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
