Phosphorus

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April - November 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Well performed and reported non-guideline study.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Materials and methods

Objective of study:

absorption

Test guideline

Qualifier:

no guideline available

Guideline:

other: n.a.

Deviations:

not applicable

Principles of method if other than guideline:

The solubility and availability for absorption through the gut wall (bioaccessibility) of Red Phosphorus is determined in a model system that simulates the dynamic conditions in the gastro-intestinal tract (TIM-1).

GLP compliance:

no

Remarks:

not applicable for this study type; the model has been validated for use in the food/nutrition and pharmaceutical area

Test material

Test material information

Constituent 1

Reference substance name:

Phosphorus

EC Number:

231-768-7

EC Name:

Phosphorus

Cas Number:

7723-14-0

IUPAC Name:

phosphine

Constituent 2

Reference substance name:

phosphorus

EC Number:

918-594-3

Cas Number:

7723-14-0

Molecular formula:

(P)n (Phosphorus red modification)

IUPAC Name:

phosphorus

Details on test material:

- Name of test material (as cited in study report): Red Phosphorus
- Molecular formula (if other than submission substance): Pn (polymeric)
- Molecular weight (if other than submission substance): polymeric
- Physical state: amorphous solid
- Analytical purity: > 99%
- Lot/batch No.: Fra 07-23
- Expiration date of the lot/batch: 24.04.2011
- Storage condition of test material: under nitrogen in an explosion proof cabinet at room temperature

Radiolabelling:

no

Test animals

Species:

other: n.a. in vitro study

Details on test animals or test system and environmental conditions:

Please refer to "Details on study design"

Administration / exposure

Route of administration:

other: n.a., in vitro study

Vehicle:

other: water/artificial saliva

Details on exposure:

Please refer to "Details on study design"

Duration and frequency of treatment / exposure:

300 min.

Doses / concentrations

Remarks:

Doses / Concentrations:
10 g Red Phosphorus per run (in artificial saliva and water added to a total of 300g)

No. of animals per sex per dose / concentration:

n.a., TIM model used

Control animals:

other: n.a.

Positive control reference chemical:

n.a.

Details on study design:

Test system and gastro intestinal conditions
The experiments were performed in the TIM-1 system (please refer to attached document 1 "scheme of TIM model") simulating the gastric and small-intestineal conditions after intake with only water on an empty stomach by a healthy adult. This presents a worse case scenario for the dissolution of Red Phosphorus, since under these conditions the gastric pH remains low, going from pH 2 to 1.5. The small intestineal pH increases from 6.5 in the first part (Duodenum) to 7.2 in the last part (Ileum). Oral, gastric and duodenal secretion products (electrolytes, digestive enzymes, bile) are secreted to mimic the fasting state. After intake of the meal, gastric juice ( "scheme of TIM model", I) is secreted in the gastric compartment ( "scheme of TIM model", A). The gastric juice contains enzymes and acid to follow the present pH profile, measured with a pH electrode ( "scheme of TIM model", P). After the gastric intake is gradually emptied into the Duodenum ( "scheme of TIM model", C), the chyme is mixed with bile and digestive enzymes ( "scheme of TIM model", J). Bicarbonate is secreted to neutralize the acidic gastric content. After the Duodenum, the chyme is transported through the jejunal and ileal compartments, where digested and dissolved compounds are dialyzed through hollow fiber membranes ( "scheme of TIM model", M). The dialyzed compounds are regarded as available for absorption (bioaccessible) through the gut wall in vivo. The undigested and undissolved compounds are collected in a vessel ( "scheme of TIM model", H). This ileal efflux is regarded as material that enters the large intestine in vivo. During the experiments, the system was flushed with nitrogen. For safety, the Red Phosphorus was handled under a CO2 blanket in an explosion proof fume cabinet and the experiments were performed in a well ventilated room.

Results and discussion

Preliminary studies:

None

Main ADME results

Main ADME results 1

Type:

absorption

Results:

1.3% bioaccessibility

Main ADME results 2

Type:

absorption

Results:

no absorption of elemental Phosphorus; only as PO species (Hypophosphite, Phosphite, Phosphate) bioaccessible

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Please refer to "any other information on results incl. tables"

Details on distribution in tissues:

n.a.

Details on excretion:

n.a.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

No absorption of elemental Phosphorus; only as PO species (Hypophosphite, Phosphite, Phosphate) bioaccessible

Any other information on results incl. tables

Recovery of Phosphorus:

In the first part of the study, all variations (please refer to Administration/Expousre "Any other information") were tested in single experiments. These experiments were performed successfully; however the recovery of Red Phosphorus was 62% and 32% for the test runs with water- and normal secretion, respectively. These low recoveries were result of sticking of the Red Phosphorus to the materials of the system. It was decided to repeat these experiments with a more intensive cleaning step after the experiments. This resulted in recoveries of 83% and 71% for the runs with water- and normal secretion. 32% and 25% of the intake was retained in the gastric compartment, respectively.

Bioaccessiblity of Phosphorus:

The total amounts of Phosphorus in the dialysate and the calculated bioaccessiblities for each run are shown in table 1.

Table 1:Amounts of dialysed total Phosphorus (corresponding to elemental Phosphorus) and bio-accessibilities for each run 

	Variation	Phosphorus (mg)	Bioaccessibility (%OI)^*
Serie 1	Blank	15.9	-
	Water secretion	145.5	1.5
	Normal secretion	98.3	0.8
Serie 2	Water secretion	170.0	1.7
	Normal secretion	185.3	1.7

^*          of the intake (OI)

The bioaccessibilities for the experiments with water secretion was 1.6 +/- 0.1% of the intake (OI), the mean bioaccessibility of the experiments with normal secretion was 1.3 +/- 0.4% OI.

The amount of total Phosphorus, expressed as a percentage of the intake, that was dialysed in time for both variations is presented in figure 1 of the attached document 3 ("Bioaccessibility of total Phosphorus"). The results show similar pattern for both experiments with water and normal secretion. Approximately 83% of the whole dialysed fraction is dialysed in the first 2 hours, approximately 15% is dialysed between the second and third hour and approximately 2% is dialysed in the last hour.

The calculated amount of total Phosphorus from Phosphorus species analysis (by ion chromatography) for each experiment is presented in table 2.

Table 2:Amounts of dialysed Phosphorus (corresponding to elemental Phosphorus) calculated from the species analysis, for each experiment

 

	Variation	Phosphorus from POspecies (mg)^*
Serie 1	Blank	16.5
	Water secretion	137.2
	Normal secretion	103.4
Serie 2	Water secretion	178.2
	Normal secretion	149.3

^*             “PO” refers to Hypophosphite, Phosphite and Phosphate

The results are similar to those obtained with the total Phosphorus analysis as shown in table 1.

The amount of dialysed Phosphorus species in time for the experiments with water- and normal secretion is shown in figures 2 and 3 of the attached document 3, ("Bioaccessibility of total Phosphorus"), respectively. The figures show similar patterns for both experiments with the highest rate of dialysis in the first 120 minutes. This is in agreement with the dialysis patterns for toal Phosphorus. The rations between the amounts of Phosphorus present in each species are shown in figure 4 of the attached document 3,("Bioaccessibility of total Phosphorus"). The results show that with the water secretion experiments, 18 +/- 9%, 48 +/- 3% and 36 +/- 6% of the Phosphorus is present in the PO₂^{3 -}, PO₃^{3 -}, PO₄^{3 -}fractions, respectively. For the experiments with normal secretion this is 7 +/- 4%, 50 +/- 1% and 43 +/- 3%.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
The bioaccessibility of Red Phosphorus under the conditions of the TIM model (fasted adult human) was determined to be 1.3 ± 0.4% (exclusively oxidized species; Hypophosphite, Phosphite and Phosphate) of the whole intake. No elemental Phosphorus was present in the bioaccessible fractions. Therefold, it is concluded that elemental Red Phosphorus is not able to pass the dialysis membrane.

Executive summary:

The solubility and availability for absorption through the gut wall (bioaccessibility) of Red Phosphorus is determined in a model system that simulates the dynamic conditions in the gastro-intestinal tract (TIM-1). The bioaccessibility for these conditions was 1.3 ± 0.4% of the applied Red Phosphorus. The majority of Phosphorus is dialysed in the jejunal compartment during the first 120 min. This suggests that the dialysed Phosphorus species were readily available from the Red Phosphorus particles. This was expected, because the particles are always covered with small amounts of Phosphorus Oxy Acids (previously denoted as PO₂^3-, PO₃^3-, PO₄^{3 –}).

No elemental Phosphorus was present in the bioaccessible fractions. This is in agreement with the likelihood of undissolved elemental Phosphorus able to pass through the dialysis membrane.