Faculty of Science

Department of Chemistry
  • LCn This abbreviation is used for the exposure concentration of a toxicant lethal to n% of a test population e.g. LC50
  • LDn This abbreviation is used for the dose of a toxicant lethal to n% of a test population.
  • Evident Toxicity - this concept is used to designate toxic effects after exposure to a substance tested, which are so severe that exposure to the next highest fixed dose would probably lead to death.

Very Toxic (T+)

Acute lethal effects:

  • R28 "Very Toxic if swallowed" : LD50 oral, rat < or = 25mg/kg : less than 100% survival at 5mg/kg oral, rat.
  • R27 "Very Toxic in contact with skin" : LD50 dermal, rat or rabbit: < or = 50mg/kg.
  • R26 "Very Toxic by inhalation" : LC50 inhalation, rat, for aerosols or particulates < or = 0.25mg/litre/4h, LC50 inhalation, rat, for gases and vapours < or = 0.5mg/litre/4h

Non-lethal irreversible effects after a single exposure:

  • R39 "Danger of very serious irreversible effects" : Irreversible damage is likely to be caused by a single exposure by an appropriate route, generally in the above dose ranges.

In order to indicate the route of exposure, combinations of Risk Phrases may be used e.g. R39/23 i.e. " Danger of very serious irreversible effects by inhalation".

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Toxic (T)

Acute lethal effects

  • R25 "Toxic if swallowed" : LD50 oral, rat 25 < LD50 < or = 200mg/kg: At 5mg/kg, oral, rat. less than 100% survival but evident toxicity.
  • R24 "Toxic in contact with skin" : LD50 dermal, rat or rabbit: 50 < LD50 < or = 400mg/kg.
  • R23 "Toxic by inhalation" : LC50 inhalation, rat, for aerosols or particulates: 0.25 < LD50< or = 1mg/litre/4h LC50 inhalation, rat, for gases and vapours < or = 0.5 < LD50 < 2mg/litre/4h

Non-lethal irreversible effects after a single exposure

  • R39 "Danger of very serious irreversible effects": Irreversible damage is likely to be caused by a single exposure by an appropriate route, generally in the above dose ranges. In order to indicate the route of exposure, combinations of Risk Phrases may be used e.g. R39/23 i.e. "Danger of very serious irreversible effects by inhalation".

Severe effects after repeated or prolonged exposure

  • R48 "Danger of serious damage to health by prolonged exposure": Serious damage is likely to be caused by repeated or prolonged exposure by an appropriate route. "Toxic with R48" is used when effects are observed at levels of the order of:
      • Oral, rat < or = 5mg/kg(bodyweight)/day
      • Dermal, rat or rabbit < or = 10mg/kg(bodyweight)/day
        Inhalation, rat < or = 0.025mg/l, 6h/day

In order to indicate the route of exposure, combinations of Risk Phrases may be used e.g. R48/23 i.e. "Danger of serious damage to health by prolonged exposure by inhalation".

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