Developing rat brain monoamine levels following in utero exposure to a mixture of 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic acids

Pregnant rats were gavaged with a 1:1 mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 0 (G0), 50 (G 50) and 100 (G 100) mg/kg per day on gestational days 6-15. Treatment significantly (P less than 0.05) delayed ontogeny of dopamine (DA), but not norepinephrine (NE) levels, in the thalamus-hypothalamus on postnatal day 7; in the pons-medulla on days 7,9 and 15; and in the olfactory lobes on day 9. On day 25, serotonin (5-HT) levels were significantly decreased in the pons-medulla of G 100 rats, whereas 5-hydroxyindoleacetic acid (5-HIAA) levels decreased in the thalamus-hypothalamus and pons-medulla of G 50 and G 100 rats.     

Distribution of three common chlorophenoxyacetic acid herbicides into the rat brain

The distribution of three common¹⁴C-labelled chlorophenoxyacetic acid herbicides (2,4-dichlorophenoxyacetic acid or 2,4-D, 2-methyl-4-chlorophenoxyacetic acid or MCPA, 2,4,5-trichlorophenoxyacetic acid or 2,4,5-T) into the different brain areas was studied in rats pretreated with toxic doses of the herbicides (238–475 mg/ kg). Also, their binding to proteins in rat plasma was determined in vitro by increasing the concentrations of chlorophenoxyacetic acids in the incubate from 0 to 1 mg/ml. Both 2,4-D and MCPA pretreatments increased brain concentrations of¹⁴C-labelled herbicides more markedly than 2,4,5-T pretreatments did. No essential differences were found in the distribution between the different brain areas. Protein-unbound fractions of 2,4-D and MCPA in the plasma were clearly higher than those of 2,4,5-T but the highest herbicide concentration increased the protein-unbound fraction of 2,4,5-T more (7-13-fold) than of 2,4-D and MCPA (5-fold). The results suggest that the greater increase in the penetration into the brain of 2,4-D and MCPA than of 2,4,5-T during their intoxication is due to some factors other than the changes in their binding to plasma proteins and mere enhanced diffusion through the blood-brain barrier.     

Effect of chlorophenoxyacetic acid herbicides on glycine conjugation of benzoic acid.

1. 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) (0.1-0.5 mmol/kg i.p.) delayed the disappearance of injected benzoate from blood and diminished the urinary excretion of the formed benzoylglycine, but elevated the blood levels of benzoylglycine in rat, suggesting that these herbicides interfere with both the formation and the renal transport of benzoylglycine. 2. Inhibition of the renal excretion of benzoylglycine by 2,4-D or 2,4,5-T (0.5 mmol/kg i.p.) was directly demonstrated in rat injected with benzoylglycine. 3. Inhibition of benzoylglycine formation from benzoic acid by 2,4-D or 2,4,5-T (0.5 mmol/kg i.p.) was directly demonstrated in renal pedicles-ligated rats injected with benzoate. 4. Neither 2,4-D nor 2,4,5-T influenced the hepatic concentrations of ATP, coenzyme A (CoA) or glycine; therefore, it is unlikely that they inhibit glycine conjugation of benzoic acid by diminishing the availability of co-substrates. 5. Although the chlorophenoxyacetic acids did not appear to be a substrate for the mitochondrial acyl-CoA synthetases, both 2,4-D and 2,4,5-T diminished the activity of benzoyl-CoA synthetase (but not that of benzoyl-CoA:glycine N-acyltransferase) in solubilized hepatic mitochondria. These findings suggest that 2,4-D and 2,4,5-T impair benzoylglycine formation in rat by inhibiting benzoyl-CoA synthetase.     

Comparative studies on the embryotoxicity of 2-methyl-4-chlorophenoxyacetic acid, mecoprop and dichlorprop in NMRI mice

From the group of herbicidal phenoxy carbonic acids, 2-methyl-4-chlorophenoxyacetic acid (MCPA; 0-500 mg/kg), 2-(4-chloro-2-methyl-phenoxy) propionic acid (mecoprop/MCPP; 0-700 mg/kg) and 2-(2,4-dichlorophenoxy) propionic acid (dichlorprop/2,4-DP; 0-500 mg/kg) as well as the dextrorotatory compounds of MCPP (MCPPD; 0-500 mg/kg) and 2,4-DP (2,4-DPD; 0-500 mg/kg) were studied in NMRI mice after oral administration between days 6-15 of pregnancy. All five substances proved to be embryotoxic and teratogenic in varying intensity. MCPA proved to be most effective: it was embryotoxic from doses of 100 mg/kg and teratogenic from 200 mg/kg. The remaining compounds (MCPP, MCPPD, 2,4-DP, 2,4-DPD) were embryotoxic from doses of 300 mg/kg and caused malformations of the skeleton from 400 mg/kg. The embryocidal and teratogenic potencies of the dextrorotatory components of MCPA and 2,4-DP exceeded those of the corresponding racemates. Influences of MCPPD and 2,4-DPD upon postimplantative loses, frequency of cleft palates and wavy ribs appeared already at dosages being 100-200 mg/kg below those of the racemates given to the respective groups of experimental animals. Additional alterations of the skeleton were observed which did not occur following administration of the racemic mixtures: deformed centrums of thoracic vertebra and exencephaly.     

Teratogenic and toxicological examination of 2,4,5-trichlorphenoxyacetic acid in developing chick embryos

Practical grade 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), dissolved in dimethylsufoxide (DMSO), was injected into the air space of fertilized chicken eggs prior to incubation. Doses of 2,4,5-T administered were 12.5, 25, 50, 75, 100, and 125 mg/kg to determine herbicide toxicity on the first day of incubation. A similar group was studied on day 5 of incubation with doses of 2,4,5-T at 50, 75, 100 and 250 mg/kg. LD₅₀ was estimated to be 62 mg/kg on day zero and 68 mg/kg on day 5. Additional, embryos were exposed to 2,4,5-T at 50 mg/kg on day zero of gestation and sacrificed after 48 h of incubation. Serial sections were examined for teratological and developmental anomalies. None were found.     

Cytoskeletal perturbation induced by herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)

To understand the mechanisms of toxicity of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), we have studied their effects on the cytoskeletal organization, particularly microtubules (MT) and microfilaments (MF), DNA synthesis, and the synthesis and composition of cytoskeletal proteins in mouse 3T3 cells. Exposure of cells to 2,4-D or 2,4,5-T resulted in a dose-dependent inhibition of DNA synthesis; 50% inhibition occurred at 2.21 mM and 0.90 mM for 2,4-D and 2,4,5-T, respectively. Furthermore, a strong synergistic inhibition of DNA synthesis was produced by mixtures (each having a total concentration of 1.25 mM) of 2,4-D with 2,4,5-T. Similarly, 2,4,5-T is more potent than 2,4-D in causing cytoskeletal perturbation as revealed by fluorescence microscopy. Treatment of cells with 2,4-D (2.5 mM) or 2,4,5-T (1.25 mM) for 20 h resulted in severe MT aggregation and the appearance of large bundles, which were organized in a rope-like structure in the former and a dramatic octopus-like pattern in the latter. Further, MT bundling is particularly severe in the cell center. Under these conditions, marked changes in MF organization also occurred as evidenced by clustering and crisscrossing of MF in the perinuclear region. A 1:1 mixture (final = 1.25 mM) of 2,4-D and 2,4,5-T, a formulation equivalent to Agent Orange composition, also induced a dramatic perturbation to the organization of MT and MF, resulting in the formation of ring-like structures. MT bundling is still apparent, especially around the outer edge of the "rings." MF are localized predominantly along the cell periphery, where they appear to be aggregated tightly forming patches. Surprisingly, the synthesis and composition of cytoskeletal proteins, which are resistant to detergent extraction but released by CaCl2, are essentially unaffected by 2,4-D or 2,4,5-T. These results suggest that the dramatic perturbation of the cytoskeletal morphology caused by these herbicides probably only results from a structural reorganization and redistribution of MT and MF.     

Effects of anionic xenobiotics on rat kidney: I—tissue and mitochondrial respiration

The polar 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) metabolite, 2,2-bis p-chlorophenyl)acetic acid (DDA), and the phenoxyacetic acid herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), were previously shown to be accumulated to high levels in liver and kidney via the organic acid transport system, raising the possibility of organ-specific toxicity secondary to transport. In these studies, accumulation of DDA was shown to depress oxygen consumption by renal cortical slices at high doses (0.1 and 1 mM). Isolated renal and hepatic mitochondria were uncoupled by low doses of DDA (5–10 nmoles/mg mitochondrial protein). Maximal uncoupling was seen at 50–70 nmoles/mg. 2,4-D and 2,4,5-T also produced uncoupling, but at doses of 70 nmoles/mg or higher. All agents were more effective with α-ketoglutarate or pyruvatemalate as substrate than with succinate. With succinate as substrate (but not α-ketoglutarate or pyruvate-malate), all three agents also depressed State 3 (ADP-stimulated) respiration. Again. DDA was more effective than 2,4-D or 2,4,5-T. These results suggest that accumulation of these or other anionic xenobiotics may lead to toxicity in those tissues possessing the organic anion transport system.     

Inhibition of Intercellular Communication in Cultures of Chinese Hamster V79 Cells by 2,4-Dichlorophenoxyacetic Acid and 2,4,5-Trichlorophenoxyacetic Acid

Inhibition of Intercellular Communication in Cultures of ChineseHamster V79 Cells by 2,4-Dicfalorophenoxyacctic Acid and 2,4,5-TrichlorophenoxyaceticAcid. RUBINSTEIN, C, JONE, C, TROSKO, J. E., AND CHANG, C. C.(1984). Fundam. Appt. Toxicol. 4, 731–739. Using the Chinesehamster V79 in vitro cell system designed to measure intercellularcommunication, 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyaceticacid (2,4,5-T), and several mixtures of these compounds weretested for their ability to inhibit this biological process.The ability of these chemicals to inhibit colony-forming abilityof these cells was tested prior to the studies to measure intercellularcommunication. 2,4-D was less cytotoxic than 2,4,5-T. Both 2,4,5-Tand 2,4-D were able to inhibit intercellular communication attheir respective noncytotoxic dose ranges. Various mixturesof both chemicals were also able to inhibit intercellular communication,snowing some kind of addititvity. No-effect levels were alsonoted in the intercellular communication assay. These resultswere interpreted as being consistent with the hypothesis thatthese compounds might be teratogenic by their ability to inhibitintercellular communication during development     

Effects of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid on peroxisomal enzymes in rat liver

The effects of feeding 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on the level of peroxisomal enzymes in rat liver were studied. The concentration of triglyceride in serum was decreased and the activity of cyanide-insensitive palmitoyl-CoA oxidation, catalase and carnitine acetyltransferase increased. However, the extent of the increase in the activity of these enzymes by treatment with 2,4-D was less pronounced than that by 2,4,5-T treatment. The administration of 2,4-D or 2,4,5-T increased the concentration of polypeptide with a mol. wt of 80,000 in the light mitochondrial fractions of the liver from the rats.     

Developmental toxicity studies in rats and rabbits on 2,4-dichlorophenoxyacetic acid and its forms.

The potential for 2,4-D and its salts and esters to induce developmental toxicity was investigated in rats (8 studies) and rabbits (7 studies). Maternal toxicity associated with exposure was dependent on the dose level expressed as 2,4-D acid equivalents. The severity of the maternal effect was correlated to the 2,4-D acid-equivalent dose, with increasing dose levels that exceeded renal clearance causing increasingly more severe maternal effects. In both species, maternal body weight effects began to be manifested at dose levels of 30 mg 2,4-D acid equivalent/kg/day. At higher dose levels (50-75 mg/kg/day in rats and 75-90 mg/kg/day in rabbits), body weights and feed consumption were more severely affected. At dose levels > or =90 mg/kg/day in rats, clinical signs of toxicity (ataxia, muscular stiffness, and decreased motor activity) and mortality were noted. The no-observed-adverse-effect level (NOAEL) for maternal toxicity in both species across the family of 2,4-D salts and esters was approximately 10 mg/kg/day. Significantly decreased fetal body weights and increased fetal variations were seen in rats only at maternally toxic dose levels in excess of 90 mg/kg/day acid equivalent. At maternally toxic doses in rabbits, embryonal and fetal development were essentially unaffected. There were no effect on maternal reproductive measures such as litter size, resorption rates, or fetal body weights, and there was no evidence of teratogenic activity. In summary, equivalent toxicity of the salts and esters is consistent with rapid and complete metabolic conversion to 2,4-D acid. No adverse fetal effects were noted at dose levels that did not also produce evidence of maternal toxicity or exceed renal clearance of 2,4-D indicating that the developing rat and rabbit fetus were not uniquely sensitive to 2,4-D and its forms.     

Specific teratogenic action of 2,4,5-trichlorophenoxyacetic acid on mouse and rat whole-embryo cultures

The effects of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were studied at concentrations ranging from 0.17 to 3.52 m on post-implanted mouse and rat embryos cultured for 48 hr, either in the absence of any metabolic activation system or in the presence of mouse and rat S-9 mix. 2,4,5-T proved to be a potential teratogen, at 0.88 and 1.76 m , on mouse embryos in the absence of any metabolic activation system. In the presence of mouse S-9 mix, 2,4,5-T showed a high teratogenic potential at 0.17, 0.88 and 1.76 m . In contrast, in the presence of rat S-9 mix, 2,4,5-T induced structural defects only at 1.76 m . At 3.52 m , 2,4,5-T was 100% embryolethal with or without S-9 mix. On rat embryos, 2,4,5-T was potentially teratogenic only in the presence of mouse S-9 mix, causing a significant increase in dysmorphogenic effects at 0.17, 0.88 and 1.76 m . With or without rat S-9 mix, 2,4,5,-T was only embryolethal to rat embryos at 1.76 and 3.52 m . The abnormalities mainly involved the forebrain, the midbrain and the branchial arches. These results are consistent with the known in vivo embryotoxic action of this compound.     

Comparison of uncoupling activities of chlorophenoxy herbicides in rat liver mitochondria

The effects of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2-(2,4,5-trichlorophenoxy)propionic acid (2,4,5-TP) on respiration and oxidative phosphorylation in rat liver mitochondria were examined in vitro. Respiration rates of glutamate, malate and succinate were investigated in the presence of each herbicide (0.1-4.0 mM). At lower concentrations, all herbicides stimulated state 4 respiration, decreased the respiratory control ratio and the ADP/O ratio. The respiration rate in state 3 and uncoupled state was unaffected. At higher concentrations all bioenergetic parameters, respiration in state 4, 3 and uncoupled state, as well as respiratory control ratio and ADP/O, were inhibited in a concentration-dependent manner. These data indicate that these herbicides alter energy metabolism in rat liver mitochondria by uncoupling of oxidative phosphorylation. 2,4,5-TP possesses the strongest uncoupling properties followed by 2,4,5-T, MCPA and 2,4-D in that order.     

Ontogeny of swimming behavior and brain catecholamine turnover in rats prenatally exposed to a mixture of 2,4-dichlorophenoxyacetic and 2,4,5-trichlorophenoxyacetic acids

Rats exposed in utero on gestational days 6-15, to nonfetotoxic and grossly nonteratogenic mixtures (50 or 100 mg/kg) of 2,4-D/2,4,5-T as found in Agent Orange (but without significant contamination with 2,3,7,8 tetrachloro-p-dioxin) manifested subtle developmental neurotoxicity. Maturation of swimming behavior was significantly delayed on postnatal day 7 in both treatment groups. The concentration of norepinephrine (NE) in whole brain was significantly increased on postnatal day 15 in both treatment groups, whereas the concentration of dopamine (DA) was increased on postnatal day 15 at 100 mg/kg. The turnover and efflux rate constant of DA in whole brain were significantly reduced whereas the turnover time increased on postnatal day 3. The efflux rate constant for NE decreased and the turnover time increased significantly on postnatal day 15 at 100 mg/kg. These data indicate the value of ontogenic assessment following exposure to small doses, which result in functional alterations in the absence of overt toxic signs.     

Uptake of phenoxyacetic acid derivatives into Caco-2 cells by the monocarboxylic acid transporters

The uptake mechanism of phenoxyacetic acid (PA) and its chlorine derivatives, 4-chlorophenoxyacetic acid (4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), was investigated using Caco-2 cells. The cells were incubated with PA, 4-CPA, 2,4-D or 2,4,5-T at pH 6.0 and 37 °C. The order of uptake and lipophilicity expressed by n-octanol partition coefficients were PA < 4-CPA < 2,4-D < 2,4,5-T. Incubation at 4 °C or at pH 7.4 significantly decreased these uptake. Furthermore, pretreatment with the protonophore, carbonylcyanide-p-(trifluoromethoxy) phenylhydrazone, or coincubation with benzoic acid, a typical substrate for the proton-linked monocarboxylic acid transporters (MCTs), significantly decreased the uptake of all compounds. The initial uptake rates of all compounds except PA were apparently saturable, suggesting the involvement of a carrier-mediated process. The order of uptake clearance of the compounds was the same as the order of their uptake and lipophilicity. Preloading of cells with benzoic acid significantly increased their uptake except for PA. These results suggest that the uptake of PA, 4-CPA, 2,4-D and 2,4,5-T from the apical membrane of Caco-2 cells is mediated via common MCTs shared, at least in part, with benzoic acid, and the increase in lipophilicity due to the chlor-substitution may increase uptake via the MCTs.     

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

Dermal absorption of the 14C-ring-labeled phenoxy herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-D amine (2,4-dichlorophenoxyacetic acid dimethylamine), 2,4-D isooctyl (2,4-dichlorophenoxyacetic acid isooctyl ester), and 2,4,5-T amine (2,4,5-trichlorophenoxyacetic acid trimethylamine) was examined following topical applications of the herbicides to the back of rabbits, the back and tail of rats, the forearm and forehead of rhesus monkeys, and the forehead of human volunteers. The effect of three pesticide vehicles (water, acetone, and Esteron LV96) was also investigated. The total percent dermal absorption was calculated from the mean percent urinary recoveries from the animal tests and corrected for nonurinary excretion of the radiolabel using data from intramuscular (im) injections. The human data are reported without im correction. The reliability of animal data for modelling human dermal absorption of pesticides is highlighted.     

Formulation and food deprivation affects 2,4-D neurobehavioral toxicity in rats

The herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) is a commonly used herbicide and one component of Agent Orange. The herbicide is commonly formulated as the butyl ester. The effects of a 50:50 mixture of n-butyl and iso-butyl esters of 2,4-D (2,4-D mixed butyl esters, 150-175 mg/kg/day SC) on photocell locomotor activity and landing foot splay were assessed in rats. Similarly the effects of 2,4-D mixed butyl esters and pure 2,4-D-n-butyl ester (150 mg/kg/day SC) on photocell locomotor activity were assessed in both food deprived and free feeding rats. In general, food deprivation tended to decrease the sensitivity of rats to the effects of either formulation. The spectrum of neurobehavioral effects varied with the ester isomers. Both 2,4-D-n-butyl ester and 2,4-D mixed butyl esters depressed photocell locomotor activity. 2,4-D mixed butyl esters failed to increase landing foot splay as reported for 2,4-D-n-butyl ester. The extent of ester hydrolysis was similar when comparable concentrations of 2,4-D acid were measured in blood and brain four hours following either formulation. 2,4-D-n-butyl ester caused significantly more activity depression than 2,4-D mixed butyl esters. Additionally, tolerance developed more rapidly for animals receiving 2,4-D mixed butyl esters than for animals receiving 2,4-D-n-butyl ester. These studies exemplify the importance of herbicide formulation and subject nutritional status in the expression of neurobehavioral toxicity.     

Comparative Subchronic and Chronic Dietary Toxicity Studies on 2,4-Dichlorophenoxyacetic Acid, Amine, and Ester in the Dog

Forms of 2,4-dichlorophenoxyacetic acid (2,4-D) are herbicidesused in the control of a wide variety of broadleaf and woodyplants. Subchronic toxicity studies in dogs were conducted onthree forms of 2,4-D: the parent form, 2,4-D acid (ACID); 2,4-Ddimethylamine salt (DMA); and 2,4-D 2-ethythexyl ester (2-EHE).The three studies were designed to allow for comparison of thetoxicity of the three forms. Doses in the subchronic studies,on an acid equivalent basis, were 0, 0.5 (ACID only), 1.0, 3.75,and 7.5 mg/ kg/day. Treatment related findings in the threestudies included reductions in body weight gain, and food consumption,and minor increases in blood urea nitrogen, creatinine, andalanine aminotransferase. The data from the three subchronicstudies demonstrated the comparable toxicity of ACID, DMA, and2-EHE and support a subchronic no observed adverse effect level(NOAEL) of 1.0 mg/kg/day for all three forms. Due to the similarityin toxicity of the three forms of 2,4-D, a 1-year chronic toxicitystudy was performed on the parent ACID to fully characterizethe potential toxicity of 2,4-D in the dog. ACID was well toleratedat doses of 0, 1.0, 5.0, and 7.5 mg/kg/day. The clinical pathologyalterations were similar to those seen in the subchronic studiesand were not progressive. The histopathology alterations observedwere not severe in nature and the no observed effect level inthe chronic study was determined to be 1.0 mg/kg/day. Therewas no indication of any immunotoxic or oncogenic response inthe studies. In conclusion, the findings of these studies indicatecomparable toxicity among representative forms of 2,4-D andtheir generally low toxicity following subchronic and chronicdietary exposure in the dog.     

Specificity of 2,4,5-trichlorophenoxyacetate on tetraethylammonium transport.

Renal cortical slices from rats pretreated acutely with 2,4,5-trichlorophenoxyacetate (2,4,5-T) show a reduced ability to transport 2,4-dichlorophenoxyacetate (2,4-D) and tetraethylammonium (TEA). The depression in renal transport is dependent on the 2,4-D or TEA concentration in the incubation medium and is surmountable at high concentrations of 2,4-D or TEA. The steady-state transport of TEA by normal renal slices is inhibited by the organic anion 2,4,5-T, in a dose-related manner. Kinetic analysis of the effect of 2,4,5-T on TEA transport appears to demonstrate that 2,4,5-T is a competitive inhibitor of the steady-state accumulation of TEA. However, the initial influx of TEA was found to be unaffected by 2,4,5-T. The transport of another organic cation, N¹-methylnicotinamide, was depressed only modestly by 2,4,5-T.     

Sequential histopathologic, hematologic, and blood chemistry changes induced in mice by a technical and a purified preparation of 2,4,5-trichlorophenoxyacetic acid.

Maternal mice were given 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) on days 6 through 14 of pregnancy in a tetratologic study at the National Center for Toxicological Research. Sick or moribund mice sacrificed after 4-8 doses of 120 mg/kg 2,4,5-T often showed severe myocardial lesions, hypocellularity of the bone marrow, and depletion of lymphocytes in the thymus, spleen, or lymph nodes. Healthy mice sacrificed on day 17, 11 days after treatment began, showed few or no severe lesions. To determine if lesions earlier in gestation contributed significantly to an increase in fetal abnormalities in the healthy 17-day survivors, dihybrid croos F2 pregnant and nonpregnant mice received by gavage 0, 60, or 120 mg/kg 2,4,5-T on days 6 through 14 of pregnancy. One group received a technical preparation containing 97.9 +/- 0.4% 2,4,5-T; another received a purified preparation containing 99 +/- 0.3% 2,4,5-T. Mice were sacrificed when they became moribund and at 6, 24, and 30 hr, as well as at 4, 6, 8, and 11 days after beginning treatment. Almost all mice given 60 mg/kg and many given 120 mg/kg 2,4,5-T appeared normal at sacrifice either early or late in pregnancy and showed little or no pathologic changes. Mice that became ill or moribund often showed severe lesions; few survived 11 days. Severe myocardial lesions were seen in 26 of 70 moribund mice fiven the technical 2,4,5-T and 24 of 33 given the purified preparation of 2,4,5-T. The moribund mice, particularly those given the purified compound, also showed a high incidence of lesions in other organs and marked hematological and blood chemistry changes. These findings indicate that the lesions are primarily due to 2,4,5-T rather than to impurities in the technical preparation; also impaired maternal health is not the primary cause of the increase in fetal abnormalities.     

Biodegradation of the herbicides 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid,and 2-methyl-4-chlorophenoxyacetic acid in a sulfate-reducing aquifer

Biodegradation of trace organic compounds is one of the main mechanisms to purify infiltrating surface water during bankfiltration and underground passage. In anaerobic zones of the underground, rate and extent of degrading processes may be totally different from those in aerobic ones. To investigate this, a model ecosystem was built that reproduces an anaerobic part of the aquifer and the behavior of the three phenoxyacetic acid herbicides 2,4-dichlorophenoxyacetic acid, (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2-Methyl-4-chlorophenoxyacetic acid (MCPA) tested. In anaerobic experiments with varying conditions they proved to be almost persistent. Only under aerobic conditions could biodegradation be observed after a lag period. © by John Wiley & Sons, Inc.