Introduction

The herbicide (2,4-diclorophenoxy) phenoxy acid (2,4-D) is the active ingredient in many herbicides, the most widely known being Weed-B-Gon® from the Monsanto Company. A member of the phenoxy herbicides, 2,4-D was introduced in 1946 and has become the most widely used herbicide in the world.1 This herbicide is currently used in agriculture, rights-of-ways, road sides, rangeland, pasturage, forestry, lawns and turfs. With over 4,400tons used in Canada annually,2 and 300,000 tons used in the US,3 2,4_D has over four decades of research and extensive user documentation to attest to the safety of this chemical.4 The USDA (United States Department of Agriculture) determined that if this chemical were no longer available that the cost to growers and other users including consumers a total $1,683 millions dollars in the US alone.1
With a molecular weight of 221.0 (Table 1), 2,4-d is soluble in organic solvents and its free acid in water at 900 mg/L.2 When MTD and NOEL doses were studied in a two generational reproduction study in rats, it was found that the NOEL for maternal toxicity well exceeded the 5 mg/kg guidelines of 5 mg/kg (Table 1) showing that both maternal and fetal toxicity level to be 31.25 mg/kg/day.6 Because of the use of 2,4-D and 2,4,5-T [(2,4,5-trichlorophenoxy) acetic acid] in combination by the military (Agent Orange), many contribute increased incidence of cancer (NHL [non-Hodgkin's lymphoma] in humans and CML [canine malignant lymphoma] in dogs).3 2,4,5-T has been banned in the United States. After an NCI study of 2,4-D,under controlled conditions by EPA/GLP laboratories, canines feed massive doses of 2,4-D failed to develop cancer.7

Physical properties and Exposure guidelines for (2,4-dichlorophenoxy)acetic acid(2,4-D)
Physical Properties:5	Exposure Guidelines:4	Exposure Guidelines:EXTOXNET,
CAS #: 94-75-7 Chemical Name: (2,4-dichlorophenoxy) acetic acid Chemical class/use: phenoxy herbicide Solubility in water: 890 mg/l Solubility in other solvents: ethanol and acetone, 9.5 g/100 g; benzene, 1.07 g/100g Melting Point: 138 degrees C Vapor Pressure: 8 x 10-6 mm Hg	IMAC - 0.1 mg/L in Drinking water2 NOEL: 21-day Dermal - 1000 mg/kg Teratology, rat - 25 mg/kg Teratology, rabbit - 30 mg/kg 2-generation, rat - 5 mg/kg 13wk subchronic, rat and mouse - 5 mg/kg 2yr chronic, rat and mouse - 5 mg/kg 1yr chronic dog - 1 mg/kg1yr neurotoxicity, rat - 5 mg/kg	NOEL (rats): 1 mg/kg ADI: 0.3 mg/kg (WHO) MCL: 0.07 mg/lHA: 70 ug/l (lifetime) TLV-TWA: 10 mg/m3 TLV STEL: 20 mg/m3 Dangerous Exposure: 500 mg/m3 (OSHA/NIOSH) RfD: 0.01 mg/kg/day LEL: 5 mg/kg/day (rat)

Table 1: Physical properties and exposure guidelines for (2,4-dichlorophenoxy)acetic acid (2,4-D).

The formulations of 2,4-D from various countries, fuels the continued debate as to the safety of 2,4-D. Dr. Simon reports to a Mr. Robinson who had a bottle of Weed-B-Gon® explode in his car, that Weed-B-Gon® products contain 2,4,D-triethylamine salt, 2,4,5-TP Silvex and that the likelihood of dioxins is great.8 According to the MSDS of two US 2,4-D products, they do not contain 2,4,5-TP Silvex.9,10 The studies of 2,4-D products manufactured in the US and Canada were tested for dioxin levels. Of the 26 Canadian amine samples eight were positive for dioxin at levels from 5 to 500 ppb (parts per billion).11 Of the 21-ester samples for Canada, all but one were positive for dioxin. Samples of 2,4-D manufactured in the United States found in three of 30 samples measurable amounts of dioxin (2,7DCOD) at amounts that do not have biological significance.11
A review of studies in scientific literature 2,4-D was found to be less toxic than caffeine and just slightly more toxic than aspirin. At concentrations found in the environment it is unlikely to present a threat to wildlife, has low reproductive toxicity, causes no birth defects, chronic effects are limited to high doses, highly improbably that it will cause cancer and does not cause genetic damage.12
Based on this data and following packaging instructions damage to adjacent plant life should have been minimal. The following is a report of three exposures to Iris Germanica and other ornamental plants and the effects seen after application of 2,4-D products.
Exposure Results
Three different exposures occurred during last year. Two occurred with direct application of the product using a paintbrush, and one exposure occurred due to aerosol cross contamination. The effect of these cross contaminations was not visible until the flowers bloom.
Exposure one occurred with the application of a 2,4-D product utilizing a paintbrush to directly apply the preparation to deep-rooted weeds within the iris bedding area adjacent to a well-established plant. As a result of this application the dwarf iris plant affected produced normal flowers (Figure 1A)13, flowers that were reduced in size, color changes and aberrant flower structure (Figure 1B)13, and flowers that were normal in size but had aberrant coloring and flower structure (Figure 1C)13.
Exposure two occurred after 2,4-D preparation was applied using a paintbrush to a deep-rooted weeds adjacent to an established dwarf iris plant. When the iris plant flowered it produced normal flowers (Figure 2A)14, and flowers with distinct color changes (Figure 2B)14. There were no size or structural changes seen after this application. The damage to the leaves was due to insects and not the application of the 2,4-D product.

Figure 1. After topical application of a 2,4-D preparation, this dwarf iris plant adjacent to the treated weed shown symptoms of exposure only after the plant bloomed. Effects include color changes (C), abnormal flower size, and abnormal flower structure (B) along with normal flowers (A). All leaves appeared unaffected.

Figure 2. After application of a 2,4-D preparation to weeds adjacent to clump, this dwarf iris plant showed only a color change (B), without changes in structure of the flowers, along with normal flowers (A).

The third application occurred during aerosol spraying of a 2,4-D product on an adjacent path by a neighboring landowner. Iris plant leave showed area of cell death however the plant and blooms seemed unaffected. However, a nearby rosebush lost all leaves and flowers.15
Conclusions
The 2,4-D in herbicidal formulations has a mean soil half-life of less than 7-days when tested in three different soil types (heavy clay, clay loam, and sandy loam),16 with microbiological degradation being the major decomposition mechanism. In the environment, 2,4-D has low soil sorption and a high potential for leachability.17 Most studies of 2,4-D movement in soil were based on vertical depth of movement in the soil and not horizontal movement. Vertically, 2,4-D has been detected in 6- to 24-inches depending on the organic matter in the soils.18 Since most iris beds are amended with organic material (manure, compost, and peat moss), it is possible that the affected iris was due to lateral movement of 2,4-D in the soil. This resulted in color changes on the exterior portion of the plant. The effects seen with the first exposure may be due to both the lateral movement of the 2,4-D in the soil as well as direct inadvertent exposure to the plant rhizome occurring during application which resulting in changes in flower structure and changes not only in coloring but in color patterns as well. As 2,4-D has no teratogenic or mutagenic properties, it is possible that these plants will bloom with normal flower structure and coloring in the following years.
Aerosol drift, which is the cause of the third exposure, is currently the reason of a tense legal stand off in the town of Fairfax in Marin County, California. The Fairfax town council passed a law forbidding property owners from spraying herbicides and pesticides unless they first notified their neighbors in 150-foot radius, 48-hours ahead, by posting signs indicating chemical spraying will occur.19 The law also forbids spraying of Fairfax parks which has state authorities prepared to act against the town stating that the law impinges on the rights of pesticide operators and land owners.
Fairfax council members call the "A public right to know law:, stating that the ordinance will enable residents to take steps to protect themselves, their families, their pets and their property from the hazards of chemical spray. Paul Helliker of the California State Department of Pesticide Regulations warned that unless the town rescinded the ordinance, the states attorney general would be instructed to prepare a lawsuit against the town. State officials also challenge Fairfax's authority to prohibit the state from using pesticides and herbicides on public parks and rights of way.
Pesticide operators have advised the town council that portions of the ordinance are pre-empted by a 1984 state law governing pesticide use and licensing requirements.
This is an example of the growing concerns throughout the country because of indiscriminant spraying of pesticides and herbicides. Many towns have been requested not to spray in schools and public areas. In 2000, California passed the Health Schools Act requiring parents be notified each year of intended pesticide spraying used in California schools, giving the parents 24-hour notice before spraying occurs.
Much of this problem is not from licensed operators but by homeowners which habitually over spray herbicides and pesticides. Most people buying these products off the shelf believe in their absolute safety and fail to read the directions. Because of this they fail to take precautions to protect themselves, their pets and control their spray drift to their neighbors.
Although the Fairfax ordinance maybe stepping on toes, it is a call for the states and federal government to control the use of over the counter pesticides and herbicides sales and allowing this suppliers to give training to those who would use these products. By allowing the home users access to training of these products, perhaps applications of these products would become inherently safer to use.