Vanadium carbide

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

concentration-driven

Effects on fertility

Description of key information

The endpoint reproductive toxicity of the vanadium category substance is not addressed by substance-specific information but rather by read-across of data available for soluble tri-, tetra- and pentavalent vanadium substances. Therefore, the remaining text in this chapter is generic for all vanadium substances and has not been adapted on a substance-specific basis.

All vanadium substances within the read-across concept represent inorganic substances, including salts or oxides, and form the vanadium category. For the substances of the inorganic vanadium substances category, it is assumed that the in vivo bioavailability of the vanadium varies in a predictable manner, which is dependent on the in vitro bioaccessibility of the respective vanadium substance, i.e. all members of the category liberate vanadium ions in aqueous media at different rates, inter alia depending on the chemical structure. Thus, this concept is based on the chemistry / composition of all substances and on experimental studies for (i) water solubility and (ii) in-vitro bioaccessibility: assessment of the solubility and speciation of vanadium substances in five different artificial physiological fluids. It is hypothesised that the systemic toxicity is dependent on the ratio at which vanadium ions are liberated during e.g. gastric passage – the toxicity correlated with the in vitro bioaccessibility. Thus, the vanadium substances, showing similar in vitro bioaccessibility are placed in the same read-across group. Further details on the read-across concept are presented in the report attached to IUCLID section 13.

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Quality of whole database:

Several studies with oral exposure are available, but the reliability is low and the results are not considered relevant for human exposure.

Effect on fertility: via inhalation route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

4 mg/m³

Study duration:

subchronic

Species:

rat

Quality of whole database:

One reliable study (RL1) with inhalation exposure of rat and mice with V2O5, and several studies with RL3 and apprpriate routes of exposure are available. Additional studies with exposure by a non-relevant route (ip) were disregarded.
4 mg/m3 V2O5 corresponds to 2.25 mg V/m3

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

An extensive literature/data search and evaluation programme on animal and human data relating to possible adverse effects of vanadium substances on reproductive toxicity has recently been conducted. As an outcome, some data are available for the soluble vanadium substances via the oral and inhalation route. Two NTP studies with inhalation exposure of V2O5 in mice and rats were conducted under GLP and although not specific reproduction toxicity study they are regarded as key studies, because effects on male and female reproductive organs were evaluated. The other studies can be regarded as studies of low reliability. The studies show supportive evidence of a potential effect of vanadium substances on male and female fertility.

In the two 3-months studies (NTP) with inhalation exposure of V2O5 in male and female rats and mice, animals (10/sex/group) were exposed to 0, 1, 2, 4, 8, or 16 mg V2O5/m3 (0, 0.56, 1.12, 2.25, 4.50, 8.99 mg V/m3) by whole-body inhalation for 6h/d, 5d/week for 3 months. In the highest dose (16 mg/m3), 3/10 females died during the study and necropsy body weight was statistically significantly lower. There was a statistically significantly increases in estrus cycle length at 8 and 16 mg/m3. However, this effect was highest in the lower dose group of 8 mg/m3, thus showing no clear relation to dose and treatment. In contrast, no deaths occurred in female mice. Final body weights started to be reduced in the exposure group of 4 mg/m³, but there was no statistically significant effect on estrus cycle length.

In male rats, severe toxicity was present in the high dose group with 7/10 males found dead during the study, and final body weights from animals in dose groups 4, 8 and 16 mg V2O5/m3 were significantly reduced. In male rats there was a statistically significant effect on necropsy body weight at 8 mg/m3, and no effects on male reproductive organ weights. Spermatid measurements (heads and counts) were not statistically significantly affected as well as epididymal sperm motility and concentration. Atrophy of the secondary reproductive organs in male rats at 16 mg/m3 is described, but at this dose level clear signs of general toxicity were shown. In addition, hypospermia of the testis and atypical cells of the epididymis at 16 mg/m3 are described, while only a very mild effects without statistical significance is evident in the 8 mg/m3 group and is most probably an unspecific effect related to general toxicity at this dose level. Thus, the findings in male rats can be considered secondary to the observed general toxicological and body weights effect in the high dose group and can thus not be attributed to a direct vanadium induced toxicological finding. In male mice, 1/10 males died during the study in the highest dose group. Necropsy body weights were statistically significantly lower at 16 mg/m3, and there was a statistically significant effect on sperm motility at 8 and 16 mg/m3. However, the effect on sperm motility was not very pronounced without a clear dose-response relationship. The lowest value was observed in the 8 mg/m3 group (mid dose) and was less pronounced in the high dose group.

In conclusion, the effects in female animals were observed only in a single species (rat) and not in the other species (mice). The effects in male animals were also observed only in a single species, but in mice, and not in the other species (rat). For both effects, there was no clear relation to dose and treatment and thus the findings must be regarded of low evidence for a vanadium induced effect on male and female fertility. Taking the results together, a dose level of 4 mg V2O5/m3 may be regarded as a NOEC for male and female fertility based on these studies.

 

In addition, there is one other study (Morgan A.M. and El-Tawil O. 2003) with ammonium metavanadate treatment via drinking water in rat available in which male and female animals were paired and effects on fertility evaluated. This study is only of RL3, because of limitations with respect to cohabitation, dose level (only one) and reporting. Sprague-Dawley rats were treated with ammonium metavanadate (200 ppm in drinking water). Male rats (n=10) were treated with 10 mg NH4VO3/kg bw/d corresponding to 4.35 mg V/kg bw/d (calculated with default factors according to ECHA (2012)) for 70 days, and 20 females with 11.43 mg NH4VO3/kg bw/d, (4.97 mg V/kg bw/d) for 61 days (14 days premating, during mating, till weaning of pups (21 days of age).

The results of this mechanistic study conducted only with one dose level show that mating and fertility indices were reduced in treated males mated with untreated females (group 1) and treated females mated with untreated males (group 2) (mating index: control: 100%, treated males 1: 65%; treated females: 70%; fertility index: 95%, 46.15%, 71.43%, respectively). In treated males, reduced weight of testes, epididymis, prostate gland, seminal vesicles, (p<0.05), with no reduction in body weight between control and treated males were observed. In females, the estrus cycle was disturbed, total number corpora lutea was reduced (control: 220, group 1: 54; group 2: 94), and signs of dystocia (no. of dams: 0, 1, 4) and delayed birth date (no. of dams: 0, 3, 5) were observed. No information on general toxicity is presented.

 

There is another rat study (Domingo et al. 1986) conducted with an appropriate route of exposure (oral) and different dose levels sodium vanadate compared to a control group (0, 5, 10 or 20 mg/kg bw/d sodium vanadate per os equivalent to 2.1, 4.2 and 8.4 mg vanadium/kg/day, respectively) available, but only of RL3. Females were treated for 14 days and males for 60 days before mating. Females continued to receive treatment with vanadium until study termination. Parameters evaluated on day 14 sacrifice were the nos. of corpora lutea, total implantations, living and dead fetuses and resorptions.

Fertility was not affected by treatment of male and female rats with sodium vanadate and there were no signs of maternal toxicity (no data presented). At interim sacrifice of females on day 14 of gestation, no significant adverse effects were observed on nos. of corpora lutea, total implantations, living and dead fetuses and resorptions. Thus, at 20 mg/kg bw/dsodium vanadate per os no effects could be determined on fertility of rats.

 

The reproductive toxicity of sodium metavanadate (Llobet 1993) was also studied in male Swiss mice exposed doses of 0, 20, 40, 60 and 80 mg/kg bw per day (equivalent to 8.4, 16.8, 25.2 and 33.6 mg vanadium/kg bw/day) given in the drinking water for 64 days. To evaluate the fertility of the vanadium-treated animals, males were mated with untreated females. A significant decrease in the pregnancy rate was observed at 60 and 80 mg/kg per day. However, the test substance did not reduce fertility in male mice at 20 and 40 mg/kg per day. Decreased body and epididymis weights were only observed in the 80 mg/kg per day group, while testicular weights were not altered by the treatment. Sperm count was significantly decreased at 60 and 80 mg/kg per day, but the sperm motility was unaffected. Histopathological examination revealed that testes were normal and that epididymis of treated male mice contained normal appearing sperm. In this reproduction toxicity study in mice, at 40 mg/kg bw/dsodium metavanadate per os (drinking water) no effects could be determined on fertility of rats.

 

Four additional references (Fortoul T.I. et al. 2007, Mussali-Galante et al. 2005, Bizarro-Nevares et al. 2016, Rodriguez-Lara V et al. 2016) are available with studies conducted with one dose of V2O5 by inhalation (1.4 mg V2O5/m3 equivalent to 0.79 mg V/m³) with a reliability of 3 conducted by the same group of researchers. The study design described in the publications is similar, but different mechanistic endpoints are addressed in the papers. The results of these publications support the evidence of a vanadium related effects on male reproductive organs at a certain exposure level. Supportive evidence might be taken also from several studies with ip injection of divanadium pentaoxide or sodium metavanadate to mice, rats or Guinea-pigs. The studies support the mechanistic evidence of a vanadium induced effect of male reproductive organs but were not taken into consideration.

Developmental Neurotoxicity

Several studies are available with exposure of suckling pups via the milk of their mothers. All studies show deficiencies with respect to methods (e.g. only one dose level, purity of the applied compound not given, no documentation of general unspecific toxicity etc.) and reporting of results and are therefore only of reliability score 3 and should thus be considered only as supportive. In these mechanistic studies, exposure of lactating mothers was conducted by IP injections in order to reach high amounts of secretion into the milk. IP injection is in general a non-relevant route of exposure, but in this case exposure of suckling pups by the milk of their mothers is the relevant route of exposure for this end point. Because of the IP administration to dams, exposure of sucklings by the milk of their mothers might be higher than under realistic exposure considerations and thus represents a worst case scenario.

 

These non-regulatory mechanistic studies were conducted with only one effective dose level of 3 mg NaVO3/kg body weight/day (1.25 mg V/kg bw/day) in comparison to a control group. In 6 of 7 studies conducted either in suckling pups, directly exposed pups or adult rats, effects were observed to a different degree on behaviour and motor coordination in open field tests. The effect on negative geotaxis investigated in 3 studies was not consistent and rotarod performance was affected in pups (exposed via milk or directly), but not in adult rats. In addition, histochemistry and immunohistochemistry investigations were conducted in these studies. There were occasions of a negative effect of vanadium treatment on myelin fibre density or demyelination in different brain areas in suckling pubs as well as in adult rats. Astrogliosis was observed in 4 studies in pubs with varying degree, and oligodendrocytes were shown to be sensitive against vanadium treatment with oligodendrocyte progenitor cells (in vivo and in vitro) being more sensitive to vanadium exposure than astrocytes or mature oligodendrocytes. Lipid peroxidation was shown in adult rats, but could not be detected in suckling pubs. In addition, a few other single endpoints were evaluated.

In conclusion, there is limited evidence that exposure of suckling pubs to vanadium via the milk of their mothers may result in neurotoxic effects evidenced by behavioural changes, myelin damage and astrogliosis under the conditions of these studies. However, based on the available information, no conclusion can be drawn with respect to effect or no effect levels and to realistic exposure scenarios of breastfed children.

The NTP testing program conducted sub-chronic drinking water studies on VOSO4 and NaVO3 as follows:

- Genetic toxicology studies, i.e. the Salmonella gene mutation assays, with NaVO3 and VOSO4 - negative

- 14 days with Harlan Sprague-Dawley rats and B6C3F1/N mice (Dose: R&M: 0, 125, 250, 500, 1000, 2000 mg/L)

- 90-d oral toxicity studies (dosed feed: NaVO3; dosed water: VOSO4) with Harlan Sprague-Dawley rats and B6C3F1/N mice (dose: rats and mice: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

- Organ systems toxicity, i.e. 28-d immunotoxicity study of NaVO3 (dosed-water) with female B6C3F1/N mice (dose: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

- post-natal developmental toxicity study: gestation day 6 (GD 6) until postnatal day 119 (PND 119) with Harlan Sprague-Dawley rats (dose: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

The results of the 14-day dose range finding experiments have already been published (Roberts et al. 2015) and also the first results of the 90-day repeated dose toxicity study and the post-natal developmental toxicity study have been shown as poster on a toxicological conference (Roberts et al. 2019). The publication of the fully study report is expected for end 2020 (personal communication with NTP staff).

These studies will address issues for which to date equivocal or no data at all exist. All hereto available information has been included in the dossier as robust study summaries. Only upon availability of the results from these studies, it will be possible to render a more meaningful decision on whether or not testing for reproductive toxicity is required. Therefore, for the time being this data requirement should be waived in consideration of animal welfare.

Effects on developmental toxicity

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

15 mg/kg bw/day

Species:

mouse

Quality of whole database:

Data of the developmental toxicity are available for very soluble tetra- and pentavalent substances via the oral route.
15 mg/kg bw/d sodium orthovanadate corresponds to 4.2 mg V/kg bw/d.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Developmental toxicity – animal data

An extensive literature/data search and evaluation programme on animal and human data relating to possible adverse effects of vanadium substances on developmental toxicity has recently been conducted. As an outcome, some data are available for very soluble tetra- and pentavalent substances (VOSO4 and Na3VO4) via the oral route.

One study (Sanchez et al. 1991) with administration of different dose levels of sodium orthovanadate of 0, 7.5, 15, 30 and 60 mg/kg body weight/day per gavage to pregnant mice on gestation days 6-15 was identified. In this study, maternal toxicity was observed at the highest doses levels, as evidenced by a significant number of deaths (60 and 30 mg/kg body weight/day) and reduced weight gain and food consumption a 30 and 15 mg/kg body weight/day. Embryo-lethality and teratogenicity were not observed at maternally toxic doses and below, but foetal toxicity was evidenced by a significant delay in the ossification process of some skeletal districts at 30 mg/kg body weight/day. The NOAEL for maternal toxicity was 7.5 mg/kg body weight/day and 15 mg/kg body weight/day represented a NOAEL for developmental toxicity in mice under the conditions of this study. However, it needs to be considered that foetal toxicity was observed at maternal toxic dose levels and can thus be regarded as secondary. Thus, the dose level of 30 mg/kg bw/d represents the LOEL for developmental effects and 15 mg/kg bw/d the NOEL for developmental effects at maternally toxic dose levels (reduced body weight gain and food consumption). These values correspond to 8.3 mg V/kg bw/d (LOEL) and 4.2 mg V/kg bw/d (NOEL).

One supportive developmental toxicity study (Paternain et al. 1990) with administration of different dose levels of vanadyl sulphate to Swiss mice was identified. Vanadyl sulphate was evaluated for its embryotoxic, fetotoxic and teratogenic potential in Swiss mice. The compound was administered by gavage to pregnant mice at doses of 0, 37.5, 75 or 150 mg/kg body weight/day on days 6 -15 of pregnancy. Maternal toxicity was observed in all vanadium-treated animals, evident by reduced weight gain, reduced body weight on gestation day 18 (corrected for gravid uterine weight) and decreased absolute liver and kidney weights at 75 and 150 mg/kg body weight/day. The number of total implants, live and dead foetuses, late resorptions, the sex ratio and the post-implantation losses were not significantly different between the vanadium-treated mice and the control. However, there was a significant increase in the number of early resorptions per litter at all dose levels. Fetotoxicity was evident by lower fetal weights and lengths and the presence of developmental variations. Malformation incidence also increased by administration of vanadium. Thus, the NOEL for maternal toxicity, embryo-/fetotoxicity and teratogenicity for vanadyl sulphate pentahydrate under these test conditions can be expected below 37.5 mg/kg body weight/day (11.72 mg V/kg bw/d) in Swiss mice.

In a study with intragastric administration of sodium metavanadate (Paternain et al. 1987), an oral NOAEL of 20 mg/kg bw/d was determined at the high dose level corresponding to 8.4 mg V/kg bw/d. There is no clear evidence of direct developmental effects in foetuses of dams exposed during gestational day 6-14 to different dose levels. However, no information on maternal toxicity was reported in the study. Additional supportive studies with administration of V2O5 by non-relevant routes of exposure (ip or iv) (Altamirano-Lozano, M. et al. 1993, Altamirano et al. 1991, Wide, 1984), or other vanadium compounds, e.g. ammonium metavandate (Morgan and El-Tawil, 2003, Carlton et al 1982) or sodium metavandate (Domingo et al. 1986, Gomez et al., 1992) could be found, but were not further considered.

From the study results it can be concluded that fetotoxic effects occurred in absence of unspecific parental toxicity, and therefore there is evidence that vanadium compounds induce developmental toxicity.

 

 

The NTP testing program conducted sub-chronic drinking water studies on VOSO4 and NaVO3 as follows:

- Genetic toxicology studies, i.e. the Salmonella gene mutation assays, with NaVO3 and VOSO4 - negative

- 14 days with Harlan Sprague-Dawley rats and B6C3F1/N mice (Dose: R&M: 0, 125, 250, 500, 1000, 2000 mg/L)

- 90-d oral toxicity studies (dosed feed: NaVO3; dosed water: VOSO4) with Harlan Sprague-Dawley rats and B6C3F1/N mice (dose: rats and mice: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

- Organ systems toxicity, i.e. 28-d immunotoxicity study of NaVO3 (dosed-water) with female B6C3F1/N mice (dose: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

- post-natal developmental toxicity study: gestation day 6 (GD 6) until postnatal day 119 (PND 119) with Harlan Sprague-Dawley rats (dose: 0, 31.3, 62.5, 125, 250, or 500 ppm) - ongoing

The results of the 14-day dose range finding experiments have already been published (Roberts et al. 2015) and also the first results of the 90-day repeated dose toxicity study and the post-natal developmental toxicity study have been shown as poster on a toxicological conference (Roberts et al. 2019). The publication of the fully study report is expected for end 2020 (personal communication with NTP staff).

These studies will address issues for which to date equivocal or no data at all exist. All hereto available information has been included in the dossier as robust study summaries. Only upon availability of the results from these studies, it will be possible to render a more meaningful decision on whether or not testing for developmental toxicity in rodents is still required. Therefore for the time being this data requirement should be waived in consideration of animal welfare.

Nevertheless, a testing proposal is added for a pre-natal developmental toxicity study in rabbits with sodium meta vanadate, being the source substances for the soluble vanadium substances read-across group.

Justification for classification or non-classification

An extensive literature/data search and evaluation programme on animal and human data relating to possible adverse effects of relevant vanadium substances on fertility and developmental toxicity has been conducted. There is only equivocal evidence for effects on fertility for the soluble vanadium substances read-across group and no evidence for the poorly-soluble vanadium substances read-across group. Due to ongoing (NTP study expected for 2021) and planned testing (see testing proposal), a definitive conclusion for classification and labelling cannot be made at this point in time. The registrant will update the dossier without undue delay, as soon as the above mentioned information will become available.