Phenoxy Herbicides (2,4-D)

Phenoxy Herbicides (2,4-D)

Chapter 84 Phenoxy Herbicides (2,4-D) Elke Kennepohl1, Ian C. Munro2 and James S. Bus3 1 Kennepohl Consulting Cantox Health Sciences International 3...

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Chapter 84

Phenoxy Herbicides (2,4-D) Elke Kennepohl1, Ian C. Munro2 and James S. Bus3 1

Kennepohl Consulting Cantox Health Sciences International 3 The Dow Chemical Company 2

84.1  Introduction Phenoxy herbicides have been commercially available for over 60 years and are the most widely used family of herbicides worldwide. 2,4-Dichlorophenoxyacetic acid (2,4-D), the most common of the phenoxy herbicides, is one of the best-studied agricultural chemicals. This chapter focuses primarily on 2,4-D since it is the most widely used herbicide and the majority of the literature on phenoxy herbicides pertains to studies with 2,4-D. The safety of using phenoxy herbicides was first questioned when a series of case-control studies was published by Lennart Hardell in the late 1970s, in which he hypothesized that the occurrence of three rare forms of cancer (Hodgkin’s disease, soft tissue sarcoma, and non-Hodgkin’s lymphoma) in workers was related to exposure to these herbicides along with dioxins known to contaminate 2,4,5trichlorophenoxyacetic acid (2,4,5-T). Since that time, several human and animal studies have been conducted which do not lend support to his hypothesis. As well, several expert panels have been convened to assess the safety of 2,4-D, and all have concluded that there is no evidence to suggest that 2,4-D poses any risk to human health under its intended conditions of use. In fact, 2,4-D has been classified by the U.S. Environmental Protection Agency (EPA) as a Group D (not classifiable as to human carcinogenicity) because “the evidence is inadequate and cannot be interpreted as showing either the presence or absence of a carcinogenic effect.” Because of the vast amount of data available on 2,4-D, this chapter provides a brief summary and overview of the available studies.

84.2  Physical and chemical properties Several phenoxy acids have been used as herbicides, including 2,4,5-T, 4-(2,4-dichlorophenoxy) butyric acid (2,4-DB), 2-(2,4-dichlorophenoxy propionic acid) (dichlorprop), 2(2-methyl-4-chlorophenoxy) propionic acid (MCPP or Hayes’ Handbook of Pesticide Toxicology Copyright © 2010 Elsevier Inc. All rights reserved

mecoprop), 2-methyl-4-chlorophenoxyacetic acid (MCPA), and 2-(2,4,5-trichlorophenoxy) propionic acid (Silvex), with the most commonly and widely used herbicide being 2,4-D. 2,4,5-T and Silvex are no longer manufactured or sold. Figure 84.1 shows the chemical structures of the phenoxy acids.

84.2.1  2,4-D Acid, Salts, and Esters The basic form of 2,4-D is the acid, but 2,4-D is often formulated as an inorganic salt, amine, or ester through various manufacturing processes, and is used in many commercial products. CAS number:

94-75-7

Chemical name:

2,4-dichlorophenoxyacetic acid

Trade names:

AC Aquacide, Acme, Agsco, Alco, Alligare, Alphaset, Aqua-Kleen, Arc-Camba, Bakker, Banvel, Barrage, Bonide, Brash, Butoxone, Butyrac, Candor, Chaser, Chemsico, CIL Lawn, Clean Crop, Confront, Cornbelt, Crossbow, Curtail, Cutback, Dexol, Dissolve, Doom, Double Kill, Double Up, Drexel, Dupon Cimarron Max, Dyvel, Escalade, Esteron, Exit, Fertilizer Plus, Five-Star, Focus, Forefront, Formula 40F, Gharda, Gladeamine, Glymix, Grazon, Green Thumb, Greenleaf, Greensweep, Growell, Hellion, Hilco-X, Hivol, Hoelon, Illoxan, Killex, Knockout, Landmaster, Later’s Weed Stop, Lawn Pro, Lazer, Maestro, Mecoturf, Millenium, Miraclo-Gro, Misty Repco Kill, Momentum, Nufarm, Oasis, Outlaw, Paramount, Pasture, Penoxsulam, Picloram, Proturf, Quadmec, Quincept, Range Star, Rangeland, Real-Kill, Recoil, Restore, Rifle-D, Riverdale, Rustler, Saber, Salvo, Savage, Savana, Selective, Shotgun, Solution, Speed Zone, Spoiler, Starane, Statesman, Strike 3, Super Plus, Target, Thundermaster, Top Gun, Toram, Tordon, Trillion, Trimec, Trooper, Turf Builder, Turf Pride, Turflon, Viper, Viterra, Weco Max, Weed Rhap, Weedar, Weedaway, Weedaxe, Weed-B-Gon, Weedex, Weedhawk, Weedmaster, Weedone, Weedstroy, Winterizer

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Hayes’ Handbook of Pesticide Toxicology

1830

CH3 Cl

O

CH2

COOH

Cl

O

Cl

(CH2)3

COOH

Cl

Cl

OCH2COOH

HN

Cl

O

Cl

Cl

O Cl

O

COOH

Cl

O

CH2

C

Cl

CH2 CH3 O

CH2

CH2 H10

CH3

O

CH

COOH

Cl

O

O

CH2

COOH

Cl

Cl 2,4-D 2-ethylhexyl ester

COOH

2,4,5-T

CH3

Cl

CH2

Cl

Mecoprop

Cl

Cl

CH

CH3 2,4-D dimethylamine salt

COOH

Dichlorprop

CH3 CH3 CH3

CH

Cl 2,4-DB

2,4-D acid

Cl

O

MCPA

Silvex

CH2COOCH2CH2OCH2CH2CH2CH2

Cl 2,4-D butoxyethanol ester

Figure 84.1  Chemical structures of phenoxy acid herbicides.

Appearance:

white powder

Molecular weight:

255.49

Empirical formula:

C8H6Cl2O3

Melting point:

156.6°C (pure acid); 150–151°C (technical acid)

Molecular weight:

221.04

Boiling point:

Decomposes

Water solubility:

278 mg/liter at 25°C (acid)

Melting point:

140.5°C

Vapor pressure:

0.022 mm Hg at 25°C

Boiling point:

130°C at 1 mm Hg (isopropyl ester)

Water solubility:

900 mg/liter at 25°C (acid)

Vapor pressure:

0.02 mPa at 25°C (acid)

Partition coefficient:

2.81

84.2.2  2,4,5-T

84.2.3  2,4-DB CAS number:

94-82-6

Chemical name:

4-(2,4-dichlorophenoxy) butyric acid

Trade names:

Butoxone, Butyrac, Butirex, Embutone, Embutox, Legumex, Venceweed

Appearance:

colorless to white crystals

Empirical formula:

C10H10Cl2O3

Molecular weight:

249.10

CAS number:

93–76–5

Chemical name:

2,4,5-trichlorophenoxyacetic acid

Trade names:

no longer manufactured or sold

Melting point:

117–119°C

Appearance:

White crystals

Water solubility:

46 mg/liter at 25°C

Empirical formula:

C8H5Cl3O3

Vapor pressure:

negligible (acid and salts)

Chapter | 84  Phenoxy Herbicides (2,4-D)

84.2.4  Dichlorprop (2,4-DP)

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84.2.7  Silvex

CAS number:

120–36–5

CAS number:

93-72-1

Chemical name:

2-(2,4-dichlorophenoxy) propionic acid

Chemical name:

Trade names:

Cornox, Hedonal, Weedone, Estaprop

2-(2,4,5-trichlorophenoxy) propionic acid

Appearance:

colorless crystals

Trade names:

no longer manufactured or sold

Empirical formula:

C9H8Cl2O3

Appearance:

white powder

Molecular weight:

235.07

Empirical formula:

C9H7Cl3O3

Melting point:

117–118°C

Molecular weight:

269.51

Water solubility:

350 mg/liter at 20°C

Melting point:

181.6°C

Water solubility:

200 mg/liter at 25°C

84.2.5  Mecoprop (MCPP) CAS number:

7085-19-0

Chemical name:

2-(4-chloro-2-methylphenoxy) propionic acid

Trade names:

Kilprop, Mecopar, Triester-II, MecAmineD, Triamine-II, Triplet, TriPower, Trimec, Trimec-Encore, U46 KV Fluid

Appearance:

White to light brown crystalline solid

Empirical formula:

C10H11ClO3

Molecular weight:

214.65

Melting point:

93–95°C

Water solubility:

very soluble at 25°C

Vapor pressure:

0.31 mPa at 20°C

Partition coefficient:

1.26 at pH7

84.2.6  Mcpa CAS number:

94-74-6

Chemical name:

2-methyl-4-chlorophenoxyacetic acid

Trade names:

Agritox, Agroxone, Agrozone, Agsco MXL, Banlene, Blesal MC, Bordermaster, Cambilene, Cheyenne, Chimac Oxy, Chiptox, Class MCPA, Cornox Plus, Dakota, Ded-Weed, Empal, Envoy, Legumex, Malerbane, Mayclene, Mephanac, Midox, Phenoxylene, Rhomene, Rhonox, Sanaphen-M, Shamrox, Selectyl, Tiller, Vacate, WeedRhap, Zhelan

Appearance:

colorless crystals

Empirical formula:

C9H9ClO3

Molecular weight:

200.62

Melting point:

118–119°C

Water solubility:

825 mg/liter at 25°C (acid)

Vapor pressure:

0.2 mPa at 20°C

84.3  History of use For over 60 years, 2,4-D has been the most commonly and widely used herbicide throughout the world. When applied to plants, 2,4-D is absorbed through the roots and leaves within 4 to 6 hours and is distributed in the plant via the phloem (WHO, 1984). Once absorbed, 2,4-D selectively eliminates broadleaf plants (due to their larger leaf area and hence, greater absorption) by mimicking the effect of auxins (i.e., plant growth-regulating hormones) and stimulating growth, rejuvenating old cells, and overstimulating young cells, leading to an abnormal growth pattern and death in some plants (Mullison, 1987). In addition, 2,4-D affects plant metabolism, which leads to interference with food transport (Mullison, 1987). 2,4-D is primarily used as a herbicide in agriculture, forestry, and lawn care practices, with the majority (60%) of the total usage in the United States being reported for use as weed control in agriculture (i.e., corn and small grains) (EPA, 1997). 2,4-D is reported to be effective against dandelion, plantain, chickweed, henbit, white clover, heal-all, red sorrel, curly dock, chicory, yellow rocket, speedwell, ground ivy, spurge, oxalis, knotweed, purslane, thistle, wild violet, wild onion, wild garlic, lespedeza, yellow nutsedge, crabgrass, sumac, willow, sagebrush, ragweed, Eurasian water milfoil, and water hyacinth (Lefton et al., 1991; Mullison, 1987; WHO, 1975). To a lesser extent, 2,4-D is used as a growth regulator on various crops ranging from potatoes to citrus fruits (WHO, 1975, 1984). In the past, 2,4-D was combined with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) for brush and weed control. Over 10 million gallons of a special concentrated mixture called Agent Orange were applied in the Vietnam War to defoliate trees (Wolfe, 1983). A reregistration eligibility review/re-evaluation of 2,4-D was conducted by the U.S. EPA in 2005, and by Health Canada in 2008, with both agencies deciding that 2,4-D was eligible for continued use.

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84.4  Formulations 2,4-D is formulated into end-use products to facilitate application. Water-soluble salts and amines are usually prepared as aqueous solutions with small amounts of additives such as water conditioners and antifoam agents. The oil-soluble esters are often formulated with petroleum solvents (e.g., kerosene or naphtha) plus emulsifiers. Such formulations are then diluted with relatively large amounts of water to make the final herbicide spray mixture. Several forms of 2,4-D can be combined with dry fertilizer ingredients to form lawn “weed and feed” products. In the past, concerns arose regarding possible contamination of 2,4-D formulations with dioxins, notably the polychlorinated dibenzo-p-dioxins (PCDDs) and more specifically 2,3,7,8-tetrachlorodibenzo-p-dioxin (T4CDD), and nitrosamines. 2,4-D formulations have been reported to contain 2,3,7,8-T4CDD but only when 2,4,5-T was present (Cochrane et al., 1981, 1982a, 1982b; Woolson et al., 1972). 2,4-D formulations currently sold in the United States contain very few PCDD contaminants. In fact, analytical studies of the more recent formulations have repeatedly shown dioxin levels to be below the limit of quantitation set by the U.S. Environmental Protection Agency (Berry, 1989; Cramer, 1996). In Canada, a limit of 10 ppb per isomer PCDD (nondetectable for 2,3,7,8-T4CDD at 1 ppb) in 2,4-D formulations has been set (Agriculture Canada, 1983). In an older analysis of 200 samples of various forms of 2,4-D (Cochrane et al., 1981, 1982a, 1982b), all but a few samples tested below the 10-ppb limit. In the past, there was some possible contamination with nitrosamines formed from nitrates used in preserving metal storage containers; however, plastic or epoxy-lining has replaced the metal used for storage containers and nitrosamine formation no longer presents a concern.

Hayes’ Handbook of Pesticide Toxicology

the highest exposures were obtained in occupational settings, with reported average estimated internal doses ranging from 0.01 to 40 g/kg body weight/day for forestry workers, and 0.35 to 6.3 g/kg body weight/day for commercial applicators and farmers (Frank et al., 1985; Grover et al., 1986; Lavy and Mattice, 1984; Lavy et al., 1987; Yeary, 1986). Average estimated internal doses reported to be reached by bystanders or home and garden users were below 0.2 g/kg body weight/day (Harris et al., 1992; Lavy and Mattice, 1984). Most of the past epidemiological studies do not reflect the growing trend toward using protective apparel when applying herbicides. With an increased awareness of worker safety and the new proposed labeling directions, workers are required to wear protective clothing consisting of eye protection, chemical-resistant gloves, long-sleeved shirt, long pants, socks, and shoes. In addition, following use of 2,4-D, it is recommended that workers thoroughly wash their hands, face, and arms with soap and water and wash any contaminated clothing separately. Human urinary biomonitoring studies estimated the absor­ bed dose of 2,4-D in farm applicators as 2.5 to 2.7 g/kg/day (Alexander et al., 2007; Thomas et al., 2009), and in farm family spouses and childen at 0.8 and 0.22 g/kg/day, respectively (Alexander et al., 2007). In a biomonitoring study of 135 preschool-aged children and their adult caregivers, Morgan et al. (2008) estimated the maximum absorbed dose in the chlidren as 0.28 g/kg/day, which, using a Biomonitoring Equivalents exposure analysis, were concluded as well below exposure guidance values developed by the US Environmental Protection Agency (Aylward et al., 2009).

84.6  Toxicological studies 84.6.1  Absorption

84.5  Human exposure to 2,4-D 2,4-D is one of the most commonly used herbicides both domestically and commercially, and exposure to it can occur via inhalation, ingestion, and dermal contact. Respiratory exposure to 2,4-D is less than 2% of total exposure (Grover et al., 1986), and residual levels in foodstuffs or drinking water are essentially nondetectable or only detected in trace amounts (Duggan and Corneliussen, 1972; Duggan and Lipscomb, 1969; Gartrell et al., 1985). By far, dermal contact during use of the product accounts for the greatest potential for exposure, with estimates that approximately 90% of total exposure occurs through dermal exposure (Feldman and Maibach, 1974). Since 2,4-D use is typically seasonal and short-term, the duration of exposure is considered repeated subchronic. In a 1992 review of 2,4-D, Munro et al. (1992) summarized exposures to 2,4-D in a variety of occupational and home-use settings. Based on several epidemiological studies,

2,4-D is rapidly absorbed through the gastrointestinal tract following oral exposure, with peak plasma levels being reached in as little as 10 minutes or up to 24 hours depending on the dose and chemical form of 2,4-D (Erne, 1966a; Khanna and Fang, 1966; Knopp and Schiller, 1992; Kohli et al., 1974; Pelletier et al., 1989; Sauerhoff et al., 1977). The rate of absorption is related to dose, with absorption occurring more rapidly at lower doses (i.e., 0.4 mg/kg body weight/day) than at higher doses (i.e., 1 mg/kg body weight/day) (Pelletier et al., 1989). Absorption of 2,4-D esters has been reported to occur more slowly than for acid or salt forms (Erne, 1966a); however, the excretion rates for the various forms are reported to be similar (Khanna and Fang, 1966; Knopp and Schiller, 1992; Pelletier et al. 1989). Dermal contact is the major route of exposure to 2,4-D. In occupationally exposed humans, dermal absorption was reported to occur rapidly based on the detection of 2,4-D in urine within 4 hours (Feldman and Maibach, 1974), and although the percentage absorbed is variable, it is usually

Chapter | 84  Phenoxy Herbicides (2,4-D)

less than 6% (EPA, 1996; Feldman and Maibach, 1974; Harris and Solomon, 1992). Studies in rats and monkeys showed these percentages to be highly variable and dependent on chemical form, vehicle, and animal species (Grisson et al., 1987; Knopp and Schiller, 1992; Moody et al., 1990, 1991; Pelletier et al., 1989, 1990). Although no controlled studies have been conducted to assess the absorption rate via inhalation exposure, epidemiological studies of occupationally exposed workers indicate that absorption is rapid by both dermal and inhalation routes (Frank et al., 1985; Kolmodin-Hedman and Erne, 1980).

84.6.2  Distribution 2,4-D is highly water soluble and therefore is widely distributed, but does not accumulate, in the body. It also does not readily cross lipid membranes, and at physiological pH, it exists predominately in the ionized form. 2,4-D uses active transport systems to enter tissues and cross the blood/ brain barrier (Kim and O’Tuama, 1981; Pritchard, 1980). Another factor which contributes to the extent of tissue distribution of 2,4-D is its ability to bind to serum proteins (Erne, 1966a; Fang and Lindstrom, 1980; Orberg, 1980). Peak tissue levels in rats have been reported anywhere from 10 minutes to 8 hours depending on the dose administered (0.4 to 240 mg/kg body weight) (Khanna and Fang, 1966; Pelletier et al., 1989). Following exposure, 2,4-D has been detected in liver, kidney, and lung of a variety of animal species (Clark et al., 1975; Erne, 1966a). Levels in brain were reported to account for only a very small percentage of the exposure dose (Erne, 1966a; Tyynela et al., 1990); however, at levels of intoxication (i.e., 300 mg/kg body weight, which is well above the level of renal saturation), levels in brain and cerebrospinal fluid of rats were increased relative to plasma levels (Elo and Ylitalo, 1977, 1979; Tyynela et al., 1990). At these high dose levels, the organic acid transport system responsible for the efflux of 2,4-D out of the brain is inhibited (Kim et al., 1983; Pritchard, 1980; Tyynela et al., 1990; Ylitalo et al., 1990). In addition, vascular damage has been reported in rats administered extremely high doses of 2,4-D (i.e., more than 300 mg/kg body weight) (Elo et al., 1988), which may facilitate an increased influx of 2,4-D through the compromised blood/brain barrier (Elo et al., 1988; Hervonen et al., 1982; Tyynela et al., 1990). Saturation of plasma protein binding also may contribute slightly to the increased brain: blood ratio of 2,4-D reported in rats at these exposure levels (Tyynela et al., 1990; Ylitalo et al., 1990). 2,4-D also has been reported to pass the placental barrier in mice, rats, and pigs, and has been detected in the uterus, placenta, fetus, and intrauterine fluid of exposed animals (Erne, 1966a; Fedorova and Belova, 1974; Lindquist and Ullberg, 1971) but was rapidly eliminated (Lindquist and Ullberg, 1971).

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84.6.3  Pharmacokinetics Depending on the chemical form of 2,4-D and the animal species tested, plasma half-lives following oral exposure of 100 mg/kg body weight range from 3.5 to 12 hours (Erne, 1966a). Lower doses (i.e., 3 mg/kg body weight) in rats showed half-lives of 0.5 to 0.8 hours (Khanna and Fang, 1966), indicating that clearance rates are highly dependent on dose. In human studies, plasma clearance of orally administered 2,4-D was found to follow first-order kinetics with urinary excretion half-lives ranging from 10.2 to 28.4 hours (Sauerhoff et al., 1977), which is consistent with the findings (urinary excretion half-life  18 hours) from a forestry worker who exhibited the highest amount of 2,4-D excretion among two groups exposed over a period of 11 or 18 days (Frank et al., 1985). The pharmacokinetics of 2,4-D following dermal absorption is apparently different from that following the oral route (Pelletier et al., 1989). Plasma levels tend to reach a plateau and decline more rapidly following oral exposure. In addition, plasma clearance has been reported to follow biphasic kinetics beginning 8 hours post-dosing, with half-lives for various tissues ranging from 0.6 to 2.3 hours for the first phase and 25.7 to 29 hours for the second phase. Furthermore, cumulative urinary excretion of 2,4-D increases more slowly following dermal rather than oral exposure.

84.6.4  Metabolism Once absorbed into body fluids and tissues, the salts and esters of 2,4-D undergo acid and/or enzymatic hydrolyzation to form 2,4-D acid. In laboratory animals and humans following oral exposures, the presence of acidhydrolyzable conjugates has been reported at 0 to 27% of the administered 2,4-D (Erne, 1966b; Grunow and Bohme, 1974; Kohli et al., 1974; Sauerhoff et al., 1977). The available data indicate that 2,4-D is not metabolized to reactive intermediates and is excreted predominately as the parent compound.

84.6.5  Excretion Regardless of the route of exposure, 2,4-D is predominately excreted in the urine (Erne, 1966a; Feldman and Maibach, 1974; Khanna and Fang, 1966; Knopp and Schiller, 1992; Moody et al., 1990, 1991; Pelletier et al., 1989). The rate of urinary excretion is inversely proportional to dose. For example, at oral doses of 3 to 30 mg/kg body weight given to rats, 93 to 96% of the dose was excreted within 48 hours, whereas at higher doses (i.e., 60 mg/kg body weight) the percentage of dose excreted within 24 hours decreased linearly with increasing dose (Khanna and Fang, 1966). In rats, 90% of oral doses of 30 mg/kg body weight or less were excreted in the urine within 24 hours (Khanna

Hayes’ Handbook of Pesticide Toxicology

1834

and Fang, 1966; Knopp and Schiller, 1992; Pelletier et al., 1989). Similarly, in humans administered an oral dose of 5 mg 2,4-D/kg body weight, 77% of the dose was excreted within 96 hours (Kohli et al., 1974) and 87 to 100% of the dose was excreted in the urine over 6 days (Sauerhoff et al., 1977). 2,4-D is predominately excreted by the kidney using an active transport system. Saturation of renal clearance appears to occur at 50 to 60 mg/kg body weight (Gorzinski et al., 1987; Khanna and Fang, 1966) based on kidney concentrations and urinary excretion rates. Another significant route of excretion in occupationally exposed workers is perspiration (Sell et al., 1982). Following a 2-hour exposure, 2,4-D was detected in T-shirt extracts (i.e., measure of perspiration) for 2 weeks and in urine for 5 days. 2,4-D also has been reported to be excreted in the milk of lactating rats exposed to 2,4-D (Fedorova and Belova, 1974).

84.6.6 Animal Studies 84.6.6.1  Acute Toxicity Numerous acute toxicological tests have been conducted on the various forms of 2,4-D as summarized in Table 84.1. Overall, oral exposure to 2,4-D shows moderate to low toxicity, whereas dermal and inhalation toxicity are low. Dermal irritation in rabbits was considered slight for the acid form of 2,4-D and minimal for the salt and ester forms. Reported eye irritation in rabbits, on the other hand, is severe for the acid and salt forms, but minimal for the ester.

84.6.6.2  Subchronic Toxicity Further to the acute toxicity data, numerous subchronic studies have been conducted on a variety of 2,4-D forms, by different exposure routes, and in various animal species. The subchronic studies conducted range from 3-week dermal studies in rabbits to 13-week dietary studies in dogs and rodents. The results of these studies are summarized in Table 84.2. Overall, at doses above the threshold

of saturation for renal clearance, the key target organs in rats appear to be primarily the kidney and, to some extent, the thyroid. The changes reported in the rat kidney were the loss of epithelial cells in the proximal tubule brush border; the changes in the thyroid were follicular cell hypertrophy in association with a reduction in serum thyroxine levels. These changes were consistent over all forms of 2,4-D tested, with a reported no-observed-adverse-effect level (NOAEL) of 15 mg/kg body weight/day (Charles et al., 1996b; Szabo and Rachunek, 1991; Yano et al., 1991a, 1991b). Some of these findings were reported at lower doses in older rat studies using the acid form of 2,4-D (Gorzinski et al., 1981a, 1981b); however, the histological effects were not statistically significant at 15 mg/kg body weight/day, which is consistent with the more recent studies. In another older study (Serota, 1983a), other minor histological effects in the kidney were reported in male rats at 5 mg/kg body weight/day and in female rats at 1 mg/kg body weight/day. These effects were not reported in any other of the subchronic studies. Although some thyroid changes have been reported at 15 mg/kg body weight/day in rats (Serota, 1983a), these changes were considered incidental and do not affect the conclusion that the subchronic NOAEL for 2,4-D is 15 mg/kg body weight/day (Munro et al., 1992). Similar results with respect to the kidney have been reported in 13-week dietary mouse studies (Serota, 1983b; Schulze, 1991). In a 13-week dog study in which 2,4-D was administered by gelatin capsules, kidney effects consisting of reduced cytoplasmic eosinophilia of the epithelial cells lining some convoluted tubules were reported at lower doses, resulting in a NOAEL of 1 mg/kg body weight/day (ITF, 1990). Thyroid changes were not reported in the mouse or dog.

84.6.6.3  Reproductive and Developmental Toxicity Several multigenerational and developmental animal studies have been conducted to assess the potential of 2,4-D to affect reproduction and the developing fetus, and are summarized in

Table 84.1  Acute Toxicitya Involving Various Chemical Forms of 2,4-D Oral LD50 (mg/kg bw/d)

Dermal LD50 (mg/ kg bw/d)

Inhalation LD50 (mg/liter)

Form of 2,4-D

Rat

Mouse

Dog

Guinea pig

Chicken

Rat

Rabbit

Rat

Acid

na

1400–  2000

1.79

639–980

312–434

25–250

397–553

358–817

Salt

863–  2000

na

na

na

na

2000

2000

3.8

Ester

440–982

na

na

na

na

na

1829–  2000

4.6

bw  body weight. na  not available. a Condensed from Munro et al. (1992).

Chapter | 84  Phenoxy Herbicides (2,4-D)

1835

Table 84.2  Summarya of Subchronic Studies on 2,4-D Tested in Various Animal Species Route

Dose (mg/kg bw/d) [in acid equivalents]

NOAELb (mg/kg bw/d)

Reference

2,4-D (100% pure)

diet

0, 15, 60, 100, 150

15 (females only)

Gorzinski et al. (1981a)

2,4-D (97.5% pure)

diet

0, 15, 60, 100, 150

15 (females only)

Gorzinski et al. (1981b)

2,4-D (97.5% pure)

diet

0, 1, 5, 15, 45

1 (males only)

Serota (1983a)

2,4-D (96.1% pure)

diet

0, 1, 15, 100, 300

15

Charles et al. (1996b)

2,4-D ethylhexyl ester

diet

0, 1, 15, 100, 300

15

Charles et al. (1996b)

2,4-D dimethylamine salt

diet

0, 1, 15, 100, 300

15

Charles et al. (1996b) Szabo and Rachunek (1991)

Chemical species 13-week: Rat

2,4-D butoxyethyl ester

diet

0, 1, 15, 100, 300

15

2,4-D triisopropanolamine salt

diet

0, 1, 15, 100, 300

15

Yano et al. (1991b)

2,4-D isopropylamine salt

diet

0, 1, 15, 100, 300

15

Yano et al. (1991a)

intraperitoneal

0, 100, 150



Lukowicz-Ratajczak and Krechniak (1988)

2,4-D acid

diet

0, 5, 15, 45, 90



Serota (1983b)

2,4-D acid

diet

0, 1, 15, 100, 300

15

Schulze (1991)

oral intubation

50, 100, 200



Kuntz et al. (1990)

diet

100



Lundgren et al. (1987)

2,4-D acid

gelatin capsule

0, 0.3, 1, 3, 10

1

ITF (1990)

2,4-D acid

diet

0, 0.5, 1.0, 3.75, 7.5

1

Charles et al. (1996c)

2,4-D dimethylamine salt

diet

0, 1.0, 3.75, 7.5

1

Charles et al. (1996c)

2,4-D 2-ethylhexyl ester

diet

0, 1.0, 3.75, 7.5

1

Charles et al. (1996c)

2,4-D acid

dermal

0, 10, 100, 1000

1000

Schulze (1990a)

2,4-D dimethylamine salt

dermal

0, 10, 100, 300

10

Schulze (1990b)

2,4-D 2-ethylhexyl ester

dermal

0, 10, 100, 1000

10

Schulze (1990c)

2,4-D triisopropanolamine salt

dermal

0, 55, 193, 553

553

Mizell et al. (1990b)

2,4-D isopropylamine salt

dermal

0, 39, 98, 275

275

Mizell et al. (1990a)

2,4-D butoxyethyl ester

dermal

0, 32, 96, 321

321

Mizell et al. (1989)

12-week: Rat 2,4-D sodium salt 13-week: Mouse

14-day: Mouse 2,4-D acid 4-day: Mouse 2,4-D acid 13-week: Dog

21-day: Rabbit

a

Adapted from Munro et al. (1992). NOAEL  no-observed-adverse-effect level.

b

Table 84.3. In general, the results of the available studies indicate that 2,4-D is not teratogenic and does not affect reproduction except at maternally toxic doses or those saturating the threshold for renal clearance (i.e., 50 mg/kg body weight/day). At doses above the maximum tolerated dose (MTD), some

developmental effects have been reported in test animals (i.e., decreased fetal weight gain, increased incidence of lumbar ribs and wavy ribs, and delayed ossification of bone). The only teratogenic effect (i.e., cleft palate) reported was in mice, but occurred only at maternally toxic doses.

Hayes’ Handbook of Pesticide Toxicology

1836

Table 84.3  Summary of Developmental and Reproductive Toxicity Studies on 2,4-D Tested in Various Animal Species Route

Exposure duration

Dose (mg/kg bw/d)

NOAELa (mg/kg bw/d)

Reference

2,4-D triisopropanolamine salt

gavage

GDb 7–19

0, 10, 30, or 75c

10d; 75e

Liberacki et al. (1994), Charles et al. (1996a)

2,4-D isopropylamine salt

gavage

GD 7–19

0, 10, 30, or 75c

10d; 75e

Liberacki et al. (1994), Charles et al. (1996a)

2,4-D butoxyethyl ester

gavage

GD 7–19

0, 10, 30, or 75c

10d; 75e

Liberacki et al. (1994), Charles et al. (1996a)

2,4-D acid

gavage

GD 6–18

0, 10, 30, or 90

30d; 90e

Hoberman (1990), Charles et al. (1996a)

2,4-D dimethylamine salt

gavage

GD 6–18

0, 10, 30, or 90c

30d; 90e

Martin (1991), Charles et al. (1996a)

2,4-D ethylhexyl ester

gavage

GD 6–18

0, 10, 30, or 75c

30d; 75e

Martin (1992a), Charles et al. (1996a)

2,4-D diethanolamine

gavage

GD 6–19

0, 10.2, 20.3, or 40.6c

10.2d; 40.6e

2,4-D isooctyl ester

oral

GD 6–15

0, 12.5, 25, 50, 75, or 87.5c

87.5d; 25e

Schwetz et al. (1971)

2,4-D propylene glycol butyl ether

oral

GD 6–15

0, 12.5, 25, 50, 75, or 87.5c

87.5d; 25e

Schwetz et al. (1971)

2,4-D acid

oral

GD 6–15

0, 12.5, 25, 50, 75, or 87.5

87.5d; 25­

Schwetz et al. (1971)

2,4-D isooctyl ester

oral

GD 5–8

0, or 87.5c

87.5d,e

Schwetz et al. (1971)

2,4-D propylene glycol butyl ether

oral

GD 5–8

0, or 87.5c

87.5d,e

Schwetz et al. (1971)

2,4-D isooctyl ester

oral

GD 8–11

0, 50, or 87.5c

87.5d; 50e

Schwetz et al. (1971)

2,4-D isooctyl ester

oral

GD 12–15

0, 50, or 87.5c

87.5d,e

Schwetz et al. (1971)

2,4-D isooctyl ester

oral

GD 6–15

0, 50, or 150

150d; 50e

Khera and McKinley (1972)

2,4-D butyl ester

oral

GD 6–15

0, 50, or 150

150d; 50e

Khera and McKinley (1972)

2,4-D butoxyethynol

oral

GD 6–15

0, 50, or 150

150d; 50e

Khera and McKinley (1972)

2,4-D dimethylamine salt (49.5%)

oral

GD 6–15

0, 100, or 300

300d; 50e

Khera and McKinley (1972)

2,4-D acid

oral

GD 6–15

0, 50, or 100

100d; 50e

Khera and McKinley (1972)

2,4-D acid

oral

GD 6–15

0, 25, 50, or 100

100d; 50e

Khera and McKinley (1972)

2,4-D acid

oral

GD 6–15

0, 25, 50, 100, or 150

150d; 50e

Khera and McKinley (1972)

Chemical species Developmental: Rabbit

Developmental: Rat

Chapter | 84  Phenoxy Herbicides (2,4-D)

1837

Table 84.3  (Continued) 2,4-D propylene glycol butyl ether

oral

GD 6–15

0, 6.25, 12.5, 25, or 87.5c

87.5d; 25e

Unger et al. (1981)

2,4-D isooctyl ester

oral

GD 6–15

0, 6.25, 12.5, 25, or 87.5c

87.5d; 25e

Unger et al. (1981)

2,4-D acid

gavage

GD 6–15

0, or 115

115d,e

Chernoff et al. (1990)

2,4-D ethylhexyl ester

gavage

GD 6–15

0, 10, 30, or 90c

10d, 30e

Martin (1992b), Charles et al. (1996a)

2,4-D dimethylamine salt

gavage

GD 6–15

0, 12.5, 50, or 100c

12.5d; 50e

Lochry (1990), Charles et al. (1996a)

2,4-D acid

gavage

GD 6–15

0, 8, 25, or 75

75d,e

Nemec et al. (1983), Charles et al. (1996a)

oral

GD 7–15

0, or 0.56 mM/kg bw

0.56d; 0.56e

Developmental: Mouse 2,4-D acid 2,4-D acid

oral

GD 11–14

0, or 0.80 mM/kg bw

0.80

2,4-D acid

oral

GD 12–15

0, or 1 mM/kg bw

1d,e d,e

d,e

subcutaneous

GD 12–15

0, or 1 mM/kg bw

2,4-D isopropyl ester

oral

GD 7–15

0, or 0.56 mM/kg bw

0.56

d,e

2,4-D n-butyl ester

oral

GD 7–15

0, or 0.56 mM/kg bw

2,4-D n-butyl ester

oral

GD 12–15

0, or 1 mM/kg bw

2,4-D isooctyl ester

oral

GD 7–15

0, or 0.56 mM/kg bw

0.56 1

Courtney (1977) Courtney (1977)

2,4-D acid

1

Courtney (1977)

Courtney (1977) d,e

d,e

Courtney (1977) Courtney (1977) Courtney (1977)

0.56

d,e

Courtney (1977)

d,e

Courtney (1977)

2,4-D propylene glycol butyl ether

oral

GD 7–15

0, or 0.56 mM/kg bw

0.56

2,4-D propylene glycol butyl ether

oral

GD 12–15

0, or 1 mM/kg bw

1d; 1e

Courtney (1977)

d,e

Kavlock et al. (1987)

2,4-D acid

oral

GD 8–12

0, or 87.5

87.5

2,4-D propylene glycol butyl ether

oral

GD 8–12

0, or 87.5

87.5d,e

Kavlock et al. (1987)

2,4-D isooctyl ester

oral

GD 8–12

0, or 87.5

87.5d,e

Kavlock et al. (1987)

2,4-D acid

subcutaneous

GD 6–14

0, or 100

100d,e

Bionetics (1968)

2,4-D acid

subcutaneous

GD 6–14

0, or 98

98d,e

Bionetics (1968)

d,e

2,4-D acid

subcutaneous

GD 6–14

0, or 215

215

2,4-D acid

subcutaneous

GD 6–14

0, or 50

50d,e

2,4-D acid

Bionetics (1968) Bionetics (1968)

d,e

oral

GD 6–14

0, or 100

100

Bionetics (1968)

2,4-D

oral

GD 6–10

0, 20, 40, 60, or 100

100e

Collins and Williams (1971)

2,4-D

oral

GD 6–10

0, 40, 60, or 100

100e

Collins and Williams (1971)

2,4-D

oral

GD 6–10

0, 40, 60, or 100

40

Collins and Williams (1971)

diet

2-generation

0, 5, 20, or 80

20d; 5e

Rodwell (1984)

Developmental: Hamster

Reproductive Toxicity: Rat 2,4-D acid a

NOAEL  no-observed-adverse-effect level. b GD  gestational days. c 2,4-D acid equivalents. d Maternal. e Fetal.

1838

The potential testicular and ovarian toxicity of 2,4-D has been extensively evaluated in a series of subchronic and chronic studies in rats. In rats fed 0, 1, 15, 100, or 300 mg/kg body weight/day of either 2,4-D acid, 2,4-D dimethylamine salt, or 2,4-D 2-ethylhexyl ester for 90 days, only minimal effects were noted in testes at the top dose of 300 mg/kg body weight/day (Charles et al., 1996b). These effects, consisting of decreased testes/body weight ratios accompanied by slight histological evidence of atrophy, occurred only at a dose which exceeded the MTD. The NOAEL for testicular effects was 100 mg/kg body weight/day, while the overall NOAEL for the subchronic studies was 15 mg/kg body weight/day based primarily on minor effects in the kidney. No 2,4-D-induced toxicity was reported in the ovaries at any dose. In a subsequent chronic toxicity/oncogenicity study conducted in rats with 2,4-D acid at doses of 0, 5, 75, or 150 mg/kg body weight/day, no treatment-related effects were reported in testes or ovaries at any dose level (Charles et al., 1996a). The findings from these studies were consistent with observations from a series of earlier 90-day (Gorzinski et al., 1987; Serota, 1983a, b; Serrone et al., 1991; Szabo and Rachunek, 1991; Yano et al., 1991a, 1991b) and chronic studies (Charles et al., 1996a; Serota, 1986) conducted with 2,4-D acid and a variety of salt and ester derivatives. The testicular and ovarian toxicity of 2,4-D acid and its dimethylamine salt and 2-ethylhexyl ester also have been examined in a series of subchronic and chronic studies in beagle dogs. Dogs administered either 0, 1, 3.75, or 7.5 mg/kg body weight/day of 2,4-D acid, 2,4-D dimethylamine salt, or 2,4-D 2-ethylhexyl ester for 13 weeks exhibited decreased testes weights at the two highest dose levels (Charles et al., 1996c). The toxicological significance of these findings is uncertain since the organ weight changes were not accompanied by any corroborative histological changes. In addition, both of the two high-dose group animals exhibited body weight gain depressions of approximately 30 to 85%. No 2,4-D-induced effects were seen in the ovaries. A NOAEL of 1.0 mg/kg body weight/ day was established from these studies based on effects in the kidneys. In a follow-up 1-year chronic study conducted at dietary doses of 0, 1, 5, or 7.5 mg/kg body weight/day of 2,4-D acid, no testes or ovary alterations were reported (Charles et al., 1996c). The findings from these dog studies were consistent with earlier 13-week (ITF, 1990) and 2-year dog studies (Hansen et al., 1971). The general lack of 2,4-D-associated testicular toxicity is entirely consistent with the failure of 2,4-D to induce changes in reproductive performance.

84.6.6.4  Immunotoxicity Several subchronic and chronic toxicity studies have provided no evidence from hematological, clinical chemistry, or histopathologic evaluations that 2,4-D is likely to

Hayes’ Handbook of Pesticide Toxicology

induce immune system dysfunction (Charles et al., 1996a, 1996b, 1996c; Szabo and Rachunek, 1991; Yano et al., 1991a, 1991b). Studies that were conducted specifically to examine the possible impact of 2,4-D on various immune system functional parameters have not provided definitive results (Blakley, 1986; Blakley and Blakley, 1986; Blakley and Schiefer, 1986; Zhamsaranova et al., 1987). These studies are difficult to interpret in that the results (1) were inconsistent when evaluated by different routes of exposure, or by comparison of findings from acute and subchronic test regimes; (2) often not reproducible; and (3) not accompanied by adequate descriptions of the normal range of immune parameter values in the test animal populations (Munro et al., 1992). Dermal exposure to 2,4-D acid, salts, or esters also has not been associated with delayed contact hypersensitivity in guinea pigs (Carreon et al., 1983; Carreon and Rao, 1985; Gargus, 1986; Jeffrey, 1986; Jeffrey and Rao, 1986; Schultz et al., 1990).

84.6.6.5  Neurotoxicity Overall, it may be concluded that 2,4-D has little, if any, potential to induce adverse effects in the nervous system at doses that do not cause overt systemic toxicity or that do not saturate processes involved with tissue clearance and renal excretion. No lesions or overt clinical signs of central nervous system toxicity were observed in any of the subchronic toxicity studies in rats (Charles et al., 1996b; Szabo and Rachunek, 1991; Yano et al., 1991a, 1991b) or mice (Schulze, 1991), at doses up to 300 to 560 mg/kg body weight/day. In a chronic rat study designed specifically to investigate the impact of 2,4-D on the nervous system, several neurological parameters were assessed, of which only forelimb grip strength was altered, to a minimal degree, at the highest dose tested, 150 mg/kg body weight/day (Jeffries et al., 1994). Other animal studies have yielded electromyogram results considered indicative of skeletal muscle myotonia following administration of high doses of 2,4-D (50 to 100 mg/kg body weight/day) (Arnold et al., 1991; Beasley et al., 1991; Elo and MacDonald, 1989; Kwiecinski, 1981; Steiss et al., 1987; Toyoshima et al., 1985). In a subchronic toxicity study on 2,4-D 2-ethylhexyl ester, some of the highdose animals were reported to show clinical signs that could possibly be related to myotonia (e.g., hunched posture, languid behavior, ataxia) (Charles et al., 1996b). Myotonia induced by high levels of exposure to 2,4-D does not appear to be the result of toxicological action upon the central nervous system (Buslovich and Pichugin, 1983), but appears to be due to effects mediated at the junction of skeletal muscle nerves and muscle tissue. The biochemical mechanism involved in the induction of myotonia in experimental animals is not well understood; however, according to Rudel and Senges (1972), alteration of chloride ion conductance in muscle fibers appears to be

Chapter | 84  Phenoxy Herbicides (2,4-D)

involved. Because the development of myotonia in animals exposed to high doses of 2,4-D was not accompanied by any pathological effects, and because the reporting of myotonia is restricted to dose levels greater than the threshold for saturation of renal tubular secretion, the effects reported in animal studies are not considered to be indicative of a potential of 2,4-D to induce peripheral polyneuropathy in humans. In an independent review of the literature, it was concluded that exposure to 2,4-D does not produce polyneuropathy in humans nor does polyneuropathy occur in several animal species exposed to high levels of 2,4-D (Mattsson and Eisenbrandt, 1990). Using tests of neurobehavioral parameters (such as the Functional Observational Battery), decreased activity levels, behavioral changes, and motor skill abnormalities have been reported in rats at doses greater than 60 mg/kg body weight/day and in rabbits at doses of approximately 30 mg/kg body weight/day (Breslin et al., 1991; de Duffard et al., 1990b; Duffard et al., 1995; Hoberman, 1990; Jeffries et al., 1994; Liberacki et al., 1991; Martin, 1991; Mattsson et al., 1994, 1997; Oliveira and Palermo-Neto, 1993; Rodwell, 1991; Schulze and Dougherty, 1988; Zablotny et al., 1991). In acute studies conducted using beagle dogs, clinical signs of central nervous system depression and/or abnormalities in electroencephalograms were only reported at doses of 175 mg/kg or greater (Arnold et al., 1991). Rats exposed to high doses of 2,4-D n-butyl ester were reported to display alterations in neurotransmitter concentrations in the brain (de Duffard et al., 1990a; Elo and MacDonald, 1989; Oliveira and Palermo-Neto, 1993). These neurochemical alterations have been hypothesized to result from compromise of the blood-brain barrier by high doses of 2,4-D (Elo et al., 1988; Tyynela et al., 1986). These authors reported that doses of 2,4-D greater than 150 mg/kg body weight resulted in extravasation of albumin in various areas of the brain. Several investigators have reported accumulation of 2,4-D in the brain or cerebrospinal fluid, following administration of high doses (40 to 300 mg/kg body weight) of 2,4-D (Elo and Ylitalo, 1977, 1979; Kim et al., 1988; Oliveira and Palermo-Neto, 1993; Tyynela et al., 1990). Kim et al. (1988) suggested that the increased accumulation of 2,4-D in the brain at high doses was likely not the result of increased permeability of the blood-brain barrier since the entry of the organic solute, 2-deoxyglucose, into rabbit brain was unaffected by 2,4-D pretreatment. Instead, it has been hypothesized that reduced elimination of 2,4-D from the brain via the choroid plexus through competitive inhibition of the organic acid transport pathway was likely responsible for the increased accumulation of 2,4-D (Kim et al., 1988; Ylitalo et al., 1990). The organic acid transport pathway normally actively eliminates acidic metabolites from the brain through the blood-brain barrier. At doses below the capacity of normal renal clearance, there is no evidence in experimental animals to indicate

1839

that 2,4-D can have an impact on the nervous system. In fact, no clinically observable adverse effects on the nervous system have been observed in animals at doses below 10 to 30 mg/kg body weight, even in long-term studies.

84.6.6.6  Chronic Toxicity and Carcinogenicity Several long-term bioassays have been conducted in rats, mice, and dogs (Arkhipov and Kozlova, 1974; Charles et al., 1996a, 1996c; Innes et al., 1969; Hansen et al., 1971; Serota et al., 1986, 1987). There has been no evidence to suggest that 2,4-D acts as a carcinogen in any of these species. Rats In one older 2-year rat feeding study (Serota et al., 1986), an increase in the incidence of brain astrocytomas was reported in male rats only at the highest dose tested of 45 mg/kg body weight/day; however, the biological characteristics of the tumors were not consistent with chemical carcinogenesis. Moreover, based on the lack of decreased latency, the lack of increased multiplicity, the lack of increased severity, the lack of preneoplastic or target organ effects, the restriction of tumor development to one species and sex, the intergroup variability exhibited among historical controls, the lack of a plausible mechanism of tumorigenesis, the low exposure of the brain to 2,4-D compared to other tissues, and the fact that these tumors have not been reproduced in subsequent studies, it is unlikely that the increased incidence of brain astrocytomas reported by Serota et al. (1986) was related to 2,4-D treatment. In another older study (Hansen et al., 1971) in which rats were fed up to 62.5 mg 2,4-D/kg body weight/day for 2 years, an overall increase in the number of randomly distributed tumors was reported to be statistically significant for male rats. As discussed by Munro et al. (1992), this study was not considered to provide any evidence that 2,4-D is carcinogenic in the rat since it did not meet the requirements of Good Laboratory Practice (GLP) standards, the dose groups were fairly small, the maximum tolerated dose (MTD) was not achieved, and the microscopic examination was not comprehensive. In a third feeding study (Arkhipov and Kozlova, 1974), rats were fed 10% of the reported LD50 (details of dosing not reported) with no significant increase in tumor incidence. More recently, a 2-year GLP-compliant study in which rats were fed 5 to 150 mg 2,4-D/kg body weight/day was completed without any evidence of carcinogenicity (Charles et al., 1996a). In particular, there was no increased incidence of brain astrocytomas even at the MTD. Noncancer endpoints reported in the animals were very similar to those reported in the subchronic studies (Charles et al., 1996b), and a NOAEL of 5 mg/kg body weight/day was established based on increased thyroid weight. Mice No evidence of carcinogenicity has been reported in three long-term mouse studies (Charles et al., 1996a; Innes et al., 1969; Serota et al., 1987). In the first study

1840

(Innes et al., 1969), mice were orally administered one of three esters of 2,4-D (i.e., isopropyl, butyl, or isooctyl ester) at a dose of 46.4 mg/kg body weight/day for 18 months. No increase in tumor incidence was reported. In the second study (Serota et al., 1987), mice were fed 1 to 45 mg 2,4-D/kg body weight/day for 106 weeks with no evidence of carcinogenicity or other treatment-related effects. In male mice administered the highest two doses (15 and 45 mg/kg body weight/day), an increase in cytoplasmic homogeneity in the renal tubular epithelium was reported. In the third and most recent GLP-compliant study (Charles et al., 1996a), female and male mice were fed 5 to 300 and 5 to 125 mg 2,4-D/kg body weight/day, respectively, for 2 years without any evidence of tumorigenesis. Noncancer effects were limited to slight depression of red blood cell parameters, minor organ weight changes, and histopathological renal effects at the top two doses in both sexes. Dogs Similar to the results from the rodent studies, there has been no evidence to suggest that 2,4-D has carcinogenic potential in dogs (Charles et al., 1996c; Hansen et al., 1971). The results of the long-term studies in dogs support the results reported in subchronic studies. In the older study by Hansen et al. (1971), small groups of beagle dogs were fed 2,4-D in the diet at concentrations reaching 500 ppm over a 2-year period. Following gross and microscopic examinations of several tissues and organs, no lesions related to 2,4-D treatment were reported. The more recent study by Charles et al. (1996c) examined the effects of feeding 0, 1, 5, or 7.5 mg 2,4-D/kg body weight/day to beagle dogs for a period of 52 weeks. The reported effects included body weight gain reduction in females, notably at the highest dose, some serum chemistry alterations (i.e., increased urea nitrogen, creatinine, cholesterol, and alanine aminotransferase activity) in the two highest dose groups, and some histopathological alterations (i.e., perivascular chronic active inflammation of the liver and an increase of pigment in tubular epithelium in both sexes in the two highest dose groups, and pigment in the sinusoidal lining cells in the females of the two highest dose groups). Overall, 2,4-D administration was well tolerated and produced no effects on clinical signs, hematology, urinalysis, or gross necropsy. A NOAEL of 1 mg/kg body weight/day was suggested by the authors.

84.6.7  Genotoxicity Numerous in vitro and in vivo genotoxicity studies have been conducted with 2,4-D. Overall, the results indicate that 2,4-D has very little genotoxic potential. This conclusion has been reached in previous reviews of 2,4-D (CCT, 1987; EPA, 1997; Munro et al., 1992) and is consistent with metabolism studies which have indicated that 2,4-D does not metabolize to reactive intermediates.

Hayes’ Handbook of Pesticide Toxicology

With very few exceptions, bacterial mutagenicity tests using Salmonella typhimurium and Escherichia coli have produced negative results with 2,4-D (Anderson and Styles, 1978; Charles et al., 1996a; Ercegovich and Rashid, 1977; Kappas, 1988; Kappas and Markaki, 1988; Kappas et al., 1984; Mersch-Sundermann et al., 1989; Rashid, 1979; Rashid and Mumma, 1986; Rashid et al., 1984; Simmon et al., 1977; Soler-Niedziela et al., 1988; Styles, 1973; Waters et al., 1980). In yeast cells, mitotic gene conversion and recombination has been reported, but was highly dependent on pH and occurred only at pH 4.3 (Simmon et al., 1977; Waters et al., 1980; Zetterberg, 1978; Zetterberg et al., 1977). Negative or weakly positive results were reported in unscheduled DNA repair and sister chromatid exchange (SCE) assays with mammalian cell systems (Charles et al., 1996a; Clausen et al., 1990; Galloway et al., 1987; Jacobi and Witte, 1991; Styles, 1977; Waters et al., 1980). For the most part, the weakly positive results occurred only in conjunction with cytotoxicity (Clausen et al., 1990; Korte and Jalal, 1982). Similar to the in vitro studies, the majority of in vivo studies with animals, using the most accepted and validated procedures, have produced negative results (Munro et al., 1992). Some studies with occupationally exposed individuals provided marginally positive results in lymphocytes but could not be directly correlated with 2,4-D exposure due to various confounding factors (e.g., age, sex, race, lifestyle habits, etc.) (Crossen et al., 1978; Kaye et al., 1985; Yoder et al., 1973). Several other studies have shown that 2,4-D exposure has no effect on chromosomal aberration or SCE frequency (Charles et al., 1996a, b; Hogstedt and Westerlund, 1980; Linnainmaa, 1983a, 1983b, 1984; Mulcahy, 1980; Mustonen et al., 1986, 1989).

84.7  Studies in humans There has been some concern over a possible association between exposure to 2,4-D and the development of cancer, specifically non-Hodgkin’s lymphoma, Hodgkin’s disease, and soft tissue sarcoma. Comprehensive critical reviews of the epidemiology literature however, have concluded that no causal association between 2,4-D and human cancer has been convincingly documented (Munro et al., 1992; Garabrant and Philbert, 2002). In overview, the majority of the studies were conducted with farmers, forestry workers, and other similar groups of potential users of herbicides. In most of the studies, there were methodological shortcomings in conducting exposure assessments specifically related to 2,4-D. Moreover, the majority of the studies involved occupational exposures to a wide variety of chemical, physical, and biological agents including phenoxy herbicides, and it was difficult to discern specific exposure to 2,4-D. Without specific information regarding exposure to 2,4-D and with the contribution

Chapter | 84  Phenoxy Herbicides (2,4-D)

of other confounding factors, the establishment of a doseresponse relationship is difficult to ascertain. In cohort studies, exposure to 2,4-D could be reasonably assumed; however, no conclusive evidence was reported to show an association between 2,4-D and cancer. The only positive correlations were reported in three large cohort studies (Saracci et al., 1991; Wigle et al., 1990; Wiklund and Holm, 1986; Wiklund et al., 1987), in which exposures were primarily to 2,4,5-T or were mixed with other herbicides, and none of the reported effects were consistent among the studies. Although there has been a persistent hypothesis that exposure to 2,4-D may be associated with an increased incidence of non-Hodgkin’s lymphoma (Hoar et al., 1986; Zahm et al., 1990), the analysis by Munro et al. (1992) concluded that the results of these case-control studies did not strongly support the hypothesis based on weaknesses in the methodology employed and lack of control for other possible risk factors for non-Hodgkin’s lymphoma (e.g., viruses and immune system modulation). Other reviews have been conducted since the work by Munro et al. (1992). A SAB/SAP Special Joint Committee from the U.S. Environmental Protection Agency (EPA, 1994) reviewed the available data on 2,4-D and concluded that “… the data are not sufficient to conclude that there is a cause and effect relationship between the exposure to 2,4-D and non-Hodgkin’s lymphoma” and 2,4-D still remains classified as a Group D (not classifiable as to human carcinogenicity) (EPA, 1997). Similarly, the Joint Meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues reviewed the data on 2,4-D and stated that the results of the available epidemiology studies are inconsistent and that any reported associations are weak (Rowland, 1997). The National Cancer Institute of Canada also convened an Ad Hoc Panel on Pesticides and Cancer which concluded that “it was not aware of any definitive evidence to suggest that synthetic pesticides contribute significantly to overall cancer mortality” (Ritter, 1997). A few additional studies have been published since the above reviews (Becher et al., 1996; Burns et al., 2001; Fleming et al., 1997; Zahm, 1997). Three of these are mortality studies in factory workers (Becher et al., 1996; Burns et al., 2001) and lawn care workers (Zahm, 1997), and one is a retrospective cohort study in pesticide applicators (Fleming et al., 1997). As with previous epidemiology studies, the findings were inconsistent and did not provide any conclusive evidence of increased cancer risk associated with exposure to 2,4-D. In fact, Fleming et al. (1997) reported that in a cohort of 33, 669 pesticide applicators, there were no confirmed cases of soft tissue sarcoma or non-Hodgkins lymphoma and Burns et al. (2001) concluded there was “no evidence of causal association between exposure to 2,4-D and mortality due to all causes and malignant neoplasm” and “no significant risk due to NHL was found.” In addition, Acquavella et al. (1998)

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conducted a meta-analysis of 37 studies in farmers and concluded that farmers did not have elevated rates of several cancers, with the exception of lip cancer. In a preliminary study with a small group of farmers, Faustini et al. (1996) reported that 2,4-D exposure affected some immunological variables; however, the data were highly variable (i.e., large standard deviations) and the group tested was very small (n  10). There has been some discussion in the literature linking immunosuppressive agents with an increased incidence of non-Hodgkin’s lymphoma (Hardell et al., 1998; Hardell and Axelson, 1998), but there has been no clear or consistent evidence in humans indicating that 2,4-D affects the immune system. This is well supported by animal studies.

84.8  Summary 2,4-D is the most common of the phenoxy herbicides and is one of the best-studied agricultural chemicals. It is primarily used as a herbicide in agriculture, forestry, and lawn care practices, and is effective against a wide variety of broadleaf plants. Occupational exposure to 2,4-D is mainly through dermal contact but can also occur, to a lesser extent, via ingestion and inhalation. Studies in humans have shown exposures to be extremely low even in all occupational groups (i.e., 40 g/kg body weight/day). The extensive database of metabolic, toxicological, and epidemiological studies on 2,4-D has provided no evidence that 2,4-D poses any health risk to humans when used according to label directions.

References Acquavella, J., Olsen, G., Cole, P., Ireland, B., Kaneene, J., Schuman, S., and Holden, L. (1998). Cancer among farmers: A meta-analysis. Ann. Epidemiol. 8(1), 64–74. Agriculture Canada (1983). “Re: 2,4-D Products Registered Under the Authority of the Pest Control Products Act,” (Memorandum to Registrants) No. R-1-216. Agriculture Canada, Food Production and Inspection Branch, Ottawa, Ontario. Alexander, B. H., Marndel, J. S., Baker, B. A., Burns, C. J., Bartels, M. J., Acquavella, J. F., and Gustin, C. (2007). Biomonitoring of 2,4-dichlorophenoxyacetic acid exposure and dose in Farm Families. Env. Hlth. Perspect 115, 370–376. Anderson, D., and Styles, J. A. (1978). The bacterial mutation test. Br. J. Cancer 37, 924–930. Arkhipov, G. N., and Kozlova, I. N. (1974). A study of the carcinogenic potential of a herbicide: 2,4-D amine salt. Voprosy Pitaniia 5, 83–84. Arnold, E. K., Beasley, V. R., Parker, A. J., and Stedelin, J. R. (1991). 2,4-D toxicosis. II. A pilot study of clinical pathologic and electroencephalographic effects and residues of 2,4-D in orally dosed dogs. Vet. Hum. Toxicol. 33(5), 446–449. Aylward, L. L., Morgan, M. K., Arbuckle, T. E., Barr, D. B., Burns, C. J., Alexander, B. H., and Hays, S. M. (2009). Biomonitoring data for 2,4-dichlorophenoxyacetic acid in the US and Canada: Interpretation

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in a public health context using Biomonitoring Equivalents. Env. Hlth. Perspect. Online 12 Aug 2009, doi: 10.1289/ehp.0900970. Beasley, V. R., Arnold, E. K., Lovell, R. A., and Parker, A. J. (1991). 2,4-D toxicosis. I. A pilot study of 2,4-dichlorophenoxyacetic acidand dicambainduced myotonia in experimental dogs. Vet. Hum. Toxicol. 33(5), 435–440. Becher, H., Flesch-Janys, D., Kauppinen, T., Kogevinas, M., Steindorf, K., Manz, A., and Wahrendorf, J. (1996). Cancer mortality in German male workers exposed to phenoxy herbicides and dioxins. Cancer Causes Control 7, 312–321. Bernard, P. A., Toyoshima, E., Eccles, C. U., Mayer, R. F., Johnson, K. P., and Max, S. R. (1985). 2,4-Dichlorophenoxyacetic acid (2,4-D) reduces acetyl-cholinesterase activity in rat muscle. Exper. Neurol. 87, 544–556. Berry, D. L. (1989). “Final Report of the Determination of Halogenated Dibenzo-p-dioxins and Dibenzofurans in 2,4-Dichlorophenoxyacetic Acid,” No. AL 89-030290. Analytical Sciences Laboratories, The Dow Chemical Company, Midland, MI. Bionetics Research Laboratory (1968). Evaluation of Carcinogenic, Teratogenic, and Mutagenic Activities of Selected Pesticides and Industrial Chemicals. Carcinogenic Study; Volume II. Terato­genic Study in Mice and Rats. National Cancer Institute (NCI), Bethesda, MD. Blakley, B. R. (1986). The effect of oral exposure to the N-butylester of 2,4-dichlorophenoxyacetic acid on the immune response in mice. Int. J. Immunopharmacol. 8(1), 93–99. Blakley, B. R., and Blakley, P. M. (1986). The effect of prenatal exposure to the n-butylester of 2,4-dichlorophenoxyacetic acid (2,4-D) on the immune response in mice. Teratology 33, 15–20. Blakley, B. R., and Schiefer, B. H. (1986). The effect of topically applied n-butylester of 2,4-dichlorophenoxyacetic acid on the immune response in mice. J. Appl. Toxicol. 6(4), 291–295. Breslin, W. J., Liberacki, A. B., and Yano, B. L.(1991). “Isopropylamine Salt of 2,4-D: Oral Gavage Teratology Study in New Zealand White Rabbits,” Unpublished Report No. M-004725-013. Dow Chemical Company, Midland, MI. Burns, C. J., Beard, K. K., and Cartmill, J. B. (2001). Mortality in chemical workers potentially exposed to 2,4-dichlorophenoxyacetic acid (2, 4-D) 1945-94: an update. Occup. Environ. Med. 58(1), 24–30. Buslovich, S. Y. and Pichugin, Y. I. (1983). Electromyographic characteristics of acute poisonings with chlorine derivatives of phenoxy acids. Farmakologiia i Tosikologiia. 46(3), 99–101. Canadian Centre for Toxicology (CCT)(1987). “Panel Report on Carcinoge­ nicity of 2,4-D,” Canadian Centre for Toxicology (CCT), Guelph, ON. Carreon, R. et al., (1983). “2,4-Dichlorophenoxyacetic Acid Isopropyl­ amine Salt: Acute Toxicological Properties. Industry Task Force II on 2,4-D Research Data,” Unpublished Report. Dow Chemical Company, Midland, MI. Carreon, R., and Rao, K. S. (1985). “DMA-6 Weed Killer: Dermal Sensitization Potential in the Guinea Pig. Industry Task Force II on 2,4-D Research Data,” Unpublished Report. Dow Chemical Company, Midland, MI. Charles, J. M., Bond, D. M., Jeffries, T. K., Yano, B. L., Stott, W. T., Johnson, K. A., Cunny, H. C., Wilson, R. D., and Bus, J. S. (1996a). Chronic dietary toxicity/oncogenicity studies on 2,4-dichlorophenoxyacetic acid in rodents. Fund. Appl. Toxicol. 33, 166–172. Charles, J. M., Cunny, H. C., Wilson, R. D., and Bus, J. S. (1996b). Comparative subchronic studies on 2,4-dichlorophenoxyacetic acid, amine and ester in rats. Fund. Appl. Toxicol. 33, 161–165. Charles, J. M., Dalgard, D. M., Cunny, H. C., Wilson, R. D., and Bus, J. S. (1996c). Comparative subchronic and chronic dietary toxicity

Hayes’ Handbook of Pesticide Toxicology

studies on 2,4-dichlorophenoxyacetic acid, amine and ester in the dog. Fund. Appl. Toxicol. 29, 78–85. Chernoff, N., Woodrow Setzer, R., Miller, D. B., Rosen, M. B., and Rogers, J. M. (1990). Effects of chemically induced maternal toxicity on prenatal development in the rat. Teratology 42, 651–658. Clark, D. E., Palmer, J. S., Radeleff, R. D., Crookshank, H. R., and Farr, F. M. (1975). Residues of chlorophenoxy acid herbicides and their phenolic metabolites in tissues of sheep and cattle. J. Agric. Food Chem. 23(3), 573–578. Clausen, M., Leier, G., and Witte, I. (1990). Comparison of the cytotoxicity and DNA-damaging properties of 2,4-D and U 46 D fluid (dimethylammonium salt of 2,4-D). Arch. Toxicol. 64, 497–501. Cochrane, W. P., Singh, J., Miles, W., and Wakeford, B. (1981). Determination of chlorinated dibenzo-p-dioxin contaminants in 2,4-D products by gas chromatography-mass spectrometric techniques. J. Chromatogr. 217, 289–299. Cochrane, W. P., Singh, J., Miles, W., and Wakeford, B. (1982a). “Levels of Polychlorinated Dibenzo-p-Dioxins in 2,4-D Technical Products,” Agriculture Canada, Food Production and Inspection Branch, Laboratory Services Division, Ottawa (ON). Cochrane, W. P., Singh, J., Miles, W., Wakeford, B., and Scott. (1982b). Analysis of technical and formulated products of 2,4-dichlorophenoxyacetic acid for the presence of chlorinated dibenzo- p-dioxins. In: Impact of Chlorinated Dioxins and Related Compounds on the Environment. Oct. 22–24, 1980, Rome. pp. 1–5. Collins, T. F. X., and Williams, C. H. (1971). Teratogenic studies with 2,4,5-T and 2,4-D in the hamster. Bulletin Environ. Contamin. Toxicol. 6(6), 559–567. Courtney, K. D. (1977). Prenatal effects of herbicides: Evaluation by the prenatal development index. Arch. Environ. Contam. Toxicol. 6, 33–46. Cramer, P. H. (1996). “2,4-Dichlorophenoxyacetic Acid: Analysis for Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Acid, Salt, and/or Ester Technical Material,” Lab Project ID MRI No. 4199. Midwest Research Institute, Kansas City, MO, for DowElanco, Indianapolis, IN. Crossen, P. E., Morgan, W. F., Horan, J. J., and Stewart, J. (1978). Cytogenetic studies of pesticide and herbicide sprayers. N. Zeal. Med. J. 88(619), 192–195. de Duffard, A. M. E., de Alderete, M. N., and Duffard, R. (1990a). Changes in brain serotonin and 5-hydroxyindolacetic acid levels induced by 2,4-dichlorophenoxyacetic butyl ester. Toxicology 64, 265–270. de Duffard, A. M. E., Orta, C., and Duffard, R. (1990b). Behavioral changes in rats fed a diet containing 2,4-dichlorophenoxyacetic butyl ester. Neurotoxicology 11(4), 563–572. Duffard, R., Bortolozzi, A., Ferri, A., Garcia, G., and Evangelista de Duffard, A. M. (1995). Developmental neurotoxicity of the herbicide 2,4-dichlorophenoxyacetic acid. Neurotoxicology 16(4), 764. Duggan, R. E., and Corneliussen, P. E. (1972). Dietary intake of pesticide chemicals in the United States (III), June 1968–April 1970. Pestic, monit. J., 5(4) 331–341. (Cited in WHO, 1984). Duggan, R. E., and Lipscomb, G. Q. (1969). Dietary intake of pesticide chemicals in the United States (II), June 1966-April 1968. Pestic. Monit. J. 2(4), 153–162. Elo, H., Hervonen, H., and Ylitalo, P. (1988). Comparative study on cerebrovascular injuries by three chlorophenoxyacetic acids (2,4-D, 2,4,5T and MCPA). Comp. Biochem. Physiol. 90C(1), 65–68. Elo, H. A., and Macdonald, E. (1989). Effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on biogenic amines and their acidic metabolites in brain and cerebrospinal fluid of rats. Arch. Toxicol. 63, 127–130.

Chapter | 84

Phenoxy Herbicides (2,4-D)

Elo, H. A., and Ylitalo, P. (1977). Substantial increase in the levels of chlorophenoxyacetic acids in the CNS of rats as a result of severe intoxication. Acta. Pharmacol. Toxicol. 41, 280–284. Elo, H. A., and Ylitalo, P. (1979). Distribution of 2-methyl-4-chlorophenoxyacetic and 2,4-dichlorophenoxyacetic acid in male rats: Evidence for the involvement of the central nervous system in their toxicity. Toxicol. Appl. Pharmacol. 51, 439–446. Environmental Protection Agency (EPA) (1994). “An SAB Report: Assessment of Potential 2,4-D Carcinogenicity. Review of the Epidemiological and Other Data on Potential Carcinogenicity of 2,4-D,” U.S. Environmental Protection Agency, Science Advisory Board (SAB), Washington, DC. Environmental Protection Agency (EPA) (1996). “Toxicology Endpoint Selection Document: 2,4-Dichlorophenoxyacetic Acid,” U.S. Environmental Protection Agency, Washington, DC. Environmental Protection Agency (EPA) (1997). “Pesticides Industry Sales and Usage. 1994 and 1995 Market Estimates,” Office of Prevention, Pesticides and Toxic Substances (733-R-97-002). U.S. Environmental Protection Agency, Washington, DC. Environmental Protection Agency (EPA) (2005). “Reregistration Eligibility Decision for 2,4-D. (EPA 738-R-05-002),” Available at: http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf. U.S. Environmental Protection Agency (U.S. EPA), Prevention, Pesticides and Toxic Substances (7508C), Washington, DC. Ercegovich, C. D., and Rashid, K. A. (1977). Mutagenesis induced in mutant strains of Salmonella typhimurium by pesticides. Am. Chem. Soc. Abstr. Pap. 174:PEST (Abstr. No. 43). Erne, K. (1966a). Distribution and elimination of chlorinated phenoxyacetic acids in animals. Acta Veterinaria Scandinavica. 7, 240–256. Erne, K. (1966b). Studies on the animal metabolism of phenoxyacetic herbicides. Acta Veterinaria Scandinavica 7, 264–271. Fang, S. C., and Lindstrom, F. T. (1980). In vitro binding of (14)C-labeled acidic compounds to serum albumin and their tissue distribution in the rat. J. Pharmacokinet. Biopharmaceut. 8(6), 583–597. Faustini, A., Settimi, L., Pacifici, R., Fano, V., Zuccaro, P., and Forastiere, F. (1996). Immunological changes among farmers exposed to phenoxy herbicides: Preliminary observations. Occup. Environ. Med. 53, 583–585. Fedorova L. M., and Belova, R. S. (1974). Inclusion of 2,4-dichlorophenoxyacetic acid in organs of animals: Paths and dynamics of its excretion. Gig. i Sanit., 39(2) 105–107 (in Russian, US NTC Translation No. 76-10918-05J). (Citied in WHO, 1984). Feldman, R. J., and Maibach, H. I. (1974). Percutaneous penetration of some pesticides and herbicides in man. Toxicol. Appl. Pharmacol. 28, 126–132. Fleming, L. E., Bean, J. A., Rudolph, M., Hamilton, K., Kasl, S., and Stolwijk, J. (1997). Retrospective cohort study of cancer incidence in Florida pesticide applicators. Amer. J. Epidemiol. 10, 249. Frank, R., Campbell, R. A., and Sirons, G. J. (1985). Forestry workers involved in aerial application of 2,4-dichlorophenoxyacetic acid (2,4-D): Exposure and urinary excretion. Arch. Environ. Contam. Toxicol. 14, 427–435. Galloway, S. M., Armstrong, M. J., Reuben, C., Colman, S., Brown, B., Cannon, C., Bloom, A. D., Nakamura, F., Ahmed, M., Duk, S., Rimpo, J., Margolin, B. H., Resnick, M. A., Anderson, B., and Zeiger, E. (1987). Chromosome aberrations and sister chromatid exchanges in Chinese hamster ovary cells: Evaluations of 108 chemicals. Environ. Mol. Mutagen. 10(Suppl. 10), 1–175. Garabrant, D. H., and Philbert, M. A. (2002). Review of 2,4-dichlorophenoxyacetic acid (2,4-D) epidemiology and toxicology. Crit. Rev. Toxicol. 32, 233–257.

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Gargus, J. L. (1986). “Dermal Sensitization Study in Guinea Pigs; 2,4-D Acid,” Unpublished Report No. 2184-105. Industry Task Force II on 2,4-D Research Data, Hazleton Laboratories America, Inc. Gartrell, M. J., Craun, J. C., Podrebarac, D. S., and Gunderson, E. L. (1985). Pesticides, selected elements, and other chemicals in infant and toddler total diet samples, October 1978-September 1979. J. Assoc. Off. Anal. Chem. 68(5), 842. Gorzinski, S. J., Kociba, R. J., Campbell, R. A., Smith, F. A., Nolan, R. J., and Eisenbrandt, D. L. (1987). Acute, pharmacokinetic, and subchronic toxicological studies of 2,4-dichlorophenoxyacetic acid. Fund. Appl. Toxicol. 9, 423–435. Gorzinski, S. J., Wade, C. E., Morden, D. C., Keyes, D. G., Dittenber, D. A., Kalnins, R. V., Schuetz, D. J., and Kociba, R. J.(1981a). “Purified 2,4-Dichlorophenoxyacetic Acid (2,4-D): Results of a 13-Week Subchronic Dietary Toxicity Study in the CDF Fischer 344 Rat,” Toxicology Research Laboratory, Midland, MI. Gorzinski, S. J., Wade, C. E., Morden, D. C., Keyes, D. G., Wolfe, E. L., Dittenber, D. A., Kalnins, R. V., Schuetz, D. J., and Kociba, R. J. (1981b). “Technical 2,4-Dichlorophenoxyacetic Acid (2,4-D): Results of a 13-Week Subchronic Dietary Toxicity Study in the CDF Fischer 344 Rat,” Toxicology Research Laboratory, Midland, MI. Grisson, R. E., Brownie, C., and Guthrie, F. E. (1987). In vivo and in vitro dermal penetration of lipophilic and hydrophilic pesticides in mice. Bull. Environ. Contam. Toxicol. 38, 917–924. Grover, R., Cessna, A. J., Muir, N. I., Reidel, D., Franklin, C. A., and Yoshida, K. (1986). Factors affecting the exposure of ground-rig applicators to 2,4-D dimethylamine salt. Arch. Environ. Contam. Toxicol. 15, 677–686. Grunow, W., and Bohme, C. H. R. (1974). Uber den stoffwechsel von 2,4,5-T und 2,4-D bei ratten und mausen. Arch. Toxicol. 32, 217–225. Hansen, W. H., Quaife, M. L., Habermann, R. T., and Fitzhugh, O. G. (1971). Chronic toxicity of 2,4-dichlorophenoxyacetic acid in rats and dogs. Toxicol. Appl. Pharm. 20, 122–129. Hardell, L., and Axelson, O. (1998). Environmental and occupational aspects on the etiology of non-Hodgkin’s lymphoma. Oncol. Res. 10(1), 1–5. Hardell, L., Lindstrom, G., Van Bavel, B., Fredrikson, M., and Liljegren, G. (1998). Some aspects of the etiology of non-Hodgkin’s lymphoma. Environ. Health Perspect. Suppl 106(Suppl 2), 679–681. Harris, S. A., and Solomon, K. R. (1992). Percutaneous penetration of 2,4-dichlorophenoxyacetic acid and 2,4-d dimethylamine salt in human volunteers. Fertil. Steril. 36, 233–240. Harris, S. A., Solomon, K. R., and Stephenson, G. R. (1992). Exposure of homeowners and bystanders to 2,4-dichlorophenoxyacetic acid (2,4-D). J. Environ. Sci. Health (Part B—Pestic. Food Contam. Agric. Wastes) B27(1), 23–38. Health Canada (2008). “Re-evaluation Decision (2,4-Dichlorophenoxy)acetic acid [2,4-D],” (RVD2008-11) Available at: http://www.hc-sc.gc.ca/cpsspc/pubs/pest/_decisions/rvd2008-11/index-eng.php. Health Canada, Pest Management Regulatory Agency (PMRA), Ottawa, Ontario. Hervonen, H., Elo, H. A., and Ylitalo, P. (1982). Blood-brain barrier damage by 2-methyl-4-chlorophenoxyacetic acid herbicide in rats. Toxicol. Appl. Pharmacol. 65(1), 23–31. Hoar, S. K., Blair, A., Holmes, F. F., Boysen, C. D., Robel, R. J., Hoover, R., and Fraumers, J. F. (1986). Agricultural herbicide use and risk of lymphoma and soft-tissue sarcoma. J. Am. Med. Assoc. 256(9), 1141–1147. Hoberman, A. M. (1990). “Developmental Toxicity (Embryo-Fetal Toxicity and Teratogenic Potential) Study of 2,4-Dichlorophenoxyacetic Acid

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(2,4-D Acid) Administered Orally Via Stomach Tube to New Zealand White Rabbits,” Protocol Number: 320-003. Performing Research Laboratories, Inc, Horsham, PA. Hogstedt, C., and Westerlund, B. (1980). Kohortstudie av dodsorsaker for skogsarbetare med och utan exposition for fenoxisyrapreparat  Cohort studies of cause of death of forest workers with and without exposure to phenoxy acid preparations. 77(19), 1828–1830. Innes, J. R. M., Ulland, B. M., Valerio, M. G., Petrucelli, L., Fishbein, L., Hart, E. R., Pallotta, A. J., Bates, R. R., Falk, H. L., Klein, M., Gart, J. J., Mitchell, I., and Peters, J. (1969). Bioassay of pesticides and industrial chemicals for tumorigenicity in mice: A preliminary note. J. Nat. Cancer Instit. 42, 1101–1114. ITF (1990). “Final Report: Subchronic Toxicity Study in Dogs with 2,4Dichlorophenoxyacetic Acid. Industry Task Force on 2,4-D Research Data,” Hazleton Laboratories America, Inc, Vienna, VA. Jacobi, H., and Witte, I. (1991). Synergistic effects of U46 D Fluid (dimethylammonium salt of 2,4-D) and CuCl2 on cytotoxicity and DNA repair in human fibroblasts. Toxicol. Letters 58, 159–167. Jeffrey, N. M. (1986). “2,4-D Butoxyethyl Ester, Technical: Dermal Sensitization Potential in the Hartley Albino Guinea Pig,” Unpublished Report No. K-007722-005. Industry Task Force II on 2,4-D Research Data, Dow Chemical Company, Midland, MI. Jeffries, T. K., Yano, B. L., and Orman, J. R. (1994). “2,4-D Chronic Neurotoxicity Study in Fischer 344 Rats,” Unpublished Report No. K-002372-064N. Dow Chemical Company, Midland MI. Kappas, A., Tziolas, V., and Demopoulos, N. (1984). Mutagenicity of herbicides in microbial short-term test systems. Mutat. Res. 130, 244 (Abstr. No. II.3B. 3). Kappas, A. (1988). On the mutagenic and recombinogenic activity of certain herbicides in Salmonella typhimurium and in Aspergillus nidulans. Mutat. Res. 204(4), 615–621. Kappas, A., and Markaki, M. (1988). Genetic activity of herbicides in Salmonella typhimurium and Aspergillus nidulans. Mutat. Res. 203(3), 241 (Abstr. No. 90). Kavlock, R. J., Short, R. D., and Chernoff, N. (1987). Further evaluation of an in vivo teratology screen. Terat. Carcin. Mutagen 7, 7–16. Kaye, C. I., Rao, S., Simpson, S. J., Rosenthal, F. S., and Cohen, M. M. (1985). Evaluation of chromosomal damage in males exposed to Agent Orange and their families. J. Craniofac. Genet. Develop. Biol. Suppl. 1, 259–265. Khanna, S., and Fang, S. C. (1966). Metabolism of C14-labelled 2,4dichlorophenoxyacetic acid in rats. J. Agric. Food Chem. 14(5), 500–503. Khera, K. S., and McKinley, W. P. (1972). Pre- and postnatal studies on 2,4,5-trichlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid and their derivatives in rats. Toxicol. Appl. Pharmacol. 22, 14–28. Kim, C. S., Keizer, R. F., and Pritchard, J. B. (1988). 2,4Dichlorophenoxyacetic acid intoxication increases its accumulation within the brain. Brain Res. 440, 216–226. Kim, C. S., and O’Tuama, L. A. (1981). Choroid plexus transport of 2,4dichlorophenoxyacetic acid: Interaction with the organic acid carrier. Brain Res. 224, 209–212. Kim, C. S., O’Tuama, L. A., Mann, J. D., and Roe, C. R. (1983). Saturable accumulation of the anionic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by rabbit choroid plexus: Early developmental origin and interaction with salicylates. J. Pharmacol. Exper. Therapeut. 225(3), 699–704. Knopp, D., and Schiller, F. (1992). Oral and dermal application of 2,4dichlorophenoxyacetic acid sodium and dimethylamine salts to male rats: Investigations on absorption and excretion as well as

Hayes’ Handbook of Pesticide Toxicology

induction of hepatic mixed-function oxidase activities. Arch. Toxicol. 66, 170–174. Kohli, J. D., Khana, R. N., Gupta, B. N., Dhar, M. M., Tandon, J. S., and Sircar, K. P. (1974). Absorption and excretion of 2,4-dichlorophenoxyacetic acid in man. Xenobiotica. 4(2), 97–100. Kolmodin-Hedman, B., and Erne, K. (1980). Estimation of occupational exposure to phenoxy acids (2,4-D and 2,4,5-T). Arch. Toxicol. Suppl. 4, 318–321. Korte, C., and Jalal, S. M. (1982). 2,4-D induced clastogenicity and elevated rates of sister chromatide exchanges in cultured human lymphocytes. J. Heredity (May/June), 224–226. Kuntz, D. J., Rao, N. G. S., Berg, I. E., Khattree, R., and Chaturvedi, A. K. (1990). Toxicity of mixtures of parathion, toxaphene and/or 2,4-D in mice. J. Appl. Toxicol. 10(4), 257–265. Kwiecinski, H. (1981). Myotonia induced by chemical agents. Crit. Rev. Toxicol. 8(4), 279–310. Lavy, T. L., and Mattice, J. D. (1984). Monitoring human exposure during pesticide application in the forest ACS Symposium Series. In Chemical and Biological Controls in Forestry (W. Y. Garner and J. Harvey Jr., eds.) Vol. 238, pp. 319–330. American Chemical Society, Washington, DC. Lavy, T. L., Norris, L. A., Mattie, J. D., and Marx, D. B. (1987). Exposure of forestry ground workers to 2,4-D picloram and dichloroprop. Environ. Toxicol. Chem. 6(3), 209–224. Lefton, J., et al. (1991). Weed Control Recommendations for Turfgrass Areas. AY-40. Pro Series, Purdue University Cooperative Extension Service. Liberacki, A. B., Yano, B. L., and Breslin, W. J.(1991). “Triisopropanolamine Salt of 2,4-D: Oral Gavage Teratology Study in New Zealand White Rabbits,” Unpublished Report, K, 008876-016. Dow Chemical Company, Midland, MI. Liberacki, A. B., Zablotny, C. I., Yano, B. L., and Breslin, W. J. (1994). Developmental toxicity studies on a series of 2,4-D salts and esters in rabbits. Toxicologist. 14(1), 162. Lindquist, N. G., and Ullberg, S. (1971). Distribution of the herbicides 2,4,5-T and 2,4,-D in pregnant mice. Accumulation in the yolk sac epithelium. Experientia 27(12), 1439–1441. Linnainmaa, K. (1983a). Sister chromatid exchanges among workers occupationally exposed to phenoxy acid herbicides 2,4-D and MCPA. Teratog. Carcinog. Mutagen 3(3), 269–279. Linnainmaa, K. (1983b). Nonmutagenicity of phenoxy acid herbicides 2,4-dichlorophenoxyacetic acid and 4-methyl-2-chlorophenoxyacetic acid. In “Chlorinated Dioxins and Dibenzofurans in the Total Environment,” Choudhary et al., eds.), p. 385. Butterworth Publishers, Woburn, MA. Linnainmaa, K., (1984). Induction of sister chromatid exchanges by the peroxisome proliferators 2,4-D, MCPA, and clofibrate in vivo and in vitro. Carcinogenesis 5, 703–707. Lochry, E. A. (1990). “Developmental Toxicity (Embryo-Fetal Toxicity and Teratogenic Potential) Study of 2,4-D Dimethylamine Salt (2,4-DDMA) Administered Orally via Gavage to Crl:CD® BR VAF/ Plus®Presumed Pregnant Rats,” Protocol Number: 320-001. Argus Research Laboratories, Inc, Horsham, PA. Lukowicz-Ratajczak, J., and Krechniak, J. (1988). Effects of sodium 2,4dichlorophenoxy acetate on renal function in the rat. Bull. Environ. Contam. Toxicol. 41, 815–821. Lundgren, B., Meijer, J., and Depierre, J. W. (1987). Induction of cytosolic and microsomal epoxide hydrolases and proliferation of peroxisomes and mitochondria in mouse liver after dietary exposure to p-chlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid and

Chapter | 84

Phenoxy Herbicides (2,4-D)

2,4,5-trichlorophenoxyacetic acid. Biochem. Pharmacol. 36(6), 815–822. Martin, T. (1991). “Developmental Toxicity (Embryo-Fetal Toxicity and Teratogenic Potential) Study of 2,4-D Dimethylamine Salt (2,4-DDMA) Administered Orally via Stomach Tube to New Zealand White Rabbits,” Protocol Number: 320-004. Argus Research Laboratories, Inc, Horsham, PA. Martin, T. (1992a). “Developmental Toxicity (Embryo-Fetal Toxicity and Teratogenic Potential) Study of 2,4-D 2-Ethylhexyl Ester (2,4-D Isooctyl Ester) Administered Orally (Stomach Tube) to New Zealand White Rabbits,” Protocol Number: 320-006. Argus Research Laboratories, Inc, Horsham, PA. Martin, T. (1992b). “Developmental Toxicity (Embryo-Fetal Toxicity and Teratogenic Potential) Study of 2,4-D 2-Ethylhexyl Ester (2,4-D Isooctyl Ester) Administered Orally via Gavage to Crl:CD® BR VAF/Plus® Presumed Pregnant Rats,” Protocol Number: 320-005. Argus Research Laboratories, Inc, Horsham, PA. Mattsson, J. L., Charles, J. M., Yano, B. L., Cunny, H. C., Wilson, R. D., and Bus, J. S. (1997). Single-dose and chronic dietary neurotoxicity screening studies on 2,4-dichlorophenoxyacetic acid in rats. Fund. Appl. Toxicol. 40, 111–119. Mattsson, J. L., and Eisenbrandt, D. L. (1990). The improbable association between the herbicide 2,4-D and polyneuropathy. Biomed. Environ. Sci. 3, 43–51. Mattsson, J. L., McGuirk, R. J., and Yano, B. L.(1994). “2,4-D Acute Neurotoxicity Study in Fischer 344 Rats,” Unpublished Report, K, 002372-006. Dow Chemical Company, Midland, MI. Mersch-Sundermann, V., Hofmeister, A., Muller, G., and Hof, H. (1989). Untersuchungen zur mutagenitat organischer mikrokontaminationen in der umwelt. III. Mitteilung: Die mutagenitat ausgewahlter herbizide und insektizide im SOS-chromotest  Examination of mutagenicity of organic microcontaminations of the environment. III. Communication: The mutagenicity of selected herbicides and insecticides with the SOS-chromotest. Zentralblatt fur Hygiene und Umweltmedizin (Int. J. Hyg. Environ. Med.) 189, 135–146. Mizell, M. J., Atkin, K. T., and Crissman, J. W. (1990a). “2,4Dichlorophenoxyacetic Acid Butoxyethyl Ester: 21-Day Dermal Toxicity Study in New Zealand White Rabbits,” K-007722-008. The Dow Chemical Company, Midland, MI. Mizell, M. J., Atkin, K. T., Haut, K. T., and Stebbins, K. E. (1990b). “2,4-D Isopropylamine Salt: 21-Day Dermal Toxicity Study in New Zealand White Rabbits,” M-004725-004. The Dow Chemical Company, Midland, MI. Mizell, M. J., Atkin, K. T., and Stebbins, K. E. (1989). “2,4-D Triisopropanolamine Salt: 21-Day Dermal Toxicity Study in New Zealand White Rabbits,” K-008866-004. The Dow Chemical Company, Midland, MI. Moody, R. P., Franklin, C. A., Ritter, L., and Maibach, H. I. (1990). Dermal absorption of the phenoxy herbicides 2,4-D, 2,4-D amine, 2,4-D isooctyl, and 2,4,5-T in rabbits, rats, rhesus monkeys, and humans: A cross-species comparison. J. Toxicol. Environ. Health 29(3), 237–246. Moody, R. P., Franklin, C. A., Ritter, L., Maibach, H. I. (1991). Errata to: Dermal absorption of the phenoxy herbicides 2,4-D, 2,4-D amine, 2,4D isooctyl, and 2,4,5-T in rabbits, rats, rhesus monkey’s and humans: a cross-species comparison. J. Toxicol. Environ. Health 31, 107–108. Morgan, M. K., Sheldon, L. S., Thomas, K. W., Eceghy, P. P., Croghan, C. W., Jones, P. A., Chuang, J. C., and Wilson, N. K. (2008). Adult and children’s exposure to 2,4-D from multiple sources and pathways. J. Exp. Sci. Env. Epidemiol. 18, 486–494.

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Mulcahy, M. T. (1980). Chromosome aberrations and “Agent Orange.”. Med. J. Austral. 2(10), 573–574. Mullison, W. R. (1987). “Environmental Fate of Phenoxy Herbicides. Fate of Pesticides in the Environment,” Publication 3320, pp. 121–131. California Agricultural Experiment Station. Munro, I. C., Carlo, G. L., Orr, J. C., Sund, K. G., Wilson, R. M., Kennepohl, E., Lynch, B. S., Jablinske, M., and Lee, N. L. (1992). A comprehensive, integrated review and evaluation of the scientific evidence relating to the safety of the herbicide 2,4-D. J. Am. Coll. Toxicol. 11(5), 559–664. Mustonen, R., Kangras, J., Vuojolahti, P., and Linnainmaa, K. (1986). Effect of phenoxyacetic acids on the induction of chromosome aberrations in vitro and in vivo. Mutagenesis 1, 241–255. Mustonen, R., Elovaara, E., Zitting, A., Linnainmaa, K., Vainio, H. (1989). Effects of commercial chlorophenolate, 2,3,7,8-TCDD and pure phenoxyacetic acids on hepatic peroxisome proliferation, xenobiotic metabolism and sister chromatid exchange in the rat. Arch. Toxicol. 63, 203–208. Nemec, M. D., Tasker, E. J., Werchowski, K. M., and Mercieca, M. D. (1983). “A Teratology Study in Fischer 344 Rats with 2,4Dichlorophenoxyacetic Acid,” Industry Task Force on 2,4-D Research Data. No, WIL, -81135. Wil Research Laboratories, Inc. Oliveira, G., and Palermo-Neto, J. (1993). Effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on open-field behaviour and neurochemical parameters of rats. Pharmacol. Toxicol. 73(2), 79–85. Orberg, J. (1980). Effects of low protein consumption on the renal clearance of 2,4-dichlorophenoxyacetic acid (2,4-D) in goats. Acta. Pharmacol. Toxicol. 46, 138–140. Pelletier, O., Ritter, L., Caron, J., and Somers, D. (1989). Disposition of 2,4-dichlorophenoxyacetic acid dimethylamine salt by Fischer 344 rats dosed orally and dermally. J. Toxicol. Environ. Health 28, 221–234. Pelletier, O., Ritter, L., Caron, J. (1990). Effects of skin preapplication treatments and postapplication cleansing agents on dermal absorption of 2,4-dichlorophenoxyacetic acid dimethylamine by Fischer 344 rats. J. Toxicol. Environ. Health 31, 247–260. Pritchard, J. B. (1980). Accumulation of anionic pesticides by rabbit choroid plexus in vitro. J. Pharmacol. Exper. Therapeut. 212(2), 354–359. Rashid, K. A. (1979). The relationship between mutagenic and DNAdamaging activity of pesticides and their potential for carcinogenesis. Diss. Abstr. Int. 39, 4726B (Abstr. No. 7909115). Rashid, K. A., Babish, J. G., and Mumma, R. O. (1984). Potential of 2,4dichlorophenoxyacetic acid conjugates as promutagens in the salmonella/microsome mutagenicity test. J. Environ. Sci. Health B19(849), 689–701. Rashid, K. A., and Mumma, R. O. (1986). Screening pesticides for their ability to damage bacterial DNA. J. Environ. Sci. Health (Part B— Pestic. Food Contam. Agric. Wastes) B21(4), 319–334. Ritter, L. (1997). Report of a panel on the relationship between public exposure to pesticides and cancer. Cancer 80(10), 2019–2033. Rodwell, D.(1991). “Teratology Study in Rabbits with Diethanolamine Salt of 2,4-D Acid,” Unpublished Report SLS 3229.13. Springborn Laboratories, Inc, OH. Rodwell, D. E. (1984). “A Dietary Two-Generation Reproduction Study in Fischer 344 Rats with 2,4-Dichlorophenoxyacetic Acid,” Project No. WIL, -81137. Wil Research Laboratories, Inc, Ashland, OH. Rowland, J.C. (1997). 2,4-dichlorophenoxyacetic acid (2,4-D). In “FAO Panel of Experts on Pesticide Residues, and WHO Expert Group on Pesticides Residues in the Food, and Environment. Pesticide Residues

1846

in Food—1996: Toxicological Evaluations.” WHO/PCS/97 1, 45–96. Food and Agriculture Organization of the United Nations (FAO), Rome, Italy. Rudel, R., and Senges, J. (1972). Experimental myotonia in mammalian skeletal muscle: Changes in membrane properties. Pflugers. Arch. 331, 324–334 (Cited in Bernard et al., 1985). Saracci, R., Kogevinas, M., Bertazzi, P. A., Demesquita, B. H. B., Coggon, D., Green, L. M., Kauppinen, T., Labbe, K. A., Littorin, M., Lynge, E., Mathews, J. D., Neuberger, M., Osman, J., Pearce, N., and Winkelmann, R. (1991). Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols. Lancet 338(8774), 1027–1032. Sauerhoff, M. W., Braun, W. H., Blau, G. E., and Gehring, P. J. (1977). The fate of 2,4-dichlorophenoxyacetic acid (2,4-D) following oral administration to man. Toxicology 8, 3–11. Schultz, S. K., Brock, A. W., and Killeen, J. C.(1990). “Dermal Sensitization Study (Closed Patch Repeated Insult) in Guinea Pigs, Rabbits with Diethanolamine Salt of 2,4-D,” Unpublished Report 90–165. Industry Task Force II on 2,4-D Research Data. Ricerca Inc, Painesville, OH. Schulze, G. E. (1990a). “21-Day Dermal Irritation and Dermal Toxicity Study in Rabbits with 2,4-Dichlorophenoxyacetic Acid,” HLA Study No. 2184-109. Hazleton Laboratories America Inc, Vienna, VA. Schulze, G. E. (1990b). “21-Day Dermal Irritation and Dermal Toxicity Study in Rabbits with Dimethylamine Salt of 2,4Dichlorophenoxyacetic Acid,” HLA Study No. 2184-111. Hazleton Laboratories America Inc, Vienna, VA. Schulze, G. E. (1990c). “21-Day Dermal Irritation and Dermal Toxicity Study in Rabbits with 2,4-Dichlorophenoxyacetic Acid-2-Ethylhexyl Ester,” HLA Study No. 2184-110. Hazleton Laboratories America Inc, Vienna, VA. Schulze, G. E. (1991). “Final Report: Subchronic Toxicity Study in Mice with 2,4-Dichlorophenoxyacetic Acid,” Industry Task Force II on 2,4-D Research Data. Hazleton Laboratories America, Inc, Vienna, VA. Schulze, G. E., and Dougherty, J. A. (1988). Neurobehavioral toxicity of 2,4-D-n-butyl ester (2,4-D ester): Tolerance and lack of cross-tolerance. Neurotoxicol. Teratol. 10, 75–79. Schwetz, B. A., Sparschu, G. L., and Gehring, P. J. (1971). The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) and esters of 2,4-D on rat embryonal, foetal and neonatal growth and development. Fd. Cosmet. Toxicol. 9, 801–817. Sell, C. R., Maitlen, J. C., and Aller, W. A. (1982). Perspiration as an important physiological pathway for the elimination of 2,4-dichlorophenoxyacetic acid from the human body. Am. Chem. Soc. Abstr. Pap. 183 PEST #74. Serota, D. G. (1983a). “Subchronic Toxicity Study in Rats with 2,4-D Acid,” Unpublished Report 2184-102. Industry Task Force II on 2,4-D Research Data. Hazleton Laboratories America, Inc, Vienna, VA. Serota, D. G. (1983b). “Subchronic Toxicity Study in Mice with 2,4-D Acid,” Unpublished Report 2184-100. Industry Task Force II on 2,4-D Research Data. Hazleton Laboratories America, Inc, Vienna, VA. Serota, D. G. (1986). “Combined chronic toxicity and oncogenicity study in rats with 2,4-D acid,” Unpublished Report 2184-103. Industry task Force II on 2,4-D Research Data. Hazleton Laboratories America, Inc, Vienna, VA. Serota, D. G. et al. (1986). “Combined Chronic Toxicity and Oncogenicity Study in Rats with 2,4-D Acid,” Unpublished Report, 2184-102. Hazleton Laboratories America, Inc, Vienna, VA. Serota, D. G. et al. (1987). “Oncogenicity Study in Mice with 2,4-D Acid,” Unpublished Report, 2184-101. Hazleton Laboratories America, Inc, Vienna, VA.

Hayes’ Handbook of Pesticide Toxicology

Serrone, D. M., Killeen, J. C., and Benz, G. (1991). “A Subchronic Toxicity Study in Rats with the Diethanolamine Salt of 2,4Dichlorophenoxyacetic Acid,” Unpublished Report 90-0186. Ricera Inc, Painesville, OH. Simmon, V. F., Kauhanen, K., and Tardiff, R. G. (1977). Mutagenic activity of chemicals identified in drinking water. In Progress in Genetic Toxicology (B. A. Bridges Scott and F. H. Sodels, eds.) Vol. 2, pp. 249–258. Elsevier/North-Holland, Amsterdam. Soler-Niedziela, L., Ong, T., Nath, J., and Zeiger, E. (1988). Mutagenicity studies of dioxin and related compounds with the Salmonella arabinose resistant assay system. Toxic. Assess 3(2), 137–145. Steiss, J. E., Braund, K. G., and Clark, E. G. (1987). Neuromuscular effects of acute 2,4-dichlorophenoxyacetic acid (2,4-D) exposure in dogs. J. Neurol. Sci. 78, 295–301. Styles, J. A. (1973). Cytotoxic effects of various pesticides in vivo and in vitro. Mutat. Res. 21(1), 50–51. Styles, J. A. (1977). Mammalian cell transformation in vitro. Br. J. Cancer 37, 931–936. Szabo, J. R., and Rachunek, B. L. (1991). “2,4-D, Butoxyethyl Ester: 13Week Dietary Toxicity Study in Fischer Rats,” ID. DECO-TXT:K007722-015. Dow Elanco, Indianapolis, IN. Thomas, K. W., Dosemeci, M., Hoppin, J. A., Sheldon, L. S., Croghan, C. W., Gordon, S. M., Jones, M. A., Reynolds, S. J., Raymer, J. H., Akland, G. C., Lynch, C. F., Knott, C. E., Sandler, D. P., Blair, A. E., and Alavanja, M. C. (25 Feb, 2009). Urinary biomarker, dermal, and air measurement results for 2,4-D and chlorpyrifos farm applicators in the Agricultural Health Study. J. Exp. Sci. Env. Epidemiol. Advance online publication; doi:10.1038/jes.2009.6. Toyoshima, E., Mayre, R. F., Max, S. R., and Eccles, C. (1985). 2,4Dichlorophenoxyacetic acid (2,4-D) does not cause polyneuropathy in rats. J. Neurol. Sci. 70, 225–229. Tyynela, K., Elo, H. A., and Ylitalo, P. (1990). Distribution of three common chlorophenoxyacetic acid herbicides into the rat brain. Arch. Toxicol. 64(1), 61–65. Tyynela, K., Elo, H., Ylitalo, P., and Hervonen, H. (1986). The central nervous system toxicity of chlorophenoxyacetic acid herbicides. Arch. Toxicol. (Suppl. 9), 355. Unger, T. M., Kliethermes, J., Van Goethem, D., and Short, R. D.(1981). “Teratology and Postnatal Studies in Rats of the Propylene Glycol Butyl Ether and Isooctyl Esters of 2,4-Dichlorophenoxyacetic Acid,” PB8, 1, 191140. U.S. Environmental Protection Agency, Research Triangle Park, NC. Waters, G. D., Simmon, V. F., Mitchell, A. D., Jorgenson, T. A., and Valencia, R. (1980). An overview of short-term tests for the mutagenic and carcinogenic potential of pesticides. J. Environ. Sci. Health B15(6), 867–906. Wigle, D. T. et al. (1990). Mortality study of Canadian male farm operators: Non-Hodgkin’s lymphoma mortality and agricultural practices in Saskatchewan. J. Nat. Cancer Inst. 82(7), 575–582. Wiklund, K., and Holm, L. E. (1986). Soft tissue sarcoma risk in Swedish agricultural and forestry workers. J. Nat. Cancer Inst. 76(2), 229–234. Wiklund, K. et al. (1987). Soft tissue sarcoma risk among agricultural and forestry workers in Sweden. Chemosphere 16(8/9), 2107–2110. Wolfe, W. H. (1983). The epidemiology and toxicology of Agent Orange. In “Proceedings of the 14th Conference on Environmental Toxicology,” Dayton, OH. Woolson, E. A., Thomas, R. F., and Ensor, P. D. J. (1972). Survey of polychlorodibenzo-p-dioxin content in selected pesticides. J. Agr. Food Chem. 20(2), 351–354.

Chapter | 84  Phenoxy Herbicides (2,4-D)

World Health Organization (WHO) (1975). “Evaluations of Some Pesticides in Food,” The Monographs, WHO Pesticide Series No. 4, pp. 159-183. World Health Organization, Geneva. World Health Organization (WHO) (1984). 2,4-Dichlorophenoxyacetic Acid (2,4-D). Environmental Health Criteria 29, pp. 1–151. IPCS International Programme on Chemical Safety, United Nations Environment Programme, International Labour Organisation, and the World Health Organisation. Yano, B. L., Cosse, P. F., Atkin, L., and Corley, R. A.(1991a). “2,4-D Isopropylamine Salt (2,4-D IPA): A 13-Week Dietary Toxicity Study in Fischer 344 Rats,” ID. HET m-004725-006. Dow Elanco, Indianapolis, IN. Yano, B. L., Cosse, P. F., Markham, D. A., and Atkin, L.(1991b). “2,4-D Triisopropanolamine Salt (2,4-D IPA): A 13-Week Dietary Toxicity Study in Fischer 344 Rats,” ID. K-008866-006. DowElanco, Indianapolis, IN. Yeary, R. A. (1986). Urinary excretion of 2,4-D in commercial lawn specialists. Appl. Ind. Hyg. 1(3), 119–121. Ylitalo, P., Narhi, U., and Elo, H. A. (1990). Increase in the acute toxicity and brain concentrations of chlorophenoxyacetic acids by probenicid in rats. Gen. Pharmacol. 21(5), 811–814.

1847

Yoder, J., Watson, M., and Benson, W. W. (1973). Lymphocyte chromosome analysis of agricultural workers during extensive occupational exposure to pesticides. Mutat. Res. 21, 335–340. Zablotny, C. L., Yano, B. L., and Breslin, W. J., (1991). “2,4-D Triiso­ propanolamine Salt (2,4-D TIPA): A 13-Week Dietary Toxicity Study in Fischer 344 Rats,” Unpublished Report No., K, 008866-006. Zahm, S. H. et al. (1990). A case-control study of non-Hodgkin’s lymphoma and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in eastern Nebraska. Epidemiology 1(5), 349–356. Zahm, S. H. (1997). Mortality study of pesticide applicators and other employees of a lawn care service company. J. Occup. Environ. Med. 39(11), 1055–1067. Zetterberg, G. (1978). Genetic effects of phenoxy acids on microorganisms. Ecol. Bull. 27, 193–204. Zetterberg, G., Busk, L., Elovson, R., Starec-Nordenhammar, I., and Ryttman, H. (1977). The influence of pH on the effects of 2,4-D (2,4dichlorophenoxyacetic acid, Na salt) on the Saccharomyces cerevisiae and Salmonella typhimurium. Mutat. Res. 42, 3–18. Zhamsaranova, S. D., Lebedeva, S. N., and Lyashenko, V. A. (1987). The immunodepressive effects of the herbicide 2,4-D in mice. Gig. I. Sanit. 5, 80–81.