thiourea; thiocarbamide

Toxicity to soil macroorganisms except arthropods

Description of key information

Two 28-d studies on the toxicity to Eisenia foetida (endpoint recorded: mortality) are available. The studies were conducted by Korte et al. (1984) and Friesel et al. (1984). The reported LC50 values(28 d) were > 1,000 mg/kg substrate and equal to 3,550 mg/kg substrate, respectively. In addition, in the limit test conducted by Korte et al. (1984), no sublethal effects could be observed at 1,000 mg/kg substrate. Therefore thiourea is considered to be non-toxic to earthworms.

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

3 550 mg/kg soil dw

Additional information

Two 28-d studies on the toxicity to soil macroorganisms (except arthropods) are available. The studies were conducted by Korte et al. (1984) and Friesel et al. (1984). Due to deficiencies in study documentation they are used in a weight-of-evidence approach in the assessment of thiourea.

In the 28 day limit test on the acute toxicity of thiourea to earthworms (Eisenia foetida) conducted by Korte et al. (1984), earthworms were exposed to thiourea at a nominal concentration of 1,000 mg/kg dry weight of artificial substrate. The substrate consisted of white peat, bentonite, cow manure, lime, quartz sand and water. The reference chemical used was chloroacetamide. The 28 day LC₅₀ for thiourea was determined to be > 1,000 mg/kg of substrate. In addition, no sublethal effects could be observed at that concentration.

In the second 28 day acute toxicity study, earthworms (Eisenia foetida) were exposed to thiourea at nominal concentrations of 0, 1500, 3000, 4500, and 6000 mg/kg dry weight of artificial substrate. The substrate had the same composition as that used by Korte et al. (1984). In addition, the exact amounts of the individual constituents were reported (65 g white peat, 32.5 g bentonite, 3.25 g cow manure, 6.5 g lime, 542.75g quartz sand, 227.5 ml water). Similar to Korte et al. (1984), chloroacetamide was used as reference substance. The experiment was carried out in accordance with the “Guideline for the testing of the toxicity of chemicals and plant treatment products in earthworms (Eisenia foetida Sav.)”. The 28 day LC₅₀ was 3,550 mg/kg of substrate.

Based on the findings summarised above thiourea is considered to be non-toxic to earthworms.

In addition, Glazer & Orion (1984) investigated the effects of thiourea on the development of nematodes. Excised tomato roots, growing on basal medium and inoculated with eggs of Meloidogyne javanica, were exposed to thiourea concentrations in the range of 6‒46 mg/litre. A 96-h exposure at thiourea concentrations of 12 mg/litre inhibited nematode development: Only 36 % matured to adults (in the untreated control: 90%) after an observation period of 4 weeks. For M. javanica (second larval stage), Tylenchulus semipenetrans (second larval stage), and Pratylenchus thornei (adult and juvenile organisms), no increased mortality was found after incubation in aqueous solutions of thiourea at concentrations up to 100 mg/litre for 96 h. The authors furthermore demonstrated that thiourea is taken up via the plant roots and that the nematicidal effect is systemic.

The endpoints investigated by Glazer & Orion (1984) are non-standard and the publication was rated as non-reliable due to deficiencies in documentation. The results are referenced for information purposes only.