diuron (ISO); 3-(3,4-dichlorophenyl)-1,1-dimethylurea

Endpoint summary

Description of key information

The most sensitive LD50 is 1017 mg/kg bodyweight for Diuron when administered after rats were fed regular laboratory chow diet 28 days prior to dosing. In addition, there are several reliable studies showing that the rather low toxicity of Diuron and that the toxicity, if observed, was attributed to the diet and vehicle used in the studies and not to the substance itself.
All available acute inhalation studies on Diuron by the inhalation route showed no toxic effect at the tested concentrations. 
All available acute inhalation studies on Diuron by the dermal route showed no toxic effect at the tested concentrations. 

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

1 017 mg/kg bw

Additional information

Acute oral toxicity:

In a reliable acute toxicity study comparable to guideline OECD 401 female rats were dosed with 25, 50, 100, 2500, 5000 and 7100 mg/kg bw Diuron (Heimann and Thyssen, 1983). At the lowest dose level, no clinical signs were noted. Higher dose levels revealed behavioural, respiratory and motility disorders. Some animals exhibited a narcosis-like state and lying on side or stomach. Signs were noted between 27 min (high dose levels) and 2 hours at lower doses following administration. Mortalities occurred at 2500 mg/kg and above within 2 days. Therefore, the LD50 was calculated to be 4150 mg/kg bw. Various other studies confirmed the low toxicity of Diuron with LD50 values > 2000 mg/kg bodyweight (Mihail, 1981, Heimann,1984 and Sanders, 2007).

However, when Diuron was dissolved in cotton seed oil and administered to rats receiving a protein-deficient diet the LD50 was 437 mg/kg bw in male Wistar rats (Boyd & Krupa, 1970). The LD50 for rats of the low protein diet was lower as compared to rats fed non-protein deicient diet. The study indicates that Wistar rats are much more susceptible to acute oral toxicity of Diruon when fed protein-deficent diet. Therefore, the LD50 value of 1017 mg/kg bw will be used to trigger C&L as this was derived from standard conditions (this LD50 was derived after feeding the test animals regular laboratory chow). Based on this study, Diuron is considered to be harmful upon ingestion (Boyd & Krupa, 1970)

Moreover, for Diuron administered in peanut oil, oral LD50 values of 1258 and 1182 mg/kg bw were reported in male and female Sherman rats (Gaines and Lindner (1986)), respectively.These studies indicate that rats are more susceptible to acute oral toxicity of Diuron when fed protein-deficient diet and that Diuron exhibited a much higher oral toxicity in cotton seed oil than watery preparations. Thus showing the toxicity could be attributed to the diet and vehicles used in the studies.

Nontheless, based on the most critical LD50 of 1017 mg/kg bodyweight, Diuron needs to be classified according to the criteria of Directives 67/548/EEC (DSD) and 1272/2008/EC (CLP).

 

Acute Inhalation Toxicity:

In a reliable acute inhalation toxicity study performed according to OECD 403, five male and female Sprague-Dawley rats were nose only exposed to 5.05 mg/L Diuron, the max. achievable atmosphere concentration (Griffith, 2007). One female rat died on day 1 post-exposure.Clinical signs noted during the study included increased respiratory rate, hunched posture, pilo-erection and wet fur. At necropsy, no macroscopic abnormalities were detected amonst surviving animals except for one instance of abnormally dark lungs. The animal that died showed abnormally dark lungs and an accentuated lobular pattern in the liver. Based on the results of this , the LC50 in the rat is considered to be > 5.05 mg/L Diuron.

 

Acute Dermal Toxicity:

In a reliable study in accordance to OECD 402 rats were dermally exposed to 2500 and 5000 mg/kg bw Diuron. At the low dose level no clinical signs were noted and at the high dose level animals only showed reduced motility and apathy for 2 to 4 days. Therefore, the LD50 is determined to be > 5000 mg/kg bw (Heimann and Thyssen, 1983).

Justification for classification or non-classification

Based on the available data on acute oral toxicity Diuron needs to be classified:

DSD: R22

CLP: acute toxicity 4

The data on acute toxicity for the inhalation and dermal route are conclusive, but not sufficient for classification according to directives DSD (67/548/EEC) or CLP (1272/2008/EC).