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EC number: 231-176-9
CAS number: 7440-67-7
Workers long term dermal DNEL
dermal DNEL derivation is based on the NOAEL from a 17 weeks (119 days)
oral study on zirconium carbonate containing 20.9% zirconium dioxide
(Harrison et al., 1951). Test animals (rats) were fed with hydrated
zirconium carbonate at different doses. The NOAEL was >15100 mg HZC/kg
bw/day i.e >3156 mg ZrO2/kg bw/day. The value of 3150 mg/kg bw/day was
used in further calculating the DNELs.
was assumed that the oral absorption rat = dermal absorption rat
overall assessment factor was obtained as follows:
overall assessment factor is: 4 x 2.5 x 5 x 2 x 2 = 200
derived DNEL for ZrO2 is therefore: 3150 / (4 x 2.5 x 5 x 2 x 2) = 3150
/200 = 15 mg/kg bw/day.
To obtain the DNEL equivalent for Zr, a conversion factor of 1.37
need to be applicated
The derived DNEL for Zr is hence: 15 / 1.37 = 11 mg/kg bw/day
Workers long term inhalation DNEL
study from Spiegl & al (1956) provides a NOAEC for zirconium dioxide >
11 mg Zr/m3 after 60 days of exposure and 75 mg Zr/m3 after 30 days,
based on no effects observed on the several species used (cat, dog,
guinea pig, rabbit and rat). Nevertheless only one dose was tested in
these studies. We can only conclude that the NOAEC will be higher than
these tested doses. Based on these unbounded
the DNEL will be unrealistically low and not representative for the
toxicity of zirconium. Indeed in all available studies (read across with
ZrO2), no health effects were observed even at higher doses (acute
toxicity tests via oral & inhalation route). This absence of effect
could be explains by the fact that, at pulmonary level, Zr particles are
deposited but, as they are under an inert form (with a passivation layer
surrounding them), no systemic toxicity occurs. Indeed, one of the
possible effects observed is lung granuloma, sometimes found in worker
exposes to Zr particles (epidemiological data): granuloma corresponds to
an inflammatory chronic reaction to the deposition of the small
particles in the alveolus. In addition, Zr particles are not soluble and
thus own a very low bioavailability as demonstrated in the toxicokinetic
exposure limits were defined in. In, NIOSH, ACGIH, OSHA have evaluated
toxicity and defined long term and short term exposure limits for
zirconium compounds. For all these organisms the same 8 hours Time
Weighted Average (TWA) of 5 mgZr/m3 was set. This value was based on the
results of Spiegl & al, 1956 as well as on the results of the study from
Hodge 1955. The study of Hodge (1955) is a 1 year experiment performed
on rats with zirconium oxide dust at a dose of 3.5 mg/m3. (Unfortunately
unpublished study not accessible).
based on all these considerations, it is considered reasonable and
sufficiently conservative to use the 8 hours TWA of 5 mg/m3 as a long
term systemic DNEL for workers. In addition, this value is advised by
the French authorities as the limit value for exposure to dusts and was
adopt for "alveolar particles". For "inhalable particles", with higher
mean aerodynamic diameter, the value was set to 10 mg/m3.
General population long term dermal/oral DNEL
dermal/oral DNEL derivation is based on the NOAEL from a 17 weeks (119
days) oral study on zirconium carbonate containing 20.9% zirconium
dioxide (Harrison et al., 1951). Test animals (rats) were fed with
hydrated zirconium carbonate at different doses. The NOAEL was >15100 mg
HZC/kg bw/day i.e >3156 mg ZrO2/kg bw/day. The value of 3150 mg/kg
bw/day was used in further calculating the DNEL.
was assumed that the oral absorption rat = dermal absorption rat.
overall assessment factor is: 4 x 2.5 x 10 x 2 x 2 = 400
derived DNEL for ZrO2 is therefore: 3150 / (4 x 2.5 x 10 x 2 x 2) = 3150
/400 = 7.5 mg/kg bw/day.
The derived DNEL for Zr is hence: 7.5 / 1.37 = 5.5 mg/kg bw/day
General population long term inhalation DNEL
DNEL selected for long term- systemic effect exposure of worker (i.e 5
mg/m3) is used for consumers applying an additional assessment factor of
2 for general population.The
value for consumer is 2.5 mg/m3.
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