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EC number: 202-607-8
CAS number: 97-77-8
Materials and methods:
The stability of 14C-labelled Thiram (10 ppm) in sterile aqueous buffers
maintained at three pH levels (5, 7 and 9) was studied. Samples were
incubated at 25 °C in the dark and under sterile conditions.
The tests were performed for 30 days at
pH 5, 8 days at pH 7 and 16 hours at pH 9.
Prior to use, all glassware, Teflon
vessels and septa were sterilized in a pressure cooker at 121°C for 30
min to minimize biodegradation.
All buffers were filtered through a
0.2-µm nylon filter. After filtration, the sterility of the buffers was
checked with Petrifilm 6400 aerobic count plates.
Results and discussion:
The hydrolysis of Thiram was analysed in pH 5, pH 7 and pH 9 at a
concentration of 7.28 ppm, 7.91 ppm and 7.15 ppm of 14C-Thiram,
respectively. Under alkaline or neutral conditions, 14C -Thiram was
rapidly hydrolysed. The majority of the radioactivity was continuously
released as volatiles during the study. The major breakdown product for
all buffers was identified as volatile CS2. The material balance for all
samples was greater than 90% after purging. The volatiles contained in
the pH 9 were released particularly upon acidification.
Further breakdown products were isolated
in the chloroform extracts; however, none comprised more than 5% of the
initial radioactivity during the study. The remaining buffer solution
after chloroform extraction contained less than 10% of the initial
radioactivity over the time studied for pH 5 and pH 7. The extracted
buffer solution at pH 9 contained up to 35% of the initial
radioactivity. After acidification of the extracted pH 9 solution, most
of the radioactivity was released as 14C CS2.
than one day to several weeks
than one day to several days
than one day
Hydrolysis may be a relevant degradation pathway for disulfiram in
aquatic systems (half-lives 68.5 days, 3.5 days and 6.9 hours under
acidic, neutral and alkaline conditions respectively)
No data on hydrolysis of disulfiram (CAS No.
97-77-8) are available. Therefore, a conclusion based on data from an
analogue substance had to be drawn. Hydrolysis of tetramethylthiuram
disulfide (CAS No.137-26-8), substance structurally and composition
related to tetraethylthiuram disulfide, was investigated in one study. This
test was conducted according to EPA’s Pesticide Assessment
Guidelines, Series 161-1, Hydrolisis Studies (1988), under GLP
conditions.14C-thiram was tested at pH 5, 7 and 9, and the
half-lives determined, being 68.5 days, 3.5 days and 6.9 hours
respectively. Hydrolysis in alkaline and neutral conditions took place
at a faster rate than under acidic conditions. The main breakdown
product was CS2.
The results from the HYDROWIN v2.00 program
support these findings, as the hydrolysis of disulfiram is predicted to
occur faster under neutral and alkaline conditions (less than one day to
several days and less than one day, respectively).
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