Hop, Humulus lupulus, ext.

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Justification for type of information:

This academic paper, although published in 1953, is well reported and the studies were carefully executed. Many experiments were performed to (i) investigate the sedative effect of hop extracts on goldfish, (ii) to distinguish between toxic and sedative effects, and (iii) to determine which components of the hop extract were responsible for which effects. Since toxicity to fish was clearly noted in several instances, and since this carefully-conducted study is available in the public domain, further animal studies are not warranted. It is possible from the published results to derive a defensible estimate of lowest toxic dose, and so it would not be right to conduct further experiments on living fish. Furthermore, the Daphnia appear to be more sensitive than the fish (see relevant endpoints) which further argues against the need to do more animal studies.

Qualifier:

according to guideline

Guideline:

other: The article refers to a method by Fauconnet on investigation of sedative drugs in fish

Principles of method if other than guideline:

Carefully conducted studies on goldfish, with nine sets of observations

GLP compliance:

not specified

Remarks:

Well-conducted and reported 1953 study

Test organisms (species):

Carassius auratus

Key result

Duration:

15 min

Dose descriptor:

other: Lowest dose causing adverse effects

Effect conc.:

ca. 80 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (dissolved fraction)

Basis for effect:

behaviour

Sublethal observations / clinical signs:

Only the aqueous extract had no effect on the fish.This is not surprising, as the alpha and beta acids, and the essential oils, are not soluble in water. For the purposes of establishing toxicity, the following two sets of extract were particularly relevant:

 

1.             Acetone extract,which will contain alpha, beta and essential oils,re-dissolved in ethanol, at 40% concentration. This was very toxic to fish at 5 cm³per litre: violent spasms, the fish went onto one side, and died in 6-7 minutes.

·        The same results were observed when the extract was dosed at 1 cm³per litre.

·        When the extract was dosed at 0.2 cm³per litre, the fish were removed from the test water when they started to go onto one side, and were re-placed into fresh, running water. The fish then revived.

2.             A dry extract was re-worked as 5% in ethanol. A dry extract would be expected to containalpha, beta and essential oils. When dosed at 5 cm³per litre, this had slight sedative effects on the fish, and caused some spams and some equilibrium problems. No death reported.

 

A 0.2 cm³per litre dose of a 40% acetone extract is equivalent to0.08 g per litre hop extract, i.e.80 mg per litre. At this dose, adverse effects started to be observed.

  

A 5 cm³per litre of a 5% extract is equivalent to0.125 g per litre hop extract, i.e.125 mg per litre. This caused some adverse effects, but not lethal.

  

Attempts to de-toxify the extracts by further solvent extractions/fractionations were not successful, apart from removal of essential oils. The essential oils seemed to be responsible for sedative activity, but not toxicity. The residue of a hop extract, once essential oils had been removed by steam distillation, and which was then re-dissolved in ethanol and dosed at 5 cm³per litre, was very toxic.

 

The toxic principles are thus found in the hop extract apart from essential oils. These are most likely to be the alpha and beta acids, and potentially the other resins too, since these contain oxidised alpha and beta acids.The fats and waxes are very insoluble and not known to be toxic.

Conclusions:

For the acetone extract of lupulin, 400 mg per litre hop extract (1 cm3 per litre of the 40% extract) and 2,000 mg per litre (5 cm3 dose) were highly toxic, but 80 mg per litre gave reversible effects. Taking a safety factor of 10, it seems reasonable that a dose of 8 mg per litre could be considered as a level which would have little effect on the fish. Furthermore, hop extract is highly insoluble. Tween 20 was used in these experiments to assist with solubility. In the Daphnia tests, a limit of solubility of approximately 2.2 mg per litre was noted. Thus, it is not likely that hop extract could accumulate in water to reach a concentration of toxicity towards fish.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

8 mg/L