[Setting a maximum allowable concentration for urea in reclaimed potable water and evaluating the nature of its biological action].

The purpose of the study was to identify maxim allowable concentrations of urea in reclaimed potable water. The urea concentration equal to 80 mg/l is the threshold dose influencing the taste and flavor of water. Urea is a low toxicity substance (LD50 = 14,300 mg/kg), the effect of which is not cumulative. However, when used in high doses it affects bioenergetic and cholinergic processes and causes changes in ECG, higher nervous activity and visceral structure. It has been shown that when applied to warm-blooded animals the acting dose of urea is 14.3 and 1.43 mg/kg (1/1000 and 1/10000 LD50), the threshold dose is 0.72 mg/kg (1/20000 LD50), and the ineffective dose is 0.36 mg/kg (1/40000 LD50) which amounts to the concentration of 10 mg/l. In terms of toxic effects the dose equal to 10 mg/l is taken to be the maximally allowable concentration of urea. It is recommended to use the Laham biotest for measuring urea in water.