Hop, Humulus lupulus, ext., isomerized, potassium salt

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

28 days

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Hop extract - CO2 extract of Humulus lupulus variety 'Cascade'. Batch number 160025. Principal components: alpha acids: 35.06% w/w; beta acids: 38.47% w/w; essential oils: 8.92% v/w

Oxygen conditions:

aerobic

Inoculum or test system:

other: secondary effluent from a predominantly domestic sewage treatment works.

Duration of test (contact time):

ca. 28 d

Initial conc.:

ca. 2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Reference substance:

acetic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

ca. 26

Sampling time:

28 d

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The study performed on hop extract is relevant for iso-alpha acids, since hop extract may contain up to ca. 60% alpha acids (the extract tested here contained 35% alpha acids), and a well-known degradation (oxidation) product of alpha acids are the humulinones, which are very similar in structure to iso-alpha acids (compare for instance iso-humulone https://pubchem.ncbi.nlm.nih.gov/compound/Isohumulone#section=Top with humulinone https://pubchem.ncbi.nlm.nih.gov/compound/534962#section=Top). The result for hop extract suggests a water soluble / biologically active component rapidly contributing to 20% of the degradation (ie about 30% of the material in view of the low results for the control) and a residual 70% or so of the material that is so insoluble it is not biologically available.

As a natural product, there will be ultimate biodegradation.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable but failing 10-day window

Additional information

This result suggests a water soluble / biologically active component rapidly contributing to 20% of the degradation (ie about 30% of the material in view of the low results for the control) and a residual 70% or so of the material that is so insoluble it is not biologically available. As a natural product, there will be ultimate biodegradation.