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Dalapon

Publication Date: 9/93

TRADE OR OTHER NAMES

2,2-Dichloropropionic acid. Some trade names include Dowpon, Basinex P, Devipon, Gramevin, Kenapon, Liropon, Unipon, Dalapon-Na (Dalapon-Sodium), Revenge, Alatex, Ded-Weed, DPA, Dalacide, Radapon.

REGULATORY STATUS

Dalapon is classified by the U. S. Environmental Protection Agency (EPA) as a general use herbicide. Containers of the herbicide must bear labels with the EPA warning word "CAUTION."

INTRODUCTION

Dalapon is an herbicide and plant growth regulator used to control specific annual and perennial grasses, such as quackgrass, Bermuda grass, Johnson grass, as well as cattails and rushes (4). It is selective, meaning that it kills only certain plants, while sparing nontarget types of vegetation. The major food crop use of dalapon is on sugarcane and sugar beets (3). It is also used on various fruits, potatoes, carrots, asparagus, alfalfa and flax (7, 13). It is used in public and domestic sites, forestry, home gardening, and in or near water to control reed and sedge growth (2, 3, 15). Dalapon is applied both before the target plant comes up, preemergence, or after the plant emerges, postemergence (12). It is usually applied as a foliar spray. Dalapon is available as a water soluble powder (23).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Dalapon is moderately toxic to humans. Skin and inhalation exposure could be of significance to dalapon production workers, pesticide applicators, and some agricultural workers (3). Effects of acute exposure include absence of appetite, slowed heartbeat, skin irritation, eye irritation such as conjunctivitis or corneal damage, gastrointestinal (GI) disturbances such as vomiting or diarrhea, tiredness, pain, and irritation of the respiratory tract (6, 9). Dalapon is an acid which may cause corrosive injury to body tissues (26). Eye exposure to this material can cause permanent eye damage. Skin burns may occur from dermal exposure to dalapon, especially when skin is moist.

The amount of a chemical that is lethal to one-half (50%) of experimental animals fed the material is referred to as its acute oral lethal dose fifty, or LD50. Oral LD50 values range from 3,860 mg/kg for female rabbits to 9,330 mg/kg for male rats, depending on whether technical material or formulated product is tested (20). The application of sodium salt of dalapon (in a dry powder formulation) to rabbit eyes produced pain and irritation, followed by severe conjunctivitis and corneal injury, which healed after several days. A 10% solution produced slight pain and conjunctivitis. A 1% solution did not appear to produce any ill effects (14).

CHRONIC TOXICITY

Repeated and/or prolonged exposure to dalapon may cause irritation to the mucous membrane linings of the mouth, nose, throat, lungs and to the eyes (9). Chronic skin contact with the herbicide can lead to moderate irritation or even mild burns, although occasional contact is not likely to produce irritation. Dalapon is not absorbed through the skin in toxic amounts (20). Long-term dalapon feeding studies in dogs and rats did not produce lesions, but did show increased kidney weights in animals fed very high daily doses (9). Rats fed 50 mg/kg/day for two years showed a slight average increase in kidney weight. No adverse effects were seen in this study in rats fed 15 mg/kg/day. In a one-year feeding study with dogs fed 100 mg/kg/day, there was a slight average increase in kidney weight. No adverse effects were seen at 50 mg/kg/day (20). These mild effects on the kidneys are consistent with data that show that ingested dalapon is rapidly excreted in the urine.

The EPA has established a Lifetime Health Advisory (LHA) level of 200 micrograms per liter (ug/l) for dalapon in drinking water. This means that EPA believes that water containing dalapon at or below this level is acceptable for drinking every day over the course of one's lifetime, and does not pose any health concerns. However, consumption of dalapon at high levels well above the LHA level over a long period of time has been shown to cause changes in kidney and liver weights in animal studies (27).

Reproductive Effects

Tests indicate that dalapon does not produce adverse effects on fertility or reproduction, except at extremely high doses. Doses of 1,500 and 2,000 mg/kg in female rats, and 1,000 and 1,500 mg/kg in rat pups resulted in reduced weight or lower rates of weight gain. No effects were seen at lower doses. Reproductive rates of birds are decreased at very high doses of dalapon (14).

Teratogenic Effects

Sodium dalapon was not teratogenic in the rat at doses as high as 2,000 mg/kg/day (28).

Mutagenic Effects

Dalapon was not mutagenic when tested in several organisms (28).

Carcinogenic Effects

No carcinogenic effects were seen in rats fed the sodium salt of dalapon at 5, 15, or 50 mg/kg/day for two years (14, 28).

Organ Toxicity

Dalapon dust and vapor may be irritating to the respiratory tract (9). Autopsies of calves that had been fed 1,000 mg/kg/day of the herbicide for 10 days showed possible involvement of the kidneys in the deaths of these animals (13). Please refer to the Chronic Toxicity section for more information on effects of long-term dalapon exposure on kidneys.

Fate in Humans and Animals

The half-life of dalapon in human blood is 1.5 - 3.0 days (3). Dalapon's half-life in the blood system of dogs is about 12 hours (3, 14). It interferes with the body's ability to make protein and to use sugar from food (6).

Dalapon and all of its known breakdown products, or 'metabolites' dissolve easily in water. They are readily washed from cells and tissues. Because dalapon is insoluble in organic solvents and lipids, it does not build up in animal tissues. In animals, dalapon is normally broken down, or hydrolyzed, in water to a metabolite, acetaldehyde, which is further degraded to acetate and carbon dioxide (CO2). A nonmetabolized form of dalapon was excreted in the urine of animals fed the herbicide. Chickens fed 25 and 50 ppm for as long as 60 days had dalapon residues of up to 40 ppm in blood, 50 ppm in kidney, 16 ppm in liver, 13 ppm in gizzard, 12 ppm in the skin and fat, 13 ppm in lean meat, and 12 ppm in eggs (3). Less than 1% of the ingested dose appeared as residues in the milk of dairy cows that were fed dalapon. The residue was primarily unchanged dalapon, with traces of dalapon glycerides (13).

ECOLOGICAL EFFECTS

Effects on Birds

The LC50 is that concentration of a material in air or water that kills half of the experimental animals exposed to it for a specific time period. When dalapon was fed to two-week old birds for five days, followed by untreated feed for three days, the LC50 of dalapon was more than 5,000 ppm in mallards, ring-necked pheasants, Japanese quail, and coturnix (10, 23). The acute oral LD50 of dalapon is 5.66 g/kg for chickens (7). While dalapon is practically non-toxic to birds, reproduction rates of birds are decreased at very high doses (14). Reproduction was depressed in mallard ducks that were fed one fourth the level of dalapon that caused death (10).

Effects on Aquatic Organisms

Dalapon is of very low toxicity to fish (7). While there were no deaths reported in goldfish after a 24-hour exposure to 100 ppm of dalapon, all fish died after a similar exposure to 500 ppm or above (13). The one to 21 day LC50 values for dalapon in fish are all on the order of 100 ppm for several species tested (14, 23). The LC50 for dalapon in bluegills is 105 ppm (23). Based on its reportedly low toxicity to fish and other aquatic organisms, use of dalapon is permitted for the control of reeds, sedges and rushes in drainage canals and ditches (21).

Its toxicity to aquatic invertebrates is highly varied depending on the species. Values can be as low as the 48-hour effective concentration (EC) of 1 ppm for brown shrimp, or as high as the 96-hour LC50 of 4,800 ppm for other crustaceans. Aquatic crustaceans and insects are the most dalapon-sensitive of the aquatic invertebrates. Dalapon is only slightly toxic to mollusks. In short exposure tests, the NOEL of dalapon for snails, dragonflies, stoneflies, and several crustaceans was at least 200 ppm (20).

Effects on Other Animals (Nontarget Species)

Dalapon is relatively nontoxic to honey bees and other insects and has low toxicity to soil microorganisms (14).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

Dalapon does not readily bind, or adsorb, to soil particles. Even in muck soils, as little as 20% of applied dalapon may adsorb. In clay and clay loam soils, there may be no adsorption. Since it does not adsorb to soil particles, dalapon has a high degree of mobility in all soil types and leaching does occur. However, dalapon movement in soil is usually prevented by rapid and complete breakdown of the herbicide into naturally-occurring compounds by soil microorganisms (25). Biological breakdown, also referred to as biodegradation, is the main route of dalapon disappearance from soils. Dalapon is not detected below the first six-inch soil layer. Some bacteria use dalapon as an energy source. Degradation depends on soil type, temperature, and moisture. Higher temperatures and increased soil moisture speed up degradation. Soils that were buffered to a pH of 6.5 provided the best conditions for the adaptation of microbes and degradation of the herbicide. At higher temperatures, dalapon can also be degraded by ultraviolet light from the sun, in a process called photodegradation (3). In a recently conducted national groundwater survey, dalapon was not found in groundwater as a result of its agricultural use (19).

Dalapon can persist in the soil for two to eight weeks. Its period of persistence in treated soils is usually less than one month (14). Dalapon has trace, or 'residual' activity in soil for three to four months when it is applied at high rates (22 kg/hectare) (7). At low rates it disappears from the soil in about two to four weeks (22). Dalapon persisted for 10 to 60 days, with little or no leaching, when it was applied to moist loam soil at a rate of five to 40 pounds per acre (lb/A) under summer conditions in a temperate climate. When it was applied at 50 ppm, dalapon persisted in soil for less than 2 to longer than 8 weeks (10).

Breakdown of Chemical in Water

In water bodies such as ponds and streams, dalapon disappears via microbial degradation, hydrolysis and photolysis (25). Microbial degradation tends to be the most active form of its breakdown in water. In the absence of microbial degradation, the half-life of dalapon, by chemical hydrolysis, is several months at temperatures less than 77 degrees F (25 degrees C). Hydrolysis is accelerated with increasing temperature and pH (e.g., in alkaline waters) (3, 14, 28).

Breakdown of Chemical in Vegetation

Dalapon is absorbed by plant roots and leaves and moved, or translocated, within plants (22). Translocation occurs from the leaves to the roots of most species given foliar treatment with the herbicide (3). It tends to build up in the areas of greatest plant metabolic activity such as developing seeds and meristems. At high rates of application, dalapon comes, or 'precipitates,' out of solution as an acid, and has immediate and local acute effects on foliage (14). It is easily washed off foliage. In addition to herbicidal activity, dalapon is a plant growth inhibitor. Conditions of increased light and high temperature may cause nutrient solutions or soil applications of dalapon to build up in the tops of plants, via transpiration (13). Dalapon- sodium remains unchanged for long time periods in plants (7). It accumulates in young tissue and is not degraded in plants (20).

PHYSICAL PROPERTIES AND GUIDELINES

Dalapon is a type of acid that is usually formulated with sodium and magnesium salts (12). The acid itself is not used directly. Commercial products usually contain 85% sodium salt or mixed sodium and magnesium salts of dalapon (2, 23). In its pure acid form, dalapon is a colorless liquid with an acrid odor. As sodium-magnesium salts, it is a white to off-white powder (3). Dalapon-sodium is a hygroscopic powder, meaning that it readily takes up water or moisture. Containers should be kept tightly closed when they are not in use (20). Aqueous solutions should not be kept for any length of time since dalapon is subject to hydrolysis. Hydrolysis is slight at 25 degrees C, but is comparatively rapid at or above 50 degrees C (22). Dalapon formulations are mildly corrosive to equipment (20). Solutions of dalapon-sodium are corrosive to iron (22). It is compatible with most other herbicides (7). It is also compatible with hard water and liquid fertilizers (20).

Dalapon is nonflammable (13). It is stable under normal temperatures and pressures, but it may pose a slight fire hazard if exposed to heat or flame. It poses a fire and explosion hazard in the presence of strong oxidizers. Thermal decomposition of dalapon will release corrosive fumes of hydrogen chloride or toxic chlorine gas (26).

Dalapon has a characteristic salty taste in the sodium form (21). Special precautions should be taken so that water, food or feed does not get contaminated by inappropriate storage or disposal of this product (2). Eye and skin contact with dalapon should be avoided. Drifting should be prevented (7). Dalapon spray solutions should be used within 24 hours of mixing with water (13).

Occupational Exposure Limits:

1 ppm (5.8 mg/m3) OSHA TWA
1 ppm (5.8 mg/m3) ACGIH TWA
1 ppm (5.8 mg/m3) NIOSH Recommended TWA (26)

Physical Properties:

CAS #: 75-99-0; Dalapon - Na: 127-20-8
Specific gravity: 1.4014 (26)
pH: 1.32 (0.99 N Soln.) (26)
H20 solubility: highly soluble; 502,00 mg/l at 25 degrees C (25)
Solubility in other solvents: very soluble in alkali solvents and ethanol (20); 1.4 g/kg at 25 degrees C in acetone; 20 mg/kg at 25 degrees C in benzene; 179 g/kg in methanol at 25 degrees C (22)
Melting Point: (with decomposition) 166.5 degrees C (sodium salt) (7)
Boiling point: 365-374 degrees F (185-190 degrees C)
Flash point: 230 degrees F (110 degrees C) (26); 20 degrees C (28)
Vapor pressure: less than 10 to the minus 5 power mbar at 20 degrees C (sodium salt)
Kow: log Kow = 0.76 (18); 6; 5.7 (17)
Koc: 1 g/ml (24)
Degradation Rate Constant (days -1): 0.0462-0.0231 (18)
Kd: Class 5, very mobile (19).
Chemical Class/Use: Chlorinated aliphatic acid; herbicide
NOEL: 15 mg/kg/day (8)
ADI: (EPA) 0.030 mg/kg body weight/day (3)
Theoretical Maximum Residue Contribution (TMRC): =1.3971 mg/day/1.5 kg diet, assuming that residues are present at tolerance levels (3)

BASIC MANUFACTURER

BASF Corp.
Agricultural Product Group
PO Box 13528
2505 Meridian Pkwy.
Research Triangle Park, NC 27709-3528

Review by Basic Manufacturer

Comments solicited: October, 1991.
Comments received:

REFERENCES

  1. American Conference of Governmental Industrial Hygienists, Inc. 1986. Documentation of the threshold limit values and biological exposure indices. Fifth edition. Cincinnati, OH: Publications Office, ACGIH.
  2. Berg, G. L., ed. 1986. Farm chemicals handbook. Willoughby, OH: Meister Publishing Company.
  3. Doyle, R. 1984 (Feb. 27). Dalapon information sheet. Food and Drug Administration. Bureau of Foods, HFF- 420.
  4. Gangstad, E. O. 1986. Freshwater vegetation management. Fresno, CA: Thomson Publications.
  5. Gosselin, R. E., et al. 1984. Clinical toxicology of commercial products. Fifth edition. Baltimore, MD: Williams and Wilkins.
  6. Hallenbeck, W. H. and K. M. Cunningham-Burns. 1985. Pesticides and human health. Springer-Verlag.
  7. Hartley, D. and H. Kidd, eds. 1983. The Agrochemicals handbook. Nottingham, England: Royal Society of Chemistry.
  8. Martin, J., ed. 1971. Pesticide manual. Worcestershire, England: British Crop Protection Council.
  9. Occupational Health Services, Inc. 1986. Material safety data sheet. Secaucus, NJ: OHS, Inc.
  10. Pimentel, D. 1971 (June). Ecological effects of pesticides on nontarget species. Executive Office of the President's Office of Science and Technology. Washington, DC: U.S. Government Printing Office.
  11. Sax, N. I. 1984. Dangerous properties of industrial materials. Sixth edition. NY: VanNostrand Reinhold Co.
  12. Thomson, W. T. 1986. Herbicides. Agricultural Chemicals, Book II. Fresno, CA: Thomson Publications.
  13. TOXNET. 1975-1986. National library of medicine's toxicology data network. Hazardous Substances Data Bank (HSDB). Public Health Service. National Institute of Health, U. S. Department of Health and Human Services. Bethesda, MD: NLM.
  14. U. S. Department of Agriculture, Forest Service. 1984 (Aug.). Herbicides. Agricultural handbook no. 633: Pesticide background statements. Vol. 1. Prepared by Mitre Corporation, McLean, VA.
  15. U. S. Environmental Protection Agency. 1987 (May). Pesticides and the consumer. in EPA Journal. Office of Public Affairs (A-107). Washington, DC.
  16. _____. 1986 (June). Pesticides fact book. (A-107/86-003). Office of Public Affairs. Washington, DC.
  17. _____. 1986 (Jan.). Estimating pesticide sorption coefficients for soils and sediments, by Richard E. Green and Samuel W. Karickhoff. Environmental Research Laboratory. Office of Research and Development. Athens, GA.
  18. _____. 1984 (Dec.). User's manual for the pesticide root zone model (PRZM). Release 1. Athens, GA: Environmental Research Laboratory.
  19. _____. 1984. Memorandum from Stuart Z. Cohen, Ph.D. List of potential groundwater contaminants. Office of Pesticides and Toxic Substances. Washington, DC. Photocopy.
  20. WSSA Herbicide Handbook Committee. 1989. Herbicide Handbook of the Weed Science Society of America, 6th Ed. WSSA, Champaign, IL.
  21. Windholz, M., ed. 1983. The Merck index. Tenth edition. Rahway, NJ: Merck and Company.
  22. Worthing, C. R., ed. 1983. The pesticide manual: A world compendium. Croydon, England: The British Crop Protection Council.
  23. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  24. U. S. Department of Agriculture, Soil Conservation Service. 1990 (Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
  25. Howard, P.H. (ed.). 1989. Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Vol. III: Pesticides. Lewis Publishers, Chelsea, MI.
  26. Occupational Health Services, Inc. 1991 (Nov. 1). MSDS for Dalapon. OHS Inc., Secaucus, NJ.
  27. U.S. Environmental Protection Agency. 1989 (Jan.). Health Advisory Summary: Dalapon. US EPA, Washington, DC.
  28. _____. 1988 (Aug.). Dalapon: Health Advisory. Office of Drinking Water, US EPA, Washington, DC.