Urea

Toxicity to birds

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to birds: dietary toxicity test

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 205 (Avian Dietary Toxicity Test)

Principles of method if other than guideline:

Chicken were fed with six levels of supplemental urea (0, 3, 6, 9, 12 and 15 9/100 g basal diet) and two strains of female chicks (White Leghorn-layer type, Shaver Starbro broiler-type). The basal diet was a chick starter containing l8% of protein. Each treatment was assigned to five replicated pens, each with 10 chicks, for a 21-day period starting when the birds were 14 days of age. The chicks were housed in electrically heated wire-floored battery brooders where they received feed and water ad libitum.

GLP compliance:

no

Dose method:

feed

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

other: Gallus gallus domesticus

Details on test organisms:

TEST ORGANISM
- Common name: chicken
- Age at test initiation (mean and range, SD): 14 days
- Kept according to standard practices: yes

Limit test:

no

Total exposure duration (if not single dose):

21 d

No. of animals per sex per dose and/or stage:

five replicated pens, each with 10 chicks

Control animals:

yes, plain diet

Nominal and measured doses / concentrations:

0, 3, 6, 9, 12 and 15 9/100 g basal diet

Reference substance (positive control):

no

Duration (if not single dose):

21 d

Dose descriptor:

LC50

Effect level:

> 150 000 mg/kg diet

Conc. / dose based on:

test mat.

Basis for effect:

mortality

Duration (if not single dose):

21 d

Dose descriptor:

NOEC

Effect level:

>= 150 000 mg/kg diet

Conc. / dose based on:

test mat.

Basis for effect:

body weight

Remarks on result:

other: The urea might have reduced weight gains by acting as a dietary diluent.

Further details on results:

The results of this experiment demonstrated that the growing chick can tolerate high levels of dietary urea for several weeks without exhibiting any obvious symptoms of toxicity. Reductions in weight gain and decreases in feed efficiency may be explained on the basis of dietary dilution. There is no reason to believe that the urea had any direct effect on the performance of the birds.

Validity criteria fulfilled:

not applicable

Conclusions:

Chicken: 21-day NOEC >= 150000 mg urea /kg feed,
"There is no reason to believe that the urea had any direct effect on the performance of the birds."

Executive summary:

In the study from Sibbald and Hamilton (1975) chicken were fed with six levels of supplemental urea (0, 3, 6, 9, 12 and 15 9/100 g basal diet) and two strains of female chicks (White Leghorn-layer type, Shaver Starbro broiler-type). The basal diet was a chick starter containing l8% of protein. Each treatment was assigned to five replicated pens, each with 10 chicks, for a 2l-day period starting when the birds were 14 days of age. The chicks were housed in electrically heated wire-floored battery brooders where they received feed and water ad libitum.

The results of this experiment demonstrated that the growing chick can tolerate high levels of dietary urea for several weeks without exhibiting any obvious symptoms of toxicity. Reductions in weight gain and decreases in feed efficiency may be explained on the basis of dietary dilution. There is no reason to believe that the urea had any direct effect on the performance of the birds.

Reference 2

Endpoint:

long-term toxicity to birds

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline followed

Principles of method if other than guideline:

Review of field studies

GLP compliance:

no

Remarks:

Publication

Test organisms (species):

other: Various bird species observed in the field

Duration (if not single dose):

36 mo

Dose descriptor:

NOEL

Effect level:

>= 720 other: kg/ha

Conc. / dose based on:

test mat.

Remarks:

urea

Basis for effect:

other: population growth

Remarks on result:

other: field studies

Validity criteria fulfilled:

not applicable

Executive summary:

Four references on responses of birds to forest fertilization (note: some studies were performed with other N-fertilizers but are considered to be relevant here as well). Included 2 from Sweden and 2 from the Yukon (Table 6). The 6 species of forest grouse showed no response to the fertilizer treatments (Ash and Bendell 1979; Ball et al. 2000; Martin et al. 2001). However, Folkard and Smith (1995) found repeated fertilizer applications also had no effect on bird species richness in spruce forest with mixed canopy closure, but found numbers of the 7 most abundant species increased by 46% over 3 years. Similarly, Edenius et al. (2011) reported that repeatedly fertilized stands had 38% more species and 21% more individuals than unfertilized stands. It was not clear whether the response in the bird community was related to changes in food resources (e.g., terrestrial invertebrates) (Edenius et al. 2012) or increased structural complexity in the forest canopy.

Description of key information

LC50 > 150 g/kg feed 21-day chicken feed test.

Key value for chemical safety assessment

Short-term EC50 or LC50 for birds:

150 g/kg food

Additional information

In a 21 day study chicks were fed with feed containing up to 15% urea (Sibbald and Hamilton 1975). It was stated that "the results of this experiment demonstrated that the growing chick can tolerate high levels of dietary urea for several weeks without exhibiting any obvious symptoms of toxicity. Reductions in weight gain and decreases in feed efficiency may be explained on the basis of dietary dilution. There is no reason to believe that the urea had any direct effect on the performance of the birds."

Field studies intemperate and boreal forestsindicate that birds might profit from fertilization with urea at rates up to 720 kg urea/ha (and potentially higher rates). This effect is considered to be secondary (change in food resources or forest canopy) (Sullivan and Sullivan 2017).