Diquat dibromide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

Sep 1990 to Dec 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Objective of study:

distribution

excretion

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: males ca 50 days; females ca 60 days
- Housing: after dosing: plastic metabowls designed for the separate collection of urine and faeces
- Diet: standard laboratory diet, ad libitum
- Water: ad libitum
- Acclimation period: ca 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 ± 3
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Radiolabelled [14C]-test substance (ca 24.7 MB) and non-radiolabelled test material monohydrate (1088.15 mg) were combined in aqueous solution (ca 25 g) in a plastic container. The concentration of radioactivity was measured and the specific activity was calculated to be 0.044 MBq/mg test material ion. Samples of the dose solution were weighed and analysed for total radioactivity. Individual doses were administered orally by gavage. The dose received by animals was assessed from the weight of the dose syringe and contents before administration and weight of dose syringe after administration.

Duration and frequency of treatment / exposure:

Single dose

Dose / conc.:

1 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

5

Control animals:

no

Positive control reference chemical:

None

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY
- Following administration the rats were placed in plastic metabowls designed for the separate collection of urine and faeces.
- Tissues and body fluids sampled: urine, faeces, final cage wash
- Urine was collected at 8, 24, 36, 48, 72, 96, 120, 144 and 168 h post dose.
- Faeces were collected at 24, 48, 72, 96, 120, 144 and 168 h.
- Cages were rinsed at 24 h and daily thereafter, and a final cage wash was made after the last collection.
- Urine and faeces were collected into containers cooled with solid CO2 for the first 48 h post dose.
- At termination the animals were killed by CO2 narcosis an the following tissues, organs and body fluids were removed for analysis: bone, brain, testes/ovaries, stomach, stomach contents, small intestine, small intestine contents, large intestine, large intestine contents, plasma, whole blood, fat, heart, kidney, liver, lens, lungs muscle, spleen
- Total radioactivity was measured in urine, faeces, cage wash, tissues, organs, body fluids and remaining carcass.

Type:

excretion

Results:

A mean of 85.5% of administered radioactivity was recovered in the faeces by 168 h post dose. Excretion via urine accounted for a mean of 5.4% of the dose administered. The mean total administered radioactivity recovered was 93.2%

Type:

distribution

Results:

Total radioactivity in tissues, organs and body fluids was close to background. Highest levels were detected in the organs of excretion, kidney and liver (mean of 0.076 and 0.036 µg equiv /g respectively)

Type:

metabolism

Results:

Radio-TLC analysis of pooled urine samples (0-48 h post dose; male and female separately) indicated the presence of a single major radiolabelled component of similar retention factor (Rf) to [14C]-test substance.

Type:

metabolism

Results:

Radio-TLC analysis of extracts of pooled faeces (0-72 h post dose; male and female separately) indicated the presence of a single radiocomponent of a similar chromatographic character to [14C]-test substance

Details on absorption:

An oral dose of the test substance was apparently poorly absorbed in the rat. Following single oral administration of [14C]-test substance to rats at a target dose level of 186.8 mg/kg a mean of 5.4% of the administered radioactivity was recovered in the urine, and most of the radiolabelled material was recovered in faeces.

Details on excretion:

There was no sex difference in the pattern of excretion.

Metabolites identified:

no

Details on metabolites:

Radio-TLC analysis of pooled urine samples (0-48 h post dose; male and female separately) indicated the presence of a single major radiolabelled component of similar retention factor (Rf) to [14C]-test substance.
Radio-TLC analysis of extracts of pooled faeces (0-72 h post dose; male and female separately) indicated the presence of a single radiocomponent of a similar chromatographic character to [14C]-test substance

Table 1. Cumulative Excretion of Total Radioactivity in Excreta Following Single Oral Administration [14C]-test substance. Results expressed as % administered dose recovered

Sample/Time (h)	Males						Females
	1	2	3	4	5	Mean	1	2	3	4	5	Mean
Urine
0 – 8	0.77	1.62	1.13	0.9	1.04	1.09	1.05	1.27	1.18	0.72	1.31	1.11
0 – 24	1.91	3.24	3.28	2.74	3.56	2.94	2.07	2.68	4.62	2.21	2.41	2.79
0 – 36	2.69	4.59	4.37	4.06	3.74	3.89	2.92	3.34	5.75	3.15	3.02	3.64
0 – 48	3.12	9.27	5.22	4.9	4.03	5.31	4.12	3.88	7.94	4.5	3.44	4.78
0 - 72	3.25	10.75	5.3	5	4.07	5.57	4.29	4.01	8.09	4.57	4.16	5.02
0 - 98	3.27	10.78	5.31	5.01	4.07	5.59	4.32	4.03	8.13	4.59	4.28	5.07
0 – 120	3.28	10.79	5.32	5.02	4.07	5.7	4.33	4.04	8.15	4.6	4.37	5.1
0 – 144	3.28	10.80	5.33	5.02	4.07	5.7	4.35	4.04	8.15	4.6	4.39	5.11
0 – 168	3.28	10.80	5.33	5.02	4.07	5.7	4.35	4.04	8.15	4.6	4.4	5.11
Faeces
0 – 24	61.73	25.45	28.34	38.08	63.61	43.44	42.19	25.28	31.1	26.58	24.63	30.16
0 - 48	85.66	61.57	73.67	79.20	85.01	77.02	83.74	73.55	67.27	68.61	54.55	69.54
0 – 72	88.83	82.22	75.37	83.59	86.50	82.90	89.1	85.57	79.89	83.67	73.75	82.4
0 – 96	88.19	84.17	75.62	84.10	86.89	83.80	90.68	86.07	82.38	86.49	80.59	85.24
0 – 120	88.25	84.58	75.63	84.96	85.95	84.08	91.1	86.11	82.92	86.62	86.12	86.57
0 – 144	88.27	84.69	75.65	84.97	86.99	84.11	91.28	86.13*	83	86.65	86.9	86.79
0 – 168	88.45	84.75	75.65	84.97	87.04	84.17	91.29	86.15	83.01*	86.67	87.05	86.83
Cage wash
0 – 24	0.28	0.83	8.7	1.39	1.54	2.55	0.81	1.37	3.94	0.45	0.39	1.39
0 - 48	0.39	1.1	8.92	1.48	1.62	2.7	0.89	1.54	4.01	0.56	0.56	1.52
0 – 72	0.41	1.28	8.97	1.63	1.63*	2.78	0.93*	1.6	4.07	0.63*	0.67	1.58
0 – 96	0.45*	1.28**	8.98**	1.64*	1.64**	2.80	0.95**	1.61**	4.10*	0.67	0.7*	1.61
0 – 120	0.45**	1.28**	8.98**	1.54**	1.64**	2.80	0.95**	1.61**	4.10**	0.67**	0.75	1.62
0 – 144	0.45**	1.28**	8.98**	1.64**	1.64**	2.80	0.95**	1.61**	4.10**	0.68**	0.77*	1.62
0 – 168	0.46**	1.32	8.98**	1.66**	2.08	2.9	1	1.66	4.2	0.73	0.95	1.71
Total excreta
0 – 8	1.05	2.45	9.83	2.29	2.57	3.64	1.86	2.64	5.12	1.17	1.7	2.5
0 – 24	63.91	29.52	40.32	42.21	68.7	48.93	45.07	30.31	39.66	29.24	27.43	34.34
0 – 36	64.69	30.87	41.41	43.53	68.88	49.88	45.92	30.99	40.79	30.18	28.04	35.18
0 – 48	89.17	71.94	87.81	85.58	90.66	85.03	88.75	78.98	79.22	73.7	58.55	75.84
0 – 72	90.49	94.25	89.64	90.22	92.2	91.36	94.32	91.18	92.05	88.87	78.58	89
0 – 96	91.91	96.23	89.91	90.75	92.61	92.28	95.95	91.71	94.61	91.75	85.57	91.92
0 – 120	91.98	96.65	89.93	91.62	92.68	92.57	96.38	91.76	95.17	91.89	91.24	93.29
0 – 144	92	96.77	89.96	91.63	92.71	92.62	96.58	91.78	95.25	91.93	92.06	93.52
0 – 168	92.19	96.87	89.96	91.65	93.2	92.78	96.64	91.85	95.36	92.01	92.4	93.65
Tissues	0	0	0	0	0	0	0	0	0	0	0	0
Carcass	0.03**	0**	0.04**	0.03**	0.01**	0.02	0**	0**	0.02**	0.01**	0**	0.01
Total recovered	92.22	96.87	90	91.68	93.21	92.78	96.64	91.85	95.38	92.02	92.40	93.66

* results derived from data <30 d.p.m. above background

** results derived from data <10 d.p.m above background

Conclusions:

An oral dose of diquat was apparently poorly absorbed in the rat. Following single oral administration of the [14C]-test substance to rats at a target dose level of 100 mg/kg test substance a mean of 5.4% of administered radioactivity was recovered in urine, and most of the radiolabelled material was recovered in faeces. The relatively low levels of radioactivity in tissues tat 168 h post dose and the presence of parent compound in extracts of pooled faeces are consistent with limited absorption of the test substance. the chromatographic profiles of pooled urine samples indicated that the low proportion of radiolabelled material absorbed is excreted unmetabolized.
A mean of 73.3% of administered radioactivity was recovered in the faeces by 48 h; by 168 h post dose the mean faecal recovery was 85.5%. Excretion by the urinary route accounted for 5.4% of the administered dose by 168 h. The mean total dose recovered was 93.2%. At 168 h post dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background.

Executive summary:

This report describes aspects of the elimination of [14C]-test substance in the rat following single oral administration at a target dose level of 186.8 mg/kg. Radioactivity was predominantly excreted via faeces. A mean of 73.3% of administered radioactivity was recovered in the faeces by 48 h; by 168 h post dose the mean faecal recovery was 85.5%. Excretion by the urinary route accounted for 5.4% of the administered dose by 168 h. The mean total dose recovered was 93.2%. At 168 h post dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background. No apparent sex difference was observed in the pattern of excretion. Radio-TLC analysis of pooled urine samples indicated the presence of a single major radiocomponent which co-chromatographed with [14C]-test substance. A similar component was observed in the extract of pooled faeces samples.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

Sep 1990 to Dec 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Objective of study:

distribution

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: ca 50 days males and ca 60 days females
- Diet: standard laboratory diet, ad libitum
- Water: ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 ± 2
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
[14C]-test substance and non-radiolabelled test substance were combined in aqueous solution in a plastic container. The concentration of radioactivity was measured and the specific activity was calculated to be the concentration of radioactivity was measured accurately and the specific activity calculated.

Duration and frequency of treatment / exposure:

Single oral dose

Dose / conc.:

1 mg/kg bw (total dose)

Remarks:

test substance ion; equivalent to 1.868 mg test substance/kg bw

Dose / conc.:

100 mg/kg bw (total dose)

Remarks:

test substance ion; equivalent to 186.8 mg test substance/kg bw

No. of animals per sex per dose / concentration:

21

Control animals:

no

Positive control reference chemical:

None

Details on study design:

ANIMAL EXPERIMENTATION
- Group A: Three male and 3 female rats were given a single oral target dose level of 1 mg test substance ion/kg bw. Following administration, blood samples of ca 250 µL were taken at 1, 2, 4, 8, 12 and 24 h post dose from the tail vein and each sample was analysed for total radioactivity.
- Group B: Three male and 3 female rats were given a single oral target dose level of 100 mg test substance ion/kg bw. Following administration blood samples were taken and analysed as described above for Group A.
- Group C: Eighteen male rats were given a single oral target dose level of 1 mg test substance ion/kg bw. Rats were sacrificed at 2, 4 , 8, 24, 48 and 96 h post dose (3 per time point) and tissues and organs were removed, weighed and analysed for total radioactivity.
- Group D: Eighteen male rats were given a single oral target dose level of 100 mg test substance ion/kg bw. Distribution in tissues was determined as described for Group C.
- Group E: Eighteen female rats were given a single oral target dose level of 1 mg test substance ion/kg bw. Distribution in tissues was determined as described for Group C.
- Group F: Eighteen female rats were given a single oral target dose level of 100 mg test substance ion/kg bw. Distribution in tissues was determined as described for Group C.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: bone, brain, fat, heart, kidney, liver, lens, lungs, muscle, spleen, testes/ovaries, stomach, stomach contents, small intestine, small intestine contents, large intestine, large intestine contents, plasma, whole blood
- Time and frequency of blood sampling: 1, 2, 4, 8, 12 and 24 h post dose
- Rats were sacrificed at 2, 4 , 8, 24, 48 and 96 h post dose (3 per time point ) and tissues and organs were removed

Type:

distribution

Results:

1 mg test substance ion: the concentration of radioactivity in tissues fell from a maximum at 2-4 h to near background at 24 h. Excluding the GI tract, highest concentrations of radioactivity at the low dose level were found in kidney

Type:

distribution

Results:

100 mg test substance ion: the rate of elimination of radioactivity was generally slower than at the low dose level. Highest concentrations of radioactivity were found in kidney, lung and liver

Details on distribution in tissues:

- Following single oral administration at 1 mg test substance ion/kg only relatively low levels of radioactivity were detected in whole blood with a maximum mean concentration of 0.012 µg equiv/g observed at 2 h post dose. At the higher dose level a maximum mean concentration of 1.428 µg equiv/g was observed at 1 h post dose. Concentrations of radioactivity in whole blood were generally in proportion to the dose received and there was apparently no sex difference.
- Following single oral administration at a target dose level of 1 mg test substance ion/kg, the concentration of radioactivity in tissues fell from a maximum at 2-4 h to near background at 24 h. Excluding the GI tract, highest concentrations of radioactivity at the low dose level were found in kidney. There was apparently no sex difference.
- Following single oral administration at a target dose level of 100 mg test substance ion/kg the rate of elimination of radioactivity was generally slower than at the low dose level. Highest concentrations of radioactivity were found in kidney, lung and liver. Concentrations of radioactivity in tissues generally appeared to be in proportion to the dose. The concentrations of radioactivity in lung appeared to be disproportionally high in the high dose group. The data are consistent with previous elimination studies which indicated limited oral absorption of the test substance and slower elimination at the high dose level.

Metabolites identified:

not measured

Table 1. Levels of total radioactivity in whole blood following a single oral dose of 1 or 100 mg test substance ion/kg

Time (h)	Whole blood radioactivity (µg equiv/g)
	1 mg test substance ion/kg dose		100 mg test substance ion/kg dose
	Mean	SD	Mean	SD
1	0.011	0.004	1.428	1.238
2	0.012	0.003	1.042	0.328
4	0.008	0.002	0.265	0.154
8	0.005	0.002	0.240	0.125
12	0.003	0.001	0.300	0.088
24	0.002	0.001	0.259	0.065

 

Table 2. Levels of Total Radioactivity in Selected Tissues and Body Fluids Following Single Oral Administration of the test substance to 18 Male Rats at a Target Dose Level of 1 mg test substance ion/kg.

Sample	Time
	2 h		4 h		8 h		24 h		48 h		96 h
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Bone	0.008	0.003	0.008	0.004	0.005	0.003	0.001	0.002	0	0	0	0
Brain	0.003	0.001	0.003	0.001	0.002	0.001	0	0.001	0	0	0	0
Fat	0.005	0.001	0.004	0.002	0.002	0.001	0	0	0	0	0	0
Testes	0.006	0.002	0.005	0.001	0.002	0.001	0	0	0	0	0	0
Heart	0.009	0.003	0.007	0.002	0.004	0.001	0	0	0	0	0	0
Kidney	0.096	0.043	0.040	0.017	0.022	0.003	0.006	0.004	0.002	0.001	0.001	0
Lung	0.012	0.004	0.009	0.005	0.003	0.001	0	0	0.001	0.002	0	0
Muscle	0.007	0.003	0.006	0.002	0.003	0.001	0	0	0.002	0.003	0	0
Spleen	0.007	0.003	0.012	0.007	0.004	0.001	0.001	0.001	0	0.001	0	0.001
Liver	0.014	0.005	0.011	0.004	0.006	0.001	0.001	0.001	0.001	0.001	0	0
Lens	0.001	0.001	0.004	0.001	0.001	0.001	0	0.001	0	0	0	0
Stomach	0.695	0.588	0.744	0.678	0.160	0.265	0.030	0.050	0.012	0.012	0.009	0.009
Small intestine	2.208	0.524	0.447	0.365	0.104	0.055	0.037	0.052	0.006	0.002	0.003	0.004
Large intestine	0.162	0.206	2.583	0.765	2.819	0.434	0.257	0.200	0.023	0.016	0.009	0.005
Carcass	0.010	0.003	0.009	0.004	0.075	0.068	0.004	0.003	0	0	0	0
Whole blood	0.010	0.002	0.006	0.002	0.003	0.001	0.001	0	0	0	0	0
Plasma	0.016	0.005	0.007	0.003	0.002	0.001	0	0	0	0	0	0
Stomach contents	25.846	22.172	4.333	3.932	0.819	0.712	22.424	37.133	0.527	0.254	0.221	0.197
Small intestine contents	117.167	10.546	20.168	15.382	4.590	3.025	1.978	2.171	0.315	0.048	0.261	0.367
Large intestine contents	3.395	2.044	78.298	8.892	99.378	31.534	0.004	8.698	0.713	0.495	0.415	0.315

  

Table 3. Levels of Total Radioactivity in Selected Tissues and Body Fluids Following Single Oral Administration of the test substance to 18 Male Rats at a Target Dose Level of 100 mg test substance ion/kg. 

Sample	Time
	2 h		4 h		8 h		24 h		48 h		96 h
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Bone	0.439	0.205	0.462	0.286	0.309	0.050	0.260	0.064	0.259	0.319	0.024	0.028
Brain	0.121	0.041	0.132	0.044	0.092	0.037	0.104	0.042	0.064	0.052	0.021	0.027
Fat	0.140	0.030	0.071	0.026	0.101	0.072	0.187	0.136	0.067	0.086	0.004	0.007
Testes	0.203	0.050	0.182	0.058	0.149	0.082	0.117	0.073	0.117	0.163	0.014	0.023
Heart	0.466	0.131	0.300	0.084	0.340	0.184	0.187	0.040	0.143	0.171	0.028	0.009
Kidney	5.751	4.286	3.057	0.728	1.755	0.373	1.814	0.215	1.574	2.264	0.194	0.013
Lung	2.429	2.610	2.413	2.059	0.945	0.243	0.452	0.196	0.186	0.261	0.025	0.018
Muscle	0.340	0.033	0.328	0.095	0.226	0.068	0.182	0.066	0.113	0.108	0.017	0.029
Spleen	0.337	0.050	0.411	0.150	0.362	0.144	0.275	0.088	0.227	0.278	0.038	0.055
Liver	0.865	0.107	0.865	0.652	0.461	0.076	0.460	0.071	0.315	0.347	0.065	0.034
Lens	0.074	0.011	0.733	0.590	0.140	0.132	1.025	0.750	0.173	0.121	0.074	0.052
Stomach	88.562	5.899	91.779	14.421	130.476	85.772	184.298	130.942	24.923	38.262	0.238	0.188
Small intestine	80.341	53.487	37.843	47.935	31.336	13.649	36.298	13.872	8.561	9.240	0.583	0.664
Large intestine	8.599	10.378	56.742	46.898	64.062	35.610	90.947	2.566	17.699	14.592	1.942	2.674
Carcass	0.482	0.107	0.499	0.298	3.424	3.201	1.357	1.175	0.395	0.320	0.116	0.118
Whole blood	0.436	0.129	0.251	0.083	0.207	0.068	0.135	0.216	0.137	0.141	0.006	0.007
Plasma	0.614	0.192	0.301	0.093	0.239	0.035	0.161	0.093	0.086	0.140	0.005	0.007
Stomach contents	9788.945	3066.075	11360.257	1619.815	10891.767	1711.899	3988.693	2285.996	3667.495	6259.573	12.099	10.371
Small intestine contents	3500.407	935.382	336.010	241.703	1276.230	635.003	926.220	169.175	232.495	263.651	23.338	33.197
Large intestine contents	358.060	451.482	3983.920	1083.469	2812.717	265.248	2815.083	361.840	618.334	390.129	60.449	68.797

Table 4. Levels of Total Radioactivity in Selected Tissues and Body Fluids Following Single Oral Administration of the test substance to 18 Female Rats at a Target Dose Level of 100 mg test substance ion/kg.

Sample	Time
	2 h		4 h		8 h		24 h		48 h		96 h
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Bone	0.285	0.108	0.441	0.336	0.157	0.048	0.154	0.021	0.140	0.138	0.085	0.018
Brain	0.131	0.107	0.123	0.041	0.058	0.042	0.056	0.011	0.490	0.650	0.119	0.196
Fat	0.216	0.087	0.127	0.073	0.115	0.039	0.209	0.188	0.322	0.308	0.094	0.085
Ovaries	0.570	0.414	0.400	0.125	0.198	0.056	0.272	0.145	0.069	0.021	0.011	0.020
Heart	0.440	0.251	0.347	0.115	0.240	0.115	0.249	0.062	0.154	0.189	0.015	0.014
Kidney	2.272	0.504	2.590	0.980	1.389	0.381	2.054	0.616	0.739	0.108	0.251	0.019
Lung	3.802	1.789	1.526	0.944	1.854	1.358	0.355	0.050	0.105	0.022	0.038	0.022
Muscle	0.247	0.082	0.231	0.077	0.151	0.034	0.111	0.049	0.156	0.172	0.032	0.011
Spleen	0.279	0.022	0.435	0.308	0.220	0.060	0.217	0.038	0.100	0.018	0.082	0.111
Liver	0.833	0.336	1.060	0.601	0.339	0.141	0.476	0.115	0.164	0.058	0.059	0.035
Lens	0.225	0.210	0.344	0.051	0.112	0.080	0.046	0.035	0.094	0.085	0.097	0.084
Stomach	134.041	40.644	198.211	35.858	137.937	61.408	154.421	88.308	7.823	3.093	0.227	0.300
Small intestine	78.972	56.977	32.170	32.832	26.889	19.150	84.240	58.083	12.033	6.303	0.833	1.257
Large intestine	49.669	40.784	112.463	61.321	89.398	28.077	84.365	22.636	38.855	25.246	2.544	3.889
Carcass	0.630	0.335	0.634	0.297	0.498	0.348	2.265	1.636	1.745	1.163	0.007	0.012
Whole blood	0.235	0.054	0.232	0.115	0.108	0.090	0.244	0.118	0.000	0.000	0.000	0.000
Plasma	0.420	0.092	0.352	0.159	0.163	0.082	0.386	0.181	0.055	0.012	0.017	0.016
Stomach contents	9258.554	2272.445	9976.876	527.531	9648.437	3002.466	5755.515	447.881	274.494	53.544	9.578	16.472
Small intestine contents	1947.400	1799.493	672.800	798.504	656.253	263.937	1388.489	532.410	192.778	101.436	17.484	28.433
Large intestine contents	1991.594	1675.181	2849.163	726.821	2050.078	1091.822	1721.129	241.008	1219.217	1088.502	79.246	126.013

 

Table 5. Levels of Total Radioactivity in Selected Tissues and Body Fluids Following Single Oral Administration of the test substance to 18 Female Rats at a Target Dose Level of 1 mg test substance ion/kg.

Sample	Time
	2 h		4 h		8 h		24 h		48 h		96 h
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Bone	0.009	0.002	0.005	0.003	0.002	0.000	0.000	0.000	0.001	0.001	0.001	0.001
Brain	0.003	0.001	0.001	0.001	0.001	0.000	0.000	0.000	0.002	0.003	0.000	0.001
Fat	0.006	0.003	0.003	0.002	0.001	0.001	0.000	0.000	0.001	0.001	0.000	0.001
Ovaries	0.010	0.002	0.007	0.003	0.002	0.002	0.001	0.001	0.000	0.001	0.000	0.001
Heart	0.010	0.002	0.007	0.003	0.003	0.002	0.001	0.001	0.001	0.001	0.000	0.001
Kidney	0.064	0.019	0.039	0.012	0.026	0.006	0.006	0.002	0.002	0.002	0.002	0.001
Lung	0.011	0.003	0.008	0.003	0.004	0.001	0.000	0.000	0.001	0.001	0.000	0.000
Muscle	0.008	0.002	0.005	0.004	0.002	0.001	0.000	0.001	0.000	0.001	0.000	0.001
Spleen	0.013	0.004	0.007	0.003	0.004	0.000	0.001	0.002	0.001	0.001	0.000	0.001
Liver	0.016	0.002	0.011	0.004	0.005	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Lens	0.005	0.006	0.004	0.002	0.001	0.002	0.001	0.002	0.003	0.003	0.001	0.001
Stomach	0.752	0.340	0.436	0.320	0.009	0.008	0.055	0.090	0.001	0.001	0.000	0.001
Small intestine	5.073	2.968	0.788	0.157	0.201	0.134	0.051	0.053	0.003	0.003	0.001	0.001
Large intestine	0.485	0.704	3.088	0.726	3.890	0.790	0.112	0.080	0.009	0.004	0.001	0.001
Carcass	0.007	0.001	0.003	0.002	0.045	0.074	0.002	0.001	0.001	0.001	0.001	0.001
Whole blood	0.012	0.003	0.006	0.003	0.001	0.001	0.002	0.001	0.001	0.001	0.001	0.000
Plasma	0.016	0.003	0.005	0.002	0.004	0.002	0.002	0.000	0.001	0.000	0.000	0.000
Stomach contents	22.985	2.265	9.664	4.139	0.267	0.438	1.682	2.831	0.054	0.085	0.005	0.004
Small intestine contents	62.674	14.003	14.225	4.139	4.109	3.209	1.362	1.372	0.052	0.018	0.007	0.002
Large intestine contents	9.333	14.753	64.573	8.008	75.043	10.311	2.295	1.550	0.183	0.069	0.013	0.004

Conclusions:

Following single oral administration of radiolabelled test substance to rats there was apparently no sex difference in blood concentrations of radioactivity in either the low or the high dose groups. Concentrations of radioactivity in whole blood appeared to be broadly in proportion to the dose levels. Following single oral administration to male rats highest concentrations of radioactivity were found in liver, kidney and lung and were broadly in proportion to the dose. However at the 100 mg test substance ion/kg dose level the concentration of radioactivity at 24 h was disproportionately high in comparison to the low dose group and this is consistent with the slower rate of excretion observed at this dose level. Concentrations of radioactivity in liver and kidney from female animals in the low and high dose groups were comparable in terms of proportionality and rates of elimination. In general terms there was apparently little or no sex difference in the distribution of radioactivity. Interestingly concentrations of radioactivity associated with lungs were observed to be disproportionally high at the high dose level in both male and female animals.

Executive summary:

This GLP compliant study, comparable to OECD TG 417, investigates the aspects of the distribution of the radiolabelled test substance in the rat at target dose levels of 1 mg test substance ion/kg and 100 mg test substance ion/kg. Following single oral administration at 1 mg only relatively low levels of radioactivity were detected in whole blood with a maximum mean concentration of 0.012 µg equiv/g observed at 2 h post dose. At the higher dose level a maximum mean concentration of 1.428 µg equiv/g was observed at 1 h post dose. Concentrations of radioactivity in whole blood were generally in proportion to the dose received and there was apparently no sex difference. Following single oral administration of the radiolabelled test substance at a target dose level of 1 mg test substance ion/kg, the concentration of radioactivity in tissues fell from a maximum at 2-4 h to near background at 24 h. Excluding the GI tract, highest concentrations of radioactivity at the low dose level were found in kidney. There was apparently no sex difference. Following single oral administration of radiolabelled test substance at a target dose level of 100 mg test substance ion/kg the rate of elimination of radioactivity was generally slower than at the low dose level. Highest concentrations of radioactivity were found in kidney, lung and liver. Concentrations of radioactivity in tissues generally appeared to be in proportion to the dose. The concentrations of radioactivity in lung appeared to be disproportionally high in the high dose group. The data are consistent with previous elimination studies which indicated limited oral absorption of the radiolabelled test substance and slower elimination at the high dose level.

 

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

Jul 1990 to Dec 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Objective of study:

distribution

excretion

metabolism

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: males ca 50 days; females ca 60 days
- Housing: after dosing: plastic metabowls designed for the separate collection of urine and faeces
- Diet: standard laboratory diet, ad libitum
- Water: ad libitum
- Acclimation period: ca 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21 ± 2
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Radiolabelled [14C]-test substance (ca. 11.3 MBq) and non-radiolabelled test material monohydrate (5.01 mg) were combined in aqueous solution (ca. 19.5 g) in a plastic container. The concentration of radioactivity was measured and the specific activity was calculated to be 3.116 MBq/mg test material ion. Samples of the dose solution were weighed and analysed for total radioactivity. Individual doses were administered orally by gavage. The dose received by animals was assessed from the weight of the dose syringe and contents before administration and weight of dose syringe after administration.

Duration and frequency of treatment / exposure:

Single dose

Dose / conc.:

1 mg/kg bw (total dose)

No. of animals per sex per dose / concentration:

5

Control animals:

no

Positive control reference chemical:

None

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY
- Following administration the rats were placed in plastic metabowls designed for the separate collection of urine and faeces.
- Tissues and body fluids sampled: urine, faeces, final cage wash
- Urine was collected at 8, 24, 36, 48, 72, 96, 120, 144 and 168 h post dose.
- Faeces were collected at 24, 48, 72, 96, 120, 144 and 168 h.
- Cages were rinsed at 24 h and daily thereafter, and a final cage wash was made after the last collection.
- Urine and faeces were collected into containers cooled with solid CO2 for the first 48 h post dose.
- At termination, the animals were killed by CO2 narcosis and the following tissues, organs and body fluids were removed for analysis: Bone, Brain, Fat, Heart, Testes/Ovaries, Stomach, Stomach contents, Small intestine, Kidney, Liver, Lens, Lungs, Muscle, Spleen, Small intestine contents, Large intestine, Large intestine contents, Plasma, Whole blood.
- Total radioactivity was measured in urine, faeces, cage wash, tissues, organs, body fluids and remaining carcass

Type:

distribution

Results:

At 168 h post dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background.

Type:

metabolism

Results:

Radio-TLC analysis of pooled urine samples indicated the presence of a single major radiocomponent which co-chromatographed with [14C]-test material ion.

Type:

excretion

Results:

A mean of 90.1% of administered radioactivity was recovered in the faeces by 24 h; by 168 h post dose the mean faecal recovery was 93.8%. Excretion by the urinary route accounted for 3.1% of the administered dose by 168 h.

Details on distribution in tissues:

At 168 h after administration of radiolabelled test material all tissues, organs and body fluids analysed were at or close to background levels of radioactivity.

Details on excretion:

Following single oral administration of radiolabelled test material to 5 male and 5 female rats at a target dose level of 1 mg test material ion/kg a mean of 90.1% of administered radioactivity was recovered by 24 h post dose; by 168 h the mean faecal recovery was 93.8%. Excretion via urine accounted for a mean of 3.1% of the administered radioactivity by 168 h. The mean total dose recovered was 97.3%.
At 168 h after administration of radiolabelled test material all tissues, organs and body fluids analysed were at or close to background levels of radioactivity.

Metabolites identified:

no

Details on metabolites:

Radio-TLC analysis of pooled urine samples (0-8 h post dose; male and female separately) in the solvent system methanol/water/acetic acid 60/30/10, v/v/v, indicated that the major radiolabelled component detected did not co-chromatograph with any of the putative metabolites. Analysis by TLC of the urine pools in the solvent system methanol/potassium iodide (100% aqueous)/butan-1-ol, 80/15/5, v/v/v, indicated that the radiolabelled component detected was of a similar chromatographic character to radiolabelled test material.
Radio-TLC analysis of extracts of pooled faeces (0-24 h post dose; male and female separately) in the solvent system methanol/potassium iodide (100% aqueous)/butan-1-ol; 80/15/5; v/v/v indicated that the single major radio-component detected was of a similar chromatographic character to radiolabelled test material.

Table 1. Cumulative Excretion of Total Radioactivity in Excreta Following Single Oral Administration of [14C]-test substance. Results expressed as % administered dose recovered

Sample/Time (h)	Males						Females
	1	2	3	4	5	Mean	1	2	3	4	5	Mean
Urine
0 – 8	1.73	2.45	1.82	1.59	1.78	1.87	2.71	2.14	1.8	2.74	4.16	2.71
0 – 24	3.24	2.94	2.11	2.33	2.44	2.51	3.15	2.88	2.68	3.15	4.93	3.36
0 – 36	3.27	2.98	2.17	2.38	2.47	2.65	3.2	3.02	2.74	3.2	5.05	3.44
0 – 48	3.31	3.01	2.19	2.4	2.49	2.68	3.22	3.05	2.77	3.24	5.11	3.48
0 - 72	3.33	3.03	2.2	2.42	2.51	2.7	3.24	3.11	2.8	3.28	5.15	3.52
0 - 98	3.34	3.04	2.21	2.43	2.53	2.71	3.25	3.13	2.82	3.3	5.17	3.53
0 – 120	3.34	3.05	2.21	2.43	2.54	2.71	3.25	3.14	2.83	3.31	5.18	3.54
0 – 144	3.34	3.06	2.21	2.43	2.54	2.72	3.25	3.14	2.83	3.32	5.19	3.55
0 – 168	3.34	3.07	2.21	2.43	2.54	2.72	3.25	3.14	2.83	3.33	5.19	3.55
Faeces
0 – 24	94.82	88.68	91.47	93.67	89.7	91.67	91.27	93.01	92.4	88.2	77.64	88.5
0 - 48	96.56	91.8	95.7	96.26	92.95	94.65	93.51	95.08	96.82	90.83	85.81	92.41
0 – 72	96.63	91.92	95.8	96.32	93.01	94.74	93.57	95.16	96.96	90.99	86.27	92.61
0 – 96	96.63*	91.94*	95.81	96.34	93.04	94.75	93.7	95.18	97	91.04	86.30	92.64
0 – 120	96.64*	92.32	95.82**	96.35*	93.05*	94.84	93.71*	95.19	97.02	91.06*	86.32	92.66
0 – 144	96.64**	92.33**	95.83*	96.36*	93.06*	94.84	93.72*	95.20*	92.02**	91.07*	86.32**	92.67
0 – 168	96.64**	92.34*	95.83*	96.36**	93.06**	94.85	93.72**	95.20**	92.02**	91.08*	86.34	92.67
Cage wash
0 – 24	0.05	0.67	0.02*	0.2	0.06	0.2	0.18	0.39	0.28	0.14	0.14	0.23
0 - 48	0.08	0.77	0.04*	0.22*	0.09*	0.24	0.2*	0.45	0.31*	0.18*	0.17*	0.25
0 – 72	0.08**	0.8*	0.04**	0.24**	0.11*	0.25	0.22**	0.48*	0.37	0.2*	0.18**	0.29
0 – 96	0.09**	0.84	0.07*	0.25**	0.14*	0.28	0.23**	0.49**	0.42*	0.22*	0.18**	0.31
0 – 120	0.1**	0.85**	0.08**	0.26**	0.15**	0.29	0.24**	0.5**	0.44**	0.24*	0.19**	0.32
0 – 144	0.1**	0.88*	0.09**	0.26**	0.16**	0.3	0.25**	0.51**	0.45*	0.25**	0.19**	0.33
0 – 168	0.14**	1.01*	0.11**	0.27**	0.17**	0.34	0.28**	0.59*	0.48*	0.32*	0.24*	0.38
Total excreta
0 – 8	1.73	2.45	1.82	1.59	1.78	1.87	2.71	2.14	1.8	2.74	4.16	2.71
0 – 24	98.11	92.29	93.6	96.2	92.2	94.48	94.6	96.28	95.36	91.49	82.71	92.09
0 – 36	98.14	92.33	93.66	96.25	92.23	94.52	94.65	96.42	95.42	91.54	82.83	92.17
0 – 48	99.95	95.58	97.93	98.88	95.53	97.57	96.93	98.58	99.9	94.25	91.09	96.15
0 – 72	100.04	95.75	98.04	98.98	95.63	97.69	97.13	98.75	100.13	94.47	91.6	96.42
0 – 96	100.06	95.82	98.09	99.01	95.71	97.74	97.18	98.8	100.24	94.56	91.65	95.49
0 – 120	100.08	96.22	98.11	99.04	95.74	97.84	97.2	98.83	100.29	94.61	91.69	96.52
0 – 144	100.08	96.27	98.13	99.05	95.76	97.85	97.22	98.85	100.30	94.64	91.7	96.54
0 – 168	100.12	96.42	98.15	99.06	95.77	97.9	97.25	98.93	100.33	94.73	91.77	96.6
Tissues	0**	0.01**	0**	0**	0**	0	0**	0**	0**	0**	0**	0
Carcass	0	0	0	0	0	0	0	0	0	0	0	0
Total recovered	100.12	96.43	98.15	99.06	95.77	97.91	97.25	98.93	100.33	94.73	91.77	96.60

* results derived from data <30 d.p.m. above background

** results derived from data <10 d.p.m above background

Conclusions:

An oral dose of the test material was apparently poorly absorbed in the rat. Following single oral administration of radiolabelled test material to rats at a target dose level of 1 mg test material ion/kg, a mean of 3.1% of the administered radioactivity was recovered in the urine. Radioactivity was rapidly excreted in the faeces. The very low levels of radioactivity in tissues at 168 h post dose and the presence of parent compound in extracts of pooled faeces are consistent with limited absorption of the radiolabelled test material. The chromatographic profiles of pooled urine samples indicate that the low proportion of radiolabelled material absorbed is excreted unmetabolised. There was apparently no sex difference in the pattern of excretion, or the radio-TLC profiles of excreta.

Executive summary:

Radioactivity was rapidly excreted via faeces following single oral administration of radiolabelled test material to rats at a target dose level of 1 mg test material ion/kg. A mean of 90.1% of administered radioactivity was recovered in the faeces by 24 h; by 168 h post dose the mean faecal recovery was 93.8%. Excretion by the urinary route accounted for 3.1% of the administered dose by 168 h. The mean total dose recovered was 97.3%. At 168 h post dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background. No apparent sex difference was observed in the pattern of excretion.

Radio-TLC analysis of pooled urine samples indicated the presence of a single major radio-component which co-chromatographed with radiolabelled test material ion. A similar component was observed in the extract of pooled faeces samples.

Reference 4

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

The absorption of the test material through human abdominal epidermis was measured from technical test material (17.13% w/v test substance ion) and a spray strength solution (0.45% w/v test substance ion), using glass diffusion cells in which the epidermal sheet forms a horizontal membrane sperating "donor" and "receptor" chambers.

GLP compliance:

no

Radiolabelling:

yes

Doses:

- Technical test material: 17.13% w/w test substance ion
- Spray strength solution: 0.45% w/v test substance ion

Details on study design:

ANALYTICAL TECHNIQUE
- Radiochemical assay: Liquid scintillation spectrometer
- Sample size: 25 µL added to scintillation fluid in vials followed by mixing
- Counting period: 10 minutes, or until 10^6 counts had been registered

Details on in vitro test system (if applicable):

In vitro model using Human abdominal whole skin (dermis plus epidermis).

Absorption in different matrices:

The mean rate of absorption of the test substance from the concentrate, through abdominal skin was 8.62 µg/cm2/hr (SEM ± 1.76; n = 12). From the spray strength solution the rate was 0.24 µg/cm2/hr (SEM ± 0.06; n = 12).
A lag phase of 10-15 hours, ie a period of increasing rate of absorption before the steady state, was detected after the concentrate contacted the skin in these experiments. When the spray strength solution contacted the skin, a lag phase of between 8-12 hours was apparent. A more precise definition of the lag phase from both formulations was not possible due to the small amounts of test substance being absorbed.

Key result

Dose:

Concentrate (17.13 % w/w test substance ion)

Parameter:

rate

Absorption:

8.62 other: µg/cm2/hr (SEM ± 1.76; n=12)

Key result

Dose:

Spray strenght solution (0.45 % w/v test substance ion)

Parameter:

rate

Absorption:

0.24 other: µg/cm2/hr (SEM ± 0.06; n=12)

Conclusions:

The mean steady rate of absorption of the test substance from the concentrate, through abdominal skin was 8.62 µg/cm2/hr (SEM ± 1.76; n = 12). From the spray strength solution the rate was 0.24 µg/cm2/hr (SEM ± 0.06; n = 12).

Executive summary:

The absorption of the test substance through human abdominal epidermis was measured from technical test substance material (17.13 % w/w test substance ion) and a spray strength solution (0.45 % w/ v test substance ion). Glass diffusion cells in which the epidermal sheet forms a horizontal membrane separating "donor” (outer) and "receptor" chambers were used for measuring skin absorption rates. 1.8 cm2 of epidermal surface was available for absorption and all experiments were done at 30 °C. Receptor solutions were stirred. The test substance material or the aqueous spray strength solution (1 mL), both containing [14C]test substance, was place in the donor chamber. At defined intervals (1 hour for the concentrate and 2 hours for the dilution) 25 µL samples were removed from the receptor chamber and put in scintillation fluid. The mean steady rate of absorption of the test substance from the concentrate, through abdominal skin was 8.62 µg/cm2/hr (SEM ± 1.76; n = 12). From the spray strength solution the rate was 0.24 µg/cm2/hr (SEM ± 0.06; n = 12).

Reference 5

Endpoint:

dermal absorption, other

Type of information:

other: Review paper

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Qualifier:

no guideline required

GLP compliance:

no

Conclusions:

The test substance is absorbed poorly through human skin. Animal studies, in which the test substance was administered by intravenous or oral routes, have shown that the small amount of the test substance which would be absorbed following dermal contact, is rapidly distributed and eliminated. Highest levels appear in the kidney (organ of excretion) and there is no accumulation into any organ including the lung. The very low permeability of human skin to the test substance together with the rapid distribution and elimination of the small amounts which would be absorbed are the important factors in preventing toxicity after human dermal exposure to the test substance.

Executive summary:

INTRODUCTION

The purpose of this paper is to review the available data on the dermal absorption and tissue distribution of the test substance. This will allow an assessment of the potential for systemic toxicity to Man as a result of dermal exposure to the test substance. It is pertinent to describe the metabolism and elimination characteristics of the test substance also. The list of references is attached.

 

ABSORPTION

Following dermal contact, a chemical must enter the systemic circulatory system to exert toxicity. This process involves diffusion through the outermost layer of the epidermis, the stratum corneum, across the viable epidermis and into the extensive capillary network located immediately below the dermo-epidermal junction (1). Once a chemical has entered the blood stream, the pharmacokinetics should be the same as after administration by intravenous, subcutaneous or intraperitoneal dosing. This has not been demonstrated with the test substance in Man, however, evidence is available from animal studies to show this is the case (2-5) and it would be expected to be so in Man also. It is particularly true for compounds, such as the test substance, which are not metabolised during percutaneous absorption (6) or other body tissues (7,8).

In order to study the potential dermal toxicity of a chemical, animal models are used. Studies using a single non-occluded application to rabbit skin showed that the dermal LD50 was > 400 mg test substance ion/kg (9). In contrast, the intravenous LD50 was 15 mg test substance ion/kg, indicating that the test substance is absorbed poorly through rabbit skin. Dermal toxicity data obtained in animals are extrapolated to Man and this can be misleading. For many chemicals, human skin is much less permeable than animal skins. It has been shown in an in vitro study that for a chemically related substance, there is no adequate animal model for human skin (10). The in vitro permeability of human skin was approximately 110 times less than rabbit skin (the species used to assess dermal toxicity) and 50 times less than rat skin. The in vitro technique predicts in vivo absorption of chemicals (11, 12) and the difference in relative permeability of rabbit and human skin indicates that there would be, therefore, a significant difference in dermal absorption, and, hence toxicity.

In an in vivo study (13) with human volunteers, the poor percutaneous absorption was confirmed. Radiolabelled test substance was applied dermally and intraperitoneally and the ratio of the test substance in the urine after intraperitoneal dosing used to calculate the amount of dermal absorption. The accuracy of this technique for assessing percutaneous absorption has been validated with a range of pesticides (14). Relative to other pesticides studied, the test substance was the most poorly absorbed with only 0.3% of the dose absorbed within 5 days. The poor penetration of the test substance through human skin has been further confirmed using an alternative (deconvolution) calculation technique (6).

The in vitro technique has also been used to measure the absorption rate of the test substance from a concentrate formulation (20%) and a spray strength solution (0.45%) through human skin (15). From the absorption rate data, permeability constants (a concentration independent expression of the rate) were calculated. The permeability constants for the concentrate and spray dilutions were similar and indicated that human skin has a low intrinsic permeability to the test substance.

The available data show that the test substance is poorly absorbed through the skin.

 

METABOLISM, DISTRIBUTION AND ELIMINATION

The test substance is not metabolised by human skin (6) or rat tissues (7, 8). Once the chemical enters the blood stream following dermal absorption, its distribution throughout the tissues and its rate of elimination from the body would be expected to be the same as after intravenous, subcutaneous or oral dosing.

Intravenous dosing in mice (50 mg test substance ion/kg) resulted in a wide distribution in the body tissues followed by rapid and complete elimination. Whole body autoradiography confirmed the rapid distribution into all tissues with the exception of the brain and spinal cord (2).

Following oral dosing at a dose equivalent to half the oral LD50, low dose levels were found in the liver, lung, heart, brain and kidney. The residues found in all tissues at 24 hours were less than those found after 2 hours. At day 5, the tissue concentrations of the test substance in the brain, heart and liver were < 2 µg/g tissue. A higher level (< 4 µg/g tissue) was seen in the kidney, but this is expected as this is the organ of excretion. However, there was no evidence of accumulation in any tissues, including the lungs (3, 4). A further oral study at a dose equivalent to the LD50 in the rat confirmed that the test substance is not accumulated in the body (16). The concentration of the test substance in the lung and heart (< 7 and 12 µg/g tissue) was higher than in the brain, liver and kidney (< 5µg/g). However, concentrations had declined in all tissues except the kidney (7 µg/g) by 48 hours. The affinity of muscle tissue has been shown to be very low and the extent of the residual pool 4 days after dosing was only 0.03% of the dose (17). A commercial formulation has also been dosed to male rats at a dose equivalent to 1/5 the LD50 of the formulation, i.e 45.7 mg test substance ion/kg (5). Highest levels of the test substance were detected after 4 hours following dosing in lungs (2.04 µg/g), kidneys (1.85 µg/g) and liver (0.64 µg/g) and after this the tissue levels declined and were very small at 48 hours. During prolonged dosing over 8 weeks, the highest tissue levels were detected in the kidney (0.17 - 1.17 µg/g) and digestive tract (0.28 - 1.18 µg/g), however, no test substance could be detected 7 days after the last dose, confirming, a lack of retention of the test substance in the body (2).

These studies clearly indicate that absorbed test substance is rapidly and completely eliminated from the body and does not accumulate in any tissues.

 

CONCLUSION

The test substance is absorbed poorly through human skin. Animal studies, in which the test substance was administered by intravenous or oral routes, have shown that the small amount of the test substance which would be absorbed following dermal contact, is rapidly distributed and eliminated. Highest levels appear in the kidney (organ of excretion) and there is no accumulation into any organ including the lung. The very low permeability of human skin to the test substance together with the rapid distribution and elimination of the small amounts which would be absorbed are the important factors in preventing toxicity after human dermal exposure to the test substance.

Description of key information

- Absorption: The test substance is poorly absorbed via the oral and dermal route, 4 % and 1 %, respectively. No data on respiratory absorption is available, therefore, a default absorption value of 100 % is assumed.

- Distribution: After a single oral administration of 1 and 100 mg test substance ion/kg, highest concentrations of radioactivity were found in kidney, lung and liver; peak blood and tissue levels were observed at approx. 2-4 h after administration followed by rapid decline

- Metabolism: Radio-TLC analysis of pooled urine samples and pooled faeces samples indicated that the majority of the test substance was excreted unchanged.

- Excretion: The main route of excretion is via faeces. For a single oral administration of 1 mg test substance ion/kg, excretion via faeces was 93.8 % (168 h) and for 186.6 mg test substance ion/kg 85.5 % (168 h). Excretion via urine was 3.1 % (168 h) for the low dose and 5.4 % (168 h) for the high dose. There was no sex difference in the pattern of excretion.

- Bioaccumulation potential: No evidence of accumulation after repeated dosing. 

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

4

Absorption rate - dermal (%):

1

Absorption rate - inhalation (%):

100

Additional information

Toxicokinetic studies

A toxicokinetic study, performed under GLP and comparable to OECD TG 417, investigated the aspects of the distribution of the radiolabelled test substance in the rat at target dose levels of 1 mg test substance ion/kg and 100 mg test substance ion/kg (Johnston, 1991b). Following single oral administration at 1 mg only relatively low levels of radioactivity were detected in whole blood with a maximum mean concentration of 0.012 µg equiv/g observed at 2 h post dose. At the 100 mg dose level a maximum mean concentration of 1.428 µg equiv/g was observed at 1 h post dose. Concentrations of radioactivity in whole blood were generally in proportion to the dose received and there was apparently no sex difference. Following single oral administration of the radiolabelled test substance at a target dose level of 1 mg test substance ion/kg, the concentration of radioactivity in tissues fell from a maximum at 2-4 h to near background at 24 h. Excluding the GI tract, highest concentrations of radioactivity at the low dose level were found in kidney. There was apparently no sex difference. Following single oral administration of radiolabelled test substance at a target dose level of 100 mg test substance ion/kg the rate of elimination of radioactivity was generally slower than at the low dose level. Highest concentrations of radioactivity were found in kidney, lung and liver. Concentrations of radioactivity in tissues generally appeared to be in proportion to the dose. The concentrations of radioactivity in lung appeared to be disproportionally high in the high dose group. The data are consistent with previous elimination studies which indicated limited oral absorption of the radiolabelled test substance and slower elimination at the high dose level. Based on these findings and oral absorption of 4% is used in the chemical safety assessment. No data on respiratory absorption is available, therefore, a default absorption value of 100% is assumed.

The elimination of the test substance was assessed in two studies. The first study describes aspects of the elimination of [14C]-test substance in the rat following single oral administration at a target dose level of 186.8 mg/kg (Johnston, 1991a). Radioactivity was predominantly excreted via faeces. A mean of 73.3 % of administered radioactivity was recovered in the faeces by 48 h; by 168 h post-dose the mean faecal recovery was 85.5 %. Excretion by the urinary route accounted for 5.4 % of the administered dose by 168 h. The mean total dose recovered was 93.2 %. At 168 h post-dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background. No apparent sex difference was observed in the pattern of excretion. Radio-TLC analysis of pooled urine samples indicated the presence of a single major radio component which co-chromatographed with [14C]-test substance. A similar component was observed in the extract of pooled faeces samples.

In the second study, radioactivity was rapidly excreted via faeces following single oral administration of radiolabelled test material to rats at a target dose level of 1 mg test material ion/kg (Johnston, 1994). A mean of 90.1 % of administered radioactivity was recovered in the faeces by 24 h; by 168 h post dose the mean faecal recovery was 93.8 %. Excretion by the urinary route accounted for 3.1 % of the administered dose by 168 h. The mean total dose recovered was 97.3 %. At 168 h post dose levels of radioactivity in tissues, organs and body fluids were at, or close to, background. No apparent sex difference was observed in the pattern of excretion. Radio-TLC analysis of pooled urine samples indicated the presence of a single major radio-component which co-chromatographed with radiolabelled test material ion. A similar component was observed in the extract of pooled faeces samples.

 

Dermal absorption

The dermal absorption potential was evaluated in a review paper describing human, animal and in vitro data. Based on these data it was concluded that the absorption of the test substance and aqueous dilutions through human epidermis is extremely low.

In addition, the dermal absorption rate of the test substance from a concentrate formulation (20%) and a spray strength solution (0.45%) through human skin was assessed in vitro (Scott, 1991). From the absorption rate data, permeability constants (a concentration independent expression of the rate) were calculated. The permeability constants for the concentrate and spray dilutions were similar and indicated that human skin has a low intrinsic permeability to the test substance.

Based on available information, the dermal absorption value used for the chemical safety assessment was conservatively set to 1%.