Oxalic acid
The toxicity of oxalic acid is due to kidney failure caused by precipitation of solid calcium oxalate, the main component of calcium kidney stones. Oxalic acid can also cause joint pain by formation of similar precipitates in the joints. Ingestion of ethylene glycol results in oxalic acid as a metabolite which can also cause acute kidney failure. Calcium hydroxide ("slaked lime") decreases urinary oxalate in both humans and rats.