MISC controls coqui frogs by spraying their habitat with a 14% solution of citric acid. MISC also provides powdered citric acid or the same 14% solution to residents for them to treat their own yards for coqui frogs as well. This results in potentially thousands of gallons of citric acid on the landscape in Maui each month. We get a lot of questions about whether this is safe for the environment, specifically for people, plants, animals, water and the soil.
Are there risks associated with Citric Acid Usage?
- Citric Acid is “Generally Recognized as Safe”
The Environmental Protection Agency (EPA) has classified citric acid as “Generally recognized as safe” or “GRAS”. Citric acid breaks down quickly when it comes in contact with naturally occurring organisms found in surface water and soil. It is classified as a severe eye and moderate skin irritant which is why our field crews wear appropriate PPE such as long pants, closed toe shoes, long sleeves and gloves while spraying and mixing citric acid solution. They also carry water to rinse off with or flush their eyes if needed.
- Citric acid does not present a hazard to the environment
Citric acid is widely used in household cleaning products and can also be found in many soft drinks and processed foods. It also naturally occurs within the tissues of many plants and is a key component of the Krebs cycle. The Human and Environmental Risk Assessment (HERA) has found that citric acid has “a very favorable ecological profile. Due to the very low aquatic toxicity and the ready biodegradability, wide dispersive use of citric acid does not present a hazard to the environment.”
- Most plants tolerate being sprayed with citric acid
Citric acid must touch the coqui frogs’ skin in order to be effective which requires that plants in the area be liberally sprayed with the citric acid solution. According to testing performed by UH-CTAHR most plants are able to withstand this treatment with no ill effects but some plants have been shown to be sensitive. Sensitive plants include mock orange, orchids, air plants, anthurium, calathea, and streptocarpus. MISC takes care to avoid these plants and if they are inadvertently sprayed they are immediately rinsed with fresh water.
- Citric acid has positive effects on the environment
If soil is too alkaline, citric acid can be applied to raise the pH of the soil until it is more suitable for plant growth. Additionally, at sites with lead contamination, adding citric acid increases the plant growth, photosynthesis and lead extraction from contaminated soils.
- Citric acid does not accumulate in the soil
Once sprayed out, citric acid begins breaking down rapidly. Again, according to HERA, “ Citric acid is rapidly degraded in both sewage works and surface waters and in soil.”
- There is minimal risk for toxic exposure for other animal species
Citric acid controls coqui frogs by absorption through the skin which quickly and humanely kills coqui frogs. Greenhouse frogs, which are another, widespread introduced species, are also killed if they come into contact with citric acid. Other soft-bodied invertebrates such as slugs and snails may be similarly affected. Other animals do not absorb citric acid through their skin and are not at high risk.
A study by Pitt etal in 2014 found that endangered Hawaiian Hoary Bats are at low risk for harmful exposure to citric acid.
Due to citric acid being a skin and eye irritant through direct exposure, MISC staff avoids spraying near areas where animals are held. We also recommend that pets be kept indoors with the windows closed if active citric spraying is happening nearby.
How is Citric Acid made?
Citric acid can be created through a few different methods including extraction from lemon juice, chemical synthesis, or through microbiological fermentation of molasses and sugar solution. Worldwide, the vast majority of citric acid is produced through the microbiological fermentation method with negligible amounts produced by extraction or chemical synthesis. The citric acid used by MISC is produced through this microbiological fermentation method. Additionally, the citric acid that MISC uses currently (as of 7/30/2020) is certified non-GMO, it may be used in organic agriculture or food production and is kosher and halal certified.* (certificates available upon request)
Let us know your questions!
If you have more questions about how we do coqui control work at MISC please get in touch with us. We are always happy to answer questions from the community. Please send an email to firstname.lastname@example.org.
Sources used in this webpage:
University of Hawaii – College of Tropical Agriculture and Human Resources & Hawaii Department of Agriculture. (2003) Response of Plants Following a Foliar Application of 25% Citric Acid
Additional sources of information on the effects of citric acid: