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Administrative data

Endpoint:
additional toxicological information
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Basic information given

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006

Materials and methods

Type of study / information:
Examines the fate of the organotins after prolonged use in PVC pipe.
Test guideline
Qualifier:
no guideline followed
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): monomethyltin stabilizer and dimethyltin stabilizer

Results and discussion

Any other information on results incl. tables

Extraction 1:

Data Analysis.  All samples show a decrease in tin concentration over the 21 day test period. The highest concentration is observed on day 1, and for most samples the concentration has fallen to near zero by day 10. 

 

We examined in depth several samples that had the highest day 1 values of tin. Using simple models we determined that a simple first order decay curve (as if modeling a chemical reaction) provided a reasonable fit to the data for these particular experiments. A good fit was obtained with an equation of the form: concentration in water = Coexp(-k[t-1])(1 – exp(-k)), where Corepresents the theoretical concentration in water on day 0 and k is a theoretical rate constant.   

 

For all samples the tin concentration on day 1 represents a considerable fraction of the total extracted tin. The values calculated for k show significant differences between the samples, which may be indicative of the different formulations and processing conditions for producing the pipe, which result in different characteristics for leaching. 

Most important, however, is the fact that for all of these samples the total concentration of tin that is extracted is around 100 µg/L. Given that total level of extracted tin, and keeping in mind that these were the pipe samples with the highest levels of extracted tin, we can calculate how much of the PVC pipe is losing tin. For pipe with a diameter of 0.5 in (1.3cm), a liter of water would be contained in a length of pipe about 815 cm in length, having a surface area of about 3200 cm2. For PVC with a density of 1.6 gm/cm3, containing 0.5% organotin stabilizer that is 20% tin metal, the 100 µg of tin that is extracted from this piece of pipe would be contained in a layer of pipe that is 200 nanometers thick (0.2 microns). 

 

NSF extraction data, tin concentrationµg/L 

Day

Sample 1

Sample 2

Sample 3

1

38.5

35.6

45.5

2

6.9

11.2

15

4

1.8

4.6

4.6

8

1.3

2.5

1.3

10

0.4

1.8

3.8

15

0.4

1.5

1.6

21

0.1

0.5

0.7

C0

67

85

105

k

1.7

1.05

1.04

 

 

 

 

 

Extraction 2:

The fusion curves were very similar and showed a reasonable processing time before decomposition began. This indicates that after 39 years of service the PVC pipe still has active stabilizers.

Measurement of the tin content of the 40 year old pipe by XRF analysis gave a value of 0.30%, in reasonable agreement with the chemical analysis. 

 

Using the SIMS profiling analysis the tin content was measured near the inner and outer surfaces, and at the center of the pipe. Analysis of the outer surface shows that the tin level is constant and is at the same level of tin as the center of the pipe. Analysis of the inside of the pipe gave a different result. At the inner surface the tin content is lower than that at the center of the pipe, but it increases to the level of the center 1 micron from the inner pipe wall. Two factors are driving the change in Sn intensity. The first being a build up of silica or silicates on the surface and extraction of the Sn. In addition, the Sn distribution suggests the organotin extraction could be diffusion limited.

Applicant's summary and conclusion

Conclusions:
The extraction tests done on new pipe by NSF show that the level of tin migrating from the pipe is low, and drops very quickly to near zero. The tests on the 40 year old pipe show that the pipe has lost very little additional tin over the 39 year service life. Furthermore, the tin that remains in the pipe is in the form of an active stabilizer, allowing the PVC to be processed without additional stabilizer needing to be added.

Based on this work, it is clear that organotins are not leaching out of the pipe at significant levels, and that they maintain their integrity as stabilizers when in the PVC. Equally important, this means that the long term durability, the longevity, of PVC pipe is not reduced by loss of stabilizer.