nitrates

Question 1

toxicity of nitrates

Answer 1

• 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

Question 2

most common route of exposure for nitrates

Answer 2

oral exposure:

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

Question 3

why is nitrite toxic

Answer 3

• 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

Question 4

why are infants more susceptible to nitrate poisoning

Answer 4

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

Question 5

who is most susceptible to nitrate poisoning

Answer 5

infants, foetus, fish and cattle most susceptible

Question 6

symptoms of nitrite poisoning

Answer 6

correlate to lack of oxygen carrying ability

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

Question 7

why are cattle more at risk of nitrite poisoning

Answer 7

Cattle can consume toxic amount of nitrate within an hour

Question 8

why are foetus more susceptible to nitrate poisoning

Answer 8

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

Question 9

why are fish more at risk of nitrite poisoning

Answer 9

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

Question 10

carbon monoxide poisoning: symptoms, treatment and whos at risk

Answer 10

• 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

Question 11

why do we need to treat nitrite poisoning

Answer 11

• 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

Question 12

treating nitrite poisoning via methylene blue

Answer 12

• 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