Oxalic acid in the yard and garden
Moderate risk for your yardOxalic acid (ethanedioic acid; (COOH)₂; C₂H₂O₄) is the simplest dicarboxylic acid, occurring naturally in many plants (rhubarb, spinach, purslane, beet greens, sorrel, chocolate, nuts) and produced endogenously as a terminal metabolite of ascorbic acid (vitamin C) and glyoxylate oxidation. Natural plant sources: rhubarb stalks contain approximately 450 mg/100g oxalic acid (leaves contain far higher concentrations — 700–1000 mg/100g — and rhubarb leaves are toxic, particularly to pets); spinach 600–750 mg/100g; purslane 1300 mg/100g. Toxicological mechanisms: oxalic acid binds calcium ions to form insoluble calcium oxalate crystals — in the urinary system, these crystals cause nephrolithiasis (calcium oxalate kidney stones, the most common kidney stone type, ~80% of all stones); acute high-dose oxalic acid poisoning causes hypocalcemia (tetany, cardiac arrhythmia), renal tubular obstruction, and renal failure. Industrial uses: metal cleaning and descaling, bleaching of textiles and wood pulp, rust removal, leather tanning, and wastewater treatment. Industrial oxalic acid (concentrated solutions and crystals) is corrosive and poses significant GI and systemic toxicity risk. Estimated acute oral lethal dose in adults: ~15–30 g (concentrated oxalic acid); typical plant food sources are orders of magnitude below toxic acute doses. Dietary intake: average dietary oxalate intake is 100–300 mg/day from plant foods — well below acute toxic thresholds, but relevant to chronic kidney stone formation in hyperoxaluric individuals. Hyperoxaluria: hereditary primary hyperoxaluria (types I, II, III — mutations in glyoxylate metabolism enzymes) causes massive endogenous oxalate production → recurrent calcium oxalate stones → progressive renal failure — treated with kidney-liver transplant or lumasiran (RNAi therapy).
What is oxalic acid?
Also known as: ethanedioic acid, Aktisal, Aquisal, Oxiric acid.
- IUPAC name
- oxalic acid
- CAS number
- 144-62-7
- Molecular formula
- C2H2O4
- Molecular weight
- 90.03 g/mol
- SMILES
- C(=O)(C(=O)O)O
- PubChem CID
- 971
Risk for people, pets,
Moderate riskOxalic acid (ethanedioic acid; (COOH)₂; C₂H₂O₄) is the simplest dicarboxylic acid, occurring naturally in many plants (rhubarb, spinach, purslane, beet greens, sorrel, chocolate, nuts) and produced endogenously as a terminal metabolite of ascorbic acid (vitamin C) and glyoxylate oxidation. Natural plant sources: rhubarb stalks contain approximately 450 mg/100g oxalic acid (leaves contain far higher concentrations — 700–1000 mg/100g — and rhubarb leaves are toxic, particularly to pets); spinach 600–750 mg/100g; purslane 1300 mg/100g. Toxicological mechanisms: oxalic acid binds calcium ions to form insoluble calcium oxalate crystals — in the urinary system, these crystals cause nephrolithiasis (calcium oxalate kidney stones, the most common kidney stone type, ~80% of all stones); acute high-dose oxalic acid poisoning causes hypocalcemia (tetany, cardiac arrhythmia), renal tubular obstruction, and renal failure. Industrial uses: metal cleaning and descaling, bleaching of textiles and wood pulp, rust removal, leather tanning, and wastewater treatment. Industrial oxalic acid (concentrated solutions and crystals) is corrosive and poses significant GI and systemic toxicity risk. Estimated acute oral lethal dose in adults: ~15–30 g (concentrated oxalic acid); typical plant food sources are orders of magnitude below toxic acute doses. Dietary intake: average dietary oxalate intake is 100–300 mg/day from plant foods — well below acute toxic thresholds, but relevant to chronic kidney stone formation in hyperoxaluric individuals. Hyperoxaluria: hereditary primary hyperoxaluria (types I, II, III — mutations in glyoxylate metabolism enzymes) causes massive endogenous oxalate production → recurrent calcium oxalate stones → progressive renal failure — treated with kidney-liver transplant or lumasiran (RNAi therapy).
Regulatory consensus
5 regulatory and scientific bodies have classified Oxalic acid. The classifications differ — that's the data.
| Agency | Year | Classification | Notes |
|---|---|---|---|
| EPA CTX / Genetox | — | Genotoxicity: negative (Ames: negative, 0 positive / 5 negative reports) | |
| EPA CTX / Genetox | — | Genotoxicity: negative (Ames: negative, 0 positive / 5 negative reports) | |
| FDA | — | GRAS as natural food component; no specific food additive approval | |
| ECHA | — | H302 harmful if swallowed; H312 harmful in contact with skin | |
| OSHA | — | PEL 1 mg/m3 TWA (respirable) |
Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.
Where your yard encounter oxalic acid
- Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
- Occupational Environments — Factories, Warehouses, Transportation vehicles
- Food — processed food, beverages, candy, baked goods
- Natural Foods — spinach, rhubarb, beets, Swiss chard, star fruit
- Cleaning Products — Bar Keepers Friend, wood bleach/deck brightener, rust removers, metal polish
- Industrial — marble polishing, textile bleaching, wastewater treatment (precipitant)
- Automotive — radiator flush, aluminum brightener
Safer alternatives
Lower-risk approaches that achieve a similar outcome to Oxalic acid:
-
Fragrance-free formulations
Trade-offs: Consumer preference for scented productsRelative cost: Lower (ingredient elimination)
-
Essential oil-based fragrances (with disclosure)
Trade-offs: Natural does not mean safe — many essential oils are skin sensitizersRelative cost: 2-5× conventional
Frequently asked questions
Is oxalic acid safe for your yard?
Oxalic acid (ethanedioic acid; (COOH)₂; C₂H₂O₄) is the simplest dicarboxylic acid, occurring naturally in many plants (rhubarb, spinach, purslane, beet greens, sorrel, chocolate, nuts) and produced endogenously as a terminal metabolite of ascorbic acid (vitamin C) and glyoxylate oxidation. Natural plant sources: rhubarb stalks contain approximately 450 mg/100g oxalic acid (leaves contain far higher concentrations — 700–1000 mg/100g — and rhubarb leaves are toxic, particularly to pets); spinach 600–750 mg/100g; purslane 1300 mg/100g. Toxicological mechanisms: oxalic acid binds calcium ions to form insoluble calcium oxalate crystals — in the urinary system, these crystals cause nephrolithiasis (calcium oxalate kidney stones, the most common kidney stone type, ~80% of all stones); acute high-dose oxalic acid poisoning causes hypocalcemia (tetany, cardiac arrhythmia), renal tubular obstruction, and renal failure. Industrial uses: metal cleaning and descaling, bleaching of textiles and wood pulp, rust removal, leather tanning, and wastewater treatment. Industrial oxalic acid (concentrated solutions and crystals) is corrosive and poses significant GI and systemic toxicity risk. Estimated acute oral lethal dose in adults: ~15–30 g (concentrated oxalic acid); typical plant food sources are orders of magnitude below toxic acute doses. Dietary intake: average dietary oxalate intake is 100–300 mg/day from plant foods — well below acute toxic thresholds, but relevant to chronic kidney stone formation in hyperoxaluric individuals. Hyperoxaluria: hereditary primary hyperoxaluria (types I, II, III — mutations in glyoxylate metabolism enzymes) causes massive endogenous oxalate production → recurrent calcium oxalate stones → progressive renal failure — treated with kidney-liver transplant or lumasiran (RNAi therapy).
What products contain oxalic acid?
Oxalic acid appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments); processed food (Food).
Why do regulators disagree about oxalic acid?
Oxalic acid has been classified by 5 agencies including EPA CTX / Genetox, EPA CTX / Genetox, FDA, ECHA, OSHA, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.
See Oxalic acid in the outdoor app
Look up products containing oxalic acid, compare to alternatives, and explore the full data record.
Open in outdoor View raw API dataSources (2)
- NIOSH: Oxalic Acid — calcium chelation; calcium oxalate nephrolithiasis; hypocalcemia; rhubarb leaf toxicity; industrial cleaner hazard; primary hyperoxaluria; ethylene glycol metabolism (2019) (2019) — regulatory
- CDC/ATSDR: Oxalic Acid Toxicological Profile — plant sources; dietary intake; renal tubular deposition; acute poisoning treatment; industrial uses; calcium oxalate crystals; pediatric rhubarb exposure (2020) (2020) — regulatory
Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →