Odor threshold

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The olfactory threshold is the threshold at which an organism perceives a fragrance or odoriferous substance . The odor threshold , or GSW for short , is the minimum concentration of a certain gaseous, sensory active substance in the surrounding medium that this living being can just about perceive through its sense of smell .

The odorous substance can already be present in the air (such as ozone ), or it can have passed over there as a volatile substance from a liquid matrix (e.g. drinking water , wine ) or a solid that contained it ( e.g. as a flavoring substance ).

In the DIN standard EN 13725, an odor threshold is defined as the odor concentration at which the probability of perception of the sample is 0.5 under defined test conditions, i.e. just 50% of the test persons indicate an odor perception.

Odor threshold

In quantitative terms, the odor threshold value can be specified either as an absolute value ( initial weight / volume) or as the ratio of volume fractions of an odor-free comparison matrix to the examined matrix in which the odor could just be perceived. In the latter method, the GSW is thus a kind of dilution factor .

Examples of thresholds

  • Odor-free water has the GSW zero. The limit value in accordance with the German Drinking Water Ordinance is 3 at a water temperature of 23 ° C.
  • The odor threshold of 2,4,6-trichloroanisole (TCA), the cause of the corkon , can be lower with a sensory trained smell , so that when tasting with retronasal aroma perception, he can also detect concentrations that come from around 2  ng per liter of wine , while an untrained person often only smells or tastes something at 100 ng · l −1 . However, the actual odor threshold values ​​are determined for orthonasal smelling and relate to a volume of air and not to a liter of wine. In relation to room air, the GSW of TCA is around 2 ng / m³ equal to 2  pg / dm³ equal to 2 · 10 −12 g / l air or 0.2 ppt equal to 200 ppq ( parts per quadrillion , parts per quadrillion ), which is around here Corresponds to 6 · 10 9 molecules per liter of air.

Odor threshold concentrations in air

One cubic meter of air contains the following threshold odor concentrations (20 ° C, 1013 hPa):

Substance group substance Odor threshold
(µg m −3 air)
Olfactory impression
Aldehydes acetaldehyde 4.8 pungent, fruity
Amines Dibutylamine 19.3 fishy
Amines Diisopropylamine 4.2 fishy
Amines Dimethylamine 57 fishy, ​​putrid
Amines Ethylamine 1000 for ammonia
Amines Methylamine 25.3 fishy, ​​putrid
Amines Triethylamine 96 fishy, ​​like ammonia
Carboxylic acids Isovaleric acid 2.2 cheesy, sweaty
Ketones Acetophenone 2.39 flowery, soapy
Ketones Octanone 120000 aromatic
Mercaptans Allyl mercaptan 0.06 like coffee, strongly like garlic
Mercaptans Amyl mercaptan 0.36 disgusting, musty
Mercaptans Benzyl mercaptan 0.23 gross, rancid
Mercaptans Crotyl mercaptan 0.035 after Skunk
Mercaptans Ethyl mercaptan 0.23 of rotting cabbage
Mercaptans Methyl mercaptan 1.3 like rotten cabbage, sulphurous
Mercaptans Propyl mercaptan 0.09 disgusting
Sulphides Dimethyl sulfide 1.2 after rotten vegetables
Sulphides Diphenyl sulfide 0.058 disgusting
Carboxylic acid ester Butyric acid ethyl ester 1.2 aromatic
Diacetyl 2.4 like butter, creamy
Alcohols Octenol 12.0 mushroom
Nitrogen heterocycles Pyridine 4.5 uncomfortable, painful
Hydrogen sulfide 0.57 for rotten eggs
Nitrogen heterocycles Skatole (methylindole) 1.4 after feces, disgusting
Thiols Thiocresol 0.12 after Skunk, rancid
Thiols Thiophenol 0.075 musty, like garlic
Vanillin 4.8 vanilla

Odor threshold concentrations (GSK) in water

With regard to drinking water pollution, odor thresholds for different substances are also given as their concentration per liter of water:

substance GSK (µg · l −1 )
acetone 5000
petrol 100
benzene 2000
Butyric acid 50
Chlorine (pH dependent) 100
Chlorobenzene 100
Chlorine dioxide 80
Chlorophenols 10
Dichlorobenzenes 10-30
acetic acid 8-10
Geosmin 0.006
Hexachlorobenzene 3000
Indole 300
menthol 6th
2-methylthiobenzothiazole 5
naphthalene 500
Nitrophenol 10,000
Pentachlorobenzene 60
phenol 1000
Pyridine 100
Hydrogen sulfide 20th
Tetrachlorobenzenes 20-400
Tetrachlorethylene 300
Thiophenol 1
2,3,4-trichloro anisole 0.003
Trichlorobenzenes 5-50

Odor thresholds in humans

Human nose

In humans, the odor thresholds are, depending on the substance, between 10 7 and 10 17 molecules per dm³ of air. At the absolute threshold , the absolute threshold or detection threshold , and just above the determination of a fragrance is not possible, but only the sensation of a vague smell ( "it smells of something"); with methyl mercaptan (e.g. used to odorize natural gas) around 4 · 10 −15 g / l are sufficient , a proportion of around 2  ppq , which corresponds to around 5 · 10 7 molecules per dm³ of air (one liter of air weighs a good 1 g and contains about 2.7 · 10 22 molecules).

For the perception of a certain substance by its specific smell (“it smells like this”) higher concentrations are necessary in each case; this detection threshold is about 50 times higher for methyl mercaptan (2 · 10 −13 g / l, 0.1  ppt , approx. 3 · 10 9 molecules / l air).

These figures are average values, since the odor threshold value for a certain odorous substance is also always a subjective variable, which differs from person to person and can be different even for the same person depending on the situation.

Odor thresholds in animals

The dog's nose is one of the most sensitive olfactory organs (here: the nose of a Samoyed )
  • Dogs : One molecule per mm³ of air is often sufficient to trigger an olfactory sensation, i.e. 10 6 / dm³. For example, a dog can perceive the few fatty acid molecules that diffuse through the sole of a shoe .
  • Bears , especially polar bears , may have the most highly developed sense of smell of any mammal. Polar bears are able to smell possible sexual partners over a distance of kilometers or smell prey such as seals, in seal caves that have been inhabited for a long time, even under ice that is centimeter thick.
  • an eel reacts to two molecules of phenylethyl alcohol , which would correspond to about 1  ml of this substance diluted with 58 times the amount of water from Lake Constance .
  • The silk moth registers the arrival of a single molecule of the female sex pheromone (if it is in a volume of air). However, sexual behavior is only influenced by 200–300 molecules.

Use in fruit growing

The low odor threshold of fragrances such as pheromones is used in fruit growing , among other things , when trying to catch so-called pests before laying eggs, for example to prevent “worm-like” fruits. For example, sticky traps impregnated with pheromones are hung in the tree for the plum and codling moth to attract the swarming males and prevent mating .

Individual evidence

  1. DIN EN 13725: 2003-07 air quality; Determination of the odor concentration with dynamic olfactometry . Beuth Verlag, Berlin.
  2. ^ Lebensministerium.at: State of the art in composting - basic study . September 29, 2005, p. 68.
  3. ^ Walter Kölle: Water analysis - judged correctly. Basics, parameters, water types, ingredients, limit values ​​according to the Drinking Water Ordinance and the EU Drinking Water Directive. 2nd updated and expanded edition. WILEY-VCH, Weinheim 2003, ISBN 3-527-30661-7 . P. 369f.
  4. According to other sources, the GSK for 2,3,4-TCA is similar to that of 2,3,6-TCA and 2,4,6-TCA and is in the range of about 0.0002 to 0.002 µg / l (0, 2 - 2 ng / l); see also Gerstel Table 1 , pdf accessed on April 2, 2014.
  5. ^ Stefan Silbernagl , Agamemnon Despopoulos : Taschenatlas Physiologie , 7. A, Thieme Verlag, 2007, ISBN 978-3-13-567707-1 , p. 346 .
  6. natur-lexikon.com: polar bear