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Environmental fate & pathways

Hydrolysis

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Description of key information

Several studies demonstrate that TEL is not stable in aquatic systems and dissolved TEL can either be lost by evaporation from the surface of the water, or decomposed by stepwise abiotic processes to form, ultimately, inorganic lead.  Half lifes of 2-5 days (Harrison et al) and 7.3 days (Jarvie et al) are reported.  Due to the consistency of the data a weight of evidence approach is used for this endpoint with the 7.3 day value selected for use in the CSA

Key value for chemical safety assessment

Half-life for hydrolysis:
7.3 d
at the temperature of:
20 °C

Additional information

Overall it is concluded that TEL is not stable in aquatic systems and dissolved TEL can either be lost by evaporation from the surface of the water, or decomposed by stepwise abiotic processes to form, ultimately, inorganic lead. The process can be represented schematically as follows:

 

(C2H5)4Pb -> (C2H5)3Pb+->(C2H5)2Pb2+->[C2H5Pb3+] -> Pb2+

 

 Half lives of about 2-5 days (Harrison et al. 1986) and 7.3 days (Jarvie et al. 1981) are reported. Due to the consistency of the data a weight-of-evidence approach is used for this endpoint with the 7.3 day value selected as a conservative value for use in the CSA.

The study from Jarvie also gave several results for hydrolysis over time providing more detail on the rate of decompositon.

 Time (days) Recovery TEL (%) 
 78
 2  63
 7  54
 13  19
 17  22
 20  19
 29  3

Aqueous degradation appears to be more rapid in daylight than in the dark, although a number of experiments are impossible to interpret since the TEL was present far above the water solubility.

The first stage of degradation, to triethyl lead can occur rapidly under the right conditions. Studies have shown that all the degradation steps are affected by conditions such as purity of water, sunlight, oxygen content, temperature etc.

Studies in rainwater and seawater at 3-20 µg/L showed the initial degradation step, TEL to Triethyl lead salt, proceeds readily, with 50% decomposition occurring within the range of 2-5 days. Hydrolysis in pure water appears to be lower than in environmental samples (Harrison, 1986)

 

Jarvie et al.(1981)found 90% of TEL was degraded after 15 days with a half life of 7.3 days. Once formed the tri and diethyl salts decompose to the unstable [monoethyl lead salt] and then to inorganic lead.

Some half life calculated values for the degradation reaction products in natural waters, such as rain water and sea water, have also been reported(Radojevic and Harrison, 1987).These are based on data from several different studies published in the peer reviewed literature and are given in the table below:

:

 

Species

Reactant conc.

 µg Pb/l

T1/2(days)

Sample

Reference

Triethyl lead salt

0.5

0.3

Lakewater

De Jonghe et al (1983)

       

10,000

8.6

Sea water

Blanchard et al (1984)

      

15

1.5

Rain water

Radojevic & Harrison

(1987)

Diethyl lead salt

10,000

6.1

Sea water

Blanchard et al (1984)

  

19

4.1

Rain water

Radojevic & Harrison

(1987)

    

700

1.1

Deionized water

Van Cleuvenbergen et al (1992)