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Flashcards in nitrates Deck (12)
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toxicity of nitrates

  • no big effect at low levels, toxic at high levels
  • nitrate not very toxic but very toxic when converted to nitrite
  • about 5% of nitrate is converted to nitrite in body


most common route of exposure for nitrates

oral exposure:

  • drinking contaminated water 
  • diet - used as preservatives in food, in some vegetables


why is nitrite toxic

  • May cause cancer (debates ongoing)
  • Binds with iron (Fe2+) to oxidise it to Fe3+
    • This is bad in Hb because it makes it form Methaemoglobin so it can no longer bind oxygen as well
  • When exposed to high levels (more than 14mg/kg or 0.9g in an adult) symptoms develop


why are infants more susceptible to nitrate poisoning

infants have high GI pH which promotes conversion of nitrate to nitrite. Methaemoglobin reductase has 1/2 the activity of an adult


who is most susceptible to nitrate poisoning

infants, foetus, fish and cattle most susceptible


symptoms of nitrite poisoning

correlate to lack of oxygen carrying ability

  • mild: skin discolouration, weakness, headache
  • moderate: fatigue, dizziness, confusion
  • severe: acidosis, seizures, respiratory distress, coma, cardiac arrest



why are cattle more at risk of nitrite poisoning

Cattle can consume toxic amount of nitrate within an hour


why are foetus more susceptible to nitrate poisoning

  • Fetal haemoglobin (2 alpha, 2 gamma) has a higher affinity for oxygen than adult haemoglobin
  • More readily oxidised by NO2 to methaemoglobin


why are fish more at risk of nitrite poisoning

Nitrates increase plant growth (weed and algae) which decreases O2 levels


carbon monoxide poisoning: symptoms, treatment and whos at risk

  • Toxicity at levels as low as 0.02% and can kill in minutes
  • Signs of toxicity include headache, shortness of breath, confusion
  • Treatment is high pressure oxygen (hyperbaric chamber)
  • Disrupts normal oxygen transport by occupying the binding site.
  • Binds with high affinity meaning it is hard to remove.
  • Fetal Hb has greater affinity for CO so smoking as a pregnant mother is v dangerous for foetus


why do we need to treat nitrite poisoning

  • Have to convert Fe3+ back to Fe2+
  • Methaemoglobin reductase (MetHb Reductase) is a naturally occurring enzyme in RBCs that maintains methaemoglobin levels < 2%
  • Need treatment when enzyme is saturated by an overload of methaemoglobin


treating nitrite poisoning via methylene blue

  • Reduces Fe3+ in metHb back to Fe2+
  • This causes the methylene blue to become oxidised.
  • Oxidised methylene blue is reduced by the enzyme methylene blue reductase.
  • The enzyme is recycled using NADPH as a co-factor