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EC number: 232-076-8 | CAS number: 7785-23-1
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Endpoint summary
Administrative data
Link to relevant study record(s)
- Endpoint:
- basic toxicokinetics in vivo
- Type of information:
- experimental study
- Adequacy of study:
- supporting study
- Study period:
- 2021
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- test procedure in accordance with generally accepted scientific standards and described in sufficient detail
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to same study
- Objective of study:
- other: investigation of copper status of rats exposed to silver powder
- Qualifier:
- no guideline available
- Principles of method if other than guideline:
- In the comparative in vivo TK study, at termination, analysis of serum for total copper concentration was undertaken in the case of the test items AgMP and AgNO3.
- GLP compliance:
- yes (incl. QA statement)
- Species:
- rat
- Strain:
- Sprague-Dawley
- Details on species / strain selection:
- Crl:CD IGS (SD)
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source:
Charles River UK
- Age at study initiation: 8-10 weeks old at start of treatment
- Weight at study initiation: min. 170 g for females and 200 g for males
- Housing: up to four animals of the same sex per cage. Within each group, cages will be blocked together (by sex). The distribution of the groups within and between racks and the position of the racks within the room will be determined to equalize environmental influences across the study while minimizing the opportunity for inter-group contamination.
- Diet (e.g. ad libitum): SDS VRF-,1 pelleted diet, non-restricted availability (diet contains no added antibiotic or other chemotherapeutic or prophylactic agent)
- Water (e.g. ad libitum): potable water from the public supply, non-restricted availability via polycarbonate bottles with sipper tubes (except during urine collection)
- Acclimation period: at least 5 days before commencement of treatment
- Health status: visually inspected at least twice daily for evidence of ill-health
ENVIRONMENTAL CONDITIONS
- Temperature (°C): monitored and maintained within the range of 20-24ºC
- Humidity (%): monitored and maintained within the range of 40-70%
- Air changes (per hr): air filtered, not recirculated
- Photoperiod (hrs dark / hrs light): 12 hours light : 12 hours dark
- Fasting period: none
IN-LIFE DATES: study performed in phases, with first phase started on 13 July 2021 and last (repeated) phase ended on 20 August 2021 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS:
Notes:
- Chloride and phosphate containing vehicles and reagents were avoided due to the potential for silver precipitation effects.
- Dissolved silver and silver particles adsorb onto material surfaces including glass and metals, and as such use of these was avoided.
- Formulations were protected from light during preparation (use of yellow-light instead).
- The formulation procedures are documented in the study data and will be included in the final report.
- The pH of the final formulations was measured and recorded in the data.
- A series of formulations at the required concentrations is prepared by dilution of individual weighing of the Test Item and dispensed in polypropylene screw top jars or similar
Method of preparation:
- 50% of the final volume of vehicle is added to an appropriate container. The required amount of Test Item is weighed and added to the vehicle whilst stirring at an appropriate speed to obtain a vortex that is half the depth of the suspension. The ‘weighing’ container is rinsed several times using 20% final volume of vehicle. After addition of the rinsing, the suspension is stirred for 60 seconds and then sonicated for approximately 30 minutes. This stir and sonicate step is then repeated, after which the remaining 30% final volume of vehicle is added and stirring continued at an appropriate speed to obtain a vortex that is half the depth of the final suspension for at least 60 minutes.
- The suspensions are sampled for formulation analysis (whilst under constant stirring, according to the previously described technique) prior to dispensing and aliquoting into suitable containers for dose administration.
Frequency of preparation:
- Repeat dose formulations were prepared weekly and split into daily aliquots.
- The suitability and homogeneity of formulations were confirmed as part of studies, undertaken separately by third parties designated by the Sponsor, and by the Principal Investigator for dose formulation analysis.
Storage of formulation: Silver AgMP suspensions: refrigerated (2 to 8°C), protected from light. - Duration and frequency of treatment / exposure:
- 28 days; frequency: once daily at approximately the same time each day
- Dose / conc.:
- 5 mg/kg bw/day (nominal)
- Dose / conc.:
- 55 mg/kg bw/day (nominal)
- Dose / conc.:
- 125 mg/kg bw/day (nominal)
- No. of animals per sex per dose / concentration:
- 4 males + 4 females
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- The dose levels selected in the case of silver nitrate (AgNO3) extend existing but limited toxicokinetic data for this compound. A previous 28-day toxicity study demonstrated that up to 100 mg/kg bw/d of AgNO3 administered to rats via oral gavage produced minimal toxicity. The high-dose treatment level has been set with due regard for the local tissues irritancy profile of AgNO3
- Details on dosing and sampling:
- TOXICOKINETIC STUDY (Absorption, distribution, excretion)
- Body fluids sampled: blood
- Sample treatment: Whole blood was left to clot according to standard operating procedures. Serum was collected and frozen upright on dry ice following centrifugation, pending transfer to frozen storage.
- Time and frequency of sampling: at termination (after 28 days treatment)
ANALYTICAL METHOD
Serum samples were analysed for copper using ICP-MS method. The method was successfully validated with a lower limit of quantification (LLOQ) of 30 ng/mL. - Statistics:
- Summary statistics (e.g. means and standard deviations) presented in the report were calculated from computer-stored individual raw data.
- Type:
- other: investigation of Cu status of rats exposed to AgNO3
- Results:
- After AgNO3 dosing, Cu conc. at LD were similar to those of controls, at MD (55 mg/kg/day) 20% lower and at HD (125 mg/kg/day) 26-38% lower.
- Details on absorption:
- n.a.
- Details on distribution in tissues:
- n.a.
- Details on excretion:
- n.a.
- Metabolites identified:
- no
- Details on metabolites:
- n.a.
- Conclusions:
- There was a treatment-related effect on the concentration of copper in serum following repeated oral dose of AgNO3, the serum concentration of copper decreased with increasing dose.
- Executive summary:
The copper status of rats exposed to an ionic Ag (AgNO3) was investigated in this study. a treatment-related effects on concentration of Cu in serum was observed after 28 days treatment via the oral route. This depression in circulating Cu levels was apparent from a quite low exposure in the case of the ionic reference compound (AgNO3) (being evident from 35 mg Ag/kg bw/day).
- Endpoint:
- basic toxicokinetics in vivo
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 2020-2021
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to same study
- Objective of study:
- absorption
- bioaccessibility (or bioavailability)
- tissue distribution
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 417 (Toxicokinetics)
- GLP compliance:
- yes (incl. QA statement)
- Radiolabelling:
- no
- Species:
- rat
- Strain:
- Sprague-Dawley
- Details on species / strain selection:
- Crl:CD IGS (SD)
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River UK
- Age at study initiation: 8-10 weeks old at start of treatment
- Weight at study initiation: min. 170 g for females and 200 g for males
- Housing: up to four animals of the same sex per cag. Within each group, cages will be blocked together (by sex). The distribution of the groups within and between racks and the position of the racks within the room will be determined to equalize environmental influences across the study while minimizing the opportunity for inter-group contamination.
- Diet (e.g. ad libitum): SDS VRF-,1 pelleted diet, non-restricted availability (diet contains no added antibiotic or other chemotherapeutic or prophylactic agent)
- Water (e.g. ad libitum): potable water from the public supply, non-restricted availability via polycarbonate bottles with sipper tubes (except during urine collection)
- Acclimation period: at least 5 days before commencement of treatment
- Health status: visually inspected at least twice daily for evidence of ill-health
ENVIRONMENTAL CONDITIONS
- Temperature (°C): monitored and maintained within the range of 20-24ºC
- Humidity (%): monitored and maintained within the range of 40-70%
- Air changes (per hr): air filtered, not recirculated
- Photoperiod (hrs dark / hrs light): 12 hours light : 12 hours dark
- Fasting period : none
IN-LIFE DATES: study performed in phases, with first phase started on 30 Sep 2020 and last (repeated) phase ended on 20 Aug 2021 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS:
Notes:
- Chloride and phosphate containing vehicles and reagents were avoided due to the potential for silver precipitation effects.
- Dissolved silver and silver particles adsorb onto material surfaces including glass and metals, and as such use of these was avoided.
- Formulations were protected from light during preparation (use of yellow-light instead).
- The formulation procedures are documented in the study data and will be included in the final report.
- The pH of the final formulations was measured and recorded in the data.
- A series of formulations at the required concentrations is prepared by dilution of individual weighing of the Test Item and dispensed in polypropylene screw top jars or similar
Method of preparation:
The required amount of test item was weighed out, (Ag Acetate was ground in a pestle and mortar) and then added to ca 50% of the final volume of vehicle and magnetically stirred to mix/disperse. The ‘weighing’ vessel was rinsed, and the rinsing is added to the container before bringing to volume with the vehicle. The mixture was then transferred to a magnetic stirrer and stirred for a minimum of 20 minutes, recording the start and finish times in the raw data. Formulation analysis sampling will occur whilst under constant stirring, prior to dispensing and aliquoting into suitable containers for dose administration (stirrer bars will be included).
Frequency of preparation:
- Repeat dose formulations were prepared weekly and split into daily aliquots.
- The suitability and homogeneity of formulations were confirmed as part of studies, undertaken separately by third parties designated by the Sponsor, and by the Principal Investigator for dose formulation analysis.
Storage of formulation: Silver solutions – ambient temperature (15 to 25°C), protected from light. - Duration and frequency of treatment / exposure:
- Two treatments:
- single oral dose: single occasion on day 1
- repeat oral doses: 28 days; frequency: once daily at approximately the same time each day - Dose / conc.:
- 5 mg/kg bw/day (nominal)
- Remarks:
- single + repeat oral doses
- Dose / conc.:
- 55 mg/kg bw/day (nominal)
- Remarks:
- repeat oral doses
- Dose / conc.:
- 125 mg/kg bw/day (nominal)
- Remarks:
- single + repeat oral doses
- No. of animals per sex per dose / concentration:
- 4 males + 4 females
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- Rationale for Dose Level Selection and Route:
The dose levels selected in the case of silver nitrate (AgNO3) extend existing but limited toxicokinetic data for this compound. A previous 28-day toxicity study demonstrated that up to 100 mg/kg bw/d of AgNO3 administered to rats via oral gavage produced minimal toxicity. The high-dose treatment level has been set with due regard for the local tissue irritancy profile of AgNO3. - Details on dosing and sampling:
- TOXICOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: blood, brain, bone marrow, small intestine, liver, spleen, ovaries, testes, uterus
- Time and frequency of sampling: blood: Day 15: PD, 6 hours post-dose, Day 28: PD, 3, 6, 9, 12, 24, 72, 96 hours post-dose. (10 time points) ; tissues: at termination (after 28 days treatment)
ANALYTICAL METHOD
Total Ag concentrations were determined in whole blood and tissues by ICP-MS after microwave digestion with nitric acid and hydrochloric acid. This method was successfully validated with a lower limit of quantification (LLOQ) of 10 ng/mL for silver in rat blood4 and 30 ng/g for silver in rat tissue. - Statistics:
- - Ag analysis data were acquired and integrated using MassHunter (version C.01.05 Agilent). Peak area results were exported to Watson LIMS (Version 7.5 SP1, Thermo Scientific) in text file format. Watson LIMS was used to calculate standard curve parameters and concentration data for Silver. The concentration and statistical data were generated by computerized techniques.
- AUC(0-t): area under the concentration-time curve from hour 0 to the last measurable concentration, estimated by the linear trapezoidal rule. - Type:
- absorption
- Results:
- Based on matched dose assessments, silver acetate (AgAc) and silver nitrate (AgNO3) exhibit very similar systemic exposure profiles while AgMP leads to appreciably lower Ag amplitude of systemic exposure.
- Type:
- distribution
- Results:
- Levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 and considerably lower in the case of AgMP .
- Details on absorption:
- - Comparisons via normalised administered doses (i.e. Ag equivalent dose) can be made between the different Ag test items. Based on these matched dose assessments, the extent of systemic exposure was similar for AgAc and AgNO3 but about 10 to 30-fold lower in the case of Ag metal powder versus AgAc
- The maximum observed Ag concentration in blood occurs between 3-9h post-dosing for repeat dose groups. - Details on distribution in tissues:
- - Levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 (but considerably lower in the case of AgMP ).
- The study shows that the testis and brain are minor sites of distribution. In contrast, the ovary has been shown to be an important site of distribution. However, ancillary investigations strongly suggest silver is present in the ovary as chemically stable silver sulphide/selenide complexes with very low local bioavailability. - Details on excretion:
- not investigated
- Key result
- Test no.:
- #1
- Toxicokinetic parameters:
- AUC: 1600
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 5 mg/kg bw/d
- Key result
- Test no.:
- #1
- Toxicokinetic parameters:
- AUC: 2240
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 5 mg/kg bw/d
- Key result
- Test no.:
- #2
- Toxicokinetic parameters:
- AUC: 581
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 55 mg/kg bw/d
- Key result
- Test no.:
- #2
- Toxicokinetic parameters:
- AUC: 601
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 55 mg/kg bw/d
- Key result
- Test no.:
- #3
- Toxicokinetic parameters:
- AUC: 476
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 125 mg/kg bw/d
- Key result
- Test no.:
- #3
- Toxicokinetic parameters:
- AUC: 601
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 125 mg/kg bw/d
- Metabolites identified:
- no
- Remarks:
- n.a.
- Details on metabolites:
- n.a.
- Conclusions:
- This in-vivo toxicokinetic study (in rats) by oral gavage comparing silver metal powder, nanosilver, silver nitrate and silver acetate shows a lower absorption/distribution and lower systemic exposure to tissues and organs for silver metal powder than for the other silver substances. The amount of Ag+ in blood and tissues is much higher for silver acetate/silver nitrate than for silver metal powder at comparable Ag dosing levels. Although all silver-containing substances have the ability to release Ag+, the extent of released silver ions is significantly different between substances. Therefore, a direct read-across of mammalian toxicity datasets for simple ionic silver salts like silver acetate or silver nitrate and nanosilver to silver metal powder/massive is not supported (from a scientifically valid toxicokinetic perspective).
- Executive summary:
This in-vivo toxicokinetic study is an oral route investigation using adult CD Sprague Dawley rats. The design conformed to OECD TG 417 and was conducted in compliance to GLP. The study was designed as a comparative toxicokinetic assessment of the test items Silver Acetate (AgAc), Silver Nitrate (AgNO3), Micron-sized Silver (AgMP) and Nanoparticulate Silver (AgNP). This included assessment of bioavailability following single oral doses relative to single intravenous doses and systemic exposure following single and repeat oral doses. Groups of 4 male and 4 female CD Sprague Dawley rats were administered the test items, either as a single intravenous dose, a single oral dose or repeated daily oral doses for 4 weeks.
The systemic exposure (28 days) results show a difference in the extent of absorption and systemic circulation for silver acetate and nitrate versus silver metal powder. Based on a matched dose assessment, the extent of systemic exposure was about 10 to 30-fold lower in the case of silver metal powder versus silver acetate (as reference ionic silver compound).
The silver tissue levels after repeated dose administration are considerably lower in the case of silver metal powder (AgMP) than for silver acetate. This suggests that AgMP represents a correspondingly lower health hazard, i.e. AgMP (and by extrapolation also massive Ag with a tremendously lower particle size/reactive surface area) is expected to cause less effects at corresponding Ag dose levels than AgAc.
In conclusion, it is assumed that the systemic toxicity of silver substances is driven by the release potential of Ag ionic species as the primary moiety for systemic circulation and tissue exposure, and hence hazard assessment. The comparative TK study is a high quality GLP investigation and the first which permits a direct comparison of systemic circulation and tissue distribution of Ag ionic species between soluble Ag salts (AgNO3and Ag acetate), AgNP and AgMP. This new evidence demonstrates that oral intake of AgMP results in markedly lower absorption, distribution and systemic tissue/organ exposure to silver than more bioavailable forms like AgAc. As a generic observation, the following trend is being observed: AgAc > AgNO3>> AgNP >>> AgMP.
The study findings show that the direct read-across of mammalian toxicity data with soluble silver salts (like silver acetate and silver nitrate) and nanosilver to silver metal (powder and massive) is not justified (based on their individual toxicokinetic profiles).
- Endpoint:
- basic toxicokinetics in vivo
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 2020-2021
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to same study
- Objective of study:
- absorption
- bioaccessibility (or bioavailability)
- tissue distribution
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 417 (Toxicokinetics)
- GLP compliance:
- yes (incl. QA statement)
- Radiolabelling:
- no
- Species:
- rat
- Strain:
- Sprague-Dawley
- Details on species / strain selection:
- Crl:CD IGS (SD)
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Source: Charles River UK
- Age at study initiation: 8-10 weeks old at start of treatment
- Weight at study initiation: min. 170 g for females and 200 g for males
- Housing: up to four animals of the same sex per cag. Within each group, cages will be blocked together (by sex). The distribution of the groups within and between racks and the position of the racks within the room will be determined to equalize environmental influences across the study while minimizing the opportunity for inter-group contamination.
- Diet (e.g. ad libitum): SDS VRF-,1 pelleted diet, non-restricted availability (diet contains no added antibiotic or other chemotherapeutic or prophylactic agent)
- Water (e.g. ad libitum): potable water from the public supply, non-restricted availability via polycarbonate bottles with sipper tubes (except during urine collection)
- Acclimation period: at least 5 days before commencement of treatment
- Health status: visually inspected at least twice daily for evidence of ill-health
ENVIRONMENTAL CONDITIONS
- Temperature (°C): monitored and maintained within the range of 20-24ºC
- Humidity (%): monitored and maintained within the range of 40-70%
- Air changes (per hr): air filtered, not recirculated
- Photoperiod (hrs dark / hrs light): 12 hours light : 12 hours dark
- Fasting period : none
IN-LIFE DATES: study performed in phases, with first phase started on 30 Sep 2020 and last (repeated) phase ended on 20 Aug 2021 - Route of administration:
- oral: gavage
- Vehicle:
- water
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS:
Notes:
- Chloride and phosphate containing vehicles and reagents were avoided due to the potential for silver precipitation effects.
- Dissolved silver and silver particles adsorb onto material surfaces including glass and metals, and as such use of these was avoided.
- Formulations were protected from light during preparation (use of yellow-light instead).
- The formulation procedures are documented in the study data and will be included in the final report.
- The pH of the final formulations was measured and recorded in the data.
- A series of formulations at the required concentrations is prepared by dilution of individual weighing of the Test Item and dispensed in polypropylene screw top jars or similar
Method of preparation:
The required amount of test item was weighed out, (Ag Acetate was ground in a pestle and mortar) and then added to ca 50% of the final volume of vehicle and magnetically stirred to mix/disperse. The ‘weighing’ vessel was rinsed, and the rinsing is added to the container before bringing to volume with the vehicle. The mixture was then transferred to a magnetic stirrer and stirred for a minimum of 20 minutes, recording the start and finish times in the raw data. Formulation analysis sampling will occur whilst under constant stirring, prior to dispensing and aliquoting into suitable containers for dose administration (stirrer bars will be included).
Frequency of preparation:
- Repeat dose formulations were prepared weekly and split into daily aliquots.
- The suitability and homogeneity of formulations were confirmed as part of studies, undertaken separately by third parties designated by the Sponsor, and by the Principal Investigator for dose formulation analysis.
Storage of formulation: Silver solutions – ambient temperature (15 to 25°C), protected from light. - Duration and frequency of treatment / exposure:
- Two treatments:
- single oral dose: single occasion on day 1
- repeat oral doses: 28 days; frequency: once daily at approximately the same time each day - Dose / conc.:
- 5 mg/kg bw/day (nominal)
- Remarks:
- single + repeat oral doses
- Dose / conc.:
- 55 mg/kg bw/day (nominal)
- Remarks:
- repeat oral doses
- Dose / conc.:
- 175 mg/kg bw/day (nominal)
- Remarks:
- single + repeat oral doses
- No. of animals per sex per dose / concentration:
- 4 males + 4 females
- Control animals:
- yes, concurrent vehicle
- Details on study design:
- Rationale for Dose Level Selection and Route:
The dose levels for silver acetate (AgAc) have been chosen to support a program of reproductive toxicology studies on this compound. Based on existing toxicity data for AgAc, from repeated administration studies in rodents the dose levels are expected to be well tolerated. - Details on dosing and sampling:
- TOXICOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: blood, brain, bone marrow, small intestine, liver, spleen, ovaries, testes, uterus
- Time and frequency of sampling: blood: Day 15: PD, 6 hours post-dose, Day 28: PD, 3, 6, 9, 12, 24, 72, 96 hours post-dose. (10 time points) ; tissues: at termination (after 28 days treatment)
ANALYTICAL METHOD
Total Ag concentrations were determined in whole blood and tissues by ICP-MS after microwave digestion with nitric acid and hydrochloric acid. This method was successfully validated with a lower limit of quantification (LLOQ) of 10 ng/mL for silver in rat blood4 and 30 ng/g for silver in rat tissue. - Statistics:
- - Ag analysis data were acquired and integrated using MassHunter (version C.01.05 Agilent). Peak area results were exported to Watson LIMS (Version 7.5 SP1, Thermo Scientific) in text file format. Watson LIMS was used to calculate standard curve parameters and concentration data for Silver. The concentration and statistical data were generated by computerized techniques.
- AUC(0-t): area under the concentration-time curve from hour 0 to the last measurable concentration, estimated by the linear trapezoidal rule. - Type:
- absorption
- Results:
- Based on matched dose assessments, silver acetate (AgAc) and silver nitrate (AgNO3) exhibit very similar systemic exposure profiles while AgMP leads to appreciably lower Ag amplitude of systemic exposure.
- Type:
- distribution
- Results:
- Levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 and considerably lower in the case of AgMP .
- Details on absorption:
- - Comparisons via normalised administered doses (i.e. Ag equivalent dose) can be made between Ag acetate and bulk Ag (AgMP). Based on these matched dose assessments, the extent of systemic exposure was about 10 to 30-fold lower in the case of Ag metal powder versus AgAc
- The maximum observed Ag concentration in blood occurs between 3-9h post-dosing for repeat dose groups. - Details on distribution in tissues:
- - Levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 (but considerably lower in the case of AgMP ).
- The study shows that the testis and brain are minor sites of distribution. In contrast, the ovary has been shown to be an important site of distribution. However, ancillary investigations strongly suggest silver is present in the ovary as chemically stable silver sulphide/selenide complexes with very low local bioavailability. - Details on excretion:
- not investigated
- Key result
- Test no.:
- #1
- Toxicokinetic parameters:
- AUC: 1770
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 5 mg/kg bw/d
- Key result
- Test no.:
- #1
- Toxicokinetic parameters:
- AUC: 2920
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 5 mg/kg bw/d
- Key result
- Test no.:
- #2
- Toxicokinetic parameters:
- AUC: 664
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 55 mg/kg bw/d
- Key result
- Test no.:
- #2
- Toxicokinetic parameters:
- AUC: 846
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 55 mg/kg bw/d
- Key result
- Test no.:
- #3
- Toxicokinetic parameters:
- AUC: 342
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for male rats at dose level of 175 mg/kg bw/d
- Key result
- Test no.:
- #3
- Toxicokinetic parameters:
- AUC: 400
- Remarks:
- Dose normalised AUC(0-t) after 28d dosing; for female rats at dose level of 175 mg/kg bw/d
- Metabolites identified:
- no
- Remarks:
- n.a.
- Details on metabolites:
- n.a.
- Conclusions:
- This in-vivo toxicokinetic study (in rats) by oral gavage comparing silver metal powder, nanosilver, silver nitrate and silver acetate shows a lower absorption/distribution and lower systemic exposure to tissues and organs for silver metal powder than for the other silver substances. The amount of Ag+ in blood and tissues is much higher for silver acetate/silver nitrate than for silver metal powder at comparable Ag dosing levels. Although all silver-containing substances have the ability to release Ag+, the extent of released silver ions is significantly different between substances. Therefore, a direct read-across of mammalian toxicity datasets for simple ionic silver salts like silver acetate or silver nitrate and nanosilver to silver metal powder/massive is not supported (from a scientifically valid toxicokinetic perspective).
- Executive summary:
This in-vivo toxicokinetic study is an oral route investigation using adult CD Sprague Dawley rats. The design conformed to OECD TG 417 and was conducted in compliance to GLP. The study was designed as a comparative toxicokinetic assessment of the test items Silver Acetate (AgAc), Silver Nitrate (AgNO3), Micron-sized Silver (AgMP) and Nanoparticulate Silver (AgNP). This included assessment of bioavailability following single oral doses relative to single intravenous doses and systemic exposure following single and repeat oral doses. Groups of 4 male and 4 female CD Sprague Dawley rats were administered the test items, either as a single intravenous dose, a single oral dose or repeated daily oral doses for 4 weeks.
The systemic exposure (28 days) results show a difference in the extent of absorption and systemic circulation for silver acetate and nitrate versus silver metal powder. Based on a matched dose assessment, the extent of systemic exposure was about 10 to 30-fold lower in the case of silver metal powder versus silver acetate (as reference ionic silver compound).
The silver tissue levels after repeated dose administration are considerably lower in the case of silver metal powder (AgMP) than for silver acetate. This suggests that AgMP represents a correspondingly lower health hazard, i.e. AgMP (and by extrapolation also massive Ag with a tremendously lower particle size/reactive surface area) is expected to cause less effects at corresponding Ag dose levels than AgAc.
In conclusion, it is assumed that the systemic toxicity of silver substances is driven by the release potential of Ag ionic species as the primary moiety for systemic circulation and tissue exposure, and hence hazard assessment. The comparative TK study is a high quality GLP investigation and the first which permits a direct comparison of systemic circulation and tissue distribution of Ag ionic species between soluble Ag salts (AgNO3and Ag acetate), AgNP and AgMP. This new evidence demonstrates that oral intake of AgMP results in markedly lower absorption, distribution and systemic tissue/organ exposure to silver than more bioavailable forms like AgAc. As a generic observation, the following trend is being observed: AgAc > AgNO3>> AgNP >>> AgMP.
The study findings show that the direct read-across of mammalian toxicity data with soluble silver salts (like silver acetate and silver nitrate) and nanosilver to silver metal (powder and massive) is not justified (based on their individual toxicokinetic profiles).
- Endpoint:
- dermal absorption in vivo
- Remarks:
- percutaneous absorption in guiena pigs
- Type of information:
- experimental study
- Adequacy of study:
- supporting study
- Study period:
- 1965
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- study well documented, meets generally accepted scientific principles, acceptable for assessment
- Remarks:
- Reasonably well-documented publication, despite major methodological deficiencies.
- Qualifier:
- no guideline followed
- GLP compliance:
- no
- Species:
- guinea pig
- Details on test animals or test system and environmental conditions:
- Guinea pig with the average weight of 374-380 g
- Type of coverage:
- occlusive
- Vehicle:
- not specified
- Remarks:
- An amount of 2.0mL of the aqueous solution of the silver nitrate was applied to a skin depot (exposure area 3.1cm2), which was subsequently covered.
- Duration of exposure:
- 5 hours
- Doses:
- 0.239 moles in 2.0 mL of aqueous solution
- No. of animals per group:
- 20 animals
- Details on study design:
- Guinea pigs were observed for symptoms, food and water intake, and number of deaths. They were weighted once a week.
- Total recovery:
- After 3 weeks no animals died after exposure to silver nitrate via dermal route.
The weight of animals treated with silver nitrate increased after 1 week - Conclusions:
- Less than 1 % of an applied dose of silver nitrate was absorbed across intact skin of
guinea pigs within 5 hours of exposure. Test system not according to current standards
(i.e., no mass balance, no analysis of actual percutaneous transfer or residual Ag in skin
layers). - Endpoint:
- dermal absorption in vivo
- Type of information:
- experimental study
- Adequacy of study:
- supporting study
- Study period:
- 1964
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- study well documented, meets generally accepted scientific principles, acceptable for assessment
- Remarks:
- Reasonably well-documented publication, despite major methodological deficiencies.
- Qualifier:
- no guideline followed
- Principles of method if other than guideline:
- This study investigated the absorption of radioactive silver nitrate through the skin of the living guinea pig by following the disappearance of the radioactivity compounds from the cutaneous surface, so called "disappearance measurements".
- GLP compliance:
- no
- Specific details on test material used for the study:
- Silver nitrate were obtained from J.T. Baker's Chemical Co (USA) 110m Ag, half-life 253 days.
- Radiolabelling:
- yes
- Remarks:
- 110mAg (Half-life = 253 days)
- Species:
- guinea pig
- Strain:
- not specified
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- weight 300-500 g
- Type of coverage:
- not specified
- Vehicle:
- water
- Remarks:
- distilled water
- Duration of exposure:
- 5 hours
- Doses:
- The concentrations were chosen which permitted direct comparison with previous investigations.
The lowest concentration was chosen on account of the specific activity of the perspective isotope.
The highest concentration was chosen by limiting solubility in distilled water at room temperature - No. of animals per group:
- 10-15 animals/dose
- Total recovery:
- The absorption of silver nitrate is relatively small, most of the value given are <1.0% after 5 hours.
- Conclusions:
- Less than 1 % of an applied dose of silver nitrate was absorbed across intact skin of
guinea pigs within 5 hours of exposure. Test system not according to current standards
(i.e., no mass balance, no analysis of actual percutaneous transfer or residual Ag in skin
layers).
Referenceopen allclose all
Systemic exposure / Ag in blood
- Figure 1 (attached below) shows the extent of systemic exposure as area under the concentration time curve (AUC) values after repeated dose administration of silver nitrate (AgNO3) for 28 days.
- Comparisons via normalised administered doses (i.e. Ag equivalent dose) can be made between different Ag test items. Based on these matched dose assessments, the extent of systemic exposure was similar for AgAc and AgNO3 but about 10 to 30-fold lower in the case of Ag metal powder versus a reference ionic Ag salt.
- Table 2 shows the blood Ag concentrations at predicted steady state (day 15) after repeated dose administration of AgNO3. The maximum observed concentration occurs between 3-9h post-dosing for repeat dose groups, hence the 6h values for the respective test substances are shown as an indicator of peak exposure.
Table 2. Blood Ag concentrations at day 15 after repeated oral dose administration of silver nitrate (AgNO3).
Dose level | Mean 6h blood [Ag] | Mean [Ag]6h/ | ||
(mg/kg Test Item bw/d) | ng/mL | Ag Equiv. Dose | ||
ng/mL | ||||
♂ | ♀ | ♂ | ♀ | |
Control | <LLOQ | <LLOQ | -- | -- |
(n=3) | ||||
5 | 131 | 199 | 26 | 40 |
± 45 | ± 71 | |||
55 | 449 | 471 | 8.2 | 8.6 |
± 204 | ± 48 | |||
(n=3) | ||||
125 | 540 | 691 | 4.3 | 5.5 |
± 111 | ± 133 |
- Comparing these data to the data for other Ag test items, this demonstrates that oral dosing of AgAc and AgNO3 lead to similar systemic exposure and AgMP leads to appreciably lower Ag amplitude of systemic exposure in comparison to ionic Ag forms.
Tissue exposure / Ag distribution
Table 3 shows the Ag tissue levels / distribution after repeated dose administration of AgNO3.
Table 3. Terminal Ag tissue levels following repeated oral dose administration for 28 days of silver nitrate (AgNO3)
Dose (mg/kg bw/d) /Sex |
|
Bone marrow |
Brain |
GI tract |
Spleen |
Testis |
Liver |
|
|
|
|
|
|
|
|
Control M |
Mean |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
|
SD |
NC |
NC |
NC |
NC |
NC |
NC |
|
|
|
|
|
|
|
|
5 M |
Mean |
73.1 |
142 |
1310 |
404 |
231 |
81.7 |
|
SD |
16.2 |
35.4 |
214 |
191 |
103 |
33.1 |
|
|
|
|
|
|
|
|
55 M |
Mean |
10739 |
632 |
5319 |
39789 |
1202 |
4668 |
|
SD |
2104 |
129 |
2412 |
5704 |
246 |
2919 |
|
|
|
|
|
|
|
|
125 M |
Mean |
46553 |
1091 |
10592 |
54070 |
1464 |
28859 |
|
SD |
26985 |
57.0 |
10669 |
21236 |
260 |
36648 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Dose(mg/kg bw/d) /Sex |
|
Bone Marrow |
Brain |
GI Tract |
Spleen |
Ovaries |
Uterus |
Liver |
|
|
|
|
|
|
|
|
|
Control F |
Mean |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
|
SD |
NC |
NC |
NC |
NC |
NC |
NC |
NC |
|
|
|
|
|
|
|
|
|
5 F |
Mean |
87.0 |
177 |
2438 |
722 |
1484 |
145 |
130 |
|
SD |
36.8 |
41.7 |
425 |
335 |
561 |
81.7 |
39.8 |
|
|
|
|
|
|
|
|
|
55 F |
Mean |
NC |
700 |
3624 |
41558 |
31357 |
8104 |
5295 |
|
SD |
NC |
96.2 |
1449 |
5668 |
8793 |
3075 |
3561 |
|
|
|
|
|
|
|
|
|
125 F |
Mean |
25200 |
1019 |
14798 |
62335 |
44025 |
22466 |
16024 |
|
SD |
4630 |
209 |
7728 |
22794 |
16158 |
4327 |
6464 |
|
|
|
|
|
|
|
|
|
BLQ <5.00
ng/mL
NC Not
calculated
- Comparing these data to the data for other Ag test items, this demonstrates that levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 but considerably lower in the case of Ag metal powder.
Systemic exposure / Ag in blood
- Figure 1 (attached below) shows the extent of systemic exposure as area under the concentration time curve (AUC) values after repeated dose administration of silver acetate (AgAc) for 28 days.
- Comparisons via normalised administered doses (i.e. Ag equivalent dose) can be made between different Ag test items. Based on these matched dose assessments, the extent of systemic exposure was similar for AgAc and AgNO3 but about 10 to 30-fold lower in the case of Ag metal powder versus a reference ionic Ag salt.
- Table 2 shows the blood Ag concentrations at predicted steady state (day 15) after repeated dose administration of AgAc. The maximum observed concentration occurs between 3-9h post-dosing for repeat dose groups, hence the 6h values for the respective test substances are shown as an indicator of peak exposure.
Table 2. Blood Ag concentrations at day 15 after repeated oral dose administration of silver acetate (AgAc).
Dose level | Mean 6h blood [Ag] | Mean [Ag]6h/ | ||
(mg/kg Test Item bw/d) | ng/mL | Ag Equiv. Dose | ||
ng/mL | ||||
♂ | ♀ | ♂ | ♀ | |
Control | <LLOQ | <LLOQ | -- | -- |
(n=3) | ||||
5 | 113 | 204 | 34.8 | 62.8 |
± 15 | ± 26 | |||
55 | 317 | 423 | 8.9 | 11.8 |
± 93 | ± 72 | |||
175 | 652 | 918 | 5.7 | 8.1 |
± 171 | ± 103 | |||
(n=3) | (n=3) |
- Comparing these data to the data for other Ag test items, this demonstrates that oral dosing of AgAc and AgNO3 lead to similar systemic exposure and AgMP leads to appreciably lower Ag amplitude of systemic exposure in comparison to ionic Ag forms.
Tissue exposure / Ag distribution
Table 3 shows the Ag tissue levels / distribution after repeated dose administration of AgAc.
Table 3. Terminal Ag tissue levels following repeated oral dose administration for 28 days of silver acetate (AgAc)
Dose (mg/kg bw/d) /Sex |
|
Bone marrow |
Brain |
GI tract |
Spleen |
Testis |
Liver |
|
|
|
|
|
|
|
|
Control M |
Mean |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
5 M |
Mean |
62.0 |
142 |
2770 |
283 |
168 |
55.4 |
|
SD |
13.5 |
36.0 |
1720 |
71.2 |
75.9 |
15.3 |
|
|
|
|
|
|
|
|
55 M |
Mean |
3500 |
637 |
19200 |
38700 |
1510 |
9470 |
|
SD |
1540 |
57.2 |
7680 |
11000 |
215 |
4120 |
|
|
|
|
|
|
|
|
175 M |
Mean |
21400 |
1460 |
83200 |
96400 |
1530 |
22700 |
|
SD |
15400 |
33.1 |
5270 |
55200 |
237 |
7630 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Dose(mg/kg bw/d) /Sex |
|
Bone Marrow |
Brain |
GI Tract |
Spleen |
Ovaries |
Uterus |
Liver |
|
|
|
|
|
|
|
|
|
Control F |
Mean |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
BLQ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
5 F |
Mean |
126 |
169 |
3800 |
990 |
2200 |
188 |
305 |
|
SD |
110 |
21.2 |
1490 |
455 |
1080 |
121 |
232 |
|
|
|
|
|
|
|
|
|
55 F |
Mean |
4500 |
805 |
50700 |
60800 |
24300 |
8000 |
16500 |
|
SD |
1420 |
35.9 |
11200 |
10400 |
2610 |
3300 |
3610 |
|
|
|
|
|
|
|
|
|
175 F |
Mean |
46800 |
1460 |
104000 |
142000 |
39700 |
11100 |
21900 |
|
SD |
19800 |
114 |
12600 |
93500 |
19800 |
2320 |
13100 |
|
|
|
|
|
|
|
|
|
BLQ <5.00
ng/mL
- Comparing these data to the data for other Ag test items, this demonstrates that levels of Ag distributed into tissues and organs are similar for AgAc and AgNO3 but considerably lower in the case of Ag metal powder.
Disappearance constant (k) and disappearance percentage during 5 hours for silver nitrate for different concentration | ||||||
k.10^5 min-1 | < 3.4 | 3.4-6.6 | 6.7 -10.1 | 10.2-13.3 | ||
%/ 5 hours | < 1.0 | 1.0-1.9 | 2.0-2.9 | 3.0-3.9 | ||
Conc. M | pH | No. | No. | No. | No. | No. |
0.00048 | 6.0 | 10 | 9 | - | 1 | - |
0.005 | 5.7 | 10 | 6 | 1 | 2 | 1 |
0.080 | 5.5 | 15 | 9 | 4 | 2 | - |
0.118 | 5.2 | 10 | 9 | - | 1 | - |
0.239 | 4.7 | 14 | 12 | 2 | - | - |
0.398 | 4.6 | 10 | 8 | 2 | - | - |
0.753 | 4.4 | 11 | 8 | 3 | - | - |
4.870 | 3.3 | 10 | 10 | - | - | - |
Disappearance constants and the disappearance percentage per 5-hours periods for silver nitrate for various concentration is presented in the table above.
Description of key information
Introduction:
Most recently, a comparative in-vivo toxicokinetic study (Melvin et al. 2021 and Charlton et al. 2021) with several test substances (silver acetate, silver nitrate, silver metal powder and nanosilver) was performed by the European Precious Metals Federation (EPMF) to supplement the Ag mammalian toxicity database and to strengthen the basis of the read-across approach. This in-vivo oral gavage toxicokinetic study (using rat as test species) shows similar systemic exposure and absorption/distribution to tissues and organs for silver acetate and silver nitrate, notably the amount of silver in blood and tissues is similar after exposure to both silver compounds. Since it is assumed that the systemic toxicity of silver is due to the potential release of Ag+, a direct read-across of mammalian toxicity datasets between simple ionic silver compounds (like silver acetate (AgAc) and silver nitrate(AgNO3)) is considered robust and scientifically valid.
No reliable and consistent in-vivo data are available to demonstrate the toxicokinetic of silver bromide. Nevertheless, in the absence of data measuring the amount of silver ions released from silver bromide, a worst-case approach was adopted to extrapolate the absorption via the different route of exposure. The oral and dermal absorption were extrapolated from silver acetate/silver nitrate and from Ag+. While the inhalation absorption has been extrapolated from the MPPD model performed with disilver oxide.
Note: in-vivo TK data have been generated since in-vitro bioaccessibility testing (‘bio elution testing’) is not applicable to assess the bioavailability of silver substances because of the strong binding of Ag+ with chloride (Cl-) resulting in an immediate and excessive AgCl precipitate.
Soluble silver salts, like silver nitrate or silver acetate, rapidly dissociate to Ag+ and the relevant counter-ion in aqueous solution:
AgL ⇌ Ag+ + L- with L = NO3, acetate...
Upon dissolution, the Ag+ ions are highly reactive to inorganic and organic ligands, especially sulfidic/thiosulfidic moieties or ammines with formation constants (‘Kf’) of logKf(AgHS) = 13.6, logKf(Ag2S) = 23.7, logKf(Ag-2-mercaptoethanol) = 13.2, logKf(Ag-cysteine) = 11.9 or logKf(Ag-thiourea) = 7.1, logKf values for Ag-NH3 complexes or Ag-amines = 3-6 and logKf(Ag-EDTA) = 7 (Bell and Kramer, 1999).
Upon ingestion and in reasonably expected conditions, Cl is excessively present in the stomach compared to the above-mentioned ligands. Considering this excess of Cl in relation to other potential ligands but also compared to Ag+ concentrations, a considerable reaction between Ag+ and Cl- will take place. AgCl (LogKf(AgCl)) = 3) or AgCln-complexes will be formed.
At first, a majority of the released silver ions will be precipitated as:
Ag+(aq) + Cl−(aq) ⇌ AgCl(s) {1}
However, a minor part of AgCl(aq) will remain in solution, and soluble AgCln-complexes might be formed at increasing Cl- concentrations as:
Ag+(aq) + Cl−(aq) ⇌ AgCl(aq) logK=3.70 {2}
AgCl(aq) + Cl−(aq) ⇌ AgCl2-(aq) logK=1.92 {3}
AgCl2-(aq) + Cl−(aq) ⇌ AgCl32−(aq) logK=0.78 {4}
Artificial stomach fluid (typically applied in bioelution testing) consists of a 0.07 N HCl solution and has an approximate pH 1.2-1.5. This is considered a good approximation of pH and Cl concentrations in human stomach. Looking at the above figure and at the relevant range of Cl-concentrations, the concentration of dissolved silver species is at its minimum and the majority of silver precipitates as AgCl(s). This is typically observed in bioelution tests as an immediate and excessive white precipitate. A minor fraction that remains in solution and does not precipitate as AgCl(s), is present as Ag+ and soluble AgCl(aq) or AgCl2–-complexes. Only these soluble Ag ionic species are considered available for systemic uptake and circulation.
Oral absorption
Melvin et al. 2021 and Charlton et al. 2021 performed a comparative in-vivo toxicokinetic study via oral route using adult CD Sprague Dawley rats. The design conformed to OECD and EU guidelines (OECD 417 (Toxicokinetics), and was conducted in compliance to GLP.
Four test items were used: two ionic Ag salts (silver acetate and silver nitrate; both > 99.5% pure); a well-characterised and small-size Ag nanoparticles reference material (surfactant stabilized aqueous dispersion with 10% Ag; d50= 15 nm); and a sub-micron sized powder form (AgMP; uncoated; >99% pure; d50~0.3 µm; crystalline powder of highly uniform spheroidal shape) of bulk elemental silver (registered under REACh). Simple soluble salts (both silver nitrate and silver acetate) do undergo some absorption when orally administered. Bioavailability via oral route is estimated at 3-5%, a value that appears consistent with other estimates presented in the scientific literature.
Boudreau et al. 2016 studied the pharmacokinetics of silver. The blood concentration-time curves of silver following a single oral gavage administration of 10 mg/kg bw of AgNP (10, 75 and 110 nm) or AgAc are shown in Figure 3 of orginial paper. The calculated half-times for distribution (4-5 h) and elimination (~24 h), and the time to reach maximum concentration levels (12 h) were similar for both male and female rats. In contrast, the analysis of the AUC (Area Under the Curve) revealed differences due to sex, form of silver, and particle size. The AUC profiles were similar for female (A) and male (B) rats; however, they were ~2-fold greater for female rats, irrespective of silver form or particle size. The AUCs were greater for AgAc than for AgNP, and among AgNP, the AUCs showed an inverse relationship with particle size (i.e. smaller particles had larger AUCs than larger particles – see CSR section).
In a well-documented comparative investigation assessing the bioavailability of radiosilver 110mAg (as silver nitrate) in mice, rats, monkeys and dogs via oral, intravenous and intraperitoneal administration, less than 10% was absorbed for all routes and more than 90% of silver was excreted in the faeces. About 1% or less of the oral dose was absorbed in all animals with the exception of dogs (<10%). The higher absorption rate in dogs can be explained by the related gut passage time which is in the order of 24 hours for dogs and a bit more than 8 hours in rats (Furchner et al. 1968).
Dermal absorption
Several publications report information on percutaneous absorption of silver.
In a well-documented study with guinea pigs less than 1% of the applied dose of silver nitrate was absorbed through the skin. However, this study has major methodical deficiencies, and is therefore considered only as supporting data (Wahlberg et al., 1965). A review article refers to earlier publications in which an in-vivo percutaneous absorption study in guinea pigs with 110Ag as tracer is described. Despite this study having considerable methodological shortcomings compared to current standards, the authors conclude on a dermal absorption rate of <1% (Skog & Wahlberg, 1964). Other similarly outdated data relate to either non-standard test systems or absorption through wounded or burned skin and is therefore not considered relevant for the assessment of percutaneous absorption through intact skin, as required for risk assessment purposes (e.g. Nguyen et al., 1999).
Overall, the available data for soluble silver substances indicate dermal absorption rates well below 1% of the applied dose.
These conclusions are consistent with the methodology proposed in HERAG guidance for metals (HERAG fact sheet – assessment of occupational dermal exposure and dermal absorption for metals and inorganic metal compounds; EBRC Consulting GmbH / Hannover /Germany; August 2007). The default dermal absorption factors (reflective of full-shift exposure, i.e. 8 hours) are considered adequately conservative for silver substances, i.e. 1% from exposure to liquid/wet media, and 0.1% from exposure to dry (dust).
Inhalation absorption
Disilver oxide is taken as a data source to extrapolate the inhaled absorption of silver bromide. Even though the likelihood of inhalation absorption of silver bromide is very limited due to the manufacturing process, an extrapolation from disilver oxide was performed in a worst-case scenario approach. This extrapolation is considered reasonable and coherent due to their similar very low water solubility (1.6 mg/L for Ag2O and 0.13 mg/L for AgBr).
Model calculation of inhalation absorption based on laboratory dustiness tests with representative materials.
Experimental investigations have been conducted on disilver oxide (2 different batches). The sample was subjected to mechanical agitation in a rotating drum apparatus and the mass fraction of the material that becomes airborne was determined (“total dustiness”). In addition, the particle size distribution or the airborne dusts was determined with a cascade impactor. Then, the MPPD model was used, to estimate the fractional deposition of such dusts in three regions of the human respiratory tract: (i) extrathoracial fraction (head), (ii) tracheo-bronchial fraction (TB) and (iii) the pulmonary fraction (ERBC, 2010: Investigations on dustiness and particle size of airborne dusts of six silver compounds samples. Unpublished report for the Precious Metals Consortium, ERBC Consulting GmbH, Hannover, Germany). The results are presented in tabular form below.
MPPD model results: Fractional deposition (%) in different regions of the respiratory tract. Data on physical particle size of the original test materials and on total dustiness is also given:
Disilver oxide Batch PMC1 | Disilver oxide Batch PMC2 | |
D50 | ca. 4 µm | ca. 7-18 µm |
Total dustiness | 149 mg/g | 126 mg/g |
Deposition (total) | 46.1 % | 49.1 % |
Deposition (head), fH | 45.3 % | 47.9 % |
Deposition (TB), fTB | 0.3 % | 0.5 % |
Deposition (pulmonary) fPU | 0.6 % | 0.8 % |
Based on the fractional deposition, an inhalation absorption factor can be calculated under the following assumption: the material deposited in the head and tracheobronchial regions would be translocated to the gastrointestinal tract without any relevant dissolution, where it would be subject to an assigned default gastrointestinal uptake at a ratio of 3 to 5% (see above).
The material that is deposited in the pulmonary region may conservatively be assumed by default to be absorbed to 100%. This absorption value is chosen in the absence of relevant scientific data regarding alveolar absorption although knowing that this is a conservative choice specifically for poorly soluble substances.
Formula (fH+ fTB) * absoral+ fPU* abspul= inhalation absorption factor.
Calculation for batch PMC1: (45.3% + 0.3%) * 5 % + 0.6 % * 100 % = 2.88%
Calculation for batch PMC2: (47.9% + 0.5%) * 5 % + 0.8 % * 100 % = 3.22%
Estimated inhalation absorption factor of disilver oxide (PMC1) | 2.88% |
Estimated inhalation absorption factor of disilver oxide (PMC2) | 3.22% |
Given the inherently conservation assumption of 100% absorption for pulmonary deposition and oral absorption of disilver oxide (extrapolated from silver acetate) at worst-case at 5%, it is considered adequate and conservative to use a value of 3% for inhalation absorption of disilver oxide and by extrapolation of silver bromide.
Key value for chemical safety assessment
- Bioaccumulation potential:
- no bioaccumulation potential
- Absorption rate - oral (%):
- 5
- Absorption rate - dermal (%):
- 1
- Absorption rate - inhalation (%):
- 3
Additional information
For details, please refer to separate report "CSR Annex 7_Read Across justification Human Health_Nov 2022" which is attached to the CSR in section 13.
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