UDC 615.285.7.099:618.33].076.9

I. L. Medved

On the Potential Hazard of the Embryotoxic Effects of the Herbicide Betanal (Experimental Data)

Kyiv Research Institute of Occupational Hygiene and Occupational Diseases

With the increasing use of chemicals in agricultural production, herbicides are becoming increasingly important; compounds of the carbamate group have proved effective among them. Although herbicides have a broad spectrum of action, under certain conditions they may exert toxic effects on workers and lead to adverse outcomes, including embryotoxic, teratogenic, gonadotoxic, and mutagenic effects [1, 3–5].

These considerations provided the rationale for experimental studies designed to identify embryotoxic effects of oral and inhalational exposure to Betanal.

Experiments were conducted on outbred white rats. Betanal was administered to the animals throughout pregnancy at a dose of \(1/100\,\mathrm{LD}_{50}\) (40 mg/kg, a subthreshold dose for repeated exposure based on integrated indices) and at concentrations of 30, 2, and 0.5 mg/m³ (threshold and subthreshold concentrations based on integrated indices).

To identify teratogenic effects, an experiment was conducted in which rats were given a single toxic dose of Betanal—\(1/2\,\mathrm{LD}_{50}\) (2000 mg/kg)—on day 9 of pregnancy (one of the critical periods of pregnancy, placentation).

Embryotoxicity was assessed by the death of zygotes before implantation and embryos after implantation. In the assessment of teratogenic effects, the number of developmental anomalies of the internal organs was recorded using Wilson’s method as modified by A. P. Dyban [2]. In each experimental series, 100 embryos were analyzed.

Nucleic acid levels in the liver and myocardium of pregnant females, embryonic tissues, and the placenta were determined by the method of Fleck and Munro. The results were analyzed using Fisher’s method for a fourfold table, the \(\chi^2\) method [6], and the method proposed by I. A. Oivin [7].

Table 1 presents the experimental results. A single oral administration of Betanal on day 9 of pregnancy at a dose of \(1/2\,\mathrm{LD}_{50}\) caused an increase in the number of resorbed fetuses and in the number of cases of hemorrhage at various sites—

Table 1

Effect of Betanal on embryogenesis in white rats

Note. Here and in Table 2, an asterisk denotes statistically significant changes.

… (subcutaneous tissue, pericardium, abdominal cavity). Developmental anomalies were present in 19% of the fetuses (cryptorchidism).

Repeated administration of Betanal at a dose equal to \(100\,\mathrm{LD}_{50}\) was accompanied by a decrease in the number of implanted embryos and an increase in the number of resorbed fetuses. Of the 23 cases of developmental anomalies of the internal organs, 82% involved abnormalities of the genitourinary system (cryptorchidism, monorchism), and 18% involved abnormal brain development (hydrocephalus). The number of embryos with hemorrhages in the experimental group was twice that in the control group.

Embryonic development is characterized by intensive proliferative processes associated with increased synthesis of nucleic acids and protein.

Table 2 presents the results of determinations of DNA and RNA content in maternal and fetal tissues following a single oral exposure to \(1/2\,\mathrm{LD}_{50}\) of Betanal on day 9 of pregnancy and repeated administration at a dose equal to \(1/100\,\mathrm{LD}_{50}\).¹

¹ The biochemical studies were conducted with the consultation of I. A. Anina, Candidate of Biological Sciences.

The data presented show that, following single and repeated exposure to the preparation, RNA content increased in the liver of the pregnant female and in the placenta. A substantial decrease in this parameter was observed in the embryonic liver, and a smaller decrease in the embryonic myocardium.

DNA content increased in the embryonic liver and myocardium by 36% and 49%, respectively. Similar changes were found in the placenta. RNA content increased in pregnant rats exposed to Betanal. This increase may have resulted from extreme strain on the protein biosynthesis system.

On the basis of these data, it may be suggested that impaired nucleic acid metabolism plays a significant role in the mechanism of Betanal’s embryotoxic and teratogenic effects.

Repeated inhalation exposure at the threshold concentration of 30 mg/m³, as determined by integral indicators, and at a concentration of 2 mg/m³ increased overall embryonic mortality through the death of zygotes before implantation, which does not rule out a mutagenic hazard from Betanal. In support of this suggestion, eviden…

Table 2

Nucleic acid content (mg/kg) in selected organs of pregnant females and embryos following exposure to Betanal (\(M\pm m\))

…is supported by data on the cytogenetic activity of Betanal [8].

As the amount of the compound entering the body through the respiratory tract decreased, so did its teratogenic effect. At a concentration of 2 mg/m³, only 3 cases of cryptorchidism were observed, compared with 14 at a Betanal concentration of 30 mg/m³. The number of embryos with hemorrhages was much greater than in the control group and in the group exposed to the compound at 2 mg/m³. Betanal may penetrate the placenta and alter vascular permeability in the embryos, resulting in the observed pathology.

Notably, embryonic weight and length decreased in all experimental series except the inhalation experiment with Betanal at 2 mg per 1 m³. At a concentration of 0.5 mg/m³, it had no adverse effect on embryogenesis in albino rats.

The experimental results indicate that 2 mg/m³ can be considered the threshold concentration and 0.5 mg/m³ a subthreshold concentration for embryotoxic effects in rats. Comparison of the threshold concentration in the chronic experiment in albino rats based on overall indices (30 mg/m³) with the threshold for embryotoxic effects (2 mg/m³) leads to the conclusion that Betanal has a pronounced embryotoxic effect when inhaled.

Thus, Betanal exerts a pronounced embryotoxic effect when inhaled or ingested at the concentrations and doses tested. Its teratogenic and embryotoxic effects diminish as the amount entering the bodies of pregnant rats decreases. Exposure to Betanal is accompanied by disturbances in nucleic acid metabolism in certain organs of pregnant females and their embryos. The threshold concentration for embryotoxic effects is 2 mg/m³. Embryotoxicity indices were the limiting indicators of harm in setting the occupational air standard for Betanal.

On the basis of these findings, a maximum permissible concentration of 0.5 mg/m³ for Betanal in workplace air was recommended and approved.

When Betanal is used in agricultural production, its concentration in workplace air must be strictly monitored.

References

1. Vashakidze, V. I. In: Problems of Occupational Hygiene, Occupational Pathology, and Industrial Toxicology. Tbilisi, 1975, vol. 14, pp. 253–266.
2. Dyban, A. P., Baranov, V. S., and Akimova, I. M. Arkh. Anat., 1970, no. 10, pp. 89–99.
3. Ilyina, V. I. In: Second All-Union Symposium on the Clinical Features, Diagnosis, and Treatment of Diseases of Chemical Etiology: Abstracts of Papers. Kiev, 1977, pp. 23–29.
4. Kurinnyi, A. I., and Pilinskaya, M. A. Tsitol. i Genet., 1978, no. 4, pp. 353–357.
5. Maritson, L. V. Comparative Study of the Effects of Certain Pesticides Derived from Dithiocarbamic Acid on Embryonic Development and Reproductive Function in Animals. Abstract of candidate’s dissertation. Kiev, 1971.
6. Mitropolskii, A. K. Techniques of Statistical Computation. Moscow, 1971, pp. 323–333.
7. Oivin, I. A. Pat. Fiziol., 1960, no. 4, pp. 76–85.
8. Pilinskaya, M. A., Kurinnyi, A. I., Lvova, T. S., et al. Tsitol. i Genet., 1980, no. 6, pp. 41–47.

Received November 2, 1983.

Summary

Betanal causes pronounced embryotoxic and teratogenic effects following its one-time oral administration (1/2 LD₅₀) on the 9th day of pregnancy, as well as in continuous exposure to 1/100 LD₅₀ and to the concentration of 30 mg/m³. A threshold dose according to the embryotoxic effect is 2 mg/m³. MAC for Betanal in the work zone air is 0.5 mg/m³.