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Key value for chemical safety assessment

Effects on fertility

Description of key information
 Lack of fertility effects observed in reproductive toxicity studies with soluble Ni compounds (Ambrose et al., 1976; Smith et al., 1993; RTI, 1988a,b; NTP, 1996; SLI, 2000a,b) combined with toxicokinetic data (Ishimatsu et al., 1995) provide sufficient justification that nickel dihydroxide should not be considered a reproductive toxicant with regards to fertility effects. However, as a substance classified for reproductive toxicity under the EU 1st ATP, CSA is necessary. The most reliable NOAEL is from the two-generation study (SLI 2000b) where the NOAEL is the highest dose investigated, i.e. 2.2 mg Ni/kg bw/day. A repeated dose toxicity study provides a NOAEL for effects on sperm and oestrus cyclicity of 0.45 mg Ni/m3 for inhalation exposure (Dunnick et al., 1989).
    
    

Value used for CSA (route: oral): NOAEL: 3.5 mg nickel dihydroxide/kg bw/day

Value used for CSA (route: inhalation): NOAEC: 0.71 mg nickel dihydroxide /m³ air

Effect on fertility: via oral route
Dose descriptor:
NOAEL
3.5 mg/kg bw/day
Effect on fertility: via inhalation route
Dose descriptor:
NOAEC
0.71 mg/m³
Additional information

Data requirements for nickel dihydroxide are fulfilled by reading across the negative results from fertility studies with soluble nickel compounds.

There is no higher-tier reliable study examining fertility endpoints with nickel dihydroxide. However, fertility impairment due to oral or inhalation exposure to nickel compounds (including the most bioavailable forms) has been extensively studied in reliable studies, and no effects on fertility have been found. Since the reproductive toxicity effects are related to the nickel ion, the lack of fertility effects following exposure to water-soluble nickel compounds (which have higher bioavailability) is relevant to water-insoluble nickel compounds (which have lower bioavailability). If adverse fertility effects are not observed with the most-bioavailable form, they will not be observed with less-bioavailable forms. There are several reliable 13 week and one- and two-generation studies utilizing inhalation or oral administration of water soluble nickel compounds in rats that have not indicated adverse effects on fertility, estrous cycling, sperm parameters, vaginal cytology, copulation and fertility indices, precoital intervals, gestation lengths, gross necropsy findings and histopathology (Ambrose et al., 1976; Smith et al., 1993; RTI, 1988a,b; NTP, 1996; SLI, 2000a,b). While water-soluble nickel compounds are classified as Repro Cat 1B due to developmental effects in rats, neither nickel metal nor any of the insoluble nickel compounds carry harmonized classifications for fertility effects (see Part 3 of Annex VI; CLP Regulation, 2009). While some effects have been reported in studies in mice with soluble nickel (e.g. Pandey and Srivastava, 2000), theEuropean Union Risk Assessment Report(EU RAR) in 2008 did not consider the data sufficient to classify insoluble compounds for reproductive or developmental toxicity.

Effects on developmental toxicity

Description of key information
Data from a reproductive toxicity study with Ni sulphate hexahydrate (SLI, 2000b) combined acute oral toxicity (EPSL, 2009a) with and toxicodynamic assessments of nickel dihydroxide through read-across from nickel oxide provide sufficient information regarding the reproductive and developmental toxicity for classification of nickel dihydroxide. A comprehensive read-across program based on water solubility and bioaccessibility data in synthetic fluids validated by in vivo toxicokinetics and acute oral toxicity data has been conducted on a series of Ni substances including Ni dihydroxide (Appendices B1 and B2). The results of this program suggest that Ni dihydroxide should not be read-across to nickel oxide and classified as Repr. 1F; H360D. While no change to the existing classification is proposed within this registration file, a complete summary of the testing program including results and discussion are provided in Section 7.8 of IUCLID and as Appendix B1 in this CSR. Read-across from nickel oxide for animal toxicokinetic data and results of a recently completed acute oral toxicity study on nickel oxide suggest that the oral absorption of nickel from nickel dihydroxide is significantly lower than from more soluble forms of nickel and strongly infers that oral exposure to nickel dihydroxide will not allow enough absorption to exceed the threshold for developmental toxicity.
    
    

The results two PNDT studies in rats and mice with Ni chloride, a soluble nickel compound (i.e., highest bioavailability), were read-across to nickel dihydroxide to fulfil the reproductive toxicity data requirements for teratogenicity effects under REACH (RTI, 1988a,b; Saini et al., 2013). In the rat study, no evidence of teratogenic effects was reported in a multi-generational study where the F2b generation was subjected to a classical teratology assessment (RTI, 1988a,b). The F2b generation was delivered by Caesarean section on gestation day 20 and were examined for external, internal, and skeletal malformations mimicking the protocol of a stand-alone PNDT study, but with extended exposure of the parental animals. This F2b cohort showed no exposure-related adverse effects. The lack of adverse effects in the F2b generation, examined on gestation day 20, indicated that the developmental effects in the other generational cohorts (i.e., perinatal mortality) were expressed during the perinatal or postnatal periods and not during gestation (RTI, 1988a,b).

Saini et al. (2013) studied the effects of oral (gavage) exposure during gestation (GD6-13) of Swiss albino mice to Ni chloride hexahydrate at doses of 0, 46, 92 and 185 mg Ni/kg b.w. per day. Maternal toxicity (decrease feed consumption, water intake and b.w.) was observed at doses ≥ 92 mg Ni/kg b.w. per day and fetotoxicity (decreases in b.w.), embryotoxicity (decrease in the number of live fetuses/dam, increases in post-implantations losses and resorptions at high dose), and teratogenicity (malformations such as open eyelids, club foot, umbilical hernia, ophthalmic anomalies, hydrocephaly, reduced ossification, dose-dependent increase in skeletal anomalies) were observed at doses ≥ 92 mg/kg b.w. per day (microphthalmia already at 46 mg/kg b.w. per day). The NOAEL for maternal toxicity was 46 mg Ni/kg b.w. per day and the LOAEL for developmental toxicity was 46 mg Ni/kg b.w. per day.

Finally, rat micronucleus studies in bone marrow after repeated oral exposure to a soluble nickel compound did not show adverse effects, even though nickel levels in plasma and bone marrow were increased >30 times and 4 times, respectively, over controls (Oller and Erexson, 2007). This study confirmed that rapidly dividing tissues (such as those in the developing organism) are not preferentially affected by nickel exposure.

The following information is taken into account for any hazard / risk assessment:

Data from a reproductive toxicity study with Ni sulphate hexahydrate (SLI, 2000b) and Ni chloride (RTI, 1988a,b) combined with toxicodynamic and acute oral toxicity (EPSL, 2009a) of nickel oxide as a source substance for read-across provide sufficient information for assessments of nickel dihydroxide regarding developmental toxicity. However, as a substance classified for reproductive toxicity under the EU 1st ATP, CSA is necessary. Based on an interpretation of an equivocal increase in postimplantation/perinatal lethality in F1 generation in a two-generation study with nickel sulphate (SLI 2000b) at 2.2 mg Ni /kg bw/day, the NOAEL used for developmental toxicity is set at 1.1 mg Ni/kg bw/day.

Value used for CSA (route: oral): NOAEL: 1.7 mg nickel dihydroxide /kg bw/day

Effect on developmental toxicity: via oral route
Dose descriptor:
NOAEL
1.7 mg/kg bw/day

Toxicity to reproduction: other studies

Description of key information

A reproductive study of female refinery workers hasnotdemonstrated an association between relatively high soluble nickel exposures (worst case scenario with higher blood and urinary levels) and the following reproductive outcomes: genital malformations (hypospadias and cryptorchidism), spontaneous abortions, small-for-gestational-age newborns, and skeletal malformations (Vaktskjoldet al., 2006, 2007, 2008a&b). Researchers created a birth registry for all births occurring in the region of a Russian nickel refinery at Monchegorsk during the period of the study, which included information on 22,836 newborns and 2,793 pregnancy outcomes surveyed for spontaneous abortions (Vaktskjoldet al.2007; 2008a). They also reconstructed the exposures (using air and urinary nickel measurements) for the female workers at the refineries so as to be able to link specific pregnancy outcomes with occupational exposures via inhalation and systemically bioavailable doses of nickel (i.e.urinary nickel levels). The study culminated in a series of manuscripts by Vaktskjoldet al.(2006, 2007, 2008a,b) describing the results of the investigation. The study demonstrated nickel compound and metal exposure was not associated with adverse pregnancy outcome for 1) male newborns with genital malformations, 2) spontaneous abortions, 3) small-for-gestational-age newborns, or 4) musculoskeletal effects in newborns of female refinery workers exposed to nickel. The data in these manuscripts showed no correlation between nickel exposures (urinary levels as high as 30-fold over background[1]) and observed reproductive impairment. It is important to note thatgenital malformations are considered as one of the most sensitive endpoints for human developmental toxicity while spontaneous abortion in humans would most closely approximate the observation of perinatal lethality associated with nickel exposure in rodents. Further evidence that nickel compound and metal exposure was not adversely affecting the reproduction of these women was provided by the lack of a “small-for-gestational-age” finding and also the lack of an association of male genital malformations with nickel exposure. Both of these findings are considered “sentinel” effects (i.e., sensitive endpoints) for reproductive toxicity in humans.

 

The work by Vaktskjoldet al.(2006, 2007, 2008a,b) is important in demonstrating that no hazard for reproductive impairment from nickel compound and metal exposure exists under the conditions of the study, which were extremely high exposure levels which are no longer present in current refinery operations.[2]Thus, the reproductive effects observed in rats 1) may not be relevant to humans or 2) may not have been observed in the exposed human population because even the highest achievable female workers’ exposure (179 µg Ni/l in urine) is lower than those achieved in rats at the LOAEL for reproductive effects (2300 µg Ni/L in urine). In either case, for classification and risk assessment purposes, the relevance of the positive results in rats with soluble nickel compounds (at what seem to be unachievable human exposures) needs to be considered together with the negative results in human studies at Monchegorsk (for the highest exposed human population) in a weight of evidence approach. At the very least, the data indicates that humans do not appear to be greatly more sensitive to reproductive effects of nickel ion than rats. While the exact mode of action for the perinatal mortality effects of Ni ion are not known, the existing data demonstrates that these are clearly threshold-mediated effects. Because the study correlated the systemically available nickel levels to reproductive outcomes, the lack of reproductive toxicity effects is relevant to nickel compounds and nickel metal. Importantly, the results from human studies showing no reproductive toxicity effects due to nickel compound and metal exposure reported by Vaktskjoldet al.were not available at the time when nickel compounds were classified as Cat. 1B reproductive toxicants.

 

The mode of action for the reproductive toxicity of soluble nickel ion observed in rodents is not currently known; thus its relevancy for humans is also unknown. What is known is that epidemiological studies of female workers exposed to the highest attainable levels of water soluble nickel compounds (via inhalation) and who had urinary nickel levels up to 30-fold above backgroundfailedto show an association between exposures to nickel and observed adverse reproductive effects. To place the animal and human results in context, we can compare the urine nickel levels in the workers’ cohort with the urine levels in rat reproductive studies. Background urinary nickel levels in the female Monchegorsk population had a geometric mean of 5.9 µg/l, the low exposure refinery workers had urinary levels up to 70 µg/l (~12-fold increase in urinary levels) and the high exposure workers had urinary levels between 70 and 179 µg/l (up to 30-fold increase in urinary levels). Urinary levels of 70 µg/l in low exposure workers corresponded to approximately 160 µg soluble nickel inhalable exposure/m3(>1000-fold over ambient air levels).

Comparison of the exposures in female workers to the exposure of rats can be made. In a rat oral study with nickel sulfate (100% bioaccessible nickel), blood and urinary nickel levels were measured after two years of exposure to 2.2 to 10 mg Ni/kg (Heim et al., 2007; Rush, 2005). A linear dose-response between oral intake of nickel and urinary nickel levels was found. An exposure of 2.2 mg Ni/kg corresponded to a mean urine value of 2300 µg Ni/L (males + females) with blood peak levels of ~70 µg Ni/l. Thus, the rat urinary nickel level at the LOAEL for reproductive developmental effects (2.2 mg Ni/kg) is 33-fold and 13-fold higher than those measured in Low and High exposure nickel refinery workers, respectively. Likewise, the rat urinary nickel level at the NOAEL for developmental effects (1.1 mg Ni/kg) are expected to be 16.5-fold and 6.5-fold higher than those measured in Low and High exposure nickel refinery workers, respectively. 

Thus, the reproductive effects observed in rats 1) may not be relevant to humans or 2) may not have been observed in the exposed human population because even the highest achievable human exposures are lower than those at which adverse reproductive effects have been observed in rats. In either case, the relevance of the positive results in rats (at unachievable human exposures) needs to be considered together with the negative results in human studies at Monchegorsk (for the highest exposed human population).  

These data show that while a reproductive “hazard” from nickel ion systemic exposure can be demonstrated in animals, this hazard has not been demonstrated in humans.

 

The full document summarizing these data in humans is attached in Sections 7.8 and 7.10.2 of IUCLID and inAppendixB4to the CSR.

 

The following information is taken into account for any hazard / risk assessment:

A summary document is attached in sections 7.8.1 and 7.8.2 of IUCLID and inAppendixB4of this CSR discussing human assessments of reproductive impairment associated with nickel exposures as a worst case scenario.In summary, there was a lack of a correlation between nickel exposure and observed (sex organ and skeletal) malformations in the human reproductive studies of nickel-exposed workers reviewed above (Vaktskjold et al., 2006, 2007; 2008a,b). Specific endpoints, their assessment methods, and the number of subjects included: genital malformations in newborns of female nickel-refinery workers were examined with a register-based, nested case-control study (n= 103 cases; 23,038 controls); small-for-gestational-age newborns of female refinery workers exposed to nickel were examined with a register-based, nested case-control study (n= 2,096 cases; 20,740 controls); spontaneous abortions among nickel-exposed female refinery workers were examined with a case-control study (n=184 cases, 1,691 controls); and maternal nickel exposure and congenital musculoskeletal defects were examined with register-based, nested case-control study (n=341 cases, 22,624 controls). In all studies, nickel exposure was not associated with adverse pregnancy outcome for any of the endpoints examined. Such large studies provide adequate statistical power to support a conclusion to exclude the risk of reproductive effects (e.g. malformations) from exposure to the chemical (EMA/CHMP Guideline, 2006). The weight of evidence from all data discussed above demonstrates a consistent lack of sufficient in vivo bioavailability by oral, inhalation and dermal routes, and no classification for reproductive toxicity of nickel dihydroxide is warranted,even though current classification is Repr. 1B;H360D in the 1st ATP to the CLP.


[1]Background urinary nickel levels in female Monchegorsk population had a geometric mean of 5.9 µg/l, the low exposure refinery workers had urinary levels up to 70 µg/l (~12-fold increase in urinary levels) and the high exposure workers had urinary levels between 70 and 179 µg /l (up to 30-fold increase in urinary levels). Urinary nickel levels are better indicators of fetal exposure, as they account for systemically absorbed nickel ion from occupational and non-occupational sources (e.g. diet) by all routes of exposure.

[2]The geometric means of the workers’ exposures in this study ranged from 0.03-0.084 mg Ni/m3in the low exposure group to 0.15-0.33 mg Ni/m3in the high exposure group.

Justification for classification or non-classification

Although current classification isRepr. 1B;H360D in the 1st ATP to the CLP,a comprehensive read-across program based on bioaccessibility data in synthetic fluids andin vivoacute oral toxicity data has been conducted on a series of Ni substances including Ni dihydroxide. The results of this program suggest that Ni dihydroxide should not be classified as Repr. 1B; H360D. While no change to the existing classification is proposed within this registration file, a complete summary of the testing program including results and discussion are provided in Section 7.8 of IUCLID and asAppendix B1in this CSR.