Toxicity evaluation and environmental risk assessment of 2-methyl-4-chlorophenoxy acetic acid (MCPA) on non-target aquatic macrophyte Hydrilla verticillata.

Aquatic plants in agricultural landscapes play a vital role in maintaining the ecological integrity within the aquatic systems while facing an array of disturbances. Among them, information on herbicide exposure on non-target aquatic plants is scarce. The present study was designed to fill this information gap by detecting the impacts of 2-methyl-4-chlorophenoxyacetic acid (MCPA) on Hydrilla verticillata using morpho-anatomical and physiological biomarkers and assessing the environmental risk of MCPA to the non-target environment. H. verticillata was exposed to different MCPA concentrations (10, 100, 500, 1000 µg/L) and control (0 µg/L) for 7 days. At the end of the experiment, plant growth, pigments, H2O2 content, peroxidase activity (POD) and plant anatomy were compared. The environmental risk was assessed using predicted environmental concentration/predicted no effect concentration (PEC:PNEC) ratio, hazard quotient (HQ) and hazard index (HI). Control plants exhibited the highest growth, and a growth decline was noted in parallel to MCPA exposure, where a similar trend was detected for the plant pigment contents. MCPA induced chlorosis and oxidative stress in H. verticillata. Risk analysis detected high values for PEC:PNEC ratios (3-9), HQ (1.92-5.79) and HI (28.15). MCPA-exposed H. verticillata could recover once those plants received natural conditions. Overall, present findings showed the negative impacts of MCPA on non-target aquatic plant H. verticillata. These findings will be useful to clarify the interaction between agrochemicals and non-target aquatic plants. Such information would benefit to decide the criteria in aquatic ecosystem management.

Kidney biomarkers in MCPA-induced acute kidney injury in rats: reduced clearance enhances early biomarker performance.

For improved early detection and assessment of severe acute kidney damage following accidental or intentional ingestion of the herbicide MCPA, we compared a panel of 14 novel kidney injury biomarkers with plasma creatinine. Male Wistar rats received four different oral doses of MCPA and plasma and urine biomarker levels were measured at 8, 24 and 48 h after MCPA exposure. Diagnostic performances using absolute levels, urine levels normalized to urine creatinine or urinary excretion rate were determined by ROC analysis. Plasma creatinine remained the best early biomarker for predicting histological changes at 48 h. The performance of plasma cystatin C in mirroring kidney function was similar to that of plasma creatinine. While urine concentrations were generally less predictive, normalization by urine creatinine greatly improved the performance of several biomarkers. This may be due to an apparent amplification of the biomarker signal on normalizing to creatinine, in the presence of a declining glomerular filtration rate prior to reaching steady state. Normalized 8 h osteopontin and albumin concentrations outperformed other normalized biomarkers in predicting histological changes at later times. Normalized urinary kidney injury molecule-1 at 48 h also correlated well with the degree of kidney damage.

Layered double hydroxides as supports for the slow release of acid herbicides.

A Mg/Al layered double hydroxide (LDH) was intercalated with the anionic herbicides 2,4-D, MCPA, and picloram by using three different methodologies: (i) direct synthesis (DS), (ii) regeneration (RE), and (iii) ion exchange (IE). The resulting complexes were characterized and assayed by batch release and column leaching tests, aiming at the controlled release of these herbicides. All the tested LDH-herbicide complexes displayed similar slow herbicide release properties in water, although the IE method seemed to result in complexes with a greater fraction of herbicide in a readily available form. Apparently, the LDH-herbicide complexes released most of the active ingredient present in the complexes at the end of the batch release experiment. This was attributed to the replacement of the intercalated herbicide by carbonate and hydroxyl anions from the aqueous solution. Compared to the free herbicides, the application of the three LDH-herbicide complexes (RE) to soil columns resulted in reduction in the maximum herbicide concentration in leachates and led to the retardation of herbicide leaching through the soil. All LDH-herbicide complexes presented an herbicidal efficacy similar to that of the free (technical) herbicides. Our results indicated the potential applicability of LDHs as supports for the preparation of slow release formulations of acid herbicides such as 2,4-D, MCPA, or picloram.

Teratological study of the herbicide 4-chloro-2-methylphenoxyacetic acid in rabbits.

4-Chloro-2-methylphenoxyacetic acid (MCPA) is an aryloxyacetic acid derivative categorised as a plant hormone herbicide. The aim of the study was to evaluate the effect of MCPA on pregnant females and the prenatal development of rabbits. The substance tested was administered orally to pregnant New Zealand White rabbits from day 6 to day 27 of gestation at doses of 5, 10 and 25 mg kg(-1) day(-1). The animals were killed on day 28 of gestation and live fetuses were examined for gross, skeletal and visceral anomalies. Administration of MPCA did not induce any signs of maternal toxicity. There was a significant decrease of fetal and placental weight compared with controls at the highest dose of MPCA. No adverse effect of the substance tested was seen on uterine content variables, e.g. corpora lutea, pre-implantation and post-implantation loss, early, late resorptions, live and dead fetuses and sex ratio. Rabbit fetuses treated with the middle and highest doses of MPCA had a significantly elevated incidence of skull and pelvic bone delays. In conclusion, prenatal administration of MCPA did not exhibit a teratogenic effect on rabbit fetus development.

Herbicide sensitivity of transgenic multiple herbicide-tolerant oilseed rape.

Glyphosate and glufosinate-ammonium herbicide tolerance traits were combined into both winter and spring lines of Brassica napus L. This allowed the study of possible interactions between these transgenes in two genetic backgrounds when treated with a variety of herbicides. Selective herbicides that are commonly used within Brassica crops showed no adverse effects on the transgenic plants or their null controls. Lines containing both glyphosate and glufosinate transgenes remained tolerant to their respective herbicides, regardless of the presence of the second tolerance transgene. Lines containing only a single transgene retained tolerance to the encoded trait and did not show cross-tolerance to the second. Null lines were killed by either herbicide. All plant lines, regardless of their transgene content, were found to be equally susceptible to three herbicides (paraquat, metsulfuronmethyl and mecoprop), commonly used to remove volunteer B napus from succeeding crops and set-a-side land.

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.

Studies on phenoxy acid herbicides. II. Oral and dermal uptake and elimination in urine of MCPA in humans.

Five healthy volunteers were given 15 micrograms MCPA per kg body weight. The highest concentration in plasma, 0.15 micrograms/ml, was found after 1 h. In urine the excretion during the first 6 h was 0.46 microgram/min and 40% of given dose was excreted during the first 24 h. About 1 g of MCPA emulsion was applied on the skin of the thigh and was washed away after 2 h. Plasma level slowly increased with maximum, 0.12 micrograms/ml, after 24 h. In urine a slow excretion continued for up to 5 days later with maximum 24-48 h after application. In agricultural field exposure urinary MCPA should be estimated immediately after stop of exposure as well as 24 h after exposure. Levels under 0.5 micrograms/ml of MCPA in urine might be used as a practical biological level for good work practice. In spot samples the concentration of urine must be considered.

[Morphological studies of chronic toxicity of Chwastox D]. / Badania morfologiczne nad skrócona przewlekla toksycznoscia chwastoxu D.

Chwastox D--herbicide for killing dicotyledonous weeds was evaluated toxicologically, basing on studies on the mass and morphological picture of internal organs of rats receiving, over 13 weeks, 15, 60, 240 and 960 mg/kg of feeding stuff containing this herbicide. The animals exposed for 13 weeks to different doses of Chwastox D were found to develop inspecific pathomorphotic changes, like disturbed circulation, retrogressive, progressive and inflammatory changes. The pathomorpohologic changes were found to be increased with 240 and 960 mg of stuff. The observations indicated that the maximum allowable dose for rats is 60 mg/kg of the feeding stuff.