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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The biodegradation is the biologically mediated degradation process or transformation of chemicals carried out by microorganisms; in particular, the ultimate biodegradation is defined as the breakdown of a chemical by microorganisms in the presence of oxygen resulting in the formation of carbon dioxide, sulphate, nitrate and new biomass or it can be defined as breakdown of a chemical in absence of oxygen resulting in the formation of carbon dioxide and final reduction products like methane, H2S, or NH3, mineral salts and new biomass. Lysozyme is an enzyme, i.e. biological material and therefore it can be considered ready biodegradable.

Lysozyme, as enzyme, is a protein; the general degradation pathway of proteins is a stepwise process starting with the splitting of peptide bonds in the protein polymer by proteolytic enzymes (proteases) forming lower-molecular oligopeptides, which are subsequently degraded by peptidases to the monomeric amino acids. Physical parameters as heating, dilution, mixing of solutions with air, etc. can impact the enzymatic function by denaturation, i.e. loss of activity and changes of the three-dimensional structure, which facilitates this proteolytic degradation process (HERA 2005).

For completeness sake, the available literature data on other enzymes are here reported in order to confirm that proteins can be regarded as readily biodegradable. Specifically, data about lipase, cellulase, amylase and subtilisin are available: according to the Enzyme Commission (EC) classification, they are all subcategorized as hydrolases enzymes acting on ester bonds in the case of lipase, acting on the peptide bonds (peptidases) and acting as glycosylases in the cases of cellulase, amylase and lysozyme. In all cases, the enzymes resulted as ready biodegradable, as expected considering their globular protein structure.

Lipase (EC 3.1.1.3)

- OECD 301 E; 99 % DOC remove. Ready biodegradable (HERA 2005; Bergman et al., 1997)

 

Cellulase (EC 3.2.1.4)

- OECD 301 E, 84 % DOC removal. Ready biodegradable (HERA 2005; Bergman et al., 1997)

- OECD 301 C, 78 % BOD/COD (HERA 2005; Greenough and Everett, 1991)

 

α-Amylase (EC 3.2.1.1)

- OECD 301 E, 99 % DOC removal (HERA 2005; Bergman et al., 1997)

- OECD 301 E, 99 % DOC removal (HERA 2005; Bergman et al., 1997)

 

Subtilisin (EC 3.4.21.62)

Studies available on biodegradation showed that there is no significant difference in the biodegradation rate and extent between wild type Subtilisins and protein engineered variants. This is in line with the general understanding of the common structure and properties of proteins irrespective of their specific activity pattern and their origin. Consequently, the exposure assessment of Subtilisins does not need to differentiate between wild type and protein engineered enzyme (HERA 2007).

REFERENCE

Bergman A, Bak J, Stavnsbjerg M (1997). Environmental fate of detergent enzymes. International Symposium Environmental Biotechnology. Oostende, Belgium. Part 2, 303-305. Edited by H. Verachtert & W. Verstraete. ISBN 90-5204-031-1

Greenough RJ, Everett DJ (1991) Safety evaluation of alkaline cellulase. Food and Chemical Toxicology 29: 781-785.

HERA (2005). Human and environmental risk assessment on ingredients of household cleaning products - alpha-amylases, cellulases and lipases.

HERA (2007). Human and environmental risk assessment on ingredients of household cleaning products - Subtilisins (Proteases). Edition 2.0. 2007.