Here's what I found about Formic Acid:
Formic acid is readily metabolized and eliminated by the body. Nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness, seen in methanol poisoning. Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen. Chronic exposure in humans may cause kidney damage. Another possible effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.
Of 16 persons
who swallowed 45 to 200 g formic acid, 9 died as a result of perforation in the gastrointestinal tract and 5 of acute kidney failure (BUA 1991).
In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg. It has been reported that the lethal oral dose is 15 to 30 grams.
Oxalate may enter cells where it is known to cause mitochondrial dysfunction.
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.
For oxalic acid, the formation of kidney stones require a daily dose upwards of 200mg/day or so, which if far in excess of anything we could encounter in the apiary. Moreover, this must be a chronic intake, happening over periods of weeks to months.
Based on the general logic of contaminants in honey. Seems to me that neither Formic nor Oxalic acid should be used with honey supers present, if one wishes to avoid contaminating honey for customers.