reaction mass of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-2H -isothiazol-3-one

Biodegradation in water and sediment: simulation tests

Administrative data

Endpoint:

biodegradation in water and sediment: simulation tests

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: no guidline GLP study available. The evaluation was published by an official EU Committee, which is considered as scientifically sound source of information and tehrefore considered to be relevant and valid for the substance evaluation.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2003

Materials and methods

Principles of method if other than guideline:

The SCCNFP evaluated the use of different stabilisers in CIT/MIT technical-grade active ingredient (TGAI) and its diluted aqueous solutions, for use in cosmetics. To this end, the stability of CIT/MIT in TGAI and its aqueous dilutions for use in the cosmetics industry were discussed. Degradation pathways and mechanisms were elucidated.

GLP compliance:

no

Test material

Test material information

Constituent 1

Study design

Inoculum or test system:

not specified

Remarks:

No information is given on materials and methods, because the document represents an evaluation of a dossier, and the dossier itself is not available.

Results and discussion

Test performance:

No detailed information are available

% Degradation

Remarks on result:

other: Dossier evaluation

Remarks:

No information is given on materials and methods, because the document represents an evaluation of a dossier, and the dossier itself is not available.

Transformation products:

no

Details on results:

The following text is a citation from the document, page 4 (Notes: the acronym MCI/MI is used for CIT/MIT in the document; references given as numbers in the original text were omitted here since they are anyway not available):

“According to the information provided in the dossier, the instability of commercial MCI/MI mixtures is due to two factors, i.e. the inherent instability of the isothiazolinone molecules, and residual impurities of the manufacturing processes.The sulphur-nitrogen bond of the isothiazolinone ring represents an electrophilic centre that may react easily with nucleophilic substances. In the MCI molecule, a further electrophilic centre, the vinyl-activated chlorine atom in the neighbourhood of the sulphur-nitrogen bond is responsible for increasing the instability of MCI in comparison to MI molecule.Deactivation is thought to proceed by means of a cascade of reactions, initiated by ring opening, loss of chlorine and sulphur, and subsequent formation of N-methylmalonamic acid. The degradation then proceeds through malonamic, malonic, acetic, and formic acids to carbon dioxide and methylamine, accompanied by several side products (N methylglyoxylamide, ethylene glycol, urea). Isothiazolinone-1-oxides are also derived by enzymic oxidation of disulphanes, elemental sulphur (as a result of breakdown of sulphurous acids) and hydrogen sulphide. This is a strong nucleophile attacking the ring and accelerating the decomposition in a self-perpetuating autocatalytic sequence of reactions, which is more rapid at higher concentrations of the MCI/MI solutions.In pure aqueous solutions the ring opening is initiated by simple hydrolytic cleavage of the S-N bond, which is the reaction occurring in the presence of strong nucleophiles such as primary and secondary amines and particularly thiol derivatives.”

Any other information on results incl. tables

Several mechanisms for degradation are possible, all starting with nucleophilic attack leading to cleavage of the N-S bond and thus ring opening. This leads to deactivation due to the loss of the active moiety.

The central intermediate metabolite is N-methylmalonamic acid. Terminal metabolites are generally small, polar and mostly naturally occurring molecules such as urea, formic acid, acetic acid; and methylamine and ethylene glycol. Mineralisation to carbon dioxide also occurs.

Ring opening in environmental media was considered to proceed mainly by attack of amines or thiols. Such groups are abundant in microbially viable media and occur at especially highly concentrations in activated sewage sludge.

An autocatalytic degradation mechanism was also proposed in the evaluation. This should be relevant only for concentrated solutions of CIT/MIT in technical applications. In environmental media, CIT/MIT is highly diluted and autocatalysis is likely to remain negligible.

CIT was expected to be degraded more rapidly than MIT, because the electrophilic chlorine activates the N-S bond for nucleophilic attack.

Applicant's summary and conclusion

Validity criteria

Validity criteria fulfilled:

not applicable

Conclusions:

The metabolic pathways of CIT/MIT were evaluated in technical-grade active ingredient and its diluted aqueous solutions. Degradation mechanisms and pathways were proposed (see attached document).

Executive summary:

The statement is giving the following information: "In pure aqueous solutions the ring openeing [of CIT and MIT] is initiated by simple hydrolytic cleavage of the S-N-bond, which is the reaction occuring in the presence of strong nucleophiles such as primary and secondary amines and particularly thiol derivatives". A scheme for autocatalytic degradation is given.