Effects of Phenoxyacetic Acid Herbicides on Chicken Embryo Liver Drug Metabolizing Enzymes

Abstract: Chick embryos were treated on day 0 of incubation with two phenoxy herbicides, 2-methyl-4-chlorophenoxyacetic acid (MCPA) (0.4, 2 mg/egg) and 2,4-dichlorophenoxyacetic acid (2, 4-D) (1, 2, 4 mg/egg). Both herbicides seemed to exert toxic effects mainly on the liver of 19-day-old embryos. Specific histological analysis indicated biliary stasis. Ethoxycoumarin O-deethylase was depressed by MCPA but raised by 2, 4-D. Other hepatic monooxygenase activities were unaffected by the herbicides and no significant changes were found in cytochromes. The higher dose of MCPA increased NADPH-cytocrome P₄₅₀ reductase. 2,4-D treatment increased by activity of glutathione-S-transferases in the hepatic post-microsomal fraction while MCPA increased them at the lower dose and significantly reduced them at the higher. The phenoxyacetic herbicides appear thus to have some effects on hepatic drug metabolizing enzymes of the chick embryo which cannot be easily interpreted. Biliary retention, produced in particular by MCPA, could be partly responsible for these effects.     

Effects of phenoxyacetic acid herbicides on chicken embryo liver drug metabolizing enzymes.

Chick embryos were treated on day 0 of incubation with two phenoxy herbicides, 2-methyl-4-chlorophenoxyacetic acid (MCPA) (0.4, 2 mg/egg) and 2,4-dichlorophenoxyacetic acid (2, 4-D) (1, 2, 4 mg/egg). Both herbicides seemed to exert toxic effects mainly on the liver of 19-day-old embryos. Specific histological analysis indicated biliary stasis. Ethoxycoumarin O-deethylase was depressed by MCPA but raised by 2, 4-D. Other hepatic monooxygenase activities were unaffected by the herbicides and no significant changes were found in cytochromes. The higher dose of MCPA increased NADPH-cytochrome P450 reductase. 2,4-D treatment increased by activity of glutathione-S-transferases in the hepatic post-microsomal fraction while MCPA increased them at the lower dose and significantly reduced them at the higher. The phenoxyacetic herbicides appear thus to have some effects on hepatic drug metabolizing enzymes of the chick embryo which cannot be easily interpreted. Biliary retention, produced in particular by MCPA, could be partly responsible for these effects.     

Hypolipidemia and peroxisome proliferation induced by phenoxyacetic acid herbicides in rats

Male Wistar rats were treated daily by gavage with two phenoxy herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D)(100-200 mg/kg body wt) and 4-chloro-2-methylphenoxyacetic acid (MCPA) (100-200 mg/kg body wt), and with the chemically different glyphosate N-phosphonomethyl glycine (300 mg/kg body wt) 5 days per week for 2 weeks. A hypolipidemic drug, clofibrate [ethyl-2-(4-chlorophenoxy)-2-methylpropionate], which is structurally related to phenoxy acids, was used as a positive control (200 mg/kg body wt). 2,4-D and MCPA had several effects similar to those of clofibrate: all three compounds induced proliferation of hepatic peroxisomes, decreased serum lipid levels, and increased hepatic carnitine acetyltransferase and catalase activities. 2,4-D and MCPA, but not clofibrate, decreased lipoprotein lipase activity in the adipose tissue to about a third of the control value but did not change the lipoprotein lipase activity in the heart muscle. The data suggest that these compounds cause hypolipidemia not by enhancing the storage of peripheral lipids in adipose tissue but by preferentially increasing lipid utilization in the liver. Glyphosate caused no peroxisome proliferation or hypolipidemia, suggesting that these effects are associated with the structural similarity between phenoxy acid herbicides and clofibrate.     

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on benzo(a)pyrene hydroxylase activity in embryos of the Japanese medaka (Oryzias latipes)

When Japanese medaka embryos were exposed to 12 ng/l 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) beginning on the day of fertilization (day 0), benzo(a)pyrene hydroxylase (B(a)PH) activity was induced in the whole embryo 105000g fraction by day 5 of development, which coincided with liver development. The induction of B(a)PH activity also coincided with the appearance of 2,3,7,8-TCDD induced hemorrhagic and edematous lesions. B(A)PH induction only occurred in embryos exposed to toxic concentrations (greater than 10 ng/l) of 2,3,7,8-TCDD. B(a)PH induction also occurred in embryos after exposure to 10 ng/l 2,3,7,8-tetrachlorodibenzofuran (TCDF) and 50 g/l 1,2,7,8-TCDD. Both 2,3,7,8-TCDF and 1,2,7,8-TCDD are toxic to Japanese medaka embryos at concentrations that resulted in the induction of B(a)PH activity. B(a)PH activity was not induced by the non-toxic congener 1,3,6,8-TCDD at concentrations as high as 50 g/l. The structure activity relationship for B(a)PH induction in Japanese medaka embryos was similar to that which is observed in other species and biological systems, suggesting that the biological activities of these compounds may also be mediated through the putativeAh receptor in these fish embryos. At 50 g/l, -naphthoflavone (BNF) induced B(a)PH activity in Japanese medaka embryos to similar levels as 2,3,7,8-TCDD did at toxic concentrations. However, at 50 g/l, BNF was not toxic to Japanese medaka embryos. Therefore, the induction of B(a)PH activity probably did not directly result in the toxicity observed in these fish embryos after exposure to 2,3,7,8-TCDD.Presented in part at the 28th Annual Meeting of the Society of Toxicology, Atlanta, GA, 1989.     

Effects of Phenoxyherbicides and Glyphosate on the Hepatic and Intestinal Biotransformation Activities in the Rat

Abstract: The effects of phenoxyacid herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methylphenoxyacetic acid), clofibrate, and glyphosate on hepatic and intestinal drug metabolizing enzyme activities were studied in rats intragastrically exposed for 2 weeks. The hepatic ethoxycoumarin O-deethylase activity increased about 2-fold with MCPA. Both 2,4-D and MCPA increased the hepatic epoxide hydrolase activity and decreased the hepatic glutathione S-transferase activity. MCPA also increased the intestinal activities of ethoxycoumarin O-deethylase and epoxide hydrolase. Glyphosate decreased the hepatic level of cytochrome P-450 and monooxygenase activities and the intestinal activity of aryl hydrocarbon hydroxylase. Clofibrate decreased the hepatic activities of UDPglucuronosyltransferase with p-nitrophenol or methylumbelliferone as the substrate. Also 2,4-D decreased the hepatic activity of UDPglucuronosyltransferase with p-nitrophenol as the substrate. MCPA decreased the intestinal activities of UDPglucuronosyltransferase with either p-nitrophenol or methylumbelliferone as the substrate. The results indicate that phenoxyacetic acids, especially MCPA, may have potent effects on the metabolism of xenobiotics. Glyphosate, not chemically related to phenoxyacids, seems to inhibit monooxygenases. Whether these changes are related to the toxicity of these xenobiotics remains to be clarified in further experiments.     

Comparative inter-species pharmacokinetics of phenoxyacetic acid herbicides and related organic acids. evidence that the dog is not a relevant species for evaluation of human health risk

Phenoxyacetic acids including 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are widely utilized organic acid herbicides that have undergone extensive toxicity and pharmacokinetic analyses. The dog is particularly susceptible to the toxicity of phenoxyacetic acids and related organic acids relative to other species. Active renal clearance mechanisms for organic acids are ubiquitous in mammalian species, and thus a likely mechanism responsible for the increased sensitivity of the dog to these agents is linked to a lower capacity to secrete organic acids from the kidney. Using published data describing the pharmacokinetics of phenoxyacetic and structurally related organic acids in a variety of species including humans, inter-species comparative pharmacokinetics were evaluated using allometic parameter scaling. For both 2,4-D and MCPA, the dog plasma half-life (t(1/2)) and renal clearance (Clr; mL/h) rates did not scale as a function of body weight across species; whereas for all other species evaluated, including humans, these pharmacokinetic parameters reasonably scaled. This exceptional response in the dog is clearly illustrated by comparing the plasma t(1/2) at comparable doses of 2,4-D and MCPA, across several species. At a dosage of 5mg/kg, in dogs, the plasma t(1/2) for 2,4-D and MCPA were approximately 92-106 and 63 h, respectively, which is substantially longer than in the rat (approximately 1 and 6 h, respectively) or in humans (12 and 11 h, respectively). This longer t(1/2), and slower elimination in the dog, results in substantially higher body burdens of these organic acids, at comparable doses, relative to other species. Although these results indicate the important role of renal transport clearance mechanisms as determinants of the clearance and potential toxicity outcomes of phenoxyacetic acid herbicides across several species, other contributing mechanisms such as reabsorption from the renal tubules is highly likely. These findings suggest that for new structurally similar organic acids, a limited comparative species (rat versus dog) pharmacokinetic analysis early in the toxicology evaluation process may provide important insight into the relevance of the dog. In summary, the substantial difference between the pharmacokinetics of phenoxyacetic acids and related organic acids in dogs relative to other species, including humans, questions the relevance of using dog toxicity data for the extrapolation of human health risk.     

Teratogenic and Embryotoxic Effects of the Herbicides Di- and Trichlorophenoxyacetic Acids (2, 4D and 2, 4, 5-T)

Abstract: Commercial solutions of phenoxyacetic acids were tested for teratogenic effects in NMRI-mice. The Swedish product Hormoslyr 500-T contained only 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) while Hormoslyr 64 was a mixture of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-T (2:1). Subcutaneous injections were given from day 6 through day 14 of pregnancy and the animals were sacrificed on day 18. The number of resorbed embryos, living embryos with gross malformations, as well as internal and skeletal malformations were recorded. It was found that both preparations at the high dosage (110 mg/kg/day) were teratogenic and embryotoxic. At the low dose level (50 mg/kg/day) the 2,4,5-T solution was more harmful than the mixture of 2,4-D and 2,4,5-T. The risks of teratogenicity in human civilian use and the role of dioxins are discussed.     

Simultaneous determination of 2,4-D and MCPA in canine plasma and urine by HPLC with fluorescence detection using 9-anthryldiazomethane (ADAM)

A method for the simultaneous determination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in canine plasma and urine has been developed. This method used derivatization of extracted samples with 9-anthrylmethane (ADAM) for analysis by reversed-phase high-performance liquid chromatography with fluorescence detection. Precision and accuracy were within the accepted limits of 15% and 85-115%, respectively, for both analytes in plasma and urine. Calibration curves for 2,4-D and MCPA in plasma were linear (r2 > 0.99) between 0.50 and 5.0 mg/L and 5.0 and 100 mg/L. Calibration curves for 2,4-D and MCPA in urine were linear (r2 > 0.99) between 5.0 and 70.0 mg 2,4-D/L and 10.0 and 70.0 mg MCPA/L. The lower limit of detection was 62.5 ng/mL for both 2,4-D and MCPA.     

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.     

Subchronic Oral Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in the Guinea Pig: Comparisons with a PCB-Containing Transformer Fluid Pyrolysate

Subchronic Oral Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxinin the Guinea Pig: Comparisons with a PCB-Containing TransformerFluid Pyrolysate. DECAPRIO, A. P., MCMARTIN, D. N., O'KEEFE,P. W., REJ, R., SILKWORTH, J. B., AND KAMINSKY, L. S. (1986).Fundam. Appl. Taxicol. 6,454–463. In contrast to the well-characterizedacute toxicity of the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin(2,3,7,8-TCDD) in the guinea pig, the effects of prolonged poexposure in this species are unknown. The present report describesthe results of administration to guinea pigs of 2,3,7,8-TCDDin the feed at levels of 0,2, 10, 76, or 430 ppt for up to 90days. Additional aims were to examine recovery following prolonged2,3,7,8-TCDD exposure in the guinea pig and to generate datato facilitate comparison of the previously reported toxicityof a transformer fluid pyrolysate with that of pure 2,3,7,8-TCDD.Animals receiving 430 pot 2,3,7,8-TCDD exhibited body weightloss, thymic atrophy, liver enlargement, and 60% mortality byDay 46 (males) and by Day 60 (females), when surviving animalsin this group were sacrificed. Total 2,3,7,8-TCDD consumptionwas approximately 1.3 and 1.9 µg/kg, respectively. Animalsreceiving 76 ppt 2,3,7,8-TCDD for 90 days (total 0.44 µg/kg)exhibited a decreased rate of body weight gain and increasedrelative (to body) liver weights. Male animals also displayeda reduction in relative thymus weights and elevated serum triglycerides,while females exhibited hepatocellular cytoplasmic inclusionbodies and lowered serum alanine arninotransferase activities.Toxic effects were generally similar to those observed afteracute 2,3,7,8-TCDD administration. No dose-related alterationswere seen in animals receiving either 10 ppt (total 0.06 µg/kg)or 2 ppt (total 0.01 µg/kg) for 90 days, establishinga no-observed-effect level of approximately 0.65 ng 2,3,7,8-TCDD/kg/day.In the recovery study, groups of guinea pigs were administered430 ppt 2,3,7,8-TCDD for 11,21, or 35 days and then allowedto recover for an additional 79,69, or 55 days, respectively.Treatment-related mortality in each group was 0, 10, and 70%,respectively, by Day 90. An effective LD5O of 0.8 µg 2,3,7,8-TCDD/kgfor prolonged exposure was calculated on the basis of theseresults, a value lower than those previously reported from thislaboratory for acute exposure. The results also suggested apossible lowering of the body weight "set point" following 2,3,7,8-TCDD exposure. Comparison of the present findings with thosepreviously reported for a trans former fluid pyrolysate containinga mixture of polychlorinated aromatic species indicated botha greater variety of toxic effects and flatter dose-responserelationships for the pyrolysate in the guinea pig.     

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.     

Pharmacokinetics and biological activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Wistar rats were treated initially with very high single doses of ¹⁴C-2,3,7,8-TCDD (either 75 or 25 g/kg body wt) followed by weekly maintenance doses of 15 and 5 g/kg body wt, respectively. ¹⁴C-radioactivity was measured in various organs over a period of 22 weeks. 1) 75 g TCDD/kg body wt (followed by the maintenance doses) was lethal for all the rats within a period of 9 weeks. While the concentration of ¹⁴C-TCDD equivalents in liver and thymus stayed reasonably constant during this period in the surviving rats, the concentration in adipose tissue and kidneys clearly increased in the same animals. 2) The dose of 25 g TCDD/kg body wt (followed by weekly doses of 5 g/kg body wt) proved to be a just tolerable dose over a period of 22 weeks for our strain of rats. 3) Within the individual variabilities the TCDD concentrations in the investigated organs showed no clear-cut decline, indicating that the animals were exposed to fairly constant levels of TCDD throughout the study. Thus, this dosing regime is suitable for maintaining constant TCDD exposure during long-term studies.Abbreviations TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin     

Acute toxicity in guinea pigs and rabbits of soot from a polychlorinated biphenyl-containing transformer fire

A fire involving a polychlorinated biphenyl (PCB)-containing transformer extensively contaminated the State Office Building in Binghamton, New York, with a sootlike material containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), 2,3,7,8-tetrachlorodibenzofuran, and high concentrations of numerous other polychlorinated dibenzodioxins, dibenzofurans, and PCBs. The oral LD50s of the soot and of its benzene extract, each administered to female guinea pigs in 0.75% aqueous methyl cellulose, were 410 mg of soot/kg and 327 mg of soot equivalent/kg, respectively. Serum triglycerides were elevated in males at 100 and 500 mg/kg and in females at 500 mg/kg. Alkaline phosphatase was lowered in females at 500 mg/kg. Histopathology revealed dose-related pancreatic duct hyperplasia and salivary gland duct metaplasia in males. Body weight loss was observed in both sexes at 500 mg/kg. Thymus weight decreased in both sexes at 100 and 500 mg/kg, and kidney weights decreased in males at these doses. Dermal application of soot to rabbits for 24 hr caused no overt toxicity, although hepatic centrilobular hypertrophy was observed in both sexes. Similar application of soot extract caused a local serous inflammation in addition to the hepatic centrilobular hypertrophy. The oral LD50 for 2,3,7,8-TCDD in female guinea pigs was 19 μg/kg in aqueous methyl cellulose and 2.5 μg/kg in corn oil. We concluded that the soot matrix alters the dermal but not the oral toxicity of its components, that the toxic effects were consistent with those reported after exposure to dibenzodioxins and dibenzofurans, and the aqueous vehicle markedly diminished the acute toxicity of 2,3,7,8-TCDD relative to that in corn oil vehicle.     

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.     

Comparative Subchronic Studies on 2,4-Dichlorophenoxyacetic Acid, Amine, and Ester in Rats

Forms of 2,4-dichlorophenoxyacetic acid (collectively knownas 2,4-D) are herbicides used to control a wide variety of broadleafand woody plants. Subchronic toxicity studies in rats were conductedon three forms of 2,4-D: the parent form, 2,4-D acid; 2,4-Ddimethylamine salt (DMA); and 2,4-D 2-ethylhexyl ester (2-EHE).Doses in the subchronic studies (on an acid equivalent basis)were 0, 1, 15, 100, and 300 mg/kg/day. Major treatment relatedfindings in the three studies included decreases in red cellmass, decreases in T3 and T4 levels, decreases in ovary andtestes weights, increases in liver, kidney, and thyroid weights,and cataracts and retina] degeneration (high-dose females).These data demonstrated the comparable toxicities of 2,4-D acid,DMA, and 2-EHE and support a subchronic no-observed-effect levelof 15 mg/kg/day for all three forms. In summary, the findingsof these studies indicate comparable low subchronic toxicitypotentials among representative forms of 2,4-D.     

Aroclor 1254 as an antagonist of the teratogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 20 micrograms/kg) to pregnant C57BL/6J mice (on day 10) resulted in 62% fetuses with cleft palate per litter without any observable maternal toxicity. In contrast, Aroclor 1254 administered at a dose of 750 mumol/kg was not teratogenic. Cotreatment of the pregnant mice with both Aroclor 1254 (244 mg/kg) and 2,3,7,8-TCDD (20 micrograms/kg) resulted in an 8.2% incidence of cleft palate per litter. In contrast, Aroclor 1254 did not afford any protection from the teratogenicity of dexamethasone in C57BL/6J mice. Previous studies have shown that Aroclor 1254 can act as a partial antagonist of the microsomal enzyme induction and immunotoxic effects of 2,3,7,8-TCDD in C57BL/6J mice and this paper demonstrates that the commercial polychlorinated biphenyl mixture also antagonizes 2,3,7,8-TCDD-mediated teratogenicity in this strain of mice.     

Aroclor 1254 as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist: effects on enzyme induction and immunotoxicity

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Aroclor 1254 induced the cytochrome P-450 dependent monooxygenases, aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II E cells and C57BL/6J mice. It has been proposed that both Aroclor 1254 and 2,3,7,8-TCDD induce these enzymes via a common mechanism which features initial binding to the aryl hydrocarbon (Ah) cytosolic receptor protein. The major difference between these compounds was the relative potency (i.e. 2,3,7,8-TCDD much greater than Aroclor 1254). Cotreatment of rat hepatoma H-4-II E cells or C57BL/6J mice with a dose of 2,3,7,8-TCDD which submaximally induces AHH and EROD and a dose of Aroclor 1254 which exhibited little or no induction activity resulted in significant antagonism of the induction effects of 2,3,7,8-TCDD. For example, cotreatment of C57BL/6J mice with 2,3,7,8-TCDD (15 nmol/kg) and Aroclor 1254 (25, 75 and 150 mumol/kg) resulted in up to 23% antagonism of AHH induction by 2,3,7,8-TCDD. Moreover, cotreatment with a higher dose of the 2,3,7,8-TCDD agonist (30 or 50 nmol/kg) partially reversed some of the antagonism by Aroclor 1254. In vivo antagonism was observed only at Aroclor 1254/2,3,7,8-TCDD molar ratios of 1667:1, 5000:1 and 10,000:1. Administration of 2,3,7,8-TCDD (3.72 nmol/kg) to C57BL/6J mice resulted in a 76% decrease in the splenic plaque forming cell response to sheep red blood cells. This T-cell mediated immunotoxic effect of 2,3,7,8-TCDD segregates with the Ah locus. In contrast, administration of 5, 15, 75 and 150 mumol/kg of Aroclor 1254 resulted in impairment of the immune response only at the highest dose level. However, cotreatment of mice with 2,3,7,8-TCDD (3.72 nmol/kg) and Aroclor 1254 (5, 15 or 75 mumol/kg) resulted in no significant decrease in the plaque forming cell response and complete protection from the immunotoxicity of 2,3,7,8-TCDD. Cotreatment of the mice with Aroclor 1254 (75 mumol/kg) and a higher dose of the 2,3,7,8-TCDD agonist resulted in partial reversal of the protective effects of Aroclor 1254. The in vitro and in vivo data suggest that within specific antagonist/agonist dose ratios, Aroclor 1254 can antagonize at least 2 Ah receptor-mediated effects of 2,3,7,8-TCDD, namely AHH induction and immunotoxicity.     

Acute, Pharmacokinetic, and Subchronic Toxicological Sudies of 2,4-Dichlorophenoxyacetic Acid

The single-dose oral LD₅₀ values in Fischer 344 rats for technical-grade2,4-dichlorophenoxyacetic acid (2,4-D), es ters, and salts rangedfrom 553 mg/kg (isobutyl ester in females) to 1090 mg/kg (dimethylaminesalt in males). The LDH values for the acid, esters, or salts,when expressed as acid equivalents, were consistent which suggeststhat the acute toxicity was due to 2,4-D per se. Acute dermalLD₅₀ values in rabbits for the acid, esters, and salts weregreater than 2000 mg/kg. Overall, these results indicate thatthe acute oral and dermal toxicity of 2,4-D are low. Pharmacokineticswere evaluated in male Fischer 344 rats given single oral dosesof 10, 25, 50, 100, or ISO mg 2,4- [¹⁴CJD/kg The amount of 2,4-Din the plasma, kidney, and urine 6 hr postdosing indicated thatthe urinary elimination of 2,4-D was saturated in male ratsgiven oral doses in excess of 50 mg/ kg. Subchronic dietarystudies in male and female Fischer 344 rats used dose levelsof 0, 15, 60, 100, or 150 mg/kg/thy of purified or technical-grade2,4-D acid for 13 weeks. Body weight gains were decreased forboth sexes at the higher dose levels of purified and technical-grade2,4-D acid. Kidney weights were increased in all treated malerats and in females given the higher three dose levels of purified2,4-D. Treatment-related cytoplasmic alterations were presentin the renal proximal tubules of most rats given 60mg/kg/thyand higher of purified or technical-grade 2,4- D; a few femalesgiven 15 mg/kg/thy also had slight alterations in the cytoplasmof the proximal tubules. A dose-related degenerative changewas identified in the descending proximal renal tubules of allmale rats given the highest three dose levels of either testmaterial and some given 15 mg/kg/thy. Dose levels of 100 or150 mg/kg/thy of either compound for both sexes produced minimalswelling and increased staining homogeneity in the liver cellsand were associated with a slight elevation of liver weightand serum glutamic pyruvic transaminase activity. Higher doselevels of technical-grade and purified 2,4-D decreased totalserum tetraiodothyronine levels in female rats, however, themorphology of the thyroid gland was normal. The no-observed-effectlevel (NOEL) was less than 15 mg/kg/day for both purified andtechnical-grade 2,4-D acid.     

The Effects of Love Canal Soil Extracts on Maternal Health and Fetal Development in Rats

The Effects of Love Canal Soil Extracts on Maternal Health andFetal Development in Rats. SILKWORTH, J.B., TUMASONIS, C, BRIGGS,R.G., NARANG, A.S., NARANG, R.S., REJ, R., STEIN, V., MCMARTIN,D.N., AND KAMINSKY, L.S. (1986). Fundam. Appl. Toxicol. 7,471-485.The effects of a solvent extract of the surface soil of theLove Canal chemical dump site, Niagara Falls, New York, andof a natural extract, or leachate, which is drained from thecanal for treatment, on the maternal health and fetal developmentwere determined in rats. The solvent extract, which was contaminatedwith 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) at 170ppb and numerous other chlorinated organic compounds with theprimary identified components being the isomers of benzenehexachloride(BHC), was dissolved in corn oil and administered by gavageto pregnant rats at 0,25,75, or 150 mg crude extract/kg/dayon Days 6-15 of gestation. A 67% mortality was observed at thehighest dose. The rats were sacrificed on Day 20. Dose-relatedincreases in relative liver weight accompanied by hepatocytehypertrophy were observed at all dose levels. Fetal birthweightwas decreased at 75 and 150 mg extract/kg/day. No major treatment-relatedsoft tissue or skeletal malformations, except for delayed ossification,were observed. Based on literature values for BHC, all of theobserved toxicity could be accounted for by the BHC contaminantsof the extract. The crude organic phase of the leachate wasadministered to pregnant rats at 0, 10, 100, or 250 mg/kg/dayas described above. Maternal weight gain decreased at 100 and250 mg/kg/day, accompanied by 5 and 14% maternal mortality,and 1 and 3 dead fetuses, respectively. Early resorptions andthe percentage of dead implants increased whereas fetal birthweightswere decreased at 250 mg/kg/day. No major treatment-relatedsoft tissue or skeletal malformations, except for delayed ossification,were observed. The primary components of the complex leachateby mass were tetrachloroethanes; however, 2,3,7,8-TCDD, whichwas present at 3 ppm, probably accounted for all the observedtoxicity.     

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.