Formaldehyde, reaction products with phenol heptyl derivs. and 1,3,4-thiadiazolidine-2,5-dithione

Endpoint summary

Description of key information

Under the conditions of this screening study, the NOAEL for systemic toxicity was 100 mg/kg/day based on effects on organ weights (lower thymus gland weights at ≥200 mg/kg/day, lower spleen and heart weights at ≥ 500 mg/kg/day, lower brain weight at 1000 mg/kg/day, and higher liver and thyroid gland weights at ≥500 mg/kg/day) and the presence of test item-related microscopic findings at ≥200 mg/kg/day. The microscopic findings were still present at the post-treatment phase necropsy, however, at lesser severity.
The NOAEL of 100 mg/kg bw/day as suggested by the Study Director is based on minor and reversible effects on organ weights and microscopic findings at 200 mg/kg bw/day whereas more significant toxic effects were noted at 500 and 1000 mg/kg bw/day. Consequently it is considered more appropriate to propose a LOAEL of 500 mg/kg bw/day, a NOAEL of 200 mg/kg bw/day and 100 mg/kg bw/day as the NOELfor systemic toxicity.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

200 mg/kg bw/day

Study duration:

subacute

Species:

rat

Additional information

The key study was performed in accordance with OECD 422: A Combined 28-Day Repeated Dose Oral (Gavage) Toxicity Study with the Reproduction/Developmental Toxicity Screening Test in Rats, with Recovery.

The test item in the vehicle (corn) was administered orally by gavage once daily to 4 groups of Crl:CD(SD) rats. The low- and 2 mid-dosage groups (Groups 2, 3, and 4, respectively) each consisted of 12 males and 12 females, and the high-dosage group (Group 5) consisted of 17 males and females. Dosage levels were 100, 200, 500, and 1000 mg/kg/day administered at a dosage volume of 5 mL/kg. A concurrent control group (Group 1) of 17 rats/sex received the vehicle on a comparable regimen. Males and females were approximately 10 weeks of age at the beginning of test item administration. Twelve males/group selected for pairing received 14 daily doses prior to mating. Males were dosed throughout the mating period through 1 day prior to euthanasia for a total of 31 doses. Twelve females/group selected for pairing received 14 daily doses prior to pairing and were dosed through lactation day 3 for a total of 39-51 doses; however, these females should also have been dosed on lactation day 4 but were not administered the test item. The females that failed to deliver were dosed through the day prior to euthanasia (post-mating or post-cohabitation day 25) for a total of 39-52 doses. The extra 5 rats/sex in the control and high-dose groups were not used for mating but were treated on a comparable regimen beginning on study day 0; following 28 doses for the males and 40 doses for the females, these animals were assigned to the post-treatment period and remained on study for a 14-day non-dosing period.

All animals were observed twice daily for mortality and moribundity. Clinical observations, body weights, and food consumption were recorded at appropriate intervals. FOB and locomotor activity data were recorded for 6 males/group following approximately 28 days of dose administration and for 6 females/group on lactation day 4. F1 clinical observations and body weights were recorded on PND 1 and 4. Clinical pathology evaluations (hematology, serum chemistry, and urinalysis) were performed on 6 F0 animals/sex/group at the treatment period necropsy and on all animals at the post-treatment period necropsy. The F0 males were euthanized following completion of the mating period, and the F0 females were euthanized on lactation day 5. The 5 rats/sex in the control and high-dosage groups assigned to the post-treatment period were euthanized following the 14-day non-dosing period. Complete necropsies were conducted on all F0 animals, and selected organs were weighed. Selected tissues were examined microscopically from all F0 animals in the control and high-dosage groups at the treatment period necropsy. In addition, the liver and thyroid glands from all animals in the low- and mid-dosage groups and all animals in the post-treatment phase were examined microscopically.

One male each in the 500 and 1000 mg/kg/day groups was found dead on study days 31 and 8, respectively. The 1000 mg/kg/day group male lost 114 g of body weight and had an unkempt appearance, red material on the urogenital area, forelimbs, ventral abdomen, nose and mouth, and decreased defecation prior to death. Findings for the 500 mg/kg/day group male were limited to red material around the mouth 1 week prior to death. These deaths were attributed to the test item. One female in each of these groups was euthanized in extremis during the treatment period due to test item-related dystocia; pale, cool body was noted for the female in the 1000 mg/kg/day group. Microscopic findings for these females included test item-related coagulative necrosis of the liver, which was considered the cause of moribundity. This finding was also noted in 2 males in the 200 mg/kg/day group and 1 female each in the control, 100, and 500 mg/kg/day groups at the treatment period necropsy. All other animals survived to the scheduled necropsies.

Test item-related clinical findings noted in the 100, 200, 500, and 1000 mg/kg/day group males and females consisted of salivation prior to dose administration or clear material around the mouth and/or nose. These findings were attributed to potentially irritating properties of the test item and were not considered adverse. Other test item-related clinical findings noted in the 200, 500, and 1000 mg/kg/day groups consisted of red material around the mouth. In the 1000 mg/kg/day group males and females, yellow material on the urogenital area, red material around the nose, and soft stool were also noted. Soft stool was considered adverse. Mean body weight losses and/or lower mean body weight gain and food consumption were observed in the 500 and 1000 mg/kg/day group males generally throughout the treatment period. As a result, mean body weights in these males were 9.2% and 13.4% lower, respectively, than the control group on study day 30. Mean body weights and body weight gain in the 1000 mg/kg/day during the post-treatment period remained lower than the control; however, mean body weight gain was slightly improved. No test item-related effects on mean body weights, body weight gains, or food consumption were noted in the 100 and 200 mg/kg/day group males. No test item-related effects on food consumption were noted in females at any dosage level during the pre-mating period. Lower mean food consumption was noted in the 1000 mg/kg/day group females generally throughout gestation, and lower mean body weight gains were noted only late in gestation (days 14-20), resulting in a mean body weight that was 5.8% lower than the control group on gestation day 20. The effects on mean body weight gain late in gestation in the 1000 mg/kg/day group females were attributed to the test item-related lower mean number of pups and an increase in the mean number of unaccounted-for sites, rather than maternal toxicity. No test item-related effects on mean body weights and body weight gain were noted in these females during lactation or in the 1000 mg/kg/day group post-treatment phase females. No test item-related effects on mean body weights, body weight gains, or food consumption were noted in the 100, 200, and 500 mg/kg/day group females throughout the treatment period.

No test item-related effects were noted at any dosage level during the FOB or motor activity evaluations during study week 4 (males) or on lactation day 4 (females). Test item-related clinical pathology findings in male rats included the following. Longer mean prothrombin and activated partial thromboplastin times and higher mean urine volumes and lower urine osmolality were noted at >100 mg/kg/day. Minimally to slightly higher mean albumin, total protein, and alkaline phosphatase levels were noted at 500 and 1000 mg/kg/day. Slightly lower mean erythrocyte and eosinophil counts, triglyceride, chloride, phosphorus, and potassium levels and slightly higher mean reticulocyte counts and red blood cell distribution width, mean globulin, total bilirubin, creatinine, and cholesterol, were noted at 1000 mg/kg/day. Test item-related findings were considered to be adverse for prothrombin at >200 mg/kg/day and for activated partial thromboplastin time at 1000 mg/kg/day. These findings resolved in the 1000 mg/kg/day group males during the recovery period with the exception of slightly lower mean erythrocyte and eosinophil counts and alanine aminotransferase level. Nonadverse, test item-related findings in female rats consisted of minimally to slightly higher mean albumin levels at >100 mg/kg/day, higher mean cholesterol levels and lower mean alanine transferase levels at >200 mg/kg/day, lower erythrocyte counts, and mean hemoglobin and hematocrit levels and urine osmolality and higher mean total bilirubin at >500 mg/kg/day, and slightly higher mean red blood cell distribution width, and alkaline phosphatase levels, and slightly lower mean triglyceride levels at 1000 mg/kg/day. Following the post-treatment period, percent and absolute mean reticulocyte counts were slightly lower than the control group in the 1000 mg/kg/day females. The mean hemoglobin distribution width in the 1000 mg/kg/day females was slightly lower than controls on study day 54 and was considered to be secondary to the lower mean reticulocyte counts. One and 2 females in the 500 and 1000 mg/kg/day groups, respectively, were noted with dystocia. This finding was attributed to the test item. No test item-related macroscopic findings were noted at the necropsy of F0 animals that were found dead, euthanized in extremis, or at the scheduled necropsies. Test item-related effects on organ weights consisted of lower mean thymus in the 200, 500, and 1000 mg/kg/day group males, lower mean spleen and heart weights in the 500 and 1000 mg/kg/day group males, lower brain weight in the 1000 mg/kg/day group males, higher mean liver weights in the 500 and 1000 mg/kg/day group males, and higher thyroid/parathyroid weights in 500 and 1000 mg/kg/day group males and females at the treatment period necropsy. Mean liver and thyroid gland weights remained higher in the 1000 mg/kg/day group females at the post-treatment necropsy. Test item-related microscopic findings were noted in the liver and thyroid of the 200, 500, and 1000 mg/kg/day groups. These findings corresponded to higher organ weights and consisted of midzonal hepatocellular vacuolation, hepatocellular cytomegaly, and thyroid follicular cell hyperplasia. Liver lesions were more severe in males than in females for all test item-treated groups. The severity of hepatocellular vacuolation and thyroid follicular cell hyperplasia in the 1000 mg/kg/day group males and females was less at the post-treatment period necropsy.

Under the conditions of this screening study, the NOAEL for systemic toxicity was 100 mg/kg/day based on effects on organ weights (lower thymus gland weights at ≥200 mg/kg/day, lower spleen and heart weights at ≥ 500 mg/kg/day, lower brain weight at 1000 mg/kg/day, and higher liver and thyroid gland weights at ≥500 mg/kg/day) and the presence of test item-related microscopic findings at ≥200 mg/kg/day. The microscopic findings were still present at the post-treatment phase necropsy, however, at lesser severity.

The NOAEL of 100 mg/kg bw/day as suggested by the Study Director is based on minor and reversible effects on organ weights and microscopic findings at 200 mg/kg bw/day whereas more significant toxic effects were noted at 500 and 1000 mg/kg bw/day. Consequently it is considered more appropriate to propose a LOAEL of 500 mg/kg bw/day, a NOAEL of 200 mg/kg bw/day and 100 mg/kg bw/day as the NOELfor systemic toxicity.

Sub-chronic studies

Oral

A 90-day repeat dose study by the oral route is scientifically unjustified.

The substance is a UCVB with the majority of components in the molecular weight range of 354-721 gm/mol. The substance is slightly soluble in water (1.14E-04 g/L), with a relatively high octanol/water partition coefficient (log Kow > 9.4) and a low vapour pressure (0.076Pa @ 25°C).

The single-dose oral application of the test material resulted in no deaths at a dose level of 2000 mg/kg bw and 9/10 deaths within 24 hours at 5000 mg/kg bw. An expert review of the data from the OECD 422 screening study with repeat oral dosing for 28-days indicates that the effects observed at 200 mg/kg/day are adaptive with animals in the recovery groups showing a reduction in symptoms. The NOAEL of 100 mg/kg bw/day as suggested by the Study Director is based on minor and reversible effects on organ weights and microscopic findings at 200 mg/kg bw/day whereas more significant toxic effects were noted at 500 and 1000 mg/kg bw/day. Consequently it is considered more appropriate to propose a LOAEL of 500 mg/kg bw/day, a NOAEL of 200 mg/kg bw/day and 100 mg/kg bw/day as the NOEL for systemic toxicity. The irritant nature of the test material at the concentrations used in the OECD 422 screening study may also have attributed to the systemic effects noted after dosing via the oral route. Classification for repeat dose effects via the oral route is not suggested as the effects seen at ≤300 mg/kg bw/day were non-adverse and reversible.

The substance is used a corrosion inhibitor. The main routes of exposure will therefore be dermal and inhalation. The physic-chemical properties of this UVCB indicate that dermal absorption will be low (1%) and that although exposure via inhalation is unlikely due to the low vapour pressure, any uptake from any inhalation is likely to occur only by means of micellar solubilisation. The potential for repeated exposure is therefore minimal and would not occur at dose levels where systemic toxicity was observed in the rat studies.

In addition human health risk mitigation measures will be in place to minimise the irritant properties of the substance, resulting in a reduction of potential human exposure.

In the absence of adverse effects at the limit of classification in a 28-day repeat oral dose study, the application of risk mitigation measures to reduce exposure in combination with the low potential for absorption via the major routes of exposure further investigations of systemic toxicity for longer dosing periods via the oral route are not considered scientifically justified.

Therefore, a 90-day repeat oral dose study is considered to be scientifically unjustified.

Inhalation

A 90-day repeat dose study by the inhalation route is scientifically unjustified. The substance is unreactive, insoluble and not inhalable and there is no evidence of dermal absorption.

The substance is a UCVB with the majority of components in the molecular weight range of 354-721 gm/mol. The substance is slightly soluble in water (1.14E-04 g/L), with a relatively high octanol/water partition coefficient (log Kow > 9.4) and a low vapour pressure (0.076Pa @ 25°C).

The single-dose dermal application of the test material resulted in no manifestations of systemic toxicity that would suggest systemic absorption through cutaneous barriers. The substance is a skin irritant, therefore systemic exposure via the dermal route would be secondary and minimal with respect to local effects. If this substance was to reach the respiratory tract, the physical chemical properties and its bioavailability, as inferred from the oral toxicity data, indicates that uptake is likely to occur only by means of micellar solubilization.

The potential for inhalation toxicity was not measured. However, the vapour pressure indicates a very low propensity to enter atmospheric air in a respirable form (predicted to be ca. 0.1 ppm under ambient conditions). Thus, respiratory absorption under normal use and handling of this material is expected to be inconsequential.

The irritant nature of the test material at the concentrations used in the OECD 422 screening study may also have attributed to the systemic effects noted after dosing via the oral route. Classification for repeat dose effects via the oral route is not suggested as the effects seen at ≤300 mg/kg bw/day were non-adverse and reversible. In the absence of adverse effects at the limit of classification in a 28-day repeat oral dose study further investigations for longer dosing periods are not considered scientifically justified.

In addition human health risk mitigation measures will be in place to minimise the irritant properties of the substance, resulting in a reduction of potential human exposure.

Therefore, a 90-day repeat inhalation dose study is considered to be scientifically unjustified.

Dermal

A 90-day repeat dose study by the dermal route is scientifically unjustified. The substance is unreactive, insoluble, irritating to skin and there is no evidence of dermal absorption.

The substance is a UCVB with the majority of components in the molecular weight range of 354-721 gm/mol. The substance is slightly soluble in water (1.14E-04 g/L), with a relatively high octanol/water partition coefficient (log Kow > 9.4) and a low vapour pressure (0.076Pa @ 25°C).

The single-dose dermal application of the test material resulted in no manifestations of systemic toxicity that would suggest systemic absorption through cutaneous barriers. The substance is poorly soluble in water and up to 91% of the test substance may have MW >500 and/or has a Log PoW within the range considered valid for prediction of dermal absorption at a default rate of 10% (EFSA Scientific Opinion: Guidance on Dermal Absorption. EFSA Journal 2012; 10(4):2665 ). The Guidance further states that Log Pow outside the range should not be used to predict absorption. However, studies with alkyl phenols indicate that skin penetration over 8 hours is only 1% of the applied dose (Monteiro-Riviere, et al, 2000). Therefore, based on the evidence and the available guidance it seems reasonable that total dermal absorption would be minimal (1%).

The substance is a skin irritant, therefore systemic exposure via the dermal route would be secondary and minimal with respect to local effects.

The irritant nature of the test material at the concentrations used in the OECD 422 screening study may also have attributed to the systemic effects noted after dosing via the oral route. Classification for repeat dose effects via the oral route is not suggested as the effects seen at ≤300 mg/kg bw/day were non-adverse and reversible. In the absence of adverse effects at the limit of classification in a 28-day repeat oral dose study further investigations for longer dosing periods are not considered scientifically justified.

In addition human health risk mitigation measures will be in place to minimise the irritant properties of the substance, resulting in a reduction of potential human exposure.

Therefore, a 90-day repeat dermal dose study is considered to be scientifically unjustified

Justification for classification or non-classification

Classification for repeat dose effects via the oral route is not suggested as the effects seen at ≤300 mg/kg bw/day were non-adverse and reversible.