Nitrate and nitrite (FINAL) Flashcards
1
Q
Explain accumulation of nitrate by plants
A
- Nitrate (NO3) is absorbed from the soil by the plant, is converted to nitrite (NO2)
- Nitrite is converted to ammonia (NH3)
- Ammonia is converted to amino acids then to vegetable protein
- Nitrase reductase converts nitrate to nitrite
- When the rate of nitrate-to-nitrite is reduced, w/ continuation of nitrite uptake from the soil, this leads to nitrate accumulation in the plant
2
Q
What plant species favor nitrate accumulation?
A
Sweet clover, alfalfa, corn, wheat, etc.
3
Q
What content/form of N in the soil favors nitrate accumulation in plants?
A
High nitrate or ammonia
4
Q
What are some soil conditions that enhance nitrate uptake?
A
- Rains or moisture
- Acidic soil (low pH)
- Low soil molybdenum, sulfur, or phosphorus
- Low soil temp (13 C)
- Soil aeration or drought
5
Q
T/F: Decreased light reduces activity of nitrate reductase
A
TRUE
6
Q
T/F: The use of phenoxy acetic acid herbicides can increase nitrate accumulation in plants
A
TRUE
7
Q
Which plant parts contain the most nitrate?
A
The stalks contain the highest concentrations
Leaves contain less than stalks or stems
The seed (grain) and flower contain little or no nitrate
8
Q
T/F: Mature plants have higher nitrate than younger plants
A
FALSE–younger plants have higher nitrate than mature plants
9
Q
Name 10 nitrate-accumulating plants
A
- Pigweed (Amaranthus retroflexus)
- Oats (Avena sativa)
- Beets (Beta vulgaris)
- Johnson grass, sudan grass, milo (Sorghum spp)
- Corn, maize (Zea mays)
- Lamb’s quarters (Chenopodium album)
- Sweet clover (Melilotus spp)
- Alfalfa (Medicago sativa)
- Wheat (Triticum aestivum)
- Sunflower (Helianthus annuus)
10
Q
What is this?
A
Pigweed (Amaranthus spp)
11
Q
Plant name?
A
Lamb’s quarters (Chenopodium album)
12
Q
What is this?
A
Alfalfa (Medicago sativa)
13
Q
What’s this?
A
Sudan grass
14
Q
What plant is this?
A
Johnson grass
15
Q
What are nitrate/nitrite used for?
A
- Fertilizers
- Sodium nitrite IV is used as a vasodilator
16
Q
Sources of nitrate/nitrite poisoning?
A
- Rapid ingestion of forages or hays containing high amounts of nitrate
- Accidental ingestion of feeds or water contaminated w/ nitrate
- Overdose w/ nitrite IV
17
Q
Are nitrates soluble in water?
A
yes
18
Q
T/F: Nitrate fertilizers are salty
A
TRUE–they’re palatable
19
Q
What are nitrates and nitrites sources of (in soil)?
A
Sources of nitrogen oxide gases
20
Q
What converts nitrate to nitrite?
A
Nitrate reductase (microflora)
21
Q
What is the LD50 for ruminants?
A
Approx. 0.5-1 g/kg
22
Q
What forage nitrate level can cause acute toxicosis?
A
Greater than 1%
23
Q
Can nitrate/nitrite tolerance develop over time?
A
Yes
24
Q
Which species is most susceptible to nitrate poisoning?
A
Ruminants (rumen microflora)
25
Which species is resistant to nitrate poisoning?
Pigs
26
Which species is very sensitive to IV nitrite?
Horses
27
T/F: Nitrate is 10x more toxic than nitrite
FALSE--Nitrite is 10x more toxic than nitrate
28
What are the types of nitrate poisoning?
Acute or chronic
(Chronic nitrate poisoning is not common)
29
T/F: Factors that stimulate rumen microflora increase nitrate reductase activity, thus increasing toxicity
TRUE
30
T/F: Young animals are more susceptible than adults
TRUE
(because that's almost always the freakn case)
31
What diseases increase toxicity?
Anemia and methemoglobinemia
32
What is nitrate reduced by/to? What is that then converted to?
Nitrate is reduced by the rumen microflora to nitrite
Nitrite is then converted to ammonia
33
What is ammonia converted to?
Amino acids and microbial proteins
34
T/F: The rate of conversion of nitrite to ammonia is slower than the rate of conversion of nitrate to nitrite
TRUE
35
What does the difference between conversion rates result in?
Accumulation of nitrite in the rumen which is rapidly absorbed
36
What occurs in erythrocytes?
The nitrite ion enters the erythrocytes in exchange for chloride ion
37
Can nitrite cross the placenta?
Yes--it crosses the placenta and enters fetal erythrocytes **(fetal hemoglobin is more sensitive)**
38
What is the half-life of nitrite?
Nitrite = less than 1 hr in dogs, sheep and ponies
Nitrate = 4-48 hrs
39
What is the mechanism of action in acute toxicosis?
* 1 molecule of nitrite interacts with 2 molecules of hemoglobin --\> oxidation of ferrous iron to ferric and conversion of hemoglobin to methemoglobin
* Methemoglobin cannot carry oxygen
* Direct vasodilation and hypotension
* Abortion due to fetal methemoglobinemia
40
What levels of methemoglobin show clinical signs? When will death occur?
* Clinical signs of anoxia develop if methemoglobin is 20-40%
* Death from anoxemia occurs when methemoglobin reaches 80-90%
41
What is the mechanism of action of chronic toxicosis?
Abortion due to decreased progesterone
42
Clinical signs of nitrate/nitrite poisoning?
* Sudden death w/ no observed signs
* Signs occur rapidly (w/in 30 min to 4 hr)
* Rapid breathing
* Restlessness
* Apprehension
* Dyspnea
* Weakness
* Ataxia
* Sternal recumbency
* Cyanosis
* Terminal convulsions
* Death w/in a day or a few hours
* Abortion (due to fetal anoxia)
43
Lesions?
Congestion in various organs
Brown-chocolate color of blood (methemoglobin)
44
What is used for chemical analysis?
What about animals that have been dead several hours?
What is best to be used prior to death?
* Forage, hay, and water for nitrate
* Ocular fluid is specimen of choice for nitrate in animals dead for several hours (\>30ppm indicates excessive exposure)
* Serum, plasma, urine, and rumen contents can be used for nitrate, but they are unstable after death
45
Methemoglobin concentration for preservation?
One part blood to 20 parts phosphate buffer (pH 6.6)
46
Diagnosis?
* History, clinical signs of resp signs w/o lung lesions, and methemoglobinemia usually allow presumptive diagnosis
* Diphenylamine test
47
What is the diphenylamine test? What do positive results indicate?
Qualitative test for nitrate in forages (hay, pasture, silage), rumen contents, and water
+ results indicate \>5,000 ppm nitrate
48
How do you perform the diphenylamine test?
* Mix 0.5g diphenylamine w/ 20mL of distilled water, then bring the total to 100mL w/ concentrated sulfuric acid
* Carefully put a drop of solution on inner tissue of the plant stem
* Dark blue color indicates + result
* Positive specimens have to be sent to the lab for quantitative analysis (false positives possible)
49
DDx (general)?
* Agents causing methemoglobinemia
* Agents inhibiting oxygen utilization by tissues
* Hemolytic agents
* Carbon monoxide (bright red blood)
* Cardiac toxicants
50
DDx for agents causing methemoglobnemia?
* Agents causing methemoglobinemia
* Nitrate in ruminants
* Nitrite
* Copper
* Acetaminophen in cats
51
DDx for agents inhibiting oxygen utilization by tissues? How can you differentiate between them?
* Cyanide (bright red blood)
* Hydrogen sulfide (dark blood)
52
What are some other hemolytic agents?
* Copper
* Zinc
* Naphthalene
* Bromate
* Iodate
* Arsine gas
* Onion
* Mustard
* Red maple
* Gossypol
* Snake venoms
* Others
53
What are some cardiac toxicants?
* Digitalis
* Magnesium
* Calcium
* Potassium
* Fluoroacetate in herbivores
* Others
54
What is the treatment for nitrate/nitrite poisoning?
* Methylene blue 1% slowly IV for ruminants and monogastrics **except cats** as a reducing agent (4-30 mg/kg)
* Activated charcoal
* Ruminal lavage w/ cold water
* Oral antibiotics may inhibit rumen microflora and nitrate reductase
55
Prognosis?
Animals usually die before treatment because death is rapid
