### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, DC 20460

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION



### MEMORANDUM DATE: December 18, 2014

SUBJECT: Oxalic Acid (PC Code 009601; DP Barcode D497398)

FROM: Thomas Steeger, Ph.D., Senior Science Advisor

Environmental Risk Branch 4

Environmental Fate and Effects Division

THRU: Jean Holmes, Branch Chief

Environmental Risk Branch 4

Environmental Fate and Effects Division

TO: Reuben Baris, Risk Manager Reviewer Venus Eagle, Risk Manager Registration Division

The Environmental Fate and Effects Division (EFED) has completed its review of the environmental fate and ecological effect data provided in support of th e Section 3 registration of oxalic acid dihydrate (PC Code 009601; CAS 6153-56-6) for the in-hive control of the varroa mite ( Varroa destructor ) in honey bee ( Apis mellifera ) colonies. Data used in evaluating the product were provided by Health Canada’s Pest Management Regulatory Agency 1 as part of a work share between regulatory agencies, the Environmental Protection Agency’s (EPA) Reregistration Eligibility Document for oxalic acid 2 , and open literature.

Varroa mites have been characterized as the most serious pests in honey bee colonies 3 as these mites feed on developing bees (larvae and pupae; brood) leading to brood mortality and the reduction of lifespan of workers that were parasitized during development 4 , and the mite are considered a major cause of overwintering colony losses 5 . Varroa can affect hypopharyngeal gland development of nurse bees and decrease brood/royal jelly production affecting nutrition in developing brood and queens 6 . Although no

data have been submitted to EPA to assess the likel ihood of adverse effects on non-target organisms from the proposed use of oxalic acid to control Varroa on adult bees ( i.e ., for control of phoretic mites), EFED

1 Health Canada. 2010. Oxalic Acid Dihydrate Proposed Registration Decision PRD2010-12.

2 USEPA. 1992. Reregistration Eligibility Document (RED). Oxalic Acid. Office of Chemical Safety and Pollution Prevention for merly the Office of Prevention, Pesticides and Toxic Substances (H7508W) December 1992. http://www.epa.gov/opp00001/reregistration/REDs/old_reds/oxalic_acid.pdf

3 USDA. 2013. Report on the National Stakeholders Conference on Honey Bee Health. Naitonal Honey Bee Health Stakeholder Confer ence Steering Committee. Alexandria, VA October 15

– 17, 2012. http://www.usda.gov/documents/ReportHoneyBeeHealth.pdf

4 DeGrandi-Hoffman, G., F. Ahumada, R. Curry, G. Probasco, and L Schantz. 2014. Population growth of Varroa destructor (Acari: Varroidae) in commercial honey bee colonies treated with beta plant acids. Exp. Appl. Acarol 64: 171

– 186. 5 Guzmán-Novoa, E., L. Eccles, Y. Calvete, J. McGowan, P. G. Kelly, A. Correa-Benítez. 2010. Varroa destructor is the main cul prit for the death and reduced populations of overwintered honey bee ( Apis mellifera ) colonies in Ontario, Canada. Apidologie 41: 443

– 450. DOI: 10.1051/apido/2009076

6 Pinto, F d’A, G. K. Souza, M. A. Sanches, and J. E. Serrão. 2011. Parasitic Effects of Varroa destructor (Acari: Varroidae) on hypopharyngeal glands of Aftricanized Apis mellifera (Hymenoptera: Apidae). Sociobiology 53(3): 769

– 778. T HOMAS

STEEGER Digitally signed by THOMAS STEEGER
DN: c=US, o=U.S. Government, ou=USEPA, ou=Staff, cn=THOMAS
STEEGER, dnQualifier=0000012192

Date: 2014.12.18 13:12:59 -05'00'

Holmes, Jean

2014.12.18 18:01:40 -05'00'Page 2 of 6 believes that the likelihood of non-target exposure is low given that the compound is proposed for use within the honey bee colony when brood are not present. While there are data to demonstrate that oxalic acid can be acutely toxic to adult bees, the proposed treatment rates have been established based on research demonstrating that oxalic acid will provide effective control of mites while minimizing adverse effects to

adult bees. The available research indicates that in the absence of effective Varr oa control measures, there is an increased likelihood of adverse effects to both individual bees and the whole colony due to parasitism of the mite. Therefore, based on the available info rmation, EFED does not have any evidence that the proposed use of oxalic acid will be detrimental to the co lony especially given that the use of oxalic acid is

intended to reduce mite loads that could otherwise be far more detrimental to individual bee and colony survival. Given the in-hive use of the product and the absence of exposure to non-target organisms other than the honey bee, EFED has determined that the pro posed in-hive use of oxalic acid will have no effect (NE) on federally listed threatened or endanger ed species and will not modify their habitat.

Nature of the Chemical Stressor

Oxalic acid is a dicarboxylic acid and its conjugate base (oxalate) is used as a chelating agent for metal

cations 7 . While the specific mode of action against V. destructor is unknown, it is hypothesized to physically injure the mites via the chemical’s low pH through direct contact with the liquid formulation or through a fine coating of small oxalic acid crystals th at can result from the vaporization of the oxalic acid 8

.

The chemical occurs naturally as the potassium or calcium salt in the sap of many plants and vegetables, notably in those of the Oxalis and Rumex familes 9 . Historically it has had a range of non-pesticidal uses ( e.g ., wood bleach); however, it was first registered as a pesticide (disinfectant/sanitizer) in 1957 10 . In 1992, oxalic acid was evaluated for reregistration 11 ; at that time, the Agency concluded that the pesticide uses of

oxalic acid would not result in unreasonable adverse effects to human health or the environment and that all registered products containing oxalic acid were eligible for reregistration. However, the uses of oxalic acid as a pesticide were cancelled in 1994 for nonpayment of fees.

In 2005, EPA evaluated oxalic acid for its use as an inert ingredient, i.e ., as a calcium chelating hard water inhibitor in pesticides used in outdoor gardens and ag ricultural crops. In that assessment, EPA determined that there is a reasonable certainty that no harm to any population subgroup would result from aggregate exposure to oxalic acid used as iner t ingredients in pesticide formulations 12

.

Use Characterization

According to the draft label, oxalic acid dihydrate (1 00% active ingredient; a.i.) is proposed for use as a varroacide using two methods of application. In one method referred to as the “solution method”, 35 g of product is dissolved in 1 L of 1:1 sugar:wa ter (weight:volume) and 5 mL (175 mg a.i.) is then “trickled” on to bees “in each occupied bee space” within the brood box. The maximum quantity applied is 50 mL (1,750 mg a.i.) per colony, whether bees are in nucleus “nuc”, single or multiple brood chambers. The second means of application is the “vaporizer method” where 2 g of product are placed in a vaporizer. The draft label specifies that the product may only be used in late fall or early spring when little to no brood (eggs, larvae, pupae) is present; furtherm ore, the product may not be used with honey supers are in place.

7 Ibid USEPA. 1992.

8 Ibid Health Canada. 2010.

9 Ibid USEPA. 1992.

10 Ibid USEPA. 1992.

11 Ibid USEPA. 1992.

12 USEPA. 2005. Inert Reassessment Oxalic Acid. http://www.epa.gov/opprd001/inerts/oxalicacid.pdfPage 3 of 6 The product has been registered in Canada since 2010. The evaluation by PMRA concluded that the available scientific information and under the approved conditions of use, oxalic acid had value and did not present an unacceptable risk to human health or the environment 13

.

Environmental Fate Assessment

Oxalic acid is a naturally occurring compound that transforms rapidly under environmental conditions. It occurs as the oxalate ion at environmentally relevant pHs (pk a1 1.25, pK a2 4.28); high mobility of the ion in soil is expected to occur based on an estimated organic carbon partition coefficient (K

oc ) value of 5. Volatilization from moist surfaces is not likely to be rapid, based on a low Henry’s Law value 1.4x10 -10

atm-m 3 /mole at 25 q C. Oxalic acid will readily dissolve in wa ter because of its high solubility (100 g/L). Rapid anaerobic and aerobic biotransformation of oxalic acid in soil and water will occur (HSDB 2003 14 ).

Many plants naturally contain oxalic acid, particularly those belonging to the Oxalis ( e.g ., sorrels) and

Rumex ( e.g ., wild rhubarb) families; several species of mold also produce oxalic acid. Anthropogenic inputs of oxalic acid into the environment may be from vehicl e exhausts and pulp mill effluents. In soil oxalic acid was found at 30 to 6 mg/kg in 0 and 540 cm depths, respectively, at a site in Germany. Lake sediment concentrations have been recorded in the range of 0.1 to 0.7 nmol/L of sediment. Oxalic acid was found in Los Angeles air samples at concentrations of 6.38 to 2.12 nmol/m 2 (HSDB 2003 15 ).

With a bioconcentration factor predicted to be 0.6 (HSDB 2003 16 ), oxalic acid is not expected to

bioaccumulate.

During the use of oxalic acid for control of Varroa mite in beehives, exposure of the chemical to the environment is expected to be limited. The product is applied as a liquid or vapour to an affected colony; environmental exposure would occur primarily through spillage or leakage during application. Based on limited exposure, the chemical’s natural occurrence and the likelihood for relatively rapid transformatio n under environmental conditions, the proposed use of oxalic acid is not expected to pose a significant risk to the environment. Therefore, further review of th e environmental chemistry, fate, and toxicology of oxalic acid was not considered necessary.

The PMRA has taken into account the federal Toxic Substances Management Policy 17 and has followed its Regulatory Directive DIR99-03 18 . It has been determined that this active ingredient and products do not

meet TSMP Track-1 criteria.

Although oxalic acid is not currently registered for use as a varroacide in the U.S., historically this has not limited the use of other unregistered products ( e.g ., amitraz) by beekeepers as evidenced by residues of unregistered products or their degradates in colonies ( e.g ., DMPF degradate of amtraz) 19 . However, these

13 Ibid Health Canada. 2010.

14 HSDB Hazardous Substances Data Bank Number 1100. Oxalic Acid. Canadian Centre for Occupational Health and Safety

15 Ibid HSDB

16 Ibid HSDB

17 The federal Toxic Substances Management Policy is available through Environment Canada’s Web Site at : www.ec.gc.ca/toxics

18 The PMRA's Strategy for Implementing the Toxic Substances Management Policy, Dir99-03, is available through the Pest Management Information Service: Phone 1-800-267-6315 within Canada or 1-613-736-3799 outside Canada (long distance charges apply); Fax (6 13) 736-3798; E-Mail pminfoserv@hc-sc.gc.ca or through our Web Site at www.hc-sc.gc.ca/pmra-arla

19 Mullin CA, M. Frazier, J. L. Frazier, S. Ashcraft, R. Simonds, D. vanEngelsdorp, and J. S. Pettis. 2010. High Levels of Miticid es and Agrochemicals in North American Apiaries: Implications for Honey Bee Health. PLoS ONE 5(3): e9754. doi:10.1371/journal.pone.000 9754Page 4 of 6 colony monitoring studies have not demonstrated simila r residues of oxalic acid. It is uncertain whether these monitoring studies included oxalic acid as an anal yte; however, the available data do not indicate that any potential misuse of the compound is resulting in de tectable residues of the parent compound. Oxalic acid though is reported to be a natural constitu ent of honey at concentrations ranging between 1

– 800 mg/kg, depending on the botanical source of the nectar used to produce the honey 20 . Concentrations of oxalic acid in honey measured after the tr eatments with oxalic acid ranged from 5

– 289 mg/kg which were considered to be within the range of natural background 21

.

Ecological Effect Assessment

Historically, EPA did not require or evaluate ecologic al effects for oxalic acid because the pesticide was only used indoors and the exposure to wildlife was not expected to occur 22 . The proposed use of oxalic

acid as a varroacide is confined to the interior of honey bee colonies and the opportunity to affect non-target organisms is limited. Therefore, additional ecological effect data have not been required to support the proposed registration of oxalic acid as a varroacide.

Given the proposed use of the compound, non-target animal exposure is likely to be limited to the honey bee itself. Although no data have been submitted to asse ss the effect of oxalic acid on non-target organisms, there are data to evaluate potential effects on bees an d these data indicate that the compound is practically non-toxic to bees on an acute contact exposure basis, i.e ., LD 50 >11 μ g/bee. Based on toxicity data contained in the ECOTOXicity (ECOTOX 23 ) database, median lethal doses for 50% of the organism tested ( i.e ., LD 50 ) ranged from 1576 μ g/bee after 24 hrs to 195 μ g/bee 24 at 72 hrs of exposure. Data in ECOTOX on the toxicity of oxalic acid to Varroa mites reports LD 50 values ranging from 0.64 to 1.90 μ g/cm 2

. 25 Although the contact toxicity values are not directly comparable to those for honey bees, these values can be put into context by expressing the honey bee toxicity values on the basis of surface area. Assuming that the surface

area of a worker bee is 1.05 cm 2 /bee 26 , then the reported honey bee LD 50 values would range of 186

– 1501

μ g/cm 2 indicating that the mite is several orders of magn itude more sensitive to oxalic acid than the adult honey bee. Research by Milani 2001 27 indicated that the addition of sucrose to oxalic acid made the material more hygroscopic and increased its toxicity to mites.

Based on research conducted by Aliano and Ellis 2008 28 , the application of a 2.8% solution of oxalic acid directly to adult bees provided effective mite control with minimal adult bee mortality. In this publication,

the researchers noted that while the use of oxalic ac id is effective for broodless colonies, the compound does not kill mites in sealed brood cells. The effectiveness of oxalic acid depends on bee-to-bee contact

20 EMEA. 2003. Committee for Veterinary Medicinal Products Oxalic Acid Summary Report. The European Agency for the Evaluation o f Medicinal Products Veterinary Medicines and Inspections. EMEA/MRL/891/03-FINAL December 2003. http://www.ema.europa.eu/docs/en_GB/document_library/Maximum_Residue_Limits_-_Report/2009/11/WC500015217.pdf

21 Ibid EMEA. 2003.

22 Ibid USEPA. 1992.

23 USEPA. 2014. ECOTOXicology database (ECOTOX). Office of Research and Development National Health and Environmental Effects Research Laboratory Mid-Continent Ecology Division. http://cfpub.epa.gov/ecotox/

24 Aliano, N.P., M. D. Ellis, B. D. Siegfried. 2006. Acute Contact Toxicity of Oxalic Acid to Varroa destructor (Acari: Varroidae) and their Apis mellifera (Hymenoptera: Apidae) Hosts in Laboratory Bioassays. J. Econ. Entomol 99(5): 1579

– 1582.

25 Milani, N. 2001. Activity of oxalic and citric acids on the mite Varroa destructor in laboratory assays. Apidologie 32: 1`2 7

– 138.

26 Poquet Y., L. Bodin, M. Tchamitchian, M. Fusellier, B. Giroud, F. Lafay, A. Buleté, S. Tachamitchian, M. Cousin, M. Pélissier, J-L. Brunet, and L. P. Belzunces. 2014. A Pragmatic Approach to Assess the Exposure of the Honey Bee ( Apis mellifera ) When Subjected to Pesticide Spray. PLoS ONE 9(11): e113728. doi:10.1371/journal.pone.0113728

27 Ibid Milani. 2001.

28 Aliano, N.P., and M. D. Ellis. 2008. Oxalic acid: a prospective tool for reducing Varroa mite populations in package bees. Experimental and Applied Acrology 48: 303

– 309.Page 5 of 6 and not trophallaxis 29 (communal feeding). Health Canada’s proposed registration decision 30 on the varroacide use of oxalic acid reported that in the ab sence of poor overwintering conditions in general, the proposed application of 3.5% solution to the colony with a maximum of 1,750 mg a.i./colony (50 mL) did not result in sufficient adult bee mortality or low surviv orship to offset the benefit afforded to the colony in

terms of mite control. The review also noted that st udies examining the efficacy of applications of oxalic acid via vaporisation found no adverse effects on bee tolerance, overwintering success or spring colony development. 31

A review of the Ecological Incident Information System on December 13, 2010, did not result in any incident reports for oxalic acid related to its use or misuse.

Risk Discussion

There are limited environmental fate and ecological effect data available with which to evaluate the potential for ecological risk. However, the proposed in-hive use of oxalic acid is expected to limit exposure of non-target organisms to honey bees and varroa mites within the treated colony. Therefore, a quantitative analysis of risk has not been conducted, Environmental fate data indicate that the compound is relatively short lived given its susceptibility to both aerobic and anaerobic metabolism, and available chemical residue monitoring data from honey bee colonies do not indicate the oxalic acid residues outside of which occur naturally in honey.

Although oxalic acid is classified as practically non-toxi c to honey bees on an acute contact exposure basis, there is uncertainty as to the extent to which indivi dual bees may be exposed to high acute doses of the compound as the compound is trickled into the spaces betw een frames containing bees and is in turn moved through the colony via bee-to-bee contact. Similarly the actual exposure levels for individual bees from the vaporization of the compound within the colony is uncertain; however, studies conducted using the proposed trickle solution and vaporization methods did not result in an appreciable level of adult bee mortality, and longer-term monitoring of these colonies did not report adverse effects on overwintering capacity of the colony or in spring development.

As noted earlier, the Varroa mite has been associat ed with brood mortality and reductions in worker bee lifespan 32 , increase overwintering colony losses 33 and reductions in nurse bee brood/royal jelly production affecting nutrition in developing brood and queens 34 . Research is also showing that varroa mites serve as vectors for bee viruses such as deformed wing virus, which has also been identified as a major cause of overwintering colony losses 35 . Synthetic mite controls such as coumaphos and tau fluvalinate have become increasingly ineffective due to mite resistance 36 and given the mode of action of the organic acids such as formic and oxalic acid, there is hope that compounds su ch as oxalic will serve as an effective means of limiting the development of resistance in Varroa mite populations 37

.

29 Aliano, N. P. and M. D. Ellis. 2008. Bee-to-bee contact drives oxalic acid distribution in honey bee colonies. Apidologie 39: 481

– 487.

30 Ibid Health Canada. 2010.

31 Ibid Health Canada. 2010.

32 Ibid DeGrandi-Hoffman et al . 2014.

33 Ibid Guzmán-Novoa et al . 2010.

34 Ibid Pinto et al . 2011.

35 DeGrandi-Hoffman, G., F. Ahumada, R. Curry, G. Probasco, and L Schantz. 2014. Population growth of Varroa destructor (Acari: Varroidae) in commercial honey bee colonies treated with beta plant acids. Exp. Appl. Acarol 64: 171

– 186.

36 Ibid . USDA. 2013.

37 Ibid Milani. 2001.Page 6 of 6 Consistent with the Agen cy’s responsibility under the Endangered Species Act (ESA), the Agency evaluates risks to Federally-listed threatened and/or endangered (listed) species from the proposed use of a pesticide. Given the proposed in-hive use of oxalic acid to control varroa mite and the limited opportunity for exposure of non-target organism, “listed” species are not expected to be affected by the proposed use. Therefore, EFED has determined that the proposed use will have no effect (NE) on listed species and will not modify habitat associated with listed species.