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Description of key information

Effects of oxalic acid can only be expected at supra-physiological concentrations of oxalate, such as in case of chronic renal failure.

Additional information

The role of oxalic acid in renal failure and kidney stone formation is studied extensively, mostly by in vitro research, based on the presence of calcium oxalate monohydrate (COM) crystals in kidney stones. A summary of the publications provided in this dossier is presented below.

Study reference

Study type

Results

Reliability

NON KEY_1986_lit_Blumenfrucht

Rat model of oxalosis after intravenous exposure (in vivo)

Appearance of point source autoradiographs in heart, liver, lungs and in occasional glomerular capillaries suggest rapid formation of minute calcium oxalate crystals

2

NON KEY_2005_lit_Guo

Cytotoxicity of oxalate ions and calcium oxalate monohydrate (COM) crystals in human and rat proximal tubule cells (in vitro)

Hemolysis of proximal tubule cells was caused by COM crystals, not by oxalate ions (in vitro).

2

NON KEY_2004_lit_Knoll

Effects of oxalate on distinct renal epithelial and endothelial cells as well as fibroblasts (in vitro)

Sodium oxalate has a negative effect on the growth and survival of renal epithelial and endothelial cells and fibroblasts.

2

NON KEY_2005_lit_Verkoelen

Effect of oxalate ions as well as COM crystals on renal proximal and collecting tubule cells (in vitro)

Oxalate ions were toxic only at superphysiological concentration, COM crystals are toxic to renal tubular cells only, which do normally not encounter crystals.

2

NON KEY_2005_lit_Schepers

Effect of oxalate to renal proximal and collecting tubule cells in culture (in vitro)

Oxalate ions were toxic only at superphysiological concentration.

2

NON KEY_1996_lit_Scheid

Effects of oxalate exposure on production/availability of free radicals in renal proximal tubule cells (in vitro)

Hyperoxaluria may contribute to the progression of renal injury in several forms of renal disease.

2

NON KEY_1988_lit_Tonon

Metabolic effects of oxalic acid in perfused liver compared to isolated liver cells

Oxalate is less toxic for the intact liver than for isolated hepatocytes.

2

Oxalic acid is toxic to renal cell lines in superphysiological concentrations only. The toxicity of calcium oxalate monohydrate crystals is higher. In vivo experiments show that after intravenous exposure to oxalate, precursors of these COM crystals may be formed. However, these effects seem to be dependent on exposure route. Furthermore, the experiment with perfused liver shows that the effect observed in in vitro studies occur at lower concentrations, and are therefore overestimating the toxicity of oxalic acid. In conclusion, effects of oxalic acid can only be expected at supra-physiological concentrations of oxalate, such as in case of chronic renal failure.

In assessing the hazard of oxalic acid, it should be kept in mind that oxalic acid is a natural substance which is present in various food substances, and in this way is consumed by the general population daily. From Gold et al (2001), the following table was derived, in which the average daily consumption of oxalic acid containing food is summarized. A total average daily consumption of 68.4 mg oxalic acid can be calculated from this table.

Food substance (average daily consumption)

Average daily oxalic acid consumption

Coffee (500 mL)

25.2 mg

Carrot (boiled, 12.1 g)

22.7 mg

Tea (60.2 mL)

6.67 mg

Chocolate (cocoa solids, 3.34 g)

3.91 mg

Tomato (88.7 g)

3.24 mg

Celery (7.95 g)

1.39 mg

Potato (54.9 g)

1.26 mg

Corn (33.8 g)

1.12 mg

Apple (32.0 g)

704 µg

(10.5 g)

651 µg

Lettuce (14.9 g)

447 µg

Broccoli (6.71 g)

268 µg

Strawberry (4.38 g)

261 µg

Cabbage (boiled, 12.9 g)

155 µg

Grapes (11 g)

138 µg

Cucumber (raw flesh, 11.8 g)

118 µg

Peach (canned, 9.58 g)

115 µg

Onions (green, cooked, 137 mg)

31.5 µg

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