Guanidinium thiocyanate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Based on data from the read-across substances Potassium Thiocyanate and Guanidine Hydrochloride there is no concern for effects on fertility of Guanidine Thiocyanate.

Link to relevant study records

Reference

Endpoint:

reproductive toxicity, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

For justification for read-across applying the analogue approach please refer to attached document in Chapter 13.2 "other assessment reports".

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Species:

rat

Strain:

Wistar

Key result

Remarks on result:

other: Chronic thiocyanate feeding (for eight weeks from weaning) produced a moderate degree of hypothyroidism in the dams

Key result

Remarks on result:

other: thiocyanate feeding (25 mg/rat/day) did not affect reproductive performance and postnatal performance of their offspring.

Key result

Reproductive effects observed:

no

Conclusions:

A reproductive toxicity study (Bala et al 2007) was conducted were three different dietary feeding regimes were used to investigate feeding of 25 mg/rat/day of KSCN in comparison to a dietary iodine deficiency at different stages during pregnancy and parturition.
In contrast to iodine deficiency dietary were marked effects were observed, feeding of dietary KSCN during pregnancy and up to 21 days of lactation, did not reveal any effects on the indices of reproductive performance such as percentage of conception, mortality of dams during pregnancy and parturition, litter size, and survival and performance of pups till weaning. Further none of the three thiocyanate feeding regimes revealed effects on the pup's birth-weight, or on the wet weight of their brains per unit body weight at weaning.
It can be stated that based on the results of the study thiocyanate feeding (25 mg/rat/day) did not affect reproductive performance and postnatal performance of their offspring.

The 2-generation study (Raghunath et al 1998) was conducted with focus on nutrient transport across blood-brain barrier and does not follow OECD guidelines or GLP.
Continued maternal feeding of KSCN (25 mg/rat/day) over two generations had no effect on the body weights of pups (F2) at birth or at weaning (21 days of age) as compared to corresponding controls (F2).
Similarly the brain weights were also not different between the control and KSCN pups (F2). However the decrease in serum T4 level at weaning was more marked in F2 (KSCN) pups compared to their F1 counterparts (1.84 µg/dl vs 3.3 µg/dl in F1 vs F2 pups). The blood-brain barrier (BBB) transport of all the three nutrients tested (2-deoxy-D-glucose, L-Leucine L-Tyrosine) was significantly reduced in F2 pups of KSCN fed mothers.

In conclusion, the observed developmental disorders were clearly linked to hypothyroidism and can therefore be considered as secondary effect of maternal toxicity.


Further, in a subchronic toxicity study according to OEDC Guideline 408 (adopted 21 September 1998), Guanidine hydrochloride was administered to 10 Wistar rats/sex/dose in water, by gavage at dose levels of 0, 50, 100 and 300 mg/kg bw/day.
In order to allow a detection of possible delayed occurrence or persistence of or recovery from toxic effects a satellite group of 5 rats/sex was exposed at dose levels of 0 and 300 mg/kg bw/day (control and HD).

To evaluate possible toxic effects on fertility, the estrous cycle was examined at defined time points of the treatment and recovery period and epididymal sperm motility, testicular sperm count and sperm morphology from vas deferens were evaluated at the end of the treatment and recovery period. Moreover, a detailed histopathological evaluation of the reproductive organs was performed.

Guanidinhydrochloride had no effect on epididymal sperm motility or testicular sperm count analyzed at the end of the treatment or recovery period of this study. Sperm staging and evaluation of sperm morphology did not reveal any indicator for toxicity induced by the test item. Guanidinhydrochloride had no biologically significant effect on the estrous cycle analyzed 4, 8 and 12 weeks after the first administration and in the last week of the recovery period.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Study duration:

subchronic

Species:

rat

Quality of whole database:

Assessment is based on data from a GLP guideline study and literature data as well as the substance evaluation conclusion document for Ammonium Thiocyanate.

Additional information

Built on the hypothesis that Guanidinium Thiocyanate dissociates in aqueous media in the corresponding ions Guanidinium and Thiocyanate, reproductive toxicity endpoints were assessed based on read-across data from Potassium Thiocyante and Guanidine Hydrochloride.

A detailed justification document for the read-across is attached in the respective target record of IUCID.

 

Assessment of fertility is based on findings observed in the sub-chronic toxicity studies with the read-across substances Ammonium Thiocyanate and Guanidine Hydrochloride.

Guanidine hydrochloride had no effect on epididymal sperm motility or testicular sperm count analyzed at the end of the treatment or recovery period of this study. Sperm staging and evaluation of sperm morphology did not reveal any indicator for toxicity induced by the test item. Guanidine hydrochloride had no biologically significant effect on the estrous cycle analyzed 4, 8 and 12 weeks after the first administration and in the last week of the recovery period.

The following is obtained from CORAP Substance evaluation conclusion document for Ammonium Thiocyanate:

“Fertility effects assessment is based also on findings observed during the sub-chronic repeated dose toxicity test (90-day) with ammonium thiocyanate: slight seminiferous epithelial degeneration in two male rats at dose 500 mg/kg/day. This effect is very weak, in a few animals only and at the highest dose level only, so that toxicological relevance of this finding is doubtful.” ….

“Based on the available information the eMSCA has not identified a concern for fertility.”

Taken together there is no concern for effects on fertility of Guanidine Thiocyanate.

Effects on developmental toxicity

Description of key information

Based on findings from the read-across substance Potassium Thiocyanate and Guanidine Hydrochloride there is no indication for adverse developmental toxicity effects require classification of Guanidine Thiocyanate.

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

For justification for read-across applying the analogue approach please refer to attached document in Chapter 13.2 "other assessment reports".

Reason / purpose for cross-reference:

read-across source

Key result

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

body weight and weight gain

mortality

Remarks on result:

other: data from guanidine hydrochloride

Key result

Dose descriptor:

NOAEL

Effect level:

350 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Remarks on result:

other: data from guanidine hydrochloride

Key result

Developmental effects observed:

no

Conclusions:

Developmental toxicity: NOAEL: 350 mg/kg bw/day
No effects on prenatal data, litter data, foetal external, visceral, skeletal and craniofacial parameters were observed up to the highest dose level

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Study duration:

subacute

Species:

rat

Quality of whole database:

Assessment is based on data from a GLP guidelinestudy and literature data as well as the Substance evaluation conclusion document for Ammonium Thiocyanate.

Additional information

Built on the hypothesis that Guanidinium Thiocyanate dissociates in aqueous media in the corresponding ions Guanidinium and Thiocyanate, reproductive toxicity endpoints were assessed based on read-across data from Potassium Thiocyante and Guanidine Hydrochloride.

A detailed justification document for the read-across is attached in the respective target record of IUCID.

Assessment of developmental toxicity is based on findings observed in studies with the read-across substances Potassium Thiocyanate and Guanidine Hydrochloride.

 

Guanidine Hydrochloride

In a developmental toxicity study according to OECD guideline 414 (adopted 22 January, 2001), Guanidine hydrochloride was administered to female Wistar rats during gestation days 5 to 19. Doses of up to 350 mg/kg bw were assessed for developmental toxicity. Due to mortality at 450 mg/kg bw/day the high dose was reduced to 350 mg/kg bw/day during study.

For maternal toxicity the NOAEL was determined to be 150 mg/kg bw/day based on statistically significantly reduced body weight gain and food consumption at 450 and 350 mg/kg bw/day. 

The NOAEL for developmental toxicity was determined to be 350 mg/kg bw/day.
No effects on prenatal data, litter data, foetal external, visceral, skeletal and craniofacial parameters were observed up to the highest dose level.

 

Thiocyanate

The following conclusion is obtained from CORAP Substance evaluation conclusion document for Ammonium Thiocyanate:

“It can be concluded that a relationship exists between lack of iodine in organism and developmental disorders of foetus. These developmental disorders are secondary effects of maternal toxicity (hypothyroidism). Lack of iodine can also be caused by thiocyanate treatment limiting intake of iodine into the body. Although the true iodine deficiency (caused by lack of iodine in the organism) may lead to permanent severe brain damage of the foetus, with thiocyanate treatment (with sufficient of iodine in the body) such severe developmental defects have not been proven. According to available data and pursuant to rules for classification of reproductive toxicity, the eMSCA concludes that the lack of iodine and the consequent developmental disorders caused by thiocyanate are not significant enough to warrant classification for reproductive toxicity.”

 

“The association between hypothyroidism and disorders of foetal development has been known for several decades. Chronic and severe iodine deficiency can cause impaired development of the brain called “endemic cretinism”(9). However, so serious effect of the thiocyanate (with sufficient intake of iodine) has not been proved, not even for smoking mothers- who have permanently elevated levels of thiocyanate in the blood serum(10).

 

Regardless of practically the same cause, differences were found between lack of dietary iodine (iodine deficient diet) and iodine deficiency induced by thiocyanate. This is corroborated by experiment(8), in which several groups of rats were fed by a low iodine diet or control diet with addition of potassium thiocyanate (with sufficiency of iodine). Treatment was discontinued or applied to particular groups in different periods (pregnancy, lactation). The study demonstrated that effect of thiocyanates has not a more significant negative effect on development of pups in comparison with the effect of a low-iodine diet.

Two-generation study(3), that is reported in registration dossier, is primarily focused on transport of some specific nutrients. Despite the fact that this study was not performed according to OECD or EU standards, it provides some useful information on reproductive toxicity. At constant dose level 25 mg/animal/day of potassium thiocyanate, variations in clinical chemistry were reported but no effect on the body weights or brain weights of the pups (F2) was observed.” 

 

Guanidine Thiocyanate

Based on the above findings there is no indication for a classification of Guanidine Thiocyanate for reproductive toxicity. The NOAELfor developmental toxicity of Guanidine hydrochloride was determined to be 350 mg/kg bw/day, while for Potassium Thiocyanate no adverse effects require a classification were observed at a dietary level of 25 mg/rat/day. Considering the highest published body weight in the study (Bala et. Al 2007) of 210 g in the second week of pregnancy this will result in a value of 119 mg/kg bw/day.This value is far above the derived NOAEL of 20 mg/kg bw/day from the sub-chronic toxicity study with Ammonium Thiocyanate.

After adaptation to molecular weight, the value is considered the appropriate dose descriptor for start of DNEL derivation. The derived DNEL will also be protective for reproductive toxicity, as developmental disorders of Thiocyanates were considered a secondary effect of maternal toxicity (hypothyroidism). At the dose level of 20 mg/kg bw/day an effect on the thyroid gland was not evident in the sub-chronic toxicity study. Further for Guanidine Hydrochloride no effects on prenatal data, litter data, foetal external, visceral, skeletal and craniofacial parameters were observed up to the highest dose level of 350 mg/kg bw/d in an OECD 414 Guideline study.

 

Justification for classification or non-classification

Generally it is assumed that Guanidine Thiocyanate dissociates in aqueous media in the corresponding ions Guanidinium and Thiocyanate. Therefore, data for both ions, independent of their source, can be considered relevant for assessment of reproductive toxicity potential.

 

Reproductive toxicity of Guanidine Thiocyanate was assessed based on data from two oral sub-chronic toxicity studies in rats, one with Guanidine Hydrochloride and one with Ammonium Thiocyanate for fertility.

Developmental toxicity was assessed based on a developmental toxicity study with Guanidine Hydrochloride and publish data on developmental toxicity and a 2-generation study on Potassium Thiocyanate, as well as information obtained from Substance evaluation conclusion document for Ammonium Thiocyanate.

 

Considering the available data it can be concluded, that according to GHS Regulation EC No 1272/2008 classification for reproductive toxicity is not warranted for Guanidine Thiocyanate.