Absorption, distribution, metabolism and excretion of 4-chloro-2-methylphenoxyacetic acid (MCPA) in rats.

The metabolism of 14C-MCPA (4-chloro-2-methylphenoxyacetic acid) in male and female rats was compared to that of 14C- MCPA dimethylamine salt (MCPA.DMA) or 14C-MCPA ethylhexyl ester (MCPA-EHE) in adsorption, distribution, metabolism and excretion studies. Compounds were administered by the oral route. The studies demonstrated the bioequivalence of the various forms of MCPA, established the extent of metabolism and metabolite identity. Following single or multiple oral administration of 5 mg/kg 14C-MCPA quantitative recovery of radioactivity, predominantly in urine, was obtained within 168 h. Rats dosed at 100 mg/kg showed similar absorption kinetics but apparent saturation of urinary excretion led to a prolonged elimination phase. MCPA was not extensively metabolised but the oxidation product HMCPA (4-chloro-2-hydroxymethylphenoxyacetic acid) was found at low levels, together with the glycine conjugate. These metabolites were more prominent shortly after dosing, suggesting that MCPA is not retained in the liver and that these metabolites may be excreted faster than MCPA itself. MCPA.DMA and MCPA-EHE were very rapidly converted into MCPA and toxicokinetics and metabolism were indistinguishable from parent compound.

Dissipation of racemic mecoprop and dichlorprop and their pure R-enantiomers in three calcareous soils with and without peat addition.

Two racemic herbicides, mecoprop (R,S-MCPP) and dichlorprop (R,S-DCPP), as well as their enantiopure R-forms, were incubated in three calcareous soils at 15 degrees C and 80% of their field capacity to try to elucidate their behaviour in soil and compare the dissipation rates when racemic and enantiopure compounds are used. Quantitation of pesticides is made by HPLC and the R/S ratio by GC-MS. The inactive S-enantiomer from the racemic forms persists longer than the R-forms in silt and sandy loam soils, but for shorter time in the clay loam soil. The pure R-enantiomers, both for MCPP and DCPP, after incubation in soil, are partially converted into their S-forms. In all cases, the dissipation of racemic and pure enatiomeric forms is lower in the clay loam soil than in the silt and sandy loam soils. The R-forms' peristence, in the three soils, is approximately two times lower when they are incubated alone than when they are incubated as racemic compounds. When peat is added, the persistence of these herbicides in the silt and sandy loam soils increases, while in the clay loam soil it decreases. Besides, in the clay loam soil, the enantiomeric ratio (ER) changes from its S-preferential degradation to a preferential degradation of its R-form, so an increase in the persistence of the inactive S-form occurs.

Biodegradation in laboratory activated sludge plants and aquatic toxicity of herbicides.

The biodegradation and the aquatic toxicity of four herbicides (isoproturon, terbuthylazine, mecoprop, metamitron) were investigated. Laboratory activated sludge plants were used for biodegradation experiments. The biodegradation of mecoprop reached nearly 100%, the other herbicides were not eliminated by biodegradation. The acute Daphnia magna 24-h assay, the algal 72-h inhibition test, and the recently developed lemna growth inhibition 7-d test were applied to evaluate the biological effects of herbicides as original substances. EC 50 and EC 10 values were determined. Algal and lemna test show that isoproturon and terbuthylazine are both much more toxic than mecoprop and metamitron. Daphnids are generally less sensitive against herbicides than plants. Biodegradation and toxicity test were coupled for mecoprop to assess biological long-term effects of possible biodegradation products of this herbicide. The effluents of the laboratory activated sludge units were used in toxicity tests (Daphnia magna 21-d reproduction test, lemna growth inhibition 7-d test). No inhibiting effect on the tested organisms was observed.

Toxicokinetics, including saturable protein binding, of 4-chloro-2-methyl phenoxyacetic acid (MCPA) in patients with acute poisoning.

Human data on protein binding and dose-dependent changes in toxicokinetics for MCPA are very limited. 128 blood samples were obtained in 49 patients with acute MCPA poisoning and total and unbound concentrations of MCPA were determined. The Scatchard plot was biphasic suggesting protein binding to two sites. The free MCPA concentration increased when the total concentration exceeded 239mg/L (95% confidence interval 198-274mg/L). Nonlinear regression using a two-site binding hyperbola model estimated saturation of the high affinity binding site at 115mg/L (95%CI 0-304). Further analyses using global fitting of serial data and adjusting for the concentration of albumin predicted similar concentrations for saturable binding (184mg/L and 167mg/L, respectively) without narrowing the 95%CI. In 25 patients, the plasma concentration-time curves for both bound and unbound MCPA were approximately log-linear which may suggest first order elimination, although sampling was infrequent so zero order elimination cannot be excluded. Using a cut-off concentration of 200mg/L, the half-life of MCPA at higher concentrations was 25.5h (95%CI 15.0-83.0h; n=16 patients) compared to 16.8h (95%CI 13.6-22.2h; n=10 patients) at lower concentrations. MCPA is subject to saturable protein binding but the influence on half-life appears marginal.

Influence of strain and sex on the metabolic profile of rats in repeated dose toxicological studies.

The impact of the strain on the metabolite profile of plasma samples in rats dosed with 2500 ppm 2-methyl-4-chlorophenoxyacetic acid (MCPA acid) or 45 mg/kg bw/day 4-chloro-3-nitroaniline (4C3N) for 4 weeks was evaluated. Four different strains were used: two Wistar strains (Crl:WI(Han), Han:RCC:WIST(SPF)), one Sprague-Dawley (Crl:CD) and one Fisher strain (F-344/Crl). The metabolite profiles in the plasma were measured by LC-MS and GC-MS. The profound changes of the metabolite values induced by the MCPA acid treatment outweighed slight deviations caused by physiological variations between the different rat strains. The metabolome changes of the MCPA acid in all strains could be related to toxicological "mode of action" patterns (peroxisome proliferator, renal organic anionic transporter inhibition) with Crl:WI(Han) rats as reference strain. 4C3N administration led to extravascular hemolytic anemia with a small number of metabolome changes, which were strain dependent. The metabolome pattern associated with "hemolytic anemia" established with the reference strain (Crl:Wi(Han)) was not sufficiently similar in other strains. Thus, comparable metabolome profiles were obtained in different rat strains for a compound inducing profound metabolite changes. For a compound with a weak profile the results were more variable and appeared to be strain dependent.

Analysis of phenoxyacetic acid herbicides as biomarkers in human urine using liquid chromatography/triple quadrupole mass spectrometry.

Phenoxyacetic acids are widely used herbicides. The toxicity of phenoxyacetic acids is debated, but high-level exposure has been shown to be hepatotoxic as well as nephrotoxic in animal studies. An inter-species difference in toxic effects has been found, with dogs particularly susceptible. In this study a method using liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) is described for the analysis of 4-chloro-2-methylphenoxyacetic acid (MCPA), and its metabolite 4-chloro-2-hydroxymethylphenoxyacetic acid (HMCPA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in human urine. The urine samples were treated by acid hydrolysis to degrade possible conjugations. The sample preparation was performed using solid-phase extraction. Analysis was carried out using selected reaction monitoring (SRM) in the negative ion mode. Quantification of the phenoxyacetic acids was performed using [(2)H(3)]-labeled MCPA and 2,4-D as internal standards. The method was linear in the range 0.05-310 ng/mL urine and has a within-run precision of 2-5%. The between-run precision in lower concentration ranges was between 6-15% and between 2-8% in higher concentration ranges. The limit of detection was determined to 0.05 ng/mL. The metabolites in urine were found to be stable during storage at -20 degrees C. To validate the phenoxyacetic acids as biomarkers of exposure, the method was applied in a human experimental oral exposure to MCPA, 2,4-D and 2,4,5-T. Two healthy volunteers received 200 microg of each phenoxyacetic acid in a single oral dose followed by urine sampling for 72 h post-exposure. After exposure, between 90 and 101% of the dose was recovered in the urine. In the female subject, 23%, and in the male subject 17%, of MCPA was excreted as HMCPA.

Acute MCPP intoxication: report of two cases.

1. Two cases of serious intoxication with phenoxy herbicides (MCPP) are reported. 2. Both patients had central nervous system involvement, became unconscious and had an inadequate respiration. Muscle cramps and rhabdomyolysis with renal failure were noted in both. Shortly after admission both patients developed a serious decrease in arterial blood pressure (160/80 mmHg to 80/45 mmHg). In one patient this was demonstrated to be caused by a reduction in peripheral vascular resistance. 3. Plasma concentration of MCPP in patient 2 was 298 mg/l (3-4 h after ingestion). The plasma t1/2 was about 17 h. MCPP plasma elimination probably follows first-order kinetics.

The pharmacokinetics of chlorinated phenoxy acid herbicides: a literature review.

The chlorinated phenoxy acid herbicides (CPAHs) appear to have similar pharmacokinetics. They are rapidly and almost completely absorbed from an oral dose. They distribute to other tissues and are highly protein-bound in the plasma. The CPAHs are rapidly eliminated unchanged in the urine by an active process in the kidneys. Increasing doses apparently influence absorption, metabolism, distribution and elimination of the CPAHs so that biological effects are increased. Combinations of CPAHs are likely to result in additive or potentiated biological effects. Data suggest that CPAH toxicosis may be alleviated by treatment with fluids and bicarbonate to increase urinary pH and volume, thereby increasing excretion.

Absorption, metabolism and excretion of 4-chloro-2-methylphenoxyacetic acid (MCPA) in rat and dog.

1. The oral no overall adverse effect level (NOAEL) for chronic toxicity of 4-chloro-2-methylphenoxyacetic acid (MCPA) in rat is approximately 1.3 mg kg(-1) and in dog is 0.2 mg kg(-1). In an attempt to explain the difference in toxicology between these species, rats and dogs were orally dosed with (14C)-MCPA at 5 or 100 mgkg(-1) and plasma toxicokinetics, rates and routes of excretion and biotransformation were investigated. 2. Elimination of radioactivity in rat plasma was biphasic and in dog was monophasic. Rat eliminated radioactivity from plasma significantly faster than dog (approximate values biased on total radioactivity: 5 mg kg(-1) rat: t 1/2 dist 3.5 h, t 1/2 elim 17.2-36.2 h, AUC(0-infinity) 230 microg equiv hg(-1); 5 mg kg(-1) dog: t 1/2 47h, AUC(0-infinity) 2,500 microg equiv h g(-1); 100 mg kg(-1) rat: t 1/2 dist 10h, t 1/2 elim 10.27-25.4h, AUC(0-infinity) 5,400 microg equiv hg(-1); l00 mg kg(-1) dog: t 1/2 h, AUC(0-infinity) 20,500 microg eqiv h g(-1). 3. For both species, the principal route of excretion was in urine but renal elimination was notably more rapid and more extensive in rat. 4. In both rat and dog, excretion of radioactivity was mainly as MCPA and its hydroxylated metabolite hydroxymethylphenoxyacetic acid (HMCPA). In rat, both were mainly excreted as the free acids although a small proportion was conjugated. In dog, the proportion of HMCPA was increased and the majority of both species was excreted as glycine or taurine conjugates. 5. These data, along with previously published accounts, indicate that renal elimination of MCPA in dog is substantially slower than in rat resulting in disproportionate elevation of AUC (based on total radioactivity) in dog compared with rat.

Activity of agricultural chemicals to modify mitomycin C induced growth inhibition of Bacillus subtilis in the rec assay.

Rec assay of agricultural chemicals, MCPA-E, MCPA, CNP and PCNB was conducted. It was found that MCPA-E and MCPA accelerated the growth-inhibition originally induced by Mitomycin C in the rec- strain.

Distribution of three common chlorophenoxyacetic acid herbicides into the rat brain.

The distribution of three common 14C-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 of 14C-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.

Plant and soil enantioselective biodegradation of racemic phenoxyalkanoic herbicides.

The biodegradation of the chiral phenoxyalkanoic herbicides 2-(2,4-dichlorophenoxy)propionic aid (2,4-DP) and 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) was investigated using enantioselective HPLC and chiroptical detection. Racemic mixtures of 2,4-DP and MCPP were applied to three species of turf grass, four species of broadleaf weeds, and soil. Preferential degradation of the S-(-) enantiomer of each herbicide was observed in most species of broadleaf weeds and soil, while the degradation in all species of grass occurred without enantioselectivity. The biodegradation in all systems appeared to follow pseudo first-order kinetics with the fastest degradation occurring in broadleaf weeds, followed by the grasses. The slowest degradation was observed in soil. The results of this work illustrate the need to characterize both enantiomers of chiral agrochemicals in order to have an accurate understanding of their distribution and fate in the environment.

Renal handling of 2-methyl-4-chlorophenoxyacetic acid (MCPA) in rats.

Following i.p. administration of various doses of 2-methyl-4-chlorophenoxyacetic acid (MCPA), ca. 50% is excreted during a 5-h diuresis experiment. After i.p. administration of MCPA, virtually no distribution occurs (Vrel = 18% of the body weight). Renal excretion of MCPA can be accelerated by inhibition of its renal tubular reabsorption. The distinct inhibition of renal excretion of MCPA by simultaneous administration of probenecid or p-aminohippurate (PAH) indicates the active tubular transport of MCPA; this transport process can be stimulated by treatment of rats with triiodothyronine. Active tubular transport of MCPA was confirmed by measurement of MCPA accumulation in renal cortical slices, both under aerobic and anaerobic conditions. Accumulation of MCPA under anaerobic conditions indicates an additional passive uptake and binding of MCPA in kidney tissue in accordance with the high degree of binding to plasma albumin (85%).

Antioxidant and detoxifying enzymes in the liver and kidney of pheasants after intoxication by herbicides MCPA and ANITEN I.

The activity of antioxidant and detoxifying enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx), glutathione reductase, glutathione-S-transferase (GST), the contents of thiobarbituric acid reactive substances, and the superoxide dismutase and glutathione-S-transferase isoenzyme patterns, were determined in the liver and kidney of pheasants after acute intoxication by herbicides MCPA and ANITEN I. In the liver, the activity of antioxidant enzymes was significantly decreased in the group given ANITEN I. New superoxide dismutase isoforms (pI 6.30, 6.85, 7.00) and higher intensity of isoform with pI 6.60 were observed after isoelectrofocusing in all experimental groups. In the kidney, the activity of superoxide dismutase was significantly decreased, and a higher intensity of superoxide dismutase isoforms (pI 6.00 and 6.60) was observed in all experimental groups. The contents of thiobarbituric acid reactive substances were significantly increased in the group with ANITEN I. The glutathione-S-transferase isoenzyme pattern was studied by using subunit-specific substrates and by Western blotting. The activity of glutathione-S-transferase with ethacrynic acid and cross-reactivity with rat subunit 7 was lower in all experimental groups in the kidney and liver, except in the liver of the group given a higher dose of ANITEN I. In this group, we have found a 2.10-fold higher activity to ethacrynic acid and a strong induction of subunit 7.