Sodium 2,4-dichlorophenoxyacetate

Endpoint summary

Additional information

In vitro genotoxicity:

In an Ames test conducted equivalently to OECD Guideline 471 (Bacterial Reverse Mutation Assay), Salmonella typhimurium strains TA 97A, TA98, TA100 and TA 102 were treated with the test substance diluted in distilled water (Key, NZPO Organika Rokita, Baranski, 1991, Ames, RL2). Test substance concentrations of 0, 1, 10, 100, 1000 µg test substance /plate were tested both with and without the addition of a rat liver homogenate metabolising system (S9-mix). In deviation to the guideline, only two technical replicates were conducted in two independent experiments. Cytotoxicity was observed in S. typhimurium TA 97A at 1000 µg/plate without metabolic activation but no significant increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test material, either with or without metabolic activation. All values of the controls and tester strains were well within the historical control range.

An in vitro Unscheduled DNA-Synthesis Test (UDS) was conducted with dimethylammonium 2,4-dichlorophenoxyacetate (CAS No. 2008-39-1) according to the EPA-Pesticide Assessment Guidelines, Subdivision F, Hazard Evaluation, Human and Domestic Animals (RA, CAS 2008-39-1, Key, Charles, 1999, UDS, RL2) to measure the DNA repair synthesis after damage and excision of DNA containing induced by the test substance. Primary hepatocytes of Fischer-344 Rats were exposed with 1.6, 3.3, 6.6, 16.5, 33.1, 66.2 µg/ml test substance based on active ingredient content.There was no significant change in the Net Nuclear Grain Count (NNG) in this UDS-assay. Therefore, the test substance is considered not genotoxicunder the conditions tested.

 

An in vitro Mammalian Cell Gene Mutation Test (HPGRT) was conducted with 2,4-D, isopropylamine salt (CAS 5742-17-6), an analogous substance to the test substance according to the methods described by O'Neill and Hsie (1979) and O'Neill et al. (1977, 1982). Chinese hamster Ovary cells (CHO-K1-BH4) were dosed with 0, 500, 1000, 1500, 2000 and 3000 µg/mL with and without metabolic activation. All values were within the historical controls and cytotoxicity was observed only in the highest dose (3000 µg/mL) without metabolic activation. There was no significant increase in the number of forward mutations at the thymidine kinase locus of cells treated with the test material, indicated by the mutation frequency (RA, CAS 5742-17-6, Key, Gollapudi, 1999, HGPRT, RL2).

In vivo genotoxicity:

A micronucleus assay was conducted with sodium 2,4-dichlorophenoxyacetate (CAS No. 2702-72-9) according to the two-phase experimental model as recommended by Przybojewska (1988).

5 animals per dose group (only 4 in the control groups) were dosed by intraperitoneal injection with 287 mg/kg for female mice and 135 and 269 mg/kg kg for female mice. Doses were based on mortality in a range finding study (80% and 40% of LD50). No increase in the incidence of micro-nucleated polychromatic erythrocytes in any sex or at any time point in the treated mice was observed. Therefore no clastogenic potential could be detected in this test (Key, NZPO "Organika-Rokita", Baranski, 1991, Micronucleus, RL2).

 

The amount of sister chromatid exchanges was tested after treatment of 5 Male Balb/c mice with sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9), an analogous substance to the test substance according to the protocol of the GENE-TOX program (Latt et al., 1981), using a method with implantation of bromodeoxyuridine tablets (Allen et al., 1977). Animals were exposed to single doses of 0, 67, 134, 201, 268 mg/kg bw by intraperitoneal injection. 50 second-generation metaphase cells from each mouse were evaluated and the dose-related increase in the number of SCEs per cell was calculated. A slight, but significant increase in the amount of SCE was observed in all doses compared to the control level. The positive control resulted in clearly positive results exceeding the results of the treatment groups by a factor of 4. Under the conditions of this study, sodium 2,4-dichlorophenoxyacetate is considered to be a weak genotoxicant (NZPO "Organika-Rokita", Baranski, 1991, SCE in vivo, RL2).

 

Human experiments

Additional information on the genotoxicity could be obtained from an evaluation of sister chromatid exchange (SCE) frequencies in peripheral blood lymphocytes from workers exposed to sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9). The test group consisted of 8 male employees in the section of 2,4-D acid production, aged 35-60 years (mean 48.5), the duration of their employment was 15-39 years ( mean 26). The control group consisted of 8 age-matched workers without exposure to 2,4-D acid. Fifty well-spread and complete second-division metaphases of blood lymphocytes were analysed and the mean number of SCE per cell were calculated.

The difference between mean SCE frequency in the exposed and the control group was not statistically significant (α = 0.05). In both groups, significant higher SCE frequencies were observed in lymphocytes of smokers. These positive results for smokers demonstrate sufficient sensitivity of the used system. According to the result of this observation sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9) has no genotoxic potential in human lymphocytes.

 

The assessment of systemic effects of salts of 2,4-D is based on data generated with 2,4-D acid. This read across is justified because 2,4-D acid and its salts are toxicologically equivalent once they have entered the system. This is due to the only diffusion-limited rate of reaching the acid-base equilibrium between the protonated acid and its deprotonated salt form in an aqueous environment like the human body. Thus, salts of 2,4-D will exert the same systemic effects as the corresponding acid.

Taken together, the results of the studies available to evaluate the genotoxic potential do not reveal a toxicological concern for a genotoxicity of sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9).

Although there is a weakly positive result for a SCE-analysis conducted in vivo, there are clearly negative results of the available in vitro studies together with the negative in vitro and in vivo experiments used as read-across and the negative results of the observations conducted with exposed workers. Therefore, it can be assumed that sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9) is not genotoxic, neither in vitro nor in vivo.

Short description of key information:
In vitro
Key, NZPO Organika Rokita, Baranski, 1991, Ames, RL2 - not mutagenic
RA, CAS 2008-39-1, Key, Charles, 1999, UDS, RL2 - not clastogenic
RA, CAS 5742-17-6, Key, Gollapudi, 1999, HGPRT, RL2 - not mutagenic

In vivo
Key, NZPO "Organika-Rokita", Baranski, 1991, Micronucleus, RL2 - not clastogenic
NZPO "Organika-Rokita", Baranski, 1991, SCE in vivo, RL2 - weak clastogen

Human experiments
NZPO "Organika-Rokita", Wyszynska, 1992, SCE human, RL2 - not clastogenic

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

According to the DSD and CLP criteria for classification and labelling of dangerous substances sodium 2,4-dichlorophenoxyacetate (CAS 2702-72-9) is not classified as mutagenic.