Oxalic acid (aka ethanedioic acid or oxalate) is an organic compound, with the chemical formula of C2H2O4. In its solid state, the acid forms white crystals, and when combined with water, creates a colourless solution. It is naturally occurring in many vegetables. The compound is classified as the simplest dicarboxylic acid. [1,2]
Oxalic acid is used in a range of chemical applications. Its primary use is as an ingredient in cleaning agents. Its corrosive nature means it is used in a range of bleaches, detergents, cleaning products, and as a rust remover. The acid is also used across the board as a sterilising agent, including in corporate and medical industries. Oxalic acid is used as a bleach in textile mills and factories and in mineral processing.
Routes of Exposure 
Oxalic acid is naturally occurring in a range of vegetables, including potatoes, leafy greens, broccoli, and sprouts. Leafy greens, such as spinach, are the most concentrated source of oxalates (in regards to vegetables). Vegetables that are high in the acid are not dangerous in small doses.
More dangerous routes of exposure are from the cleaning products where oxalic acid is included as an ingredient.
Oxalic acid poisoning affects a range of systems, including the urinary and integumentary systems.
Acute Effects [1,3]
Severity of symptoms depend on the level and type of exposure.
Acute doses of oxalic acid can occur if large quantities of the acid are accidentally ingested—as a pure substance, or through vegetables that are highly concentrated. High levels of ingestion can cause death. Oxalic acid crystals can cause chemical burns, and acute exposure to the vapour can result in internal chemical burns.
Chronic Effects [1,3]
Chronic exposure to oxalic acid is toxic to multiple body systems. Long term exposure to the acid can corrode tissue throughout the body. This includes on the mucosa of the mouth, the oesophagus, and the stomach. It can also cause great thirst, bloody vomit, convulsions, coma, and death. Over time, oxalate crystals can break down in the body, forming kidney stones. This can cause various gastrointestinal complications and/or kidney failure. People who consume a lot of vitamin C are also in the higher risk category, as when the vitamin is broken down, it releases oxalic acid, which can, again, result in kidney stones.
First Aid Measures 
Ingestion: DO NOT INDUCE VOMITING. If spontaneous vomiting occurs, place the victim’s head below their hips to prevent the acid moving into their lungs. Get immediate medical attention.
Skin contact: Remove all contaminated clothing, footwear and accessories. Do not re-wear clothing until it has been thoroughly decontaminated. Immediately rinse affected areas with plenty of water. If symptoms persist, contact a doctor immediately.
Eye contact: Flush eyes (including under the eyelids), with water for several minutes. Check for, and remove, any contact lenses (if easy to do so). Continue rinsing. If irritation persists, contact a medical professional.
Inhalation: Take victim to the nearest fresh air source and monitor their breathing. Keep the victim warm. If the victim is not breathing, and you are qualified, you may perform CPR with a one-way valve or protective mask. Immediately contact a medical professional.
General: Never administer anything by mouth to an unconscious, exposed person.
Exposure Controls/Personal Protection 
Engineering controls: Emergency eyewash fountains and quick-drench areas should be accessible in the immediate area of the potential exposure. Ensure there is adequate ventilation. Use a local exhaust ventilation or process enclosure, to limit the amount of acid in the air.
Personal protection: Safety glasses, protective and dustproof clothing, gloves, an apron and an appropriate mask or dusk respirator. Wear impervious shoes. Do not wear contact lenses. For specifications regarding other PPE, Follow the guidelines set in your jurisdiction.
The Occupational Safety and Health Administration (OSHA) has set an 8-hour time weighted average (TWA) concentration limit for oxalic acid of 1mg/m3.
Safe Work Australia has set an 8-hour time TWA for oxalic acid of 1mg/m3.