Potassium hydrogencarbonate

Carcinogenicity

Description of key information

Reliable oral long-term studies on potassium hydrogencarbonate give no indications on intrinsic carcinogenicity relevant to humans. In addition, available information from assessments carried out within the OECD work on investigation of high production volume chemicals on compounds which have a carbonate or a potassium moiety gives no indication on a carcinogenic potency of potassium or carbonate either.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: This study is invalid for assessing a carcinogenic potential of potassium hydrogencarbonate because of improper study design

Qualifier:

no guideline followed

Principles of method if other than guideline:

Method: other: initiation-promotion-test

GLP compliance:

no

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Strain: [Bor:WISW (SPF CpB)]; Wistar
- Source: F. Winkelmann, Institute for the Breeding of Laboratory Animals  GmbH & Co.KG, Borchen, Germany
- Age at study initiation: 5 weeks
- Weight at study initiation: no data
- Fasting period before study: no
- Housing: in groups of 4 rats/gage (no further data)
- Diet: ad libitum
- Water: tap water ad libitum
- Acclimation period:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 40- 70
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: feed

Details on exposure:

- Vehicle: 
-- drinking water for pre-treatment with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)
-- feed for treatment with potassium hydrogencarbonat 

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

In total 36 weeks:
- 4 weeks pre-treatment with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in drinking water
- 32 weeks treatment with potassium hydrogencarbonat in feed

Frequency of treatment:

continuous

Post exposure period:

none

Remarks:

Doses / Concentrations:
4% KHCO3
Basis:
nominal in diet

No. of animals per sex per dose:

20

Control animals:

other: pre-treated with BBN and thereafter maintained on normal feed without any supplements

Details on study design:

- Treatment:
-- Initiation by BBN: For initiation several groups of rats (20  rats/group) were given drinking water containing 0.05%  N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 4 weeks. 
-- Treatment with potassium hydrogencarbonate (KHCO3): After initiation by BBN, animals were maintained on basal diet containing 4% potassium  hydrogencarbonate for 32 weeks
- Control groups:
-- Untreated control (neither initiated nor maintained on KHCO3 supplemented diet): not performed
-- Not initiated control: not performed
-- BBN control group: initiated by BBN and thereafter maintained on basal diet
- Satellite groups:
-- Treatment with sodium hydrogencarbonate and potassium hydrogencarbonate: After initiation by BBN, animals were maintained on  basal diet containing 1.68% sodium hydrogencarbonate and 2% potassium hydrogencarbonate for 32 weeks.
-- Several further groups were treated with NaCl, KCl, or NaHCO3 but received no K2CO3 and were therefore not further reported.  

Positive control:

none

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS AND FREQUENCY
- Mortality: not reported
- Clinical signs: not reported
- Body weight: periodically (no further information)
- Food consumption: periodically (no further information)
- Water consumption: periodically (no further information)

Sacrifice and pathology:

ORGANS EXAMINED AT NECROPSY (MACROSCOPIC AND MICROSCOPIC)
GROSS PATHOLOGY: no
HISTOPATHOLOGY:  only urinary bladder examined
-- The animals were killed in week 37 and the urinary bladder was inflated by intraluminal injection of a neutral, aqueous, 10%  phosphate-buffered formalin solution and removed. The urinary bladder was processed for microscopy by conventional methods, step-sectioned (approximately 10 sections/bladder) at 5µm, stained with haematoxylin and eosin and examined by light microscopy. In addition, the total length of the basement membrane was measured by morphometry with a Zeiss/Kontron MiniMOP Image Analyzer, and the number of lesions per 10 cm of basement  membrane was calculated. The lesions found in the urinary bladder  epithelium were classified into simple hyperplasia, papillary or nodular hyperplasia, papilloma and carcinoma.

Other examinations:

- Ophthalmoscopic examination: not performed
- Clinical chemistry: not performed
- Haematology: not performed
- Urine analysis: Volume (calibrated tubes), density, and electrolytes  (potassium, sodium, calcium, magnesium, chloride, phosphate, and  sulphate) were measured in weeks 9, 13, 24, and 36 in 24-h urine samples collected from each gage (4 rats/gage). Urinary pH (pH meter) was determined in weeks 9, 13, 18, 24, 30, and 36 in 2-h spot samples, collected per gage in the early morning.

Statistics:

STATISTICAL METHODS: Analysis of variance techniques followed by  Dunnett´s multiple comparison test (body weights) or by least significance difference (LSD) test (food and water intake, urinalysis). Urinary pH values were analyses with the Mann/Whitney U-test. Data on microscopic lesions were analysed with the two-sided Fisher exact probability test (incidences) or Student´s t-test.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

GROUP INITIATED BY BBN AND THEREAFTER MAINTAINED ON BASAL DIET CONTAINING 4% POTASSIUM HYDROGENCARBONAT:
- Mortality: not reported
- Clinical signs: haematuria
- Body weight: no significant differences among the various groups
- Food consumption: comparable in all groups (approximately 18.5g/rat/day)
- Water consumption: Water intake during pretreatment comparable in all  groups, thereafter, water intake in all groups fed diets with added salts was higher than in BBN-initiated control group (statistical significance  not mentioned)
- Ophthalmoscopic examination: not performed
- Clinical chemistry: not performed
- Haematology: not performed
- Urine analysis: urinary volume, pH, and potassium concentration increased; density and concentrations of sulphate, phosphate, chloride, sodium, magnesium, and calcium decreased compared to BBN-initiated  control group
- Organ weights: not reported
- Gross pathology: one of the 20 rats exhibited gross abnormalities suspected of being bladder tumors
- Histopathology: compared to BBN-initiated control, the numbers (number of lesions per 10 cm of basement membrane) but not  the incidence (number of animals with these lesions/group) of simple epithelial hyperplasia, incidence and number of  papillary/nodular hyperplasia, and incidence and number of papillomas  were significantly increased 

GROUP INITIATED BY BBN AND THEREAFTER MAINTAINED ON BASAL DIET CONTAINING  1.68% SODIUM HYDROGENCARBONAT AND 2% POTASSIUM HYDROGENCARBONAT:
- Mortality: 3/20 animals died during the final stage of the study
- Clinical signs: haematuria
- Body weight: no significant differences among the various groups
- Food consumption: comparable in all groups (approximately 18.5g/rat/day)
- Water consumption: Water intake during pretreatment comparable in all  groups, thereafter, water intake in all groups fed diets with added salts  was higher than in BBN-initiated control group (statistical significance  not mentioned)
- Ophthalmoscopic examination: not performed
- Clinical chemistry: not performed
- Haematology: not performed
- Urine analysis: urinary volume, pH, potassium, and sodium concentration increased; density and concentrations of sulphate, phosphate, chloride,  magnesium, and calcium decreased compared to BBN-initiated control group
- Organ weights: not reported
- Gross pathology: three of the 20 rats exhibited gross abnormalities suspected of being bladder tumors
- Histopathology: compared to BBN-initiated control, the numbers (but not  the incidence) of simple epithelial hyperplasia, incidence and number of  papillary/nodular hyperplasia, and incidence and number of papillomas were significantly increased

Relevance of carcinogenic effects / potential:

The assessed urinary bladder alterations are without relevance to humans.
The relevance to humans of preneoplastic or neoplastic urinary bladder findings in rats induced by high dose alkali intakes and associated by alkalinization of the urine, elevated urine volumes, altered urine electrolytes composition with or without renal pelvic mineralization or urine precipitation have been discussed for a long time (e.g. by the International Agency for Research on Cancer as part of the World Health Organization (IARC) in the IARC Monography Vol. 73 (1999) and in the IARC Scientific Publication No 147 (1999) or more recently by the European Food Safety Authority (EFSA) in the option on Aspartam (2006)). It is widely accepted that these high dose effects are specific to the rat and are of no relevance to humans.

Following treatment with the tumour initiating agent N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) rats were kept on a diet containing 4% potassium hydrogencarbonate. The alkalizing salt potassium hydrogencarbonate induced increases in urinary pH and urinary potassium ion concentration. Calcium and phosphate concentration was decreased. The incidences of papillary/nodular hyperplasia and papilloma in the urinary bladder were significantly higher than in the control group. The only control group used in this study was also initiated by BBN. A untreated control group (neither initiated by BBN nor maintained on KHCO3 supplemented feed) or a control group maintained on KHCO3 supplemented feed without prior initiation by BBN initiated were not included in this study.

The potassium hydrogencarbonat dose used in this study, exceeded the limit dose of 1000 mg/kg bw/day of standard guidelines for repeated dose toxicity or carcinogenicity studies (e.g. EEC or OECD) by at least a factor of two: In an further publication (B.A.R. Lina, M.H.M. Kuijpers: Toxicity and carcinogenicity of acidogenic or alkalogenic diets in rats; effects of feeding NH4Cl, KHCO3 or KCl Food and Chemical Toxicology 42 (2004) 135–153, also cited in this IUCLID) the authors reported, that male rats maintained on diets supplemented with 4% KHCO3 consumed 20.7 mmol (=2073 mg)/kg body weight/day as medium value during a 18 month study. The values for studies with 13 or 4 week duration and thus younger animals were even higher (31,3 and 43.8 mmol/kg bw/day, respectively (3134 and 4385 mg/kg bw/d, respectively (molecular weight of KHCO3= 100.12 g/mol))).

In the thesis paper, the relevance to humans of the findings were discussed more detailed. The study author concluded that KHCO3 exerted promoting activity similar to NaHCO3 and that both potassium and sodium ions are strong mitogenic bladder tumour promotors under conditions of elevated urinary pH. Similar effects have also been seen with other potassium or sodium compounds in previous studies: sodium or potassium salts of a broad group of non-genotoxic anions, including ascorbate, glutamate, erythorbate, aspartate, citrate, succinate, bicarbonate and carbonate have been found to induce hyperplasia and tumours in rat urinary bladder epithelium. An effect of alkalosis as enhancing factor in tumorigenesis was demonstrated in rats only in the epithelial cells of the urinary bladder where environmental pH can reach very high values in comparison to the systemic pH. However, in humans the urinary pH generally tends to be acidic and the concentrations of sodium and potassium are generally lower than those observed with alkalizing salts in studies on rats, a persistent combination of elevated urinary pH and high sodium and/or potassium levels is unlikely in humans. Hence the author concluded, that the response of the bladder to high pH and high sodium or potassium levels depends on the species and the species specificity of the bladder response and the fact that it is a high-dose phenomenon makes its relevance to man at least doubtful.

The relevance to humans of preneoplastic or neoplastic urinary bladder findings in rats induced by high dose alkali intakes (e.g. as counterions in food additives like artificial sweetener or flavour enhancer) and associated by alkalinization of the urine, elevated urine volumes, altered urine electrolytes composition with or without renal pelvic mineralization or urine precipitation which leads to a cyctotoxic effect on the bladder epithelium with consequent regenerative proliferation and ultimately tumors have been discussed for a long time (e.g. by the International Agency for Research on Cancer as part of the World Health Organization (IARC) in the IARC Monography Vol. 73 (1999) and in the IARC Scientific Publication No 147 (1999) or more recently by the European Food Safety Authority (EFSA) in the option on Aspartam (2006) or a review by Cohen, SM on Thresholds in Genotoxicity and Carcinogenicty: Urinary Bladder Carcinogenisis (2008)). It is widely accepted that these high dose effects are specific to the rat and are of no relevance to humans.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

Non-guideline 18-month-study to examine the effects of died-induced acid-base disturbances. Diets were supplemented with high amounts of potassium hydrogencarbonate (2% or 4%, base-forming diets), ammonium chloride (2.1% acid forming diet) or potassium chloride (3%, neutral diet, providing K+ and Cl- in amounts equimolar to those in the 4% potassium hydrogencarbonate and the 2.1% ammonium chloride diet, respectively).

Species:

rat

Strain:

Wistar

Sex:

male/female

Route of administration:

oral: feed

Duration of treatment / exposure:

78 weeks (18 months)

Frequency of treatment:

daily

Remarks:

Doses / Concentrations:
2 and 4 % in the diet
Basis:
nominal in diet

No. of animals per sex per dose:

15

Control animals:

yes, plain diet

Details on study design:

Study groups:
- control group: unsupplemented institutes cereal based rodent diet
- 2% potassium hydrogencarbonate in diet (approximately 1299 mg/kg bw/d for males and 1686 mg/kg bw/d for females)
- 4% potassium hydrogencarbonate in diet (approximately 2861 mg/kg bw/d for males and 3566 mg/kg bw/d for females)
- Satellite groups: 2.1% NH4Cl (acid-forming diet) and neutral diet supplemented with 3% KCl providing K+ and Cl- in amounts equimolar to those in the 4% KHCO3 diet and the 2.1% NH4Cl diet, respectively
Post-exposure period: none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily, including evaluation regarding grossly visible or palpable masses at regular intervals

BODY WEIGHT: Yes
- Time schedule for examinations: weekly or (from 3 months) once every 4 weeks

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes, measured weekly or (from 3 months) once every 4 weeks per cage
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes, calculated per cage

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

WATER CONSUMPTION: Yes,
- Time schedule for examinations: daily per cage in weeks 1, 4, 6, 8, 12, 55, and 75 (24 hours consumption)

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: weeks 4, 13, 32, 55, and 75 (tail tip blood)
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 per group and sex
- Parameters examined: haemoglobin concentration, packed cell volume, red blood cells, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, thrombocytes, total white blood cells, prothrombin time, and differential white blood cells

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: weeks 5, 14, 32, 56, and 76 (for blood gas analysis), weeks 17 and 38 and month 18 (clinical chemistry parameters), weeks 4, 12, 36, and 77 (glucose analysis)
- Animals fasted: No data (except on glucose analysis)
- How many animals: 10 per group and sex
- Parameters examined.:
--Blood gas analysis (tail tip blood): determination of pH, pCO2 and pO2 directly after sampling in capillary tubes, and calculation of bicarbonate and base excess
-- Clinical chemistry:
--- month 18, plasma from the abdominal aorta obtained at necropsy, and in weeks 17 and 38 in samples obtained by orbita puncture: alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, gamma glutamyl transferase, lactate dehydrogenase, total protein, albumin, total bilirubin, urea, creatinine, calcium, inorganic phosphate, chloride, sodium, and potassium
--- Whole blood collected from the tip of the tail of 10 animals per group and sex in weeks 4, 12, 36, and 77 after overnight fasting: glucose

URINALYSIS: Yes (Urinary acid indices)
- Time schedule for collection of urine: weeks 1, 4, 6, 10, 14, 36, 57, and 76
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (no food and water for 2-3 h at the start of the light period)
- How many animals: all
- Parameters examined in fasted animals: urinary pH was measured in individual samples, mean pH values were calculated as the negative logarithm of the mean of the hydrogen concentrations instead of as the arithmetical mean of the individual pH values; bicarbonate, titratable acid, ammonia, and urea were measured in pooled samples (two samples per group and sex) and related to creatinine

URINALYSIS: Yes (standard urine parameter)
- Time schedule for collection of urine: weeks 6, 16, 38, and 78
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- How many animals: 10 per group and sex
- Parameters examined: volume (calibrated tubes), density, gamma glutamyl transferase, creatinine, urea, calcium, potassium, sodium, phosphate, and sulphate

URINALYSIS: Yes (hydroxyprolin)
- Time schedule for collection of urine: weeks 11 and 76
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- How many animals: 10 per group and sex (two samples from five rats per group and sex)
- Parameter examined: hydroxyproline

URINALYSIS: Yes (Concentrating ability of the kidneys)
- Time schedule for collection of urine: weeks 4, 7, 13, 14, 36, 57, and 77
- Metabolism cages used for collection of urine: No data
- Animals fasted: Yes, urine collected during the last 16 h of a 24-h water deprivation period, during the 16-h collection period no feed was available
- Parameters examined: volume (graduated tubes), density, and in addition, examinations for protein, glucose, occult blood, ketones, bilirubin, and urobilinogen; appearance, and microscopy of the sediment were carried out in the individual samples collected in weeks 4, 13, and 77

NEUROBEHAVIOURAL EXAMINATION: No

OTHER:
- CALCIUM CONTENT in FEMUR: month 18 at autopsy, the right femur from 10 animals per group and sex was removed, cleaned from adherent soft tissue and weighed, dried at 100 °C, subjected to fat extraction (petroleum ether), redryed and the weight recorded as fat free solid, the fat free femur was ashed at 550 °C and the calcium content was determined by atomic absorption spectrophotometry
- CALCIUM and PHOSPHORUS EXCRETION in URINE and FAECES: In week 53, six rats per sex and group were placed in metabolism cages. Faeces and urine were collected over a 4-day period, and the excretion of calcium and phosphorus (atomic absorption) was determined and related to the dietary intake

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
- end of month 18, all rats were killed on a number of successive working days by exsanguination from the abdominal aorta, under light ether anaesthesia, and subjected to a thorough post-mortem examination. Any abnormalities were recorded and the adrenals, brain, pituitary, kidneys, liver, spleen, testes, ovaries, thyroid, and heart were weight. Paired organs were weighed together.

HISTOPATHOLOGY: Yes
- The following tissues were preserved in 10% neutral phosphate buffered formalin: adrenals, aorta, axillary lymph nodes, brain, caecum, coagulating gland, colon, epididymides, exorbital lachrimal gland, eyes, heart, kidneys, liver, lungs, mammary gland, mesenteric lymph nodes, oesophagus, ovaries, pancreas, parathyroids, parotic salivary glands, pituitary, preputial/clitoral glands, prostate, rectum, seminal vesicles, skeletal muscle, skin, small intestine (duodenum, ileum, jejunum), spleen, sternum with bone marrow, stomach, submaxillary salivary glands, testes, thymus, thyroid, urinary bladder, uterus, and all gross lesions. The lungs and urinary bladder were inflated with the fixative. Paraffin-embedded, 5 µm sections of the above tissues from all animals of each sex in the control group, the potassium hydrocarbon and the ammonium chloride high-dose group were stained with haematoxylin and eosin and examined microscopically. Adrenals, heart, kidneys, stomach, thyroid, testes, urinary bladder, and uterus were also examined in the intermediate-dose groups.

Clinical signs:

no effects observed

Description (incidence and severity):

- Clinical signs: no treatment-related abnormalities in condition or behaviour; there was only the usual random incidence of ageing symptoms that occur in this strain of rats when maintained over a period of time
- Grossly visible or palpable masses: no treatment-related effects

Mortality:

no mortality observed

Description (incidence):

- Mortality and time of death: mortality rate was not affected

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

- mean body weights decreased in males of the high dose group (decrease in the range of 4 to 10%, no exact data given)

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

- Food consumption: no treatment-related effects
- ACTUAL DOSE RECEIVED BY DOSE LEVEL BY SEX:
-- males: 1299 and 2861 mg/kg bw/d (9.4 and 20.7 mmol/kg bw/d)
-- females: 1686 and 3566 mg/kg bw/d (12.2 and 25.8 mmol/kg bw/d)
(recalculation of dose from data given in mmol/kg bw/d (molecular weight=138.21 mg/mmol) )

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

- in the 2% and the 4% dose group approximately 10% and 40% increased, respectively

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

- no consistent or treatment-related effects on red blood cell variables, clotting potential or total and differential white blood cell counts

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

- Blood gas analysis: dose-related increase in base excess, associated with higher blood pH and bicarbonate concentrations
- Clinical biochemistry:potassium levels in plasma were generally increased in males and females fed 2 or 4% potassium hydrogencarbonate, although the differences with the controls were not always statistically significant; significant base excess in both sexes of both dose groups; no treatment-related effects on further measured blood clinical biochemistry parameters

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

- Urine parameter of non-fasted animals: urine volume increased in both sexes of the high dose group, in females, this finding was no longer apparent in the later stages of the study, which may have been due to the high values obtained in the control group; the urinary density did not show consistent differences but tended to be decreased in males of the high dose group; potassium excretion increased in both sexes in both dose groups; urinary sodium excretion tended to be relatively high at various occasions in rats fed 4% potassium hydrogencarbonate, which may be ascribed to the natriuretic effect of high potassium intake but the figures showed large variations; no treatment related effects on excretion of calcium, phosphate, sulphate, gamma glutamyl transferase or hydroxyproline
- Urinary pH and acid indices: pH increased in both dose groups, net acid excretion (= ammonium ion (NH4+) excretion + urinary titratable acidity - bicarbonate excretion) considerable decreased in both sexes of the high dose group, and to a lesser extend in the low dose group
- Concentrating ability of the kidneys: the renal concentration test (no food and water available prior to and during urine sampling) showed a slightly increased volume associated with a somewhat decreased density of the urine in males of both dose groups and in females of the high dose group in week 77; brownish discoloration of the urine and haematuria, as detected with urinary test stripes and by microscopic examination of the urinary sediment were occasionally increased, but there were no consistent or dose-related differences in incidence or severity of haematuria among the groups; the occurrence of crystals was not affected in any group

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

- Kidney weights: relative kidney weights in both sexes of both dose groups tendentiously but except of low dose female group not statistically significant increased
- Further examined organ weights: there were no consistent or treatment-related changes in the weights of adrenals, brain, testes, liver, spleen, ovaries, pituitary, thyroid, or heart

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

- Macroscopic examination of the urine bladder: some animals showed thickening and/or induration of the urinary bladder wall, irregular serosal surface and/or luminal dilatation; on male of the 4% group was found to have a grossly visible bladder mass, which extended into the dorsal prostate; bladder stones were not observed
- Macroscopic examination of further organs and tissues: no significant differences among the treatment groups and the controls

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

- Adrenals: in both sexes of the high dose group, the zona glomerosa was distinctly wider than in controls, the cells in this area were enlarged and showed a finely vacuolar cytoplasm (13-15 animals per sex and dose examined (both survivors and intercurrent deaths), findings in the low and high dose group in 3 (not significant) and 10 males (significant, control: 0), respectively, and 2 (not significant) and 9 females (significant, control: 0), respectively. This microscopic finding was interpreted by the study authors as adaptive response to chronic simulation of the adrenal cortex by potassium cations.
- Kidneys: in both sexes of both dose groups, oncocytic tubules but no treatment-related significant severe or very severe nephrosis or urothelial hyperplasia in the pelvis (13-15 animals per sex and dose examined (both survivors and intercurrent deaths), findings in the low and high dose group in 4 (significant) and 15 males (significant, control: 0), respectively, and 5 (significant) and 13 females (significant, control: 0), respectively. The oncocytic tubules were characterised by tubules lined with, often hypertrophy, epithelial cells containing eosinophilic granular cytoplasm (oncocytes), often showing a cystically dilated lumen with epithelial cells protruding into the lumen. As discussed by the study authors, oncocytic tubules do occur spontaneously in untreated rat and are commonly observed in aged males, regarded as regenerative hyperplasia or as a functional tubular hyperplasia in order to meet increased work load. The authors suggested that the hydrogen carbonate anion mainly determined the increased occurrence of this lesion.
- Urinary bladder: in both sexes of both dose groups, the incidences of simple epithelial hyperplasia, of papillary hyperplasia and nodular hyperplasia were increased. However significantly and dose depended increases were limited to simple epithelial hyperplasie in both males and females of the low and the high dose group and papillary epithelial hyperplasia, nodular epithelial hyperplasia and transitional-cell papilloma (one or multiple) in the high dose females.
--Simple epithelial hyperplasia in 0/15, 5/13 (significant) and 6/15 (significant) males, and 1/15, 5/15 (not significant) and 9/15 (significant) females in the control, the low- and the high-dose group, respectively
-- Papillary epithelial hyperplasia in 0/15, 4/13 (significant) and 1/15 (not significant) males, and 0/15, 1/15 (not significant) and 5/15 (significant) females in the control, the low- and the high-dose group, respectively
-- Nodular epithelial hyperplasia in 0/15, 2/13 (not significant) and 0/15 (not significant) males, and 0/15, 1/15 (not significant) and 4/15 (not significant) females in the control, the low- and the high-dose group, respectively
-Reproductive organs: no treatment-related effects (coagulating gland, epididymides, prostate, seminal vesicles, testes, mammary gland, ovaries, uterus, and preputial/clitoral glands examined)
-Further examined organs and tissues: no treatment-related effects

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

- Urinary bladder:
-- Transitional-cell papilloma (one or multiple) in 0/15, 0/13 (not significant) and 0/15 (not significant) males, and 0/15, 0/15 (not significant) and 2/15 (not significant) females in the control, the low- and the high-dose group, respectively
-- Transitional-cell carcinoma in 0/15, 0/13 (not significant) and 1/15 (not significant) males, and 0/15, 0/15 (not significant) and 2/15 (not significant) females in the control, the low- and the high-dose group, respectively
- Total tumour incidence: Apart from preneoplastic and neoplastic lesions in the urinary bladder, there were no treatment-related changes in any specific tumor type among the groups; potassium hydrogencarbonate did neither affect type, incidence and multiplicity of tumours, nor time of tumor appearance and the ratio benign-malignant tumours.

HISTORICAL CONTROL DATA
- Neoplastic alterations of urinary bladder: Historical control data obtained in 18 different chronic (exact duration not mentioned) studies with Wistar rats of the laboratory revealed no papillomas or carcinomas of the urinary bladder in 795 male and 777 female control rats.

Other effects:

no effects observed

Description (incidence and severity):

- Calcium content in femur: no treatment-related effects
- Excretion of calcium and phosphorus in faeces and urine: no treatment-related effects

Dose descriptor:

NOAEL

Effect level:

2 861 mg/kg bw/day (actual dose received)

Sex:

male

Basis for effect level:

other: see 'Remark'

Dose descriptor:

NOAEL

Effect level:

3 566 mg/kg bw/day (actual dose received)

Sex:

female

Basis for effect level:

other: see 'Remark'

Critical effects observed:

no

Conclusions:

No carcinogenic potential for potassium hydrogencarbonate has been concluded by evaluating the results of this study. By read across the same conclusion can be drawn for potassium carbonate.

Executive summary:

In a 78 -week (18-month) toxicity study potassium hydrogencarbonate (a.i. >99.5%) was administered to 15 Wistar rats, strain SPF Cpb:WU/sex/dose in the diet at dose levels of 0, 2 and 4% (0, 1299 and 2861 mg/kg bw/d (9.4 and 20.7 mmol/kg bw/d) in males, respectively and 0, 1686 and 3566 mg/kg bw/d (12.2 and 25.8 mmol/kg bw/d) in females, respectively, based on body weight and food consumption.

Object of the study was to examine the effects of died-induced acid-base disturbances. Albeit the study was not performed according to a explicit mentioned international guideline, accomplishment and documentation cover a broad range of the requirements of the usual guidelines for repeated dose toxicity studies. The dose level exceeds the guideline limit dose for repeated dose toxicity studies which is 1000 mg/kg bw/d in the low dose group by almost 30 or 70 % and in the high dose group by almost 190 or 260 % for males and females, respectively.

The rats adapted relatively easily to the feeding of these very high doses and were free of treatment related adverse effects relevant to humans. Most treatment related changes seen are an expression of the physiological adaptation to the very high ion intake and regarded as of no toxicological relevance. In the urinary bladder significant preneoplastic histopathological epitelial alterations have developed, which are common findings in rats after long term high dose alkali intakes. The relevance to humans of preneoplastic or neoplastic urinary bladder findings in rats induced by high dose alkali intakes (e.g. as counterions in food additives like artificial sweetener or flavour enhancer) and associated by alkalinization of the urine, elevated urine volumes, altered urine electrolytes composition with or without renal pelvic mineralization or urine precipitation which leads to a cyctotoxic effect on the bladder epithelium with consequent regenerative proliferation and ultimately tumors have been discussed for a long time (e.g. by the International Agency for Research on Cancer as part of the World Health Organization (IARC) in the IARC Monography Vol. 73 (1999) and in the IARC Scientific Publication No 147 (1999) or more recently by the European Food Safety Authority (EFSA) in the option on Aspartam (2006) or a review by Cohen, SM on Thresholds in Genotoxicity and Carcinogenicty: Urinary Bladder Carcinogenisis (2008)). It is widely accepted that these high dose effects are specific to the rat and are of no relevance to humans.

Apart from the discussed preneoplastic histopathological epithelial alterations in the urinary bladder, there were no treatment-related changes in any specific tumor type among the groups; potassium hydrogencarbonate did neither affect type, incidence and multiplicity of tumors, nor time of tumor appearance and the ratio benign-malignant tumours.

The NOAEL relevant to humans is the highest dose tested of 4 % in diet, based on body weight and diet intake corresponding to 2861 mg/kg bw/d (20.7 mmol/kg bw/d) in males and 3566 mg/kg bw/d (25.8 mmol/kg bw/d) in females.

The study has been part of a study set comprising of this 78 -week (18 month) study, a 4 -week study, a 13 -week study and a 30-month study. The dose levels in all studies were 2 and 4% in diet. A summarizing discussion of the results of the whole study set is given in the endpoint summary on repeated dose toxicity.

Reference 3

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

Non-guideline 30-month-study to examine the effects of died-induced acid-base disturbances. Diets were supplemented with high amounts of potassium hydrogencarbonate (2% or 4%, base-forming diets), ammonium chloride (2.1% acid forming diet) or potassium chloride (3%, neutral diet, providing K+ and Cl- in amounts equimolar to those in the 4% potassium hydrogencarbonate and the 2.1% ammonium chloride diet, respectively).

Species:

rat

Strain:

Wistar

Sex:

male/female

Route of administration:

oral: feed

Remarks:

Doses / Concentrations:
2 and 4 % in the diet
Basis:
nominal in diet

No. of animals per sex per dose:

50

Control animals:

yes, plain diet

Details on study design:

Study groups
- control group: unsupplemented institutes cereal based rodent diet
- 2% potassium hydrogencarbonate in diet (approximately 1285 mg/kg bw/d for males and 1576 mg/kg bw/d for females)
- 4% potassium hydrogencarbonate in diet (approximately 2667 mg/kg bw/d for males and 3330 mg/kg bw/d for females)
- Satellite groups: 2.1% NH4Cl (acid-forming diet) and neutral diet supplemented with 3% KCl providing K+ and Cl- in amounts equimolar to those in the 4% KHCO3 diet and the 2.1% NH4Cl diet, respectively
Post-exposure period: none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily, including evaluation regarding grossly visible or palpable masses at regular intervals

BODY WEIGHT: Yes
- Time schedule for examinations: weekly or (from 3 months) once every 4 weeks

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes, measured weekly or (from 3 months) once every 4 weeks per cage
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes, calculated per cage

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

WATER CONSUMPTION: Yes,
- Time schedule for examinations: daily per cage in weeks 1, 4, 6, 8, 12, 55, and 75 (24 hours consumption)

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: weeks 4, 13, 32, 55, and 75 (tail tip blood)
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 per group and sex
- Parameters examined: haemoglobin concentration, packed cell volume, red blood cells, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, thrombocytes, total white blood cells, prothrombin time, and differential white blood cells

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: weeks 5, 14, 32, 56, 76, and 121 (for blood gas analysis)
- Animals fasted: No data
- How many animals: 10 per group and sex
- Parameters examined.:
--Blood gas analysis (tail tip blood): determination of pH, pCO2 and pO2 directly after sampling in capillary tubes, and calculation of bicarbonate and base excess
-- Clinical chemistry: not performed

URINALYSIS: Yes (Urinary acid indices)
- Time schedule for collection of urine: weeks 1, 4, 6, 10, 14, 36, 57, 76, and 129
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (no food and water for 2-3 h at the start of the light period)
- How many animals: all
- Parameters examined in fasted animals: urinary pH was measured in individual samples, mean pH values were calculated as the negative logarithm of the mean of the hydrogen concentrations instead of as the arithmetical mean of the individual pH values; bicarbonate, titratable acid, ammonia, and urea were measured in pooled samples (two samples per group and sex) and related to creatinine

URINALYSIS: Yes (standard urine parameter)
- Time schedule for collection of urine: weeks 6, 16, 38, and 78
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- How many animals: 10 per group and sex
- Parameters examined: volume (calibrated tubes), density, gamma glutamyl transferase, creatinine, urea, calcium, potassium, sodium, phosphate, and sulphate

URINALYSIS: Yes (hydroxyprolin)
- Time schedule for collection of urine: weeks 11 and 76
- Metabolism cages used for collection of urine: No data
- Animals fasted: No
- How many animals: 10 per group and sex (two samples from five rats per group and sex)
- Parameter examined: hydroxyproline

URINALYSIS: Yes (Concentrating ability of the kidneys)
- Time schedule for collection of urine: weeks 4, 7, 13, 14, 36, 57, 77, and 129
- Metabolism cages used for collection of urine: No data
- Animals fasted: Yes, urine collected during the last 16 h of a 24-h water deprivation period, during the 16-h collection period no feed was available
- Parameters examined: volume (graduated tubes), density, and in addition, examinations for protein, glucose, occult blood, ketones, bilirubin, and urobilinogen; appearance, and microscopy of the sediment were carried out in the individual samples collected in weeks 4, 13, 77, 129

NEUROBEHAVIOURAL EXAMINATION: No

OTHER:
- CALCIUM CONTENT in FEMUR: month 30 at autopsy, the right femur from all surviving animals was removed, cleaned from adherent soft tissue and weighed, dried at 100 °C, subjected to fat extraction (petroleum ether), redryed and the weight recorded as fat free solid, the fat free femur was ashed at 550 °C and the calcium content was determined by atomic absorption spectrophotometry
- CALCIUM and PHOSPHORUS EXCRETION in URINE and FAECES: In week 53, six rats per sex and group were placed in metabolism cages. Faeces and urine were collected over a 4-day period, and the excretion of calcium and phosphorus (atomic absorption) was determined and related to the dietary intake

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
- week 122 (males) and week 131 (females), all rats were killed on a number of successive working days by exsanguination from the abdominal aorta, under light ether anaesthesia, and subjected to a thorough post-mortem examination. Any abnormalities were recorded and the adrenals, brain, pituitary, kidneys, liver, spleen, testes, ovaries, thyroid, and heart were weight. Paired organs were weighed together.

HISTOPATHOLOGY: Yes
- The following tissues were preserved in 10% neutral phosphate buffered formalin: adrenals, brain, caecum, coagulating gland, colon, epididymides, exorbital lachrimal gland, heart, joint (knee), kidneys, liver, lungs, mammary gland, mesenteric lymph nodes, oesophagus, ovaries, pancreas, parathyroids, parotic salivary glands, pituitary, preputial/clitoral glands, prostate, rectum, seminal vesicles, small intestine (duodenum, ileum, jejunum), spleen, stomach, submaxillary salivary glands, sublingual salivary glands, testes, thymus, thyroid, urinary bladder, uterus, Zymbal glands, and all gross lesions. The lungs and urinary bladder were inflated with the fixative. Paraffin-embedded, 5 µm sections of the above tissues from all animals of each sex in the control group, the potassium hydrocarbon and the ammonium chloride high-dose group were stained with haematoxylin and eosin and examined microscopically. Adrenals, heart, kidneys, stomach, thyroid, testes, urinary bladder, and uterus were also examined in the intermediate-dose groups.

Clinical signs:

no effects observed

Description (incidence and severity):

- Clinical signs: no treatment-related abnormalities in condition or behaviour; there was only the usual random incidence of ageing symptoms that occur in this strain of rats when maintained over a period of time
- Grossly visible or palpable masses: no treatment-related effects

Description (incidence):

- Mortality and time of death: mortality rate was not affected by treatment; males were killed in week 122 because mortality in the low-dose group reached 70%,; females were killed after completion of this study in week 131; overall mortality rates at termination in control, low- and high-dose group were 62, 70, and 56% for males, respectively, and 69, 65, and 72% for females, respectively

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

- mean body weights decreased in males and females of the high dose group (decrease in the range of 4 to 10%, no exact data given); body weights were also statistically significantly decreased in females of the low dose group at various stages of the study (no further data given)

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

- ACTUAL DOSE RECEIVED BY DOSE LEVEL BY SEX:
-- males: 1285 and 2667 mg/kg bw/d (9.3 and 19.3 mmol/kg bw/d)
-- females: 1576 and 3331 mg/kg bw/d (11.4 and 24.1 mmol/kg bw/d)
(recalculation of dose from data given in mmol/kg bw/d (molecular weight=138.21 mg/mmol) )

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

- in the 2% and the 4% dose group approximately 10% and 40% increased, respectively

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

- no consistent or treatment-related effects on red blood cell variables, clotting potential or total and differential white blood cell counts

Clinical biochemistry findings:

not examined

Description (incidence and severity):

- Blood gas analysis: dose-related increase in base excess, associated with higher blood pH and bicarbonate concentrations
- Clinical biochemistry: not performed

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

- Urine parameter of non-fasted animals: urine volume increased in both sexes of the high dose group, in females, this finding was no longer apparent in the later stages of the study, which may have been due to the high values obtained in the control group; the urinary density did not show consistent differences but tended to be decreased in males of the high dose group; potassium excretion increased in both sexes in both dose groups; urinary sodium excretion tended to be relatively high at various occasions in rats fed 4% potassium hydrogencarbonate, which may be ascribed to the natriuretic effect of high potassium intake but the figures showed large variations; no treatment related effects on excretion of calcium, phosphate, sulphate, gamma glutamyl transferase or hydroxyproline
- Urinary pH and acid indices: pH increased in both dose groups, net acid excretion (= ammonium ion (NH4+) excretion + urinary titratable acidity - bicarbonate excretion) considerable decreased in both sexes of the high dose group, and to a lesser extend in the low dose group
- Concentrating ability of the kidneys: the renal concentration test (no food and water available prior to and during urine sampling) showed a slightly increased volume associated with a somewhat decreased density of the urine in males of both dose groups and in females of the high dose group in week 77; brownish discoloration of the urine and haematuria, as detected with urinary test stripes and by microscopic examination of the urinary sediment were occasionally increased, but there were no consistent or dose-related differences in incidence or severity of haematuria among the groups; the occurrence of crystals was not affected in any group
- Calcium content in femur: no treatment-related effects

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

- Kidney weights: relative kidney weights in females tendentiously but neither dose related nor statistically significant increased, relative kidney weights in males tendentiously and dose related but not statistically significant decreased
- Further examined organ weights: there were no consistent or treatment-related changes in the weights of adrenals, brain, testes, liver, spleen, ovaries, pituitary, thyroid, or heart

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

- Macroscopic examination of the urine bladder: thickening and/or induration of the urinary bladder wall, irregular serosal surface and/or luminal dilatation. Tumorous enlargement of the bladder was seen in one female animal of the 4% ; the mass filled the bladder lumen and was confined to the bladder, i.e. it did not show invasion into, or adhesions with, adjacent tissues. Bladder stones were not observed.
- Macroscopic examination of further organs and tissues: no significant differences among the treatment groups and the controls

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

- Adrenals: in both sexes of both dose groups, the zona glomerosa was distinctly wider than in controls, the cells in this area were enlarged and showed a finely vacuolar cytoplasm (47-50 animals per sex and dose examined (both survivors and intercurrent deaths), findings in the low and high dose group in 22 (significant) and 41 males (significant, control: 4), respectively, and 8 (not significant) and 32 females (significant, control: 7), respectively. This microscopic finding was interpreted by the study authors as adaptive response to chronic simulation of the adrenal cortex by potassium cations.
- Kidneys: in both sexes of both dose groups, oncocytic tubules but no treatment-related significant severe or very severe nephrosis or urothelial hyperplasia in the pelvis (47-50 animals per sex and dose examined (both survivors and intercurrent deaths), findings in the low and high dose group in 32 (significant) and 36 males (significant, control: 18), respectively, and 22 (significant) and 22 females (significant, control: 1), respectively. The oncocytic tubules were characterised by tubules lined with, often hypertrophy, epithelial cells containing eosinophilic granular cytoplasm (oncocytes), often showing a cystically dilated lumen with epithelial cells protruding into the lumen. As discussed by the study authors, oncocytic tubules do occur spontaneously in untreated rat and are commonly observed in aged males, regarded as regenerative hyperplasia or as a functional tubular hyperplasia in order to meet increased work load. The authors suggested that the hydrogen carbonate anion mainly determined the increased occurrence of this lesion.
- Urinary bladder: in both sexes of both dose groups, the incidence of simple epithelial hyperplasia, of papillary and nodular hyperplasia, and of papillomas were increased. However, except of simple hyperplasia , significance was only reach in high dose female group.
-- Cystitis: in 1/48, 0/50 and 0/49 males, and 1/48, 0/48 and 1/47 (not significant) females in the control, the low- and the high-dose group, respectively
-- Simple epithelial hyperplasia in 1/48, 12/50 (significant) and 22/49 (significant) males, and 1/48, 23/48 (significant) and 24/47 (significant) females in the control, the low- and the high-dose group, respectively
-- Papillary epithelial hyperplasia in 0/48, 0/50 and 0/49 males, and 0/48, 2/48 (not significant) and 5/47 (significant) females in the control, the low- and the high-dose group, respectively
-- Nodular epithelial hyperplasia in 0/48, 2/50 (not significant) and 4/49 (not significant) males, and 0/48, 1/48 (not significant) and 11/47 (significant) females in the control, the low- and the high-dose group, respectively
- Reproductive organs: no treatment-related effects (coagulating gland, epididymides, prostate, seminal vesicles, testes, mammary gland, ovaries, uterus, and preputial/clitoral glands examined)
- Further examined organs and tissues: no treatment-related effects

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

- Urinary bladder:
--Transitional-cell papilloma (one or multiple) in 0/48, 4/50 (not significant) and 2/49 (not significant) males, and 0/48, 1/48 (not significant) and 6/47 (significant) females in the control, the low- and the high-dose group, respectively
--Transitional-cell carcinoma in 0/48, 1/50 (not significant) and 1/49 (not significant) males, and 0/48, 1/48 (not significant) and 3/47 (not significant) females in the control, the low- and the high-dose group, respectively
- Total tumour incidence: Apart from preneoplastic and neoplastic lesions in the urinary bladder, there were no treatment-related changes in any specific tumor type among the groups; potassium hydrogencarbonate did neither affect type, incidence and multiplicity of tumours, nor time of tumor appearance and the ratio benign-malignant tumours.

HISTORICAL CONTROL DATA
- Neoplastic alterations of urinary bladder: Historical control data obtained in 18 different chronic (exact duration not mentioned) studies with Wistar rats of the laboratory revealed no papillomas or carcinomas of the urinary bladder in 795 male and 777 female control rats.

Other effects:

no effects observed

Description (incidence and severity):

- Calcium content in femur: no treatment-related effects
- Excretion of calcium and phosphorus in faeces and urine: no treatment-related effects

Dose descriptor:

NOAEL

Effect level:

2 667 mg/kg bw/day (actual dose received)

Sex:

male

Basis for effect level:

other: see 'Remark'

Dose descriptor:

NOAEL

Effect level:

3 331 mg/kg bw/day (actual dose received)

Sex:

female

Basis for effect level:

other: see 'Remark'

Critical effects observed:

no

Conclusions:

No carcinogenic potential for potassium hydrogencarbonate has been concluded by evaluating the results of this study. By read across the same conclusion can be drawn for potassium carbonate.

Executive summary:

In a 130 -week (30-month) toxicity study potassium hydrogencarbonate (a.i. >99.5%) was administered to 15 Wistar rats, strain SPF Cpb:WU/sex/dose in the diet at dose levels of 0, 2 and 4% (0, 1285 and 2667 mg/kg bw/d (9.3 and 19.3 mmol/kg bw/d) in males, respectively and 0, 1576 and 3331 mg/kg bw/d (11.4 and 24.1 mmol/kg bw/d) in females, respectively, based on body weight and food consumption.

Object of the study was to examine the effects of died-induced acid-base disturbances. Albeit the study was not performed according to a explicit mentioned international guideline, accomplishment and documentation cover a broad range of the requirements of the usual guidelines for repeated dose toxicity studies. The dose level exceeds the guideline limit dose for repeated dose toxicity studies which is 1000 mg/kg bw/d in the low dose group by almost 30 or 60 % and in the high dose group by almost 170 or 230 % for males and females, respectively.

The rats adapted relatively easily to the feeding of these very high doses and were free of treatment related adverse effects relevant to humans. Most treatment related changes seen are an expression of the physiological adaptation to the very high ion intake and regarded as of no toxicological relevance. In the urinary bladder significant preneoplastic and neoplastic histopathological epitelial alterations have developed, which are common findings in rats after long term high dose alkali intakes.The relevance to humans of preneoplastic or neoplastic urinary bladder findings in rats induced by high dose alkali intakes (e.g. as counterions in food additives like artificial sweetener or flavour enhancer) and associated by alkalinization of the urine, elevated urine volumes, altered urine electrolytes composition with or without renal pelvic mineralization or urine precipitation which leads to a cyctotoxic effect on the bladder epithelium with consequent regenerative proliferation and ultimately tumors have been discussed for a long time (e.g. by the International Agency for Research on Cancer as part of the World Health Organization (IARC) in the IARC Monography Vol. 73 (1999) and in the IARC Scientific Publication No 147 (1999) or more recently by the European Food Safety Authority (EFSA) in the option on Aspartam (2006) or a review by Cohen, SM on Thresholds in Genotoxicity and Carcinogenicty: Urinary Bladder Carcinogenisis (2008)). It is widely accepted that these high dose effects are specific to the rat and are of no relevance to humans.

Apart from the discussed preneoplastic and neoplastic histopathological epithelial alterations in the urinary bladder, there were no treatment-related changes in any specific tumor type among the groups; potassium hydrogencarbonate did neither affect type, incidence and multiplicity of tumors, nor time of tumor appearance and the ratio benign-malignant tumours.

The NOAEL relevant to humans is the highest dose tested of 4 % in diet, based on body weight and diet intake corresponding to 2667 mg/kg bw/d (19.3 mmol/kg bw/d) in males and 3331 mg/kg bw/d (24.1 mmol/kg bw/d) in females.

The study has been part of a study set comprising of this 130 -week study, a 4 -week study, a 13 -week study, and a 78 -week (18 -month) study. The dose levels in all studies were 2 and 4% in diet. A summarizing discussion of the results of the whole study set is given in the endpoint summary on repeated dose toxicity.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

There is no evidence for an intrinsic carcinogenicity of potassium hydrogencarbonate relevant to humans obtained from the results of reliable long-term studies. Additional information from assessments carried out within the OECD work on investigation of high production volume chemicals on compounds which have a carbonate or a potassium moiety also gave no indications on an intrinsic carcinogenic activity of potassium hydrogencarbonate. Moreover, there is no evidence for a clastogenic or mutagenic potential of potassium hydrogencarbonate from reliable studies on closely related read-across substances potassium carbonate or potassium chloride and in addition, based on chemistry considerations on the structure of potassium hydrogencarbonate, no carcinogenicity is expected.

Therefore, no classification is required for carcinogenicity according to CLP Regulation (EC) No 1272/2008.

Additional information

Reliable, adequate and relevant studies on potassium hydrogencarbonate covering the endpoint carcinogenicity are available and described in more detail in chapter 5.6 Repeated Dose Toxicity. These studies include two long-term studies (18 -months, and 30 -months) in which rats were treated with very high doses of potassium hydrogencarbonate in their feed (2 and 4%). The studies were not performed according to explicitly mentioned international guidelines, but their accomplishment and documentation cover a broad range of the requirements of the usual guidelines for repeated dose toxicity and carcinogenicity studies. Thus, these studies are relevant, reliable and adequate for the purpose of assessing repeated dose toxicity as well as carcinogenicity. Even the low dose level of this study set exceeds the guideline limit dose for repeated dose toxicity studies to a considerable degree, no treatment related toxic effects relevant to humans were seen.

After 18-months and 30-months of treatment few potassium hydrogencarbonate-fed animals showed thickening and/or induration of the urinary bladder wall and irregular serosal surface and/or luminal dilatation of the urinary bladder. At 18 months 1/15 males of the 4% group was found to have a grossly visible bladder mass, which extended into the dorsal prostate. At 30 months tumorous enlargement of the bladder was seen in 1/47 female in the 4% group. Bladder stones were not observed. Microscopic examination of the urinary bladder showed very slight to slight simple epithelial hyperplasia in both dose groups, which was not significant after 4 or 13 weeks of treatment, and became significant after 18 months of treatment in low and high dose males and high dose females, and was also significant after 30 months of treatment in both sexes of both dose groups. Significant papillary epithelial hyperplasia of the urinary bladder was seen in the high dose females treated 18 months and dose independently in the low dose males of this study, and the high dose females treated 30 months, which also showed significant nodular epithelial hyperplasia and transitional-cell papilloma.

The relevance to humans of preneoplastic or neoplastic urinary bladder findings in rats induced by high dose alkali intakes (e. g. as counter ions in food additives like artificial sweetener or flavour enhancer) have been discussed for a long time (e. g. by the International Agency for Research on Cancer as part of the World Health Organization (IARC) in the IARC Monography Vol. 73 (1999) and in the IARC Scientific Publication No 147 (1999) or more recently by the European Food Safety Authority (EFSA) in the option on Aspartam (2006) or a review by Cohen, SM (2008)). Preneoplastic or neoplastic urinary bladder findings in the rat in connection with high dose alkali intakes are in general associated with alkalinization of the urine, elevated urine volumes, altered urine electrolytes composition with or without renal pelvic mineralization or urine precipitation which leads to cytotoxic effect on the rat bladder epithelium with consequent regenerative proliferation and ultimately tumors. It is widely accepted that these high dose effects are specific to the rat and are of no relevance to humans.

In conclusion, there were no treatment-related changes in any specific tumor type among the groups; potassium hydrogencarbonate did neither affect type, incidence and multiplicity of tumors, nor time of tumor appearance and the ratio benign-malignant tumours.