Following are the up-to-date recommendations for the use oxalic acid as a treatment for varroa mites in honey bee colonies. The article includes:
- Oxalic Acid Treatment Protocol — Trickle Method (preferred) and Vaporization Method
- Oxalic Acid Safety Sheet — including an Emergency Overview
- Oxalic Acid Facts
This information is published here by kind permission of the Tech-Transfer Team of the Ontario Beekeepers Association.
Oxalic Acid Treatment Protocol
Trickle Method
(Recommended method in Ontario)
Preparation:
• Prepare 50% sugar syrup (eg. 1 kg of sugar in 1 L of water).
• Measure 1 L of syrup and add 35 g of oxalic acid dihydrate (min. 99.6% purity) crystals.
• Agitate the solution by stirring vigorously or shaking.
• The crystals dissolve best if the sugar solution is warm (not hot). All of the crystals must be dissolved.
• Prepare the solution within days of treating the colonies and keep refrigerated until use.
• 1L of the oxalic acid solution will treat 20 colonies.
Trickle Application:
Oxalic acid should be applied late in the fall after brood rearing has ceased. Treat when the temperatures are cooler (in the morning or evening) to ensure that the bees are in the hive to receive the treatment. Using a 60 ml syringe or an oral drench gun (both available at farm supply stores), apply 50 ml of the solution directly onto the bees in the cluster. Trickle the solution between each frame containing bees. When treating doubles, split the boxes and treat the bees in both boxes (25 ml in the bottom box and 25 ml in the top box). The colony may be wrapped for winter immediately after application.
Safety:
When handling the oxalic acid crystals, always wear gloves and a dust mask. Gloves and protective clothing should be worn when treating colonies using the trickle method. If oxalic acid crystals or the treatment solution contact your skin, wash affected area with water.
Storage:
In all forms, oxalic acid is odorless. The crystalline powder should be stored at room temperature in an airtight container. This will prevent absorption of moisture, which causes the loose powder to solidify. Do not store leftover oxalic acid treatment solution. The oxalic acid changes in composition and becomes toxic to the bees.
Vaporization Method
There are different vaporizers available for use in the hive. Instructions for use are specific to the vaporizer purchased. Goggles, gloves and a respirator should be used when vaporizing oxalic acid crystals.
OXALIC ACID SAFETY SHEET
oxalic acid — liquid contains dissolved oxalic acid dihydrate. Also known as ethanedionic acid.
oxalic acid dihydrate — solid form, a white crystalline powder, crystals, granules, pellets.
oxalic acid vapour — gaseous form, created by heating and vaporizing liquid oxalic acid or solid oxalic acid dihydrate
In all forms, oxalic acid is odourless, and dissolves readily in water.
Storage:
Keep in a tightly closed, airtight container when not in use, to prevent absorption of moisture, which causes the loose crystalline powder to solidify into a hard rock. Store in a cool, dry, well-ventilated area away from sources of heat, moisture and incompatible substances. Containers of this material may be hazardous when empty since they retain product residues.
Incompatibilities with Other Materials:
Strong oxidizing agents, mercury, hypochlorite, silver, strong alkalies, chlorites, furfuryl alcohol. Avoid contact with metals, alkali metals.
Handling:
Wash thoroughly after handling. Minimize dust generation and accumulation. Do not get in eyes, on skin, or on clothing. Do not ingest or inhale. Discard contaminated shoes. Use only with adequate ventilation.
SAFETY PRECAUTIONS
Always wear impenetrable gloves when handling any form of oxalic acid. Protective clothing should be worn to prevent contact of the liquid or powder with skin. Goggles and respirator should be used when vaporizing oxalic acid crystals.
HEALTH EFFECTS
Target Organs:
Kidneys, heart, eyes, skin, brain, nerves, mucous membranes.
Oxalic acid is corrosive to tissue and causes burns.
Inhalation may cause severe respiratory tract irritation with possible burns.
May cause severe digestive tract irritation with possible burns.
May cause kidney damage.
May cause eye and skin irritation with possible burns.
Harmful in contact with skin and if swallowed.
Possible risk of harm to the unborn child.
Ingestion:
Oxalic acid is toxic because of its acidic and chelating properties. May cause burns, nausea, severe gastroenteritis and vomiting, shock and convulsions. It is especially toxic when ingested. As little as 5 to 15 grams (71 mg/kg) may be fatal. Ulcerations of the mouth, vomiting of blood, and rapid appearance of shock, convulsions, twitching, tetany, and cardiovascular collapse may occur following ingestion of oxalic acid or its soluble salts. Oxalic acid can bind calcium from the blood to form calcium oxalate, which can precipitate in the kidney tubules and the brain. Renal damage may result as evidenced by bloody urine. Hypocalcemia secondary to calcium oxalate formation might disturb the function of the heart and nerves.
Inhalation:
Harmful if inhaled. Can cause severe irritation and burns of nose, throat, and respiratory tract. Inhalation of oxalic acid dust or vapor can also cause protein in the urine, nosebleed, ulceration of the mucous membranes, headache, nervousness, cough, vomiting, emaciation, back pain (due to kidney injury), and weakness.
Skin Contact:
Causes severe skin irritation. Harmful if absorbed through the skin. Rare chemical burns may occur from oxalic acid and may cause hypocalcemia. Gangrene has occurred in the hands of people working with oxalic acid solutions without rubber gloves. The skin lesions are characterized by cracking of the skin and the development of slow-healing ulcers. The skin may be bluish in color, and the nails brittle and yellow.
Eye Contact:
May cause severe eye irritation. It may produce corrosive effects. May result in corneal injury.
Chronic Exposure:
Inhalation of oxalic acid dust or mist over a long period of time might result in weight loss and respiratory tract inflammation. Rats administered oxalic acid at 2.5 and 5% in the diet for 70 days developed depressed thyroid function and weight loss. Prolonged skin contact can cause dermatitis, cyanosis of the fingers and possible ulceration. A study of railroad car cleaners in Norway who were heavily exposed to oxalic acid solutions and vapors revealed a 53% prevalence of urolithiasis (the formation of urinary stones), compared to a rate of 12% among unexposed workers from the same company.
Aggravation of Pre-existing Conditions:
Persons with pre-existing skin disorders or eye problems, or impaired kidney or respiratory function may be more susceptible to the effects of the substance.
EMERGENCY OVERVIEW
Inhalation:
Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Call a physician immediately.
Ingestion:
DO NOT INDUCE VOMITING! Give large quantities of limewater or milk to drink. Never give anything by mouth to an unconscious person, wash out mouth with water instead. Call a physician immediately.
Skin Contact:
In case of contact, wipe off excess from skin then immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. Call a physician immediately.
Eye Contact:
Immediately flush eyes with gentle but large stream of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Call a physician immediately.
Oxalic Acid Facts
500 g of oxalic acid dihydrate (approx. $12.00 from the drugstore) will treat 142 colonies using the trickle method (8.5 cents per colony!) or 500 hive bodies using the VARROX vaporizor method.
Make sure you are using the proper type of oxalic acid!
Molecular Weights:
U oxalic acid dihydrate: 126
V oxalic acid anhydrous: 90
Oxalic acid occurs naturally in quite a large number of plants. The human body also synthesizes oxalic acid from ascorbic acid (Vitamin C). Oxalic acid may combine with calcium, iron, sodium, magnesium, or potassium to form less soluble salts known as oxalates. Oxalates also occur naturally in plants.
Since oxalic acid binds with important nutrients, making them inaccessible to the body, regular consumption of large amounts of foods high in oxalic acid over a period of weeks to months may result in nutrient deficiencies, most notably of calcium.
Oxalic acid is a strong acid, and is irritating to tissue all by itself. Extremely high doses are fatal. Oxalates, on the other hand, form tiny little insoluble crystals with sharp edges, which are also irritating to tissue. So, high levels of oxalic acid/oxalates in the diet lead to irritation of the digestive system, and particularly of the stomach and kidneys. They may also contribute to the formation of kidney stones (the most common form of kidney stone is composed of calcium oxalate).
Foods containing these chemicals may be consumed in moderation. However, if you suffer from kidney disease, kidney stones, rheumatoid arthritis, or gout, it is usually recommended that you avoid foods that are high in oxalates or oxalic acid. Foods generally found on the list include: chocolate, cocoa, coffee, most berries (especially strawberries and cranberries), most nuts (especially peanuts), beans, beets, bell peppers, black pepper, parsley, rhubarb, spinach, swiss chard, summer squash, sweet potatoes, and tea.
Plant foods with high concentrations of oxalic acid (over 200 ppm) include (but are not limited to): lamb’s-quarter, buckwheat, star fruit, black pepper, purslane, poppy seeds, rhubarb, tea, spinach, plantains, cocoa and chocolate, ginger, almonds, cashews, garden sorrel, mustard greens, bell peppers, sweet potatoes, soybeans, tomatillos, beets and beet greens, oats, pumpkin, cabbage, green beans, mango, eggplant, tomatoes, lentils, and parsnips. The amount or oxalic acid in rhubarb depends on the age of the plant, the season, the climate and the type of soil. Highest concentrations are in the leaves and these should not be eaten.
Oxalic acid poisoning can cause muscle twitching, cramps, decreased breathing and heart action, vomiting, pain, headache, convulsions and coma.
Other uses of oxalic acid:
Stripping/cleaning/polishing wood, stone and metal surfaces, rust remover.
Published by permission of the Tech-Transfer Team of the Ontario Beekeepers Association.
Written by beekeepers
Topics: How to Keep Bees