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Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Remarks:
Bioaccessibility - transformation/dissolution in artificial physiological media
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Objective of study:
other: Bioaccessibility
Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media
Deviations:
yes
Remarks:
Bioaccessibility testing: loading of 100 mg/L; five artificial physiological media agitated at 100 rpm, at 37 °C ± 2 °C; sampling after 2 h and 24 h; determination of Pb, Sb concentrations after filtration by AAS-GF
Principles of method if other than guideline:
Solubility of test item in simulated human fluids. Principle of test is similar to Transformation/Dissolution testing according to OECD Series 29 (2001)
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Details on test material:
- Name of test material: Pyrochlore Antimony Lead Yellow
- Substance type: Inorganic pigment
- Physical state: Yellow powder
- Storage condition of test material: Keep the container always tightly closed in an adequately ventilated storage.

Test animals

Species:
other: in vitro (simulated human body fluids)

Administration / exposure

Details on exposure:
The test item was exposed to five different test media at a pH range from 1.7 to 7.4. The following synthetic biological fluids were used:
• Gamble’s solution (GMB, pH 7.4) which mimics the interstitial fluid within the deep lung under normal health conditions (de Meringo et. Al. 1994).
• Phosphate-buffered saline (PBS, pH 7.2), which is a standard physiological solution that mimics the ionic strength of human blood serum. It is widely used in the research (e.g. Norlin et al, 2002) and medical health care community (e.g. Hanawa et al, 2004, Okazaki and Gotoh, 2005) as a reference test solution for comparison of data under simulated physiological conditions.
• Artificial sweat (ASW, pH 6.5) which simulates the hypoosmolar fluid, linked to hyponatraemia (loss of Na+ from blood), which is excreted from the body upon sweating. The fluid is recommended in the available standard for testing of nickel release from nickel containing products (EN 1811, 1998).
• Artificial lysosomal fluid (ALF, pH 4.5), which simulates intracellular conditions in lung cells occurring in conjunction with phagocytosis and represents relatively harsh conditions (Moss 1979).
• Artificial gastric fluid (GST, pH 1.7), which mimics the very harsh digestion milieu of high acidity in the stomach (Hamel et al, 1998; ASTM, 2003).

The test media were selected in order to simulate human exposure as far as possible, e.g. skin contact. Ingestion to the gastro-intestinal tract can either be direct, or previously inhaled particles can be translocated from the respiratory tract to the gastro-intestinal tract by mucociliary clearance. It should be stressed though, that the different test media only simulate physiological conditions to a limited extent, as the complexity and function of the real body fluids are difficult to simulate. However, in vitro results in such synthetic biological media can, in a simple way, provide information that could be relevant for a real situation.

The test solutions were prepared using ultra-pure water and chemicals of analytical grades.

The pH of ALF and GMB was adjusted using 50 % NaOH and 25 % HCl, respectively. The pH of ASW and PBS was adjusted with 1 % ammonia solution and 50 % NaOH, respectively.

Artificial gastric fluid, pH 1.6, was prepared according to the ASTM standard using 4 g of 25 % HCl solution diluted with ultra -pure water to 1 L (ASTM D5517, 2003).
Duration and frequency of treatment / exposure:
Samples were taken after 2 h and 24h.
Doses / concentrations
Dose / conc.:
100 other: mg of the test item /L artificial media
Details on study design:
Experimental Procedure
Triplicate samples were prepared for exposure in different test media, each for two different time periods. In addition, one blank sample (without addition of test item) containing only the test solution was incubated together with the triplicate samples for each time period. 5 ± 0.5 mg of the test item was weighed using a Mettler AT20 balance with readability of 2 μg, and placed in a PMP Nalgene® jar. 50 mL of the test solution (no adjustment of solution volume to powder mass was made) was then added to the Nalgene® jar containing the test item, before incubated in a Platform-Rocker incubator SI 80 regulated at 37 ± 2 °C. The solution was gently shaken (billinearly) with an intensity of 25 cycles per minute for 2 and 24 hours, respectively.
Details on dosing and sampling:
A “standard loading” of 0.1 g/L was selected, which has some physiological relevance. It further allows a comparison of the generated data with results from the OECD Transformation/Dissolution test (OECD, 2001) and similar bioaccessibility tests conducted with other materials under the same conditions .

The time periods for exposure of the test item were selected to have some relevance to the inhalation/ingestion scenario and to enable comparison with other reported metal release/dissolution data generated for similar time periods. The approximate time for the gastric phase of digestion is about 2 hours, and therefore this exposure time period was considered relevant for testing in artificial gastric fluid (Hamel et al, 1998). The
24 hour exposure was selected as a standard time duration that is relatively easy to compare with existing metal release/dissolution data as well as toxicity data for further evaluation of the bioaccessibility of released metals. Moreover, it can be assumed that human exposure to particles last no longer than 24 hours at ambient conditions.

After exposure, the samples were allowed to cool to ambient room temperature before the final pH of the test solution was measured. The test medium was then separated from the powder particles by centrifugation at 10000 rpm for 10 minutes, resulting in a visually clear supernatant with remaining particles in the bottom of the centrifuging tube. Dynamic light scattering, (Malvern Zetasizer nano ZS instrument) was used to confirm the successful removal of all pigment particles. The supernatant solution was decanted into a polypropylene storage flask and acidified to a pH less than 2 (not needed in the case of artificial gastric fluid) with 65 % pure HNO3 prior to solution analysis

Results and discussion

Main ADME results
Type:
other: Bioaccessibility
Results:
Highest dissolution at a loading of 0.1 g/L after 24 hours: Pb: 5634 ± 148 µg/L (GST), Sb: 105 ± 4.4 µg/L (GST); after 2 hours: Pb: 6201 ± 667 µg/L (GST), Sb: 84.3 ± 12.0 µg/L (GST)

Any other information on results incl. tables

BET-analysis:

The specific surface area, measured by BET-analysis is 1.03 m²/g. It should be underlined that this specific surface area is measured by nitrogen absorption and includes also the surface of surface pores.

Abbreviations:

GMB: Gamble´s solution, PBS: phosphate buffered saline, ASW: artificial sweat, ALF: artificial lysosomal fluid, GST: gastric fluid.

Average total concentration of released elements [μg/L] and the standard deviation of triplicate samples in the different media. Blank values for each individual media and exposure period have been subtracted.

(test item)    Exposure    GMB    PBS    ASW    ALF    GST  
Material    period    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
PbSb  2 h   137 ± 12   24.4 ± 4.7 2890 ± 392 4960 ± 358 6201 ± 667
Pb release  24 h   4.9 16.4 ± 2.0 3669 ± 421 5354 ± 317 5634 ± 148
PbSb   2 h   3.6 ± 1.3 6.0 ± 1.4 8.2 ± 2.3 67.8 ± 8.8 84.3 ± 12.0
Sb release  24 h   7.9 ± 2.9 28.9 ± 3.8 47.4 ± 6.5 91.0 ± 4.6 105 ± 4.4

Release rate of elements given by the BET surface area [μg/cm².h].

 (test item)    Exposure    GMB    PBS    ASW    ALF    GST  
 Material    period    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
PbSb  2 h   0.069 ± 0.0059 0.012 ± 0.0023 1.4 ± 0.22 2.5 ± 0.13 2.9 ± 0.41
Pb release    24 h   0.0002 0.0007 ± 0.0001 0.16 ± 0.019 0.23 ± 0.13 0.24 ± 0.0008
PbSb  2 h   0.0018 ± 0.0006 0.0030 ± 0.0007 0.0040 ± 0.0010 0.034 ± 0.0038 0.039 ± 0.0065
Sb release    24 h   0.0003 ± 0.0001 0.0012 ± 0.0002 0.0020 ± 0.0003 0.0038 ± 0.0002 0.0044 ± 0.0001

Released/dissolved amount of elements per total amount of loaded material [μg/μg].

 (test item)    Exposure    GMB    PBS    ASW    ALF    GST  
 Material    period    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
  PbSb  2 h   0. 0014 ± 0.00012 0.00025 ± 0.000047 0.029 ± 0.0046 0.051 ± 0.0027 0.059 ± 0.0084
Pb release    24 h   0.00005  0.00017 ± 0.000018 0.038 ± 0.0046 0.055 ± 0.0033 0.059 ± 0.0002
 PbSb  2 h   0.00004 ± 0.00001 0.00006 ± 0.00001 0.00008 ± 00002 0.0007 ± 0.00008 0.0008 ± 0.0001
Sb release    24 h   0.00008 ± 0.00003 0.0003 ± 0.00004 0.0005 ± 0.00007 0.0009 ± 0.00005 0.0011 ± 0.00002

Elements transformed [mass %], equivalent to their percentage of the elemental content of the total amount of particles loaded; shown as average of triplicate samples in the different media. Blank values for each individual media and exposure period have been subtracted.

 (test item)    Exposure    GMB    PBS    ASW    ALF    GST  
 Material    period    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
 PbSb  2 h   0.14 ± 0.012 0.025 ± 0.0047 2.9 ± 0.46 5.1 ± 0.27 5.9 ± 0.84
Pb release    24 h   0.005   0.017 ± 0.0018 3.8 ± 0.46 5.5 ± 0.33 5.9 ± 0.02
  PbSb  2 h   0.0037 ± 0.0013 0.0061 ± 0.0014 0.0081 ± 0.0020 0.069 ± 0.0077 0.080 ± 0.013
Sb release    24 h   0.082 ± 0.0030 0.030 ± 0.0044 0.050 ± 0.0070 0.094 ± 0.0052 0.11 ± 0.0021

Total released/dissolved amount of elements per total amount of loaded material [μg/μg] in %.

 Exposure    GMB    PBS    ASW    ALF    GST  
 Test item    time    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
 PbSb  24 h   0.013 ± 0.003 0.046 ± 0.006 3.88 ± 0.47 5.64 ± 0.33 5.97 ± 0.02

Elements transformed [mass %], equivalent to the percentage of the released element compared to its amount within the amount of particles loaded.

 (test item)    Exposure    GMB    PBS    ASW    ALF    GST  
 Material    period    pH 7.4    pH 7.2    pH 6.5    pH 4.5    pH 1.7  
  PbSb  2 h   0. 26 ± 0.022 0.045 ± 0.0086 5.3 ± 0.84 9.2 ± 0.50 10.8 ± 81.5
Pb release    24 h   0.0094 0.030 ± 0.0034 7.0 ± 0.85 10.1 ± 0.60 10.7 ± 0.037
 PbSb  2 h   0.016 ± 0.0056 0.026 ± 0.0060 0.035 ± 0.0088 0.30 ± 0.033 0.34 ± 0.057
Sb release    24 h   0.035 ± 0.013 0.13 ± 0.019 0.21 ± 0.030 0.40 ± 0.022 0.47 ± 0.0089

Applicant's summary and conclusion

Conclusions:
Dissolved Pb and Sb concentrations were below 6201 µg/L and 84.3 µg/L, respectively, even at the highest loading of 0.1 g/L, referring to a solubility of the pigment of 6.2 % and 0.08 %, respectively.
Executive summary:

The bioaccessibility of Pyroclor, antimony lead yellow has been investigated experimentally in vitro by simulating dissolution under physiological conditions considered to mimic the most relevant exposure routes (oral, dermal and inhalation), as follows:

- Gamble’s solution (GMB, pH 7.4) which mimics the interstitial fluid within the deep lung under normal health conditions,

- Phosphate-buffered saline (PBS, pH 7.2), which is a standard physiological solution that mimics the ionic strength of human blood serum,

- Artificial sweat (ASW, pH 6.5) which simulates the hypoosmolar fluid, linked to hyponatraemia (loss of Na+ from blood), which is excreted from the body upon sweating,

- Artificial lysosomal fluid (ALF, pH 4.5), which simulates intracellular conditions in lung cells occurring in conjunction with phagocytosis and represents relatively harsh conditions and

- Artificial gastric fluid (GST, pH 1.5), which mimics the very harsh digestion milieu of high acidity in the stomach.

The dissolution of lead of the test item lead antimony pyrochlore is at a loading of 0.1 g/L in a range of < 24.4 µg/L (pH 7.2) and 6201 µg/L (pH 1.7) after 2 hours and below 5634 µg/L after 24 hours.

The dissolution of antimony of the test item lead antimony pyrochlore is at a loading of 0.1 g/L in a range of < 3.6 (pH 7.2) and 84.3 µg/L (pH 1.7) after 2 hours and below 105 µg/L after 24 hour.