mancozeb (ISO); manganese ethylenebis(dithiocarbamate) (polymeric) complex with zinc salt  

Neurotoxicity

Description of key information

Based on effects in the nervous system, classification of mancozeb with STOT RE 2 is justified.

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Additional information

The summary below is taken from the RAC Opinion proposing harmonised classification and labelling at EU level (March 2019) of Mancozeb.

The table below summarises findings related to neurotoxicity in the rat oral and inhalation studies including several studies which were negative with respect to neurotoxicity (however, negative studies with relatively low top doses have been omitted from the table). No specific signs of neurotoxicity were seen in the other three species tested (mouse, dog, rabbit) nor the in the rat dermal studies.

RAC notes that functional tests were probably not conducted in any of the available studies with the exception of the developmental neurotoxicity study by Anon. (2008c), which was negative. However, the top dose in this study was rather low (30 mg/kg bw/d).

 

Observations related to neurotoxicity in rat oral and inhalation repeated dose studies
Type of study; Reference	Observations related to neurotoxicity
28-day gavage Anon. 1994b	500 mg/kg bw/d: 1/6 females hind limb paralysis and killed for humane reasons on day 21; 2/6 females hind limb paralysis on day 28 200 mg/kg bw/d: 1/8 females ataxia and killed for humane reasons on day 13; 2/8 females ataxia 50 mg/kg bw/d: no effects
12-week dietary (males only) Szépvölgyi et al. 1989	379 mg/kg bw/d: mortality 4/12 week 1-6; clinical signs: prostration, weakness and posterior distal paralysis before death of the 4 animals; signs were transient in survivors and absent at 12 weeks 253 mg/kg bw/d: no neurotoxicity-related findings
90-day gavage Anon. 1999c	400 mg/kg bw/d: mortality 2/24; no neurotoxicity-related findings
90-day neurotoxicity, dietary Anon. 1991e	339/413 mg/kg bw/d (m/f): Mortality: 1/10 males and 4/10 females weeks 2-4; treatment of females discontinued from day 15; large reductions in food consumption and bw loss in initial females during the first 2 weeks Clinical signs: abnormal gait and/or limited or no use of hind limbs (all animals, from week 2-3, some improvement by day 60), general weakness Histopathology: demyelination and Schwann cell proliferation in males and females; posterior thigh muscle atrophy (10/16 females)   50/63 mg/kg bw/d (m/f): No clinical signs of toxicity Histopathology: demyelination, Schwann cell proliferation (incidences provided in a separate table below)   8.2/10.5 mg/kg bw/d (m/f): no effects
90-day dietary Anon. 1986b	57/75 mg/kg bw/d: no neurotoxicity-related findings
Prenatal developmental toxicity, gavage, dosing GD 6-15 Anon. 1980	512 mg/kg bw/d: 1/22 died, 2/22 killed after abortion; clinical signs: lethargy, ataxia, scruffy coat, diarrhoea or soft faeces, hunched, dehydrated
Prenatal developmental toxicity, gavage, dosing GD 6-15 Anon. 1988c	360 mg/kg bw/d: 1/25 killed in extremis, preceded by clinical sings (marked body weight loss, hind limb paralysis); further 4/25 slight, transient hind limb paralysis at the end of the dosing period
2-week gavage (females only) Anon. 2015b	300 mg/kg bw/d: no clinical signs of toxicity
Prenatal developmental toxicity, gavage, dosing GD 6-19 Anon. 2015d	160 mg/kg bw/d: no clinical signs of toxicity
Developmental neurotoxicity, gavage, dosing GD 7 – PND 16 Axelstad et al. 2011	Range-finding study: 500, 350 and 200 mg/kg bw/d: severe weight loss and hind limb paralysis in all groups by GD 12 (severity was dose-dependent), most dams sacrificed on GD 14 Main study: 150 mg/kg bw/d: severe weight loss, mild hind limb paralysis
Prenatal developmental toxicity, inhalation, GD 6-15 Lu and Kennedy 1986	0.89 mg/L: mortality 30/37; hind limb weakness 11 animals (mild to moderate) 0.11 mg/L: mortality 3/37; hind limb weakness 24/37 (mild; onset after 7 exposures, persisted for 3 days after the last exposure) 0.055 mg/L: hind limb weakness 6/27 (mild)
90-day inhalation Anon. 1986d	0.33 mg/L: no clinical signs of toxicity

 

The following table shows incidences of the histopathological findings at the mid-dose in the 90-day dietary neurotoxicity study Anon. (1991e).

Incidences of histopathological findings in the 90-day neurotoxicity study Anon. (1991e) at 750 ppm (50/63 mg/kg bw/d)
	Males	Females
Number of animals examined	10	10
Cervical, dorsal root ganglion sections: Myelin bubbles Myelin phagocytosis Schwann cell proliferation	1 1 1	1
Lumbar, dorsal root sections: Myelin bubbles* Myelin phagocytosis Schwann cell proliferation	1 1 1
Lumbar, dorsal root ganglion sections: Myelin bubbles* Myelin phagocytosis Schwann cell proliferation	2 1 1
Lumbar, ventral root sections: Myelin bubbles Myelin phagocytosis Schwann cell proliferation	3 1 1	1
Tibial nerve, lower: Myelin bubbles Myelin phagocytosis Schwann cell proliferation	2 2

* observed also in 1 control female

Clinical signs of neurotoxicity (hind limb weakness or paralysis, ataxia) were observed in several rat studies, in the oral studies mostly above 200 mg/kg bw/d, starting within the first few weeks of treatment. Demyelination and Schwann cell proliferation were identified as the histopathological correlate in the 90-day neurotoxicity study (Anon., 1991e) and appeared at a low incidence without clinical signs also at 50 mg/kg bw/d, which was below the GV for Category 2.

RAC considers the histopathological findings at the mid-dose in the 90-day neurotoxicity study sufficient for classification in Category 2, noting that similar damage may have occurred also in other rat studies without being detected due to lack of specific investigations (e.g., nerve fibre teasing). The clinical signs of neurotoxicity, although appearing mostly above the GVs, are considered to provide additional support for classification. Moreover, manganese, contained in mancozeb at a relatively high percentage, is an established neurotoxicant, and mancozeb itself has been shown to affect various neuronal cell populations in vitro (Domico et al., 2006), which further strengthens the case for classification.

ETU is most likely not the metabolite causing the neurotoxic effects, since ETU produced no evidence of neurotoxicity or developmental neurotoxicity in an extended one-generation reproduction toxicity study in rats, which included the cohort for developmental neurotoxicity (Anon., 2013).

Although neurotoxicity was only observed in the rat and not in the other species (the mouse and the dog), there is no information disproving human relevance of the rat findings. RAC notes that the mode of action of mancozeb-induced neurotoxicity is largely unknown.

Therefore, RAC agrees with the DS that classification of mancozeb with STOT RE 2 for effects on the nervous system is justified.

The consideration of other organs by RAC did not lead to proposed STOT RE classification and is discussed in the Background Document.

Route of exposure

According to the CLP regulation, the exposure route should be stated if it is conclusively proven that no other routes of exposure cause the hazard. As thyroid effects in the dog contributed to classification and no dog studies via the dermal and inhalation routes are available, effects warranting classification via those routes cannot be excluded in this species. In addition, neurotoxicity below the GVs was seen not only in oral studies but also after inhalation exposure in the rat (Lu and Kennedy, 1986). Hence, the conditions for specifying the exposure route are not fulfilled.

 

 

Justification for classification or non-classification

The overall conclusion on classification below is taken from the RAC Opinion proposing harmonised classification and labelling at EU level (March 2019) of Mancozeb.

RAC agrees with the DS that classification of mancozeb with STOT RE 2; H373 (thyroid; nervous system) is justified. This classification is based on reduced T4 levels in the dog and the rat and on neurotoxic findings in the rat. Mortality in the rat, the dog and the rabbit provides additional support for classification but in this case is not sufficient to trigger classification on its own. Contrary to the dossier submitter’s proposal, RAC does not consider it appropriate to specify the exposure route.

 

The registrant follows this conclusion.