Manganese dinitrate

Endpoint summary

Description of key information

Please refer to the RAAF report attached to section 13 of this dataset which discusses the cateogory approach for sharing of data between the three soluble manganese salts Mn chloride, Mn nitrate and Mn sulphate.

There is a body of publicly available literature data on repeated application of MnCl2 however, these data are not conducted according to standardised test guidelines or the principles of GLP and are of varying quality and reliability.  Whilst the literature for repeated dose toxicity of MnCl2 shows a variety of effects on repeated application of MnCl2, these studies are not consistent in their dosing methods, duration, or with the species of test animals that are used.  As a consequence of this, the results are variable and not aligned with observations from more reliable studies conducted to standardised international guidelines and GLP.  Therefore the effects observed in the reproductive and developmental toxicity studies on MnCl2 via the inhalation route are given more weight than the lower reliability literature references and are considered to be the better indicator of the long term toxicological effects of this substance via the inhalation route rather than the older literature data.

In the reproductive toxicity study by Grieve (2017) subsequently published by McGough & Jardine (2016) clinical signs of reaction to treatment to inhalation exposure of MnCl2 were confined to a few animals with wheezing respiration in the F0 generation exposed to 10 and 20 μg/L.  At 20 μg/L, overall body weights and food consumption of the F0 males throughout the study were lower than controls.  At target 10 and 20 μg/L, there was a statistically significant increase in kidney weights compared to the controls, however there was no alteration in the normal structure of these organs.  In all treated F0 females, there was a statistically significant increase in lung weights compared to the controls which was not evident in the F1 females.  The NOEL for adult effects was not established due to effects on the respiratory tract.  However, the respiratory tract effects observed are commonly observed in irritant materials and were considered not to be a unique effect of MnCl2 and therefore, when the local irritant effects are disregarded, the parental NOAEL was considered to be 20 μg/L (Grieve, 2017).

In the developmental toxicity study (Dettwiler, 2015) conducted in accordance with OECD Guideline 414, treatment with MnCl2 caused breathing noises in eight females in exposed to 15 μg/L air and eighteen females exposed to 25 μg/L air.  Treatment caused a dose dependent reduction in food consumption in groups exposed to 15 μg/L air and 25 μg/L air. This reduction was statistically significant during the most of the study and was accompanied by reduced body weights, reduced body weight gain during the study and reduced corrected body weight gain at termination at both dose levels and therefore effect on food consumption was considered to be adverse.  Histopathology examination performed on the lungs from six selected pregnant females per group revealed lesions with a dose dependent frequency and severity in groups exposed to 15 μg/L and 25 μg/L.  The macroscopically identified foci in two females in groups exposed to 25 μg/L were correlated to alveolar haemorrhage or phagocytic alveolar macrophage foci. Based on these results, the NOAEL as well as the NOEL for the toxicity in pregnant females were considered to be 5 μg/L air.  In non-pregnant females, the NOEL for systemic toxicity was established at 15 μg/L air, whereas the NOAEL was established at 25 μg/L air.  These observations are consistent with a number of literature references indicating a loss of body weight during administration of MnCl2 and a developmental neurotoxicity study which also noted this loss and a dose-dependent reduction in food consumption (Dettwiler, 2016).

The repeated dose studies on MnSO4 were from the US National Toxicology Program technical report on the toxicology and carcinogenesis of manganese(II) sulphate monohydrate in F344/N rats and B6C3F1 mice (feed studies) (NTP, 1993).  The studies were not conducted to then-standardised guidelines but to peer reviewed methods as specified by the NTP and as such are considered wholly reliable. The high level of MnSO4 consumed by rats on a daily basis for 13 weeks in this study, without mortality, supports the lack of acute toxicity.  In the two-year study survival of male rats exposed to 15 000 ppm was significantly lower than that of the controls attributed to increased incidences of advanced renal disease relating to the ingestion of MnSO4. The final mean bodyweight of male rats exposed to 15 000 ppm was 10 % lower than that of the controls. The mean body weights of all the other exposed groups were similar to the controls (NTP, 1993).  At both the 9- and 15-month interim evaluations, tissue concentrations of manganese were significantly elevated in the livers of male and female rats exposed to 5 000 and 15 000 ppm, with an accompanying depression of hepatic iron.  The ingestion of diets containing 15 000 ppm MnSO4 was associated with a marginal increase in the average severity of nephropathy in male rats. In these rats, lesions associated with renal failure, uraemia, and secondary hyperparathyroidism were observed.  No increased incidence of neoplasms in male or female rats was attributed to ingestion of MnSO4.  There was no evidence of carcinogenic activity of manganese sulphate monohydrate in male or female F344/N rats (NTP, 1993).

In mice, no clinical findings were attributed to manganese sulphate ingestion at 13 weeks (NTP, 1993).  Concentrations of manganese were significantly elevated in the livers of mice exposed to 5 000 and 15 000 ppm at the 9 and 15 month evaluations. It was uncertain if the slightly increased incidence of follicular cell adenoma is related to the ingestion of MnSO4. The study suggests equivocal evidence of carcinogenicity in male and female mice. Based on marginally increased incidences of thyroid gland follicular cell adenoma and significantly increased incidences of follicular cell hyperplasia (NTP, 1993).

There are no data available on manganese dinitrate itself.

As stated above, given that the toxicity of the soluble manganese salts is generally accepted to be attributed to the Mn2+ ion it is proposed to use read across to maximise the use of the available data.

The lack of GLP, guideline studies performed on MnCl2 to specifically investigate the repeated dose effects warrants the application of the information generated in the reproductive and developmental  toxicity studies on this substance.  These studies are conducted under GLP conditions to modern standardised guidelines and are considered to provide adequate information with regards to the long term effects of the substance via the inhalation route.  Similarly it is considered appropriate to use these same studies as the source of data to address the repeated dose toxicity of MnSO4 via the  inhalation route as no data are available on the toxicity of the sulphate via this route  of exposure.

The repeated dose toxicity studies conducted on MnSO4 in support of the NTP programme are well conducted and reliable studies and are considered to be the most appropriate source of data on the long term effects of exposure to the Mn2+ ion via the oral route.  As such it is considered appropriate to use these studies to support this endpoint in both the MnSO4 dossier and as read across in the MnCl2 dossier.  These studies on MnSO4 via the oral route do not result in the classification of the substance and in conjunction with studies via the inhalation route conducted on MnCL2 are considered to represent the “worst case scenario” in relation to the effects of long term exposure to soluble manganese salts.

No repeated dose toxicity studies are available on Mn(NO3)2 manganese dinitrate  and read-across is proposed for these endpoints. As described above, given that the toxicity of the soluble manganese salts is generally accepted to be attributed to the Mn2+ ion in conjunction with the lack of any modern studies performed on Mn(NO3)2 , it is considered appropriate to utilise read-across to the key studies performed on MnCl2 (inhalation exposure) and MnSO4 ( Oral exposure). Furthermore, it is considered that these guideline studies can be considered to give an accurate representation of the toxicity of the Mn2+ ion in Mn(NO3)2 and should therefore be considered adequate to address these endpoints. These studies via the oral route (MnSO4) do not result in the classification of the substance and as such the studies via the inhalation route as conducted on MnCL2 are considered to represent the “worst case scenario” in relation to the effects of long term exposure to soluble manganese salts.

Read-across between the three salts is considered to be justified based on the high water solubility and ultimate identical physiological fate all three salts share once the anions disassociate into the respective endogenous physiological pools.  In the case of both MnCl2 and MnSO4, evidence suggests that repeated dosing triggers a strong homeostatic response which reduces the toxicity by presumably increasing excretion/decreasing absorption (Vrcic and Kello, 1988).  This can be taken as further evidence that read-across between these three soluble manganese salts  is justified.

Toxicokinetic and toxicity data confirm  that the manganese cations are the driving factor for any human health effects observed.  The respective anions, chloride (Cl-), sulphate (SO42-) and nitrate (NO3 ), are readily absorbed and excreted from the human body, and their contribution on toxicological effects is not considered significant.

Justification for classification or non-classification

Manganese dinitrate is not proposed for classification via the oral route for repeated exposure. This is based on read-across from the NTP oral studies (13- week and 2 -year) on manganese sulphate (IUCLID section 7.5.1) which did not indicate any significant oral toxicity. Specifically, Mn2+ contributes 30.7% to any given weight of manganese nitrate administered to an animal, whereas Mn2+ contributes 36% in manganese sulphate . Therefore for the same dose of substance (anhydrous equivalent), any systemic effect from manganese nitrate is likely to be less than manganese sulphate, based on the anions having comparable systemic toxicity, once any local effects from the nitrate ion have been ruled out by careful dose selection. Although manganese sulphate is currently classified in Annex I of Directive 67/548/EEC as R48/20/22, a self-classification for R48/20 only and STOT RE2 (inhalation) has been proposed for manganese sulphate, based on the lack of oral effects in the NTP studies and therefore this same classification will be read across to the manganese nitrate.

Manganese dinitrate is proposed for classification via the inhalation route for repeated exposure. This is based on read-across from manganese sulphate's classification and supported by animal data for the inhalation route (see IUCLID section 7.9.1). Although manganese dinitrate is classified as corrosive, the effects at high dilutions (e.g. diluted sprays) will be based on systemic toxicity caused by the Mn2 +, rather than local effects. It is also likely that any effect seen via inhalation will not be any worse than manganese sulphate, for equivalent intake of substance, due to the difference in the relative molecular weight contribution of Mn2+ in each substance.

Specifically, Mn2+ contributes 30.7% to any given weight of manganese nitrate administered to an animal, whereas Mn2+ contributes 36% to any given weight of manganese sulphate . Therefore for the same dose of substance(anhydrous equivalent), any systemic effect from manganese nitrate is likely to be less than manganese sulphate, based on the anions having comparable systemic toxicity, once any local effects from the nitrate ion have been ruled out by careful dose selection. So, for repeat dose the proposal to match the classification to manganese sulphate is considered scientifically valid.

Manganese dinitrate is not proposed for classification via the dermal route for repeated exposure.

No dermal classification is justified by the expected low dermal absorption of manganese dinitrate, based on a dermal absorption study on MnCl2 showing only 2% absorption of Mn2+. Manganese dinitrate has a bigger, more polar anion than the chloride anion and this is likely to lead to an even lower dermal absorption. This is supported by the knowledge that manganese chloride has greater oral absorption than the sulphate (Bales et al (1987), IUCLID section 7.1.1), which is considered a more structurally analogous anion to the nitrate. Therefore the dermal absorption would not be expected to be significant for the registered substance.

Read-across from manganese sulphate to manganese nitrate is justified based on having both high water solubility and structural similarities and comparable percentage of Mn2+ in the molecular formulae.