0.006 mg As/kg/day or less (EPA 1981b; Harrington et al., 1978; Hindmarsh et al., 1977). There is emerging evidence suggesting that exposure to arsenic may be associated with intellectual deficits in children. For example, Wasserman et al. (2004) conducted a cross-sectional evaluation of intellectual function in 201 children, 10 years of age, whose parents were part of a larger cohort in Bangladesh. After adjustment for confounding factors, a dose-related inverse effect of arsenic exposure was seen on both performance and Full-Scale subset scores. For both endpoints, exposure to ≥50μg/L resulted in statistically significant differences (p<0.05) relative to the lowest exposure group (<5.5μg/L). A study of 351 children age 5–15 years from West Bengal, India, found significant associations between urinary arsenic concentrations and reductions in scores of tests of vocabulary, object assembly and picture completion. The magnitude of the reductions varied between 12 and 21% (von Ehrenstein et al., 2007). In this cohort, the average lifetime peak arsenic concentration in well water was 0.147 mg/L. However, no clear pattern was found for increasing categories of peak arsenic water concentrations since birth and children’s scores in the various neurobehavioral tests conducted. Furthermore, using peak arsenic as a continuous variable in the regression models also did not support an adverse effect on the tests results (ATSDR, 2007).

Renal effects:

Most case studies of chronic arsenic toxicity do not report clinical signs of significant renal injury, even when other systems are severely impaired (e.g., Cullen et al. 1995; Franzblau and Lilis, 1989; Jenkins, 1966; Kersjes et al., 1987; Mizuta et al., 1956; Silver and Wainman, 1952) (ATSDR, 2007).

Other organ systems:

No reliable studies of musculoskeletal or immunological effects in humans after oral exposure to inorganic arsenicals have been reported (ATSDR, 2007).

Effects in animals

Respiratory effects:

There are only few data regarding respiratory effects in animals following oral exposure to inorganic arsenic. An infant Rhesus monkey that died after 7 days of oral exposure to a complex arsenate salt at a dose of 3 mg As/kg/day exhibited bronchopneumonia with extensive pulmonary haemorrhage, oedema and necrosis (Heywood and Sortwell, 1979). Two other monkeys in this treatment group survived a 1-year exposure period and had no gross or microscopic pulmonary lesions at sacrifice. Increased relative lung weights were seen in rats exposed to 6.66 mg As/kg/day as sodium arsenite 5 days/week for 12 weeks (Schulz et al., 2002). Chronic oral studies in dogs and rats treated with arsenate or arsenite failed to find respiratory lesions (Byron et al., 1967; Kroes et al., 1974; Schroeder et al., 1968) (ATSDR, 2007).

Cardiovascular effects:

Alterations in vascular reactivity was noted in rats given repeated oral doses of arsenic trioxide (11 mg As/kg/day) for several weeks (Bekemeier and Hirschelmann, 1989), although no histological effects could be detected in the hearts of rats or dogs exposed to up to 30 mg As/kg/day as arsenate or arsenite for 2 years (Byron et al., 1967; Kroes et al., 1974; Schroeder et al., 1968). Guinea pigs exposed to arsenic trioxide for 1 day (0, 7.6, 22.7, or 37.9 mg As/kg) or 8 days (0 or 3.8 mg As/kg/day) showed prolongation of the cardiac QT interval and action potential duration (Chiang et al., 2002) (ATSDR, 2007).

Gastrointestinal effects:

Clinical signs of gastrointestinal irritation were observed in monkeys and rats given repeated oral doses of arsenic (6 and 11 mg As/kg/day, respectively) for 2 weeks (Bekemeier and Hirschelmann, 1989; Heywood and Sortwell, 1979). Hemorrhagic gastrointestinal lesions have also been reported in animal studies. A monkey that died after repeated oral treatment with 6 mg As/kg/day for approximately 1 month was found to have acute inflammation and hemorrhage of the small intestine upon necropsy (Heywood and Sortwell, 1979). This lesion was not found in other monkeys that died in this study, or in the survivors. Two pregnant mice that died after repeated gavage treatment with 24 mg As/kg/day as arsenic acid had haemorrhagic lesions in the stomach (Nemec et al., 1998). Gross gastrointestinal lesions (stomach adhesions, eroded luminal epithelium in the stomach) were seen frequently in rats treated by gavage with 8 mg As/kg/day as arsenic trioxide starting before mating and continuing through the end of gestation (Holson et al., 2000). The lesions were not found in rats treated with 4 mg As/kg/day in this study. No histological evidence of gastrointestinal injury was detected in rats exposed to arsenate or arsenite in the feed for 2 years at doses up to 30 mg As/kg/day, but dogs fed a diet containing 2.4 mg As/kg/day as arsenite for 2 years had some bleeding in the gut (Byron et al., 1967; Kroes et al. 1974) (ATSDR, 2007).

Haematological effects:

Long-term studies found mild anaemia in dogs fed arsenite or arsenate for 2 years at 2.4 mg As/kg/day, but no haematological effect in dogs fed 1 mg As/kg/day for 2 years or 1.9 mg As/kg/day for 26 weeks (Byron et al., 1967; Neiger and Osweiler, 1989). Chronic rat studies found little or no evidence of anaemia at doses up to 30 mg As/kg/day, even with co-exposure to lead (Byron et al., 1967; Kroes et al., 1974). No haematological effects were found in monkeys exposed to arsenic doses of 3–6 mg As/kg/day for 1 year (Heywood and Sortwell, 1979).Exposure of rats to ≥5 ppm of arsenic (0.30 mg As/kg/day as sodium arsenite) in the drinking water for 4 weeks resulted in increased platelet aggregation, while 10 or 25 ppm (0.60 or 1.5 mg As/kg/day) was associated with increased P-selectin-positive cells and decreased occlusion time (Lee et al. 2002), representing a change in platelet function. Similarly, exposure of rats or guinea pigs to 10 or 25 ppm of arsenic as arsenite (approximate doses of 0, 0.92, or 2.3 mg As/kg/day for rats and 0, 0.69, or 1.7 mg As/kg/day for guinea pigs) in the drinking water for 16 weeks (Kannan et al. 2001) resulted in decreases in erythrocyte and leukocyte numbers (rats and guinea pigs), increased blood mean corpuscular volume and corpuscular haemoglobin mass (guinea pigs only), and decreased mean corpuscular haemoglobin concentration (rats only) (ATSDR, 2007).

Hepatic effects:

Studies in dogs or mice have not detected clinically significant hepatic injury following exposure to either arsenite or arsenate (Byron et al., 1967; Fowler and Woods, 1979; Kerkvliet et al., 1980; Neiger and Osweiler, 1989; Schroeder and Balassa, 1967), although enlargement of the common bile duct was noted in rats fed either arsenate or arsenite in the diet for 2 years (Byron et al., 1967; Kroes et al., 1974) and lipid vacuolation and fibrosis were seen in the livers of rats exposed to 12 mg As/kg/day as arsenate in the drinking water for 6 weeks (Fowler et al., 1977). Similarly, fatty changes and inflammatory cell infiltration were seen in the livers of both normal and metallothionein-null mice exposed to 5.6 mg arsenic/kg/day in the drinking water for 48 weeks (Liu et al., 2000).

An increase in indices of peroxidation was reported in rats dosed with approximately 0.02 mg As/kg/day for 60 days from drinking water containing 2.5 mg sodium arsenite/L (Bashir et al., 2006); absolute liver weight was also increased at this dose level. Exposure of guinea pigs to 0.69 or 1.7 mg As/kg/day in the drinking water for 16 weeks, but not in rats exposed to 0.92 or 2.3 mg As/kg/day, resulted in increases in delta-aminolaevulinic acid synthetase (ALAS) levels (Kannan et al., 2001). Exposure of BALB/C mice to 0.7 mg arsenic/kg/day in the drinking water for 15 months resulted in increased liver weights, changes in liver enzymes (glutathione S-transferase, glutathione reductase, catalase, glucose-6-phosphate dehydrogenase, glutathione peroxidase), fatty liver, and fibrosis (Santra et al., 2000) (ATSDR, 2007).

Dermal effects:

Dermal lesions similar to those observed in humans have not been noted in oral exposure studies in monkeys (Heywood and Sortwell, 1979), dogs (Byron et al., 1967) or rodents (Schroeder et al., 1968) (ATSDR, 2007).

Neurological effects:

Neurological effects have been observed in animal studies. Rodriguez et al. (2001) evaluated neurobehavioral changes in male Sprague-Dawley rats exposed to 0, 5, 10 or 20 mg As/kg/day as sodium arsenite by gavage for 2 or 4 weeks. Significant effects were seen in spontaneous locomotor activity and the food pellet manipulation test in the high-dose animals, while no effects were seen in the low- or mid-dose rats. Decreased performance in open field tests were also seen in rats exposed to 26.6 mg As/kg/day, but not to 13.3 mg/kg/day or less, as sodium arsenite for 4 weeks (Schulz et al., 2002). Curiously, the behavioural changes were no longer present at 8 and 12 weeks of exposure, which may suggest an adaptive response. Heywood and Sortwell (1979) reported salivation and uncontrolled head shaking in two monkeys given several doses of 6 mg As/kg/day as arsenate, while no such effects were noted in monkeys given 3 mg As/kg/day for 2 weeks. Nemec et al. (1998) observed ataxia and prostration in pregnant female rabbits treated with 1.5 mg As/kg/day repeatedly during gestation, but not in rabbits treated with 0.4 mg As/kg/day (ATSDR, 2007).

In a subacute oral toxicity study in rats, arsenic and fluoride exposure on motor behavior and general toxicity were modelled in young adult male rats which received sodium (meta) arsenite (10 mg/kg bw), sodium fluoride (5 mg/kg bw), and their combination by gavage, once daily, 5 days a week for 6 weeks. After 6 weeks, 6 animals per group were dissected, while the other 6 were kept for 6 more weeks untreated. Body weight, together with food and water consumption, was measured daily. Arsenic, alone or along with fluoride, caused significant decrease in rearing, and increase in immobility and local activity in the open field in the 3rd and 6th week. By the 12th week, these changes mostly diminished. Weight gain, and food and water consumption were significantly reduced by arsenic but normalized post treatment. Fluoride had no own effect and mostly no influence on effects of arsenic. Massive deposition of arsenic in the rats’ blood, cerebral cortex, and liver by the 6th week, and partial elimination by the 12th week, was seen. The study author concluded that the results underline the risk of neuro-functional damage by arsenic and called for further investigations (Sárközi et al., 2015).

Reproductive organ effects:

A study was conducted to determine the sub-chronic exposure effect of sodium arsenite on reproductive organs of female Wistar rats. Mature female rats were divided into 4 groups of 12 animals each. Group I received distilled water, whereas the other 3 groups received sodium arsenite at 10, 30, and 50 µg/L doses for 60 days through drinking water. Half of the animals from each group were dissected after 30 days and the remaining after 60 days. A disruption in estrous cycle was observed with prolonged diestrous and metestrous phases. A significant increase in ovarian surface epithelium and follicular atresia was observed in treated rats (p ≤ 0.05). A significant decrease (p ≤ 0.05) in the uterine myometrium was observed. A significant increase (p ≤ 0.05) in the levels of lipid peroxidation along with decrease in the activities of antioxidant enzymes was observed. The study author based on the results concluded that the sub-chronic exposure to sodium arsenite causes degenerative changes in reproductive organs and induces oxidative stress in female rats (Mehta et al., 2016).

In a subacute toxicity study in mice, the effects of As2O3 on sperm and testicular morphology, androgen receptor (AR) immunoreactivity in testes and epididymis, in addition to evaluation of fertility parameters in adult male mice were determined. 30 adult Swiss mice were divided into three experimental groups: control; received distilled water (vehicle) while treated received 0.3 or 3 mg/kg/day As2O3 subcutaneously, for 5 days per week, followed by 2 days of interruption, for 5 weeks. Results showed that As2O3 (1) decreased spermatozoa number, (2) produced seminiferous epithelium degeneration and exfoliation of germ cells tubule lumen (3) altered nucleus/cytoplasm proportion of Leydig cells and (4) reduced AR immunoreactivity in both Leydig and epithelial epididymal cells. Further, fetal viability tests demonstrated an increase in post-implantation loss in females that were mated with As2O3-treated males. Data indicate that As2O3 exposure altered the spermatogenic process and subsequently fetal viability (Da Silva et al., 2017).

Other organ systems:

No reliable studies of musculoskeletal or immunological effects in humans after oral exposure to inorganic arsenicals have been reported (ATSDR, 2007). Studies in animals also indicate that the kidney is not a major target organ for inorganic arsenic (Byron et al., 1967; Schroeder and Balassa, 1967; Woods and Southern, 1989) (ATSDR, 2007).

Mode of action

The mechanism by which inorganic arsenic produces its effects in various organs and systems is not entirely elucidated. There is growing evidence for a mode of action involving the formation of reactive trivalent metabolites interacting with critical cell sulfhydryl groups, leading to cytotoxicity and regenerative cell proliferation. The cytotoxicity results in non-cancer toxicities and the cell proliferation enhances the development of epithelial cancers (see section on Carcinogenicity). In other tissues such as vascular endothelium, different toxicities develop, not cancer (Cohen et al., 2013).

References not cited in ATSDR (2007)

Cohen SM et al. (2013). Evaluation of the carcinogenicity of inorganic arsenic. Crit. Rev. Toxicol. 43(9):711-752.

Ghosh A (2013). Evaluation of chronic arsenic poisoning due to consumption of contaminated ground water in West Bengal, India. Int. J. Prev. Med. 4(8):976-9.

Das D et al. (2014). Chronic low-level arsenic exposure reduces lung function in male population without skin lesions. Int. J. Public Health 59(4):655-63.

Sárközi K et al. (2015). Behavioral and general effects of subacute oral arsenic exposure in rats with and without fluoride. Int. J. Environ. Health. Res. 25(4):418-31.

Mehta M and Hundal SS (2016). Effect of sodium arsenite on reproductive organs of female Wistar rats. Arch. Environ. Occup. Health. 71(1):16-25.

Moon KA et al. (2013). Association between exposure to low to moderate arsenic levels and incident cardiovascular disease. Annals Int. Med. http://annals.org.

Da Silva RF et al.(2017). Arsenic trioxide exposure impairs testicular morphology in adult male mice and consequent fetus viability. J. Toxicol. Environ. Health A. 80 (19-21):1166-1179.

Rahman M et al. (2019). Arsenic exposure and young adult’s mortality risk: a 13-year follow-up study in Matlab, Bangladesh. Environ. Int. 123:358-367.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Referenceopen allclose all

Endpoint:
chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
A long-term carcinogenicity bioassay on sodium arsenite (NaAsO2) was performed. NaAsO2 was administrated with drinking water at concentrations of 200, 100, 50, or 0 mg/L, for 104 weeks to Sprague-Dawley rats (50/sex/group), 8 weeks old at the start of the study. The animals were monitored until spontaneous death at which time each animal underwent complete necropsy. Histopathological
evaluation of all pathological lesions and of all organs and tissues collected was routinely performed on each animal. Also, drinking water and feed consumption were monitored during the study as well
as body weight. Lastly, the animals were clinically examined during the study.
GLP compliance:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Age at study initiation: 8 weeks old
- Housing: animals were housed in groups of five in makrolon cages (41 cm X 25 cm X 15 cm) with
stainless-steel wire tops and a shallow layer of white wood-shavings as bedding.
- Diet: standard Corticella diet (Corticella S.p.A., Bologna, Italy)
- Water (ad libitum): tap water
ENVIRONMENTAL CONDITIONS
- Temperature: 21 ± 2°C
- Relative humidity: 50 - 60%
- Photoperiod (hrs dark / hrs light): 12/12 (natural and artificial light sources)
After weaning at 4 -5 weeks of age, the experimental animals were randomized in order to have no
more than one male and one female from each litter in the same group.
Route of administration:
oral: drinking water
Vehicle:
water
Details on oral exposure:
Each morning, leftover solution from the previous day was removed and glass drinking bottles were washed and refilled with fresh solution.
Analytical verification of doses or concentrations:
not specified
Details on analytical verification of doses or concentrations:
No data.
Duration of treatment / exposure:
104 weeks
Frequency of treatment:
ad libitum
Dose / conc.:
0 mg/L drinking water
Dose / conc.:
50 mg/L drinking water
Dose / conc.:
100 mg/L drinking water
Dose / conc.:
200 mg/L drinking water
Remarks:
Based on test substance
No. of animals per sex per dose:
20/sex/group
Control animals:
yes, concurrent no treatment
Details on study design:
NaAsO2 was administrated with drinking water at concentrations of 200, 100, 50, or 0 mg/L, for 104
weeks to Sprague-Dawley rats (50/sex/group), 8 weeks old at the start of the study. The animals
were monitored until spontaneous death at which time each animal underwent complete necropsy.
Histopathological evaluation of all pathological lesions and of all organs and tissues collected was
routinely performed on each animal. Also, drinking water and feed consumption were monitored duri
ng the study as well as body weight. Lastly, the animals were clinically examined during the study.
Positive control:
No data.
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: the animals were clinically examined for gross changes every 2 weeks for the durat
ion of the study.

DETAILED CLINICAL OBSERVATIONS: No data

DERMAL IRRITATION: No data

BODY WEIGHT: Yes
- Time schedule for examinations: body weight was measured individually once weekly for the first 13
weeks and then every 2 weeks until 111 weeks of age. Measurement of body weight contiuned every
8 weeks until the end of the experiment.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Mean daily feed consumption was measured once weekly per cage
for the first 13 weeks, and then every 2 weeks until 111 weeks of age.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted a
verages from the consumption and body weight gain data: No data

WATER CONSUMPTION: Yes
- Time schedule for examinations: mean daily drinking water was measured once weekly per cage for
the first 13 weeks, and then every 2 weeks until 111 weeks of age.

OPHTHALMOSCOPIC EXAMINATION: No data

HAEMATOLOGY: No data

CLINICAL CHEMISTRY: No data

URINALYSIS: No data

NEUROBEHAVIOURAL EXAMINATION: No data
OTHER: extensive historical data are available on the tumor incidence among untreated rats.
Sacrifice and pathology:
The biophase ended at 159 weeks, with the death of the last animal at 167 weeks of age. Upon death, all animals underwent complete necropsy. Histopathology was routinely performed on the following organs and tissues of each animal from each group: skin and subcutaneous tissue, the brain (three sagittal sections), pituitary gland, Zymbal glands, salivary glands, Harderian glands, cranium
(five sections, with oral and nasal cavities and external and internal ear ducts), tongue, thyroid, parathyroid, pharynx, larynx, thymus and mediastinal lymph nodes, trachea, lung and mainstem bronchi,
heart, diaphragm, liver, spleen, pancreas, kidneys, adrenal glands, esophagus, stomach (fore and glandular), intestine (four levels), urinary bladder, prostate, gonads, interscapular brown fat pad,
subcutaneous and mesenteric lymph nodes, and other organs or tissues with pathological lesions.
All organs and tissues were preserved in 70% ethyl alcohol, except for bones, which were fixed in 10% formalinand the decalcified with 10% formaldehyde and 20% formic acid in water solution. The
normal specimens were trimmed, following SOP. Trimmed specimens were processed as paraffin blocks and 3 - 5 μm sections of every specimen were obtained. Sections were routinely stained with
Hematoxylin-Eosin.
Statistics:
Mutilple tumors of different types and sites, of different types in the same site, of the same types in bilateral organs, of the same types in the skin, subcutaneous tissue or mammary glands, or at distant sites of diffuse tissue (i.e., bones aand skeletal muscle) were plotted as single/independent tumors. Multiple tumors of the same type in the same tissue and organ, apart from those mentioned above, were plotted only once.
Three statistical tests were used to analyze neoplastic and non-neoplastic lesion incidence data. The Chi-square test and the Fisher's exact test (HAseman, 1978)* were used to evaluate differences in tumor incidence between treated and control groups. The Cochran-Armitage trend test (Armitage, 1971; Gart et al., 1979)** was used to test for linear trends in tumor incidence.

References
*, *** HASEMAN, J.K. 1978. Exact sample sizes with the Fisher-Irwin test for 2×2 tables. Biometrics 34:
106–109.
** ARMITAGE, P. 1971. Statistical Methods in Medical Research. JohnWiley & Sons. New York.
** GART, J.J., K.C. CHU & R.E. TARONE. 1979. Statistical issues in interpretation of chronic tests for
carcinogenicity. J. Natl. Cancer Inst. 62: 957–974.
Clinical signs:
not specified
Mortality:
mortality observed, treatment-related
Description (incidence):
Differences in survival rates were observed in both males and females; a slight decrease in the survival rate was observed in males treated at 200 and 100 mg/L, particularly from 40 weeks of age until
88 weeks of age, whereas in females, a decrease in survival rate was observed from 104 weeks of a ge until the end of the experiment.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
A dose related difference in mean body weight was observed in males. The difference was more evident in the males treated at 200 mg/L (circa 15% when compared with controls). Differences
in mean body weight were also observed in females of the groups treated at 200 and 100 mg/L. Mean body weight was about 20% less in females treated at 200 mg/L compared with control and
about 10% less in females treated at 100 mg/L. No treatment-related differences in body weight were observed in females treated at 50 mg/L.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
A dose-related lower intake of feed was also observed in both male and female rats. This difference was less marked between the group treated at 50 mg/L and the control in both males and females.
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
effects observed, treatment-related
Description (incidence and severity):
A dose-related lower intake of water containing various levels of NaAsO2 was observed in both male and female rats. In females, water consumption became similar between the group treated at 50 mg/L and the control after 88 weeks of age.
Ophthalmological findings:
not specified
Haematological findings:
not specified
Clinical biochemistry findings:
not specified
Urinalysis findings:
not specified
Behaviour (functional findings):
not specified
Immunological findings:
not specified
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Neuropathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Long-term exposure of sodium arsenite administered in drinking water to Sprague-Dawley rats has been shown to induce toxic effects on the kidneys at concentrations as high as 200 mg/L and, to a
lesser extent 100 mg/L and 50 mg/L. Nephropathies were characterized by diffuse acute/chronic inflammation, tubular enlargement with deposits of ialin casts and marked fibrosis around glomeruli with distension of Bowman’s space.
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
The main oncologic results of the experiment are attached below in the field "Attached background material" (Tables 1 and 2). Among males treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and a statistically significant increased number of total malignant tumors (P < 0.05) were observed when compared to controls. Sparse very infrequent benign and malignant tumors were observed in the treated groups, namely, one adenocarcinoma of the lung in a male treated at 200 mg/L; one carcinoma of the kidney and one papilloma of the pelvis in a male treated at 100 mg/L and two papillomas of the renal pelvis in another rat treated at the same dose. Renal pelvis papillomas were also observed in two males treated at 50 mg/L. Among females treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and an increase d number of total malignant tumors were observed when compare to controls. Among the females treated at 200 mg/L, one adenocarcinoma of the lung was observed. The same group also included two animals bearing kidney adenomas, two bearing kidney carcinomas, and one bearing a renal pelvis carcinoma. In the group treated at 100 mg/L, three animals were observed bearing kidney adenomas,
one bearing a kidney carcinoma and one bearing a renal pelvis papilloma. One animal bearing a bladder carcinoma was also observed among the females treated at 100 mg/L.
Other effects:
not specified
Details on results:
HISTORICAL CONTROL DATA
It must be noted that among the untreated Sprague-Dawley rats used in study experiment laboratories over the last 20 years (2265 males and 2274 females), the overall incidence of lung adenomas was 0.2% in males (range: 0–2.0%) and 0.1% in females (range: 0–1.0%), while the overall incidence of lung carcinomas was 0.1% in both males (range: 0–1.0%) and females (range: 0–1.3%). The overall incidence of the kidney adenomas was 0.1% in males (range: 0–1.3%) and 0.2% in females (range: 0–2.0%), while the overall incidence of kidney carcinomas was 0.2% in males (range: 0–0.3%) and 0.3% in females (range: 0–1.8%). With regard to historical data on the transitional cell epithelium of the renal pelvis and ureter, no papillomas were observed in either males or females, while only one
carcinoma was observed in a female (overall incidence: 0.04% and range: 0–1.0%). No carcinomas in the transitional cell epithelium of the bladder were observed in either males or females.
Key result
Dose descriptor:
LOEL
Effect level:
100 mg/L drinking water
Based on:
test mat.
Sex:
male/female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
water consumption and compound intake
Critical effects observed:
no

NaAsO2 induces sparse benign and malignant tumors among treated rats  (not statistically significant).

Executive summary:

A 2-year (104-week) carcinogenicity dose–response study was conducted with sodium arsenite (NaAsO2) administered via drinking water to Sprague-Dawley rats (50/sex/group, 8 weeks old at the start of the study) at concentration of 0, 50, 100 and 200 mg/L ad libitum. Mean daily drinking water and feed consumption were measured once weekly per cage for the first 13 weeks, then every 2 weeks until 111 weeks of age. Body weight was measured individually once weekly for the first 13 weeks, then every 2 weeks until 111 weeks of age (however, dose levels expressed in mg/kg bw/day are not provided in the publication). The rats were maintained until spontaneous death, at which time each animal underwent complete necropsy. Histopathological evaluation of all pathological lesions and of all organs and tissues collected was routinely performed.

A dose-related lower intake of water was observed in both male and female rats. In females, water consumption became similar between the group treated at 50 mg/L and the control after 88 weeks of age. A dose-related lower intake of feed was also noted in both male and female rats. This difference was less marked between the group treated at 50 mg/L and the control. A dose-related difference in mean body weight was observed in males. The difference was more evident at 200 mg/L (circa 15% when compared with controls). Mean body weight in females was about 20% less at 200 mg/L compared with control and about 10% less at 100 mg/L. No treatment-related differences in body weight were observed in females at 50 mg/L. A slight decrease in the survival rate was observed in males at 200 and 100 mg/L, particularly from 40 to 88 weeks of age, whereas in females, a decrease in survival rate was observed from 104 weeks of age until the end of the experiment.

Among males treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and a statistically significant increase in number of total malignant tumors (p<0.05) were observed when compared to controls. One adenocarcinoma of the lung was seen at 200 mg/L, one carcinoma of the kidney and one papilloma of the pelvis at 100 mg/L and two papillomas of the renal pelvis in another rat at the same dose. Renal pelvis papillomas were also observed in two males at 50 mg/L.

Among females treated at 100 mg/L, a slightly increased incidence of animals bearing malignant tumors and an increased number of total malignant tumors were observed when compared to controls. Three animals were found bearing kidney adenomas, one bearing a kidney carcinoma and one bearing a renal pelvis papilloma. One animal with a bladder carcinoma was also noted in this group. At 200 mg/L, one adenocarcinoma of the lung was observed. The same group also included two animals bearing kidney adenomas, two bearing kidney carcinomas and one bearing a renal pelvis carcinoma.

The authors concluded that, under the conditions of their study, sodium arsenite induced sparse benign and malignant tumours amongst treated rats. They noted that the types of tumours observed were infrequent in the strain of Sprague-Dawley rats of the colony used in their laboratory (Soffritti et al., 2006).

Endpoint:
chronic toxicity: oral
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
a short-term toxicity study does not need to be conducted because a reliable sub-chronic (90 days) or chronic toxicity study is available, conducted with an appropriate species, dosage, solvent and route of administration
Reason / purpose for cross-reference:
data waiving: supporting information
Critical effects observed:
not specified
Endpoint conclusion
Endpoint conclusion:
adverse effect observed

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Endpoint conclusion:
adverse effect observed

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Justification for classification or non-classification

Based on sufficient human evidence that meets the classification criteria given in Table 3.9.1 of Regulation (EC) No. 1272/2008, a self-classification for arsenic metals as Specific target organ toxicity-repeated exposure STOT Rep. Exp. 1 – H373 (May cause damage to organs) is proposed (see endpoint summary).