Toxicity of hercides 2,4-D and MCPA for Rats and Rabbits

Kobal S., M. V. Budihna: Toxicity of Herbicides 2,4-D and MCPA for Rats and Rabbits. Acta Vet. Brno 1999, 68: 281-290. A subacute toxicity test using 2,4-dichlorophenoxyacetic acid (2,4-D, 10 mg.kg-1 and 100 mg.kg-1) and 4-chloro-2-methylphenoxyacetic acid (MCPA, 15 mg.kg-1 and 150 mg.kg-1) was carried out on Wistar rats (n = 60) and New Zealand White rabbits (n = 30) of both sexes. The lower doses of 2,4-D and MCPA used in our experiments were chosen based on the estimate that such doses would be present in feed of plant origin treated with the concentrations of both herbicides recommended by the manufacturer; the higher ones were sublethal doses. Herbicides 2,4-D and MCPA in our trial did affect neither body weight in adult rats and rabbits and their offspring nor weights of inner organs or the red and white blood cell count. The mucous membrane of the stomach and small intestines in rats treated with high doses of both herbicides was slightly inflamed and swollen. In rabbits, some of the semen characteristics changed during the trial; both herbicides acted in different directions. At the end of the trial the concentration of serum testosterone was significantly higher (p < 0.05) in rabbits treated with MCPA than in controls. The number of surviving young per litter at weaning in the MCPA group of rabbits was lower than in controls. No evident toxic effects on the viability and the ossification processes were observed in the young of treated rabbits. Aryloxyacetic acid-derivative herbicides, plants, recommended dose, subacute toxicity, reproduction toxicity Substances used as herbicides should exert highly selective effects on plants, and have low toxicity for micro-organisms, fish, insects, domestic and wild animals, and humans. In acute poisoning of rats, poultry, cattle, dogs, and humans with aryloxyacetic acid derivative herbicides, cases of metabolic acidosis, respiratory alkalosis, neuropathy, myopathy (Beasley et al. 1991; Paggiaro et al. 1974; Park et al. 1977; Prescot t et al. 1979), bradycardia, changes in electrocardiogram (Prokofyeva 1988), a drop in acetylcholinesterase activity and necrosis of the muscles (Bernard et al. 1985), changes in blood constituent values (Prokofyeva 1988), necrosis of the liver, hyperplasia of Bowman’s capsule, and adenomas (Loktionov 1986) were repeatedly diagnosed. A dose of 200 mg.kg-1 of body weight of the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide has been cited as exceptionally toxic for cows, causing apathy, anaemia of the mucous membranes, along with a drop in body temperature (Lokt ionov 1986). In chronic poisoning of poultry and pregnant sows motor disorders, albuminuria, degeneration of liver and kidney appeared, and increased mortality among newborn piglets or reduced egg production in poultry were found (Loktionov 1986). Administration of aryloxyacetic acid-derivative herbicides during organogeny led to disorders in foetuses such as dropping eyelids, hydrocephalus, split hard palate, anomalies of the heart, kidneys, and skeleton (Abbott et al. 1989; Birnbaum et al. 1989; Courtney et al. 1970; Courtney and Moore 1971; Emerson et al. 1970; Khera et al. 1971; Loktionov and Tsyrempilov 1987; Vos et al. 1974). ACTA VET. BRNO 1999, 68: 281–290 Address for correspondence: Dr. Silvestra Kobal, PhD Institute of Physiology, Pharmacology and Toxicology Veterinary Faculty University of Ljubljana Gerbiaeva 60, 1000 Ljubljana, Slovenia Phone: +386 61 177 91 00 Fax: +386 61 332 243 E-mail: KobalSi@mail.vf.uni-lj.si http://www.vfu.cz/acta-vet/actavet.htm In the synthesis of aryloxyacetic acid-derivative herbicides, tetrachlorodibenzo-p-dioxin (TCDD), having a teratogenic effect, is formed as a by-product (Abbott and Birnbaum 1989; Abbott and Birnbaum 1990; Bernard et al. 1985). The maximum permitted amount of TCDD in herbicides is 0.1 mg.kg-1 of herbicide (Janj ia 1985). In rats treated with TCDD the serum concentration of testosterone was found to be 10 -75% lower than in non-treated animals (Kleeman et al. 1990), whereas secretion of the LH hormone was not changed (Bookstaff et al. 1990a; Bookstaff et al. 1990b). Also decreased concentrations of cortisone and of thyroid hormones T3 and T4 were observed (Hermansky et al. 1988; Roth et al. 1988). MCPA and 2,4-D were found to be slightly mutagenic at concentrations between 250 and 750 μg/plate in the strain Salmonella typhimurium TA 97 (Kappas 1988). In the present study we determined whether sublethal doses of aryloxyacetic acid derivative herbicides 2,4-D and MCPA, substances categorised as plant hormone herbicides were able to produce toxic effects in either adult rats and rabbits or in their offspring. We were particularly interested in the possible effect of the herbicides on processes linked to reproduction in females and males as well as on foetuses, and the development of the young until weaning. For this purpose we chose the doses of 2,4-D and MCPA which could be contained in the feed of plant origin treated with the concentrations of both herbicides as recommended by the manufacturer. Materials and Methods We carried out two sets of experiments on 60 Wistar rats and 30 New Zealand rabbits, using the herbicides 2,4D and MCPA. Experiments on rats Sixty Wistar rats (30 females and 30 males aged two months, body weight 200 230 g) were divided into four test groups and one control group, each comprising five females and five males in the control group, ten males and ten females were included. The groups of animals received 2,4-D, 100 mg.kg-1 b. w., 2,4-D, 10 mg.kg-1 b. w., MCPA, 150 mg.kg-1 b. w., MCPA, 15 mg.kg-1 b. w., tap water (control group). Experiments lasted 90 days for male rats. In females, experiments with low doses of 2,4-D and MCPA lasted 45 days (30 days before and during mating, and 10 days after the last mating day), and in those with high doses 35 days (30 days before and during mating). Animals were administered either aqueous solution of the herbicide or clean tap water (control group) in equal volumes of 1 ml.kg-1 of body weight orally onto the root of the tongue with a stomach tube, each second day. Experiments were carried out on two-month-old sexually mature females that were kept with males of the same age (one male to five females of the same group). After five days together the males were returned to the cages holding males in a single group. On day 15 of pregnancy, the females were moved to cages with barriers for the individual parturition. The administration of herbicides began one week after transfer of the animals. The adult rats were sacrificed one to three days following administration of the last herbicide dose, and all rat offspring on day 21 after birth. All rats were anaesthetised by ether and bled to death. Experiments on rabbi ts In experiments on rabbits only low herbicide doses were used. Thirty New Zealand White rabbits (15 females aged five months and 15 males aged six months, body weight 2940 4070 g) were divided into three groups with five females and five males in each. These groups of animals received 2,4-D 10 mg.kg-1 b. w., MCPA 15 mg.kg-1 b. w., tap water (control group). The females were included into the experiment after first parturition. They were individually bred with the males of the same group, each female bred twice with the same male. The experiment using males lasted 90 days, the experiment using females lasted 48 days (30 days before and 18 days after mating). Animals received aqueous solution of the herbicide or tap water, 1 ml.kg-1 b. w., on the root of the tongue with a stomach tube, every second day. 282