Nickel bis(dibutyldithiocarbamate)

Carcinogenicity

Description of key information

In an oral mouse carcinogenicity study (pre-guideline and pre-GLP) there was no significant increased incidence of tumours in females. However, the carcinogenic potential of the substance is still evaluated as this has been described for nickel-containing compounds. See the information in 'Additional information' for more details.

Based on the available data, the substance is considered a suspected carcinogen (Carc. Cat. 2: H351).

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available data on genotoxicity and carcinogenicity of the substance and on structural analogues, there is limited evidence for carcinogenicity in human or animal studies. Therefore, the substance has to be classified as Carc. Cat. 2: H351 (suspected of causing cancer), in accordance with EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation No. (EC) 1272/2008.

Additional information

Justification for the classification of Nickel dibutyldithiocarbamate (CAS nr. 13927-77-0) as carcinogenic category 2: Suspected human carcinogens

 

Available physicochemical properties

The substance has a Ni(II) ion bound to two dithiocarbamate groups. The nitrogen in the dithiocarbamate moiety is bound to two identical butane groups. The substance is a solid with a molecular weight of 467.54 g/mol. The log P value was estimated using a QSAR model, resulting in a value of 5.44. The water solubility was determined to be 0.0893 mg/L (at 20°C).

 

Available experimental data

For the substance (CAS nr. 13927-77-0) two Ames tests, a MLA and a MN test are available, as well as a 18-month carcinogenicity study. In all in vitro assays the test substance was dissolved in DMSO. In an Ames test according to OECD TG 471 and GLP, TA 1535, TA 1537, TA 98, TA 100 and WP2uvrA were exposed to 62, 185, 556, 1667, 5000 μg/plate in a single test (plate incorporation) with and without metabolic activation (S9-mix) (Triskelion B.V., 2017). Under the conditions of this test, the test substance did not induce a more than 2-fold and/or dose related increase in the mean number of revertant colonies compared to the background spontaneous reversion rate observed with the negative control. In a supporting Ames test (HRC, 1985), S. typhimurium strains TA 1535, TA 1537, TA 1538, TA 98 and TA 100 were exposed to 50, 150, 500, 1500, and 5000 µg/plate of the test substance dissolved in DMSO with and without metabolic activation (S9-mix). No substantial increases in revertant colony numbers of any of the five tester strains were observed following treatment at any dose level, either in the presence or absence of metabolic activation.

The test substance was examined for its potential to induce gene mutations at the Tk-locus of cultured mouse lymphoma L5178Y cells, in both the absence and the presence of an exogenous metabolic activation system (S9-mix), in a study according to OECD TG 490 and GLP (Triskelion B.V., 2018a). Two independent experiments were performed. In the first experiment, the treatment period was 4 hours in the presence and absence of S9-mix. In the second experiment, the treatment period was 24 hours in the absence of S9-mix. In both experiments the final concentrations tested ranged from 500 to 3.9 μg/mL. Single cultures were used. All acceptance criteria for the positive and negative control substances were met. In both the first and second experiment, the test substance was slightly cytotoxic to the cells resulting in a reduction of the relative total growth (RTG). In both the absence and presence of S9-mix no increase in mutant frequency (MF) by more than 126 mutants per 1,000,000 cloneable cells, i.e. no positive response, compared to the negative control was observed at any of the concentrations tested.

The test substance was examined for its potential to induce micronuclei in cultured binucleated human lymphocytes, in the absence and presence of metabolic activation (S9-mix) in a study according to OECD TG 487 and GLP (Triskelion B.V., 2018b). Two independent experiments were performed. In the first experiment the treatment/recovery time was 4/20 hours (pulse treatment), both in the presence and absence of S9-mix. In the second experiment, the treatment/recovery time was 24/0 hours in the absence of S9-mix (continuous treatment). In both experiments the final concentrations tested ranged from 500 to 1 μg/mL. Duplicate cultures were used. Cytotoxicity was determined from the Cytokinesis-Block Proliferation Index (CBPI). In both experiments, acceptance criteria of the negative and positive controls were met. No cytotoxicity was observed at any concentration analysed when compared to the concurrent solvent control cultures in both experiments. In both experiments, the test substance did not show a statistically significant increase in the number of binucleated cells containing micronuclei at any of the concentrations analysed when compared to the concurrent solvent control cultures.

 

In the carcinogenicity study (Bionetics Research Laboratories, 1968), the substance was tested in two mice strains: B6C3F1 and B6AKF1. 18 male and 18 female mice per strain were exposed for 18 months to the test substance at 0.1 mg/kg bw in 0.5% gelatin by oral gavage for the first 3 weeks followed by exposure via feed. Of the B6AKF1 mice, in 3 male and 3 females pulmonary adenoma were observed. No other tumours were detected in this strain. One female B6C3F1 mice had also a pulmonary adenoma. In one male B6C3F1 mice a reticulum cell sarcoma, Type A was observed, one male mice had a pulmonary adenoma, and in 3 male mice hepatoma were observed. The observed tumours in exposed mice were not statistically different from the control animals. As this study has been performed prior to the implementations of official guidelines, several limitations exist in the design of this study. First of all only mice and no rats were studied. Only 18 animals per sex were tested instead of the required 50 per sex. Furthermore, animals were exposed for only 18 months instead of two years and finally only one dose level has been tested.

 

Carcinogenicity of nickel compounds

Several international agencies have evaluated the evidence regarding the carcinogenic effects of nickel, including IARC, ATSDR, and NTP. The most recent evaluation is the one of the IARC (2012). The IARC considers nickel compounds to be carcinogenic to humans (Group 1). However, not all nickel substances are carcinogenic in the performed tests. Both water soluble and poorly water-soluble nickel species are taken up by cells. Soluble nickel compounds after inhalation exposure are rapidly absorbed through the lungs, and excreted in the urine. Insoluble nickel species are absorbed by phagocytosis and nickel ions are gradually released. According to IARC, the ultimate genotoxic agent is Ni(II). Direct reaction of Ni(II) with DNA does not seem to be relevant under realistic exposure conditions, but several indirect mechanisms have been identified, such as oxidative stress, inhibition of DNA repair, and epigenetic mechanisms.

In general, nickel compounds are not mutagenic in bacterial test systems, and are only weakly mutagenic in cultured mammalian cells. For water insoluble nickel compounds the likely determinant of carcinogenicity is the bioavailability of the nickel ion released from these compounds to the critical site in the target cells in the lung. Nickel substances with very low bioavailability may not cause tumours at all.

 

CLP Classification

Two articles in the Classification, Labelling, and Packeging (CLP) Regulation (EC) No. 1272/2008 are relevant for classifying the substance for carcinogenicity in accordance with CLP Regulation (EC) No. 1272/2008. According to section 3.6.2.1. of this regulation:

“For the purpose of classification for carcinogenicity, substances are allocated to one of two categories based on strength of evidence and additional considerations (weight of evidence). […]

The placing of a substance in Category 2 is done on the basis of evidence obtained from human and/or animal studies, but which is not sufficiently convincing to place the substance in Category 1A or 1B, based on strength of evidence together with additional considerations. Such evidence may be derived either from limited evidence of carcinogenicity in human studies or from limited evidence of carcinogenicity in animal studies.”

 

According to section 3.6.2.2.7 of the CLP Regulation (EC) No. 1272/2008:

“A substance that has not been tested for carcinogenicity may in certain instances be classified in Category 1A, Category 1B or Category 2 based on tumour data from a structural analogue together with substantial support from consideration of other important factors such as formation of common significant metabolites, e.g. for benzidine congener dyes.”

 

In addition, 100 nickel compounds are harmonized classified as carcinogenic category 1 in Annex VI of the CLP Regulation (EC) No. 1272/2008. This classification is based on a report commissioned by the Danish EPA (Hart, 2008). In this report all nickel compounds have been evaluated and a read-across is performed to classify these nickel compounds based on the data available from a limited number of nickel compounds. The substance under consideration in this dossier is however excluded from this read-across approach.

 

Conclusion

The available data indicates that the substance is not mutagenic or cytogenic in vitro and not carcinogenic in an 18-months carcinogenicity test. Negative in vitro genotoxicity tests are quite common for nickel compounds as they are assumed not to directly interact with DNA. In the 18-months carcinogenicity study, no increase in tumours has been observed. However, this does not exclude the possibility that the substance is carcinogenic. First of all limitations exist in the design of the study but more importantly the inhalation route has not been investigated.

As most of the nickel compounds have been classified as carcinogenic category 1, the substance under consideration in this dossier could also be carcinogenic. It appears that the ionic form of nickel is the ultimate carcinogenic specie. However, it is uncertain whether the nickel in the substance may sufficiently dissociate from the organic moiety to reach concentrations at critical sites and subsequently cause carcinogenic effects. Therefore, as a precautionary measurement, the substance will be classified as carcinogenic category 2 according to CLP Regulation (EC) No. 1272/2008.

 

References

Bionetics Research Laboratories, Evaluation of Carcinogenic, Teratogenic, & Mutagenic Activities of Selected Pesticides and Industrial Chemicals. Volume I: Carcinogenic Study, August 1968, National Cancer Institute (NCI)

Hart, J., Nickel compounds – a category approach for metals in EU legislation, prepared on behalf of the Danish Environmental Protection Agency, January 2008

Huntingdon Research Centre Ltd., Ames metabolic activation test to assess the potential mutagenic effect of Naugard NBC, 25 November 1985.

IARC Monographs on the evaluation of carcinogenic risks to humans, Volume 100C, Arsenic, Metals, Fibres and Dustsm, 2012, page 169-218.

Triskelion B.V. 2017: Bacterial reverse mutation test with Nickel dibutyldithiocarbamate (study report), Testing laboratory: Triskelion B.V., Utrechtseweg 48, 3704 HE Zeist, The Netherlands, Report no: V21005/02. Owner company; Performance Additives Italy S.p.A., Report date: Sep 8, 2017

Triskelion B.V. 2018a: In vitro mammalian cell gene mutation test at the TK-locus of L5178Y cells with Nickel dibutyldithiocarbamate (study report), Testing laboratory: Triskelion B.V., Utrechtseweg 48, 3704 HE Zeist, The Netherlands, Report no: V21003/03. Owner company; Performance Additives Italy S.p.A., Report date: Apr 19, 2018

Triskelion B.V. 2018b: In vitro micronucleus test with Nickel dibutyldithiocarbamate in cultured human lymphocytes (study report), Testing laboratory: Triskelion B.V., Utrechtseweg 48, 3704 HE Zeist, The Netherlands, Report no: V21017/02. Owner company; Performance Additives Italy S.p.A., Report date: Apr 12, 2018