Introduction:
Over the last thirty years, new, fourth-generation herbicides from the class of sulfonylurea derivatives have been widely used. They are used in small doses (5–50 g/ha), providing high efficiency. Considering the possibility of contact with pesticides by the general population and their entry into the body with food, water and air, it is important to assess the degree of toxicity and danger of pesticides in different ways of drug administration.

Methods:
To establish the degree of damaging effect on the body with long-term administration, a study of the chronic action of a drug based on chlorsulfuron was conducted. The experiments were performed on outbred sexually mature white male rats weighing 220–240 g, 20 animals per group. The statistical group included 6 animals. Chlorsulfuron was administered with a metal probe in a 30% solution into the stomach. The doses tested were 0.5; 5.0; 25 and 50 mg/kg b.w. The toxic effect was judged by changes in integral, hematological, biochemical and physiological indices. A morphofunctional assessment of the long-term effect of chlorsulfuron on the body of warm-blooded animals was carried out.

Results:
The toxicological parameters of chlorsulfuron were determined during long-term oral exposure. It was found that the studied substance has a polytropic effect during chronic oral administration to warm-blooded animals at doses of 25 and 50 mg/kg b.w. The experimental animals showed changes in a number of hematological and biochemical parameters, as well as changes in the activity of antioxidant defense enzymes. At a dose of 50 mg/kg b.w., after 3 months from the start of the challenge, a reliable dose-dependent increase in SOD activity was observed. With an increase in the exposure time (after 12 months), a reliable dose-dependent decrease in SOD activity was recorded in the rats' bodies. The structural and functional parameters of the studied organs revealed their varying degrees of sensitivity to the effects of different doses of chlorsulfuron. At the maximum effect of chlorsulfuron at a dose of 50 mg/kg (Group IV), among the studied structural and functional parameters, no statistical differences from the control values were found in the following organs: heart, testicle, thymus, spleen, large intestine, pancreas and thyroid gland, which allows us to assume that this drug does not affect these organs. The absence of pathological changes in the internal organs of the experimental animals and morphofunctional changes and activity of antioxidant defense enzymes when exposed to chlorsulfuron at a dose of 0.5 and 5.0 mg/kg b.w. allowed to establish a no-effect (NOEL) dose of 5 mg/kg.

Conclusions:
Based on the results of the studies, the no-effect level (NOEL) of chlorsulfuron was set at 5 mg/kg b.w., and the effective level was 25 mg/kg b.w.