Nitrite Toxicity

[Skavatar]

As fish keepers we're not looking at LC50 or LC90, we're looking for LC0, we don't want any fish to die from nitrite poisoning.

What is a safe level for nitrites. Safe as in 0 deaths, and no negative effects, like lethargy, bottom sitting, gasping for air at the surface, etc.

https://www.addl.purdue.edu/newsletters/1998/spring/nitrate.shtml
Nitrites are actively transported across the gills and readily oxidize hemoglobin to form methemoglobin. Methemoglobinemia results in hypoxia severe enough to cause sudden death but often the fish will live until they exert themselves. The term "brown blood disease" comes from the appearance of the blood that has high levels of methemoglobin (which is brown).
- by Melanie Greeley, DVM

- edited by TI'm Muench,

 

[david1978]

And it can be measured in blood.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3489475/

 

[Kjeldsen]

Good thread. Such a small amount of salt needed to treat nitrite toxicity! 50 mg/l works out to:200 mg per gallon, or 1000 mg per 5 gallons.
1000 mg = 1 ml, and 5 ml = 1 teaspoon

Math isn't my strong suit but I think at this rate 1 teaspoon salt per 20 gallons is more than enough to treat nitrite toxicity with no ill effects to anything else in the tank.

 

[toosie]

As fish keepers we're not looking at LC50 or LC90, we're looking for LC0, we don't want any fish to die from nitrite poisoning.

What is a safe level for nitrites. Safe as in 0 deaths, and no negative effects, like lethargy, bottom sitting, gasping for air at the surface, etc.

https://www.addl.purdue.edu/newsletters/1998/spring/nitrate.shtml
Nitrites are actively transported across the gills and readily oxidize hemoglobin to form methemoglobin. Methemoglobinemia results in hypoxia severe enough to cause sudden death but often the fish will live until they exert themselves. The term "brown blood disease" comes from the appearance of the blood that has high levels of methemoglobin (which is brown).
- by Melanie Greeley, DVM

- edited by TI'm Muench,

I don't know at what level nitrites become lethal, but toxicity is linked to pH to at least some degree, just as ammonia toxicity is related to pH. Ammonia as you know, increases toxicity as pH increases, but nitrite toxicity increases as pH decreases. So ammonia is more toxic in the ammonia form, but nitrite is more toxic in the nitrous acid form. Nitrite and nitrous acid shift according to pH, just as ammonia and ammonium do.

I know none of that answers your question, but there are pH charts for ammonia toxicity, so possibly there are pH charts for nitrite toxicity? I can't say I've ever looked for one, but you seem to have great research skills, so maybe you'd like to see if you can search one out?

 

[Coptapia]

It’s very easy to keep nitrite at zero... in fact in a cycled tank properly maintained there’s no excuse for it ever being anything but zero... so why not just keep it at zero?

 

[AvalancheDave]

How do you calculate LC0? Or is it NOEC? Or NOAEL? Or NOEL?

You realize nothing is ever truly at zero. What is the minimum detection level of the API ammonia test? Nitrite?

In the context of Prime saving fish, the chances that a hobbyist correctly reported that Prime saved their fish is the inverse of the probability that their fish would have died at that nitrite level. So at, say 100 ppm nitrite, that may still be only 50%.

I don't know at what level nitrites become lethal, but toxicity is linked to pH to at least some degree, just as ammonia toxicity is related to pH. Ammonia as you know, increases toxicity as pH increases, but nitrite toxicity increases as pH decreases. So ammonia is more toxic in the ammonia form, but nitrite is more toxic in the nitrous acid form. Nitrite and nitrous acid shift according to pH, just as ammonia and ammonium do.

I know none of that answers your question, but there are pH charts for ammonia toxicity, so possibly there are pH charts for nitrite toxicity? I can't say I've ever looked for one, but you seem to have great research skills, so maybe you'd like to see if you can search one out?

Kroupova 2005:

The effect of the hydrogen ion concentration on toxicity of nitrite is still uncertain. Contributions to the literature on this subject are not frequently definitive because they fail to separate possible effects of anions from those of acidity, or they use pH ranges outside the normal adaptive range of fish (as reviewed by Lewis and Morris, 1986). The effect of pH on nitrite toxicity within the natural pH range appears to be minute.

It has been considered that some nitrite may enter fish via diffusion of HNO2, but this route seems insignificant in most cases (Jensen, 2003). Only a minute fraction of nitrite will be present as HNO2 at natural pH values (pKa for nitrous acid is ~ 3.35). This means that NO2– highly prevails over HNO2 at pH > 5, and both forms appear in a molar ratio of 1 : 1 at pH 3.35 (Pitter, 1999). Additionally, diffusion of HNO2 does not explain the well-docu- mented protective effect of environmental chloride (Jensen, 2003).

Nevermind. The Lewis and Morris 1986 paper (don't you ever read these?) that you (Skavatar) originally cited has the answer:

Westin (1974) reported the relative 96-h and 7-d toxicity of nitrite to chinook salmon (1 and 11 g). According to the trend line she established for percent mortality, the 7-d LC50 was approximately two-thirds of the 96-h LC50. In similar experiments involving rainbow trout, Russo et al. (1974) showed that the LC50 became asymptotic after 8 d at concentrations approximately 60% of the 96-h LC50. The maximum concentration of nitrite for no mortality was essentially equal at 96 h and at 8 d, and varied between 30 and 50% of the 96-h LC50. Thurston et al. (1978) found that the 10-d LC50 for cutthroat trout (3 g) was equal to or greater than 75% of the 96-h LC50; the LC50 appeared to be asymptotic after about 5 d. The LC50 for small cutthroat trout (1 g) exposed for periods as long as 36 d converged on an asymptote close to that for the shorter exposures on slightly larger fish. Although LC50s for periods longer than 96 h are unavailable for warmwater fishes, the work of Tucker and Schwedler (1983) with channel catfish demonstrated, on the basis of methemoglobin levels, a degree of acclimation over long intervals. This supports the impression from bioassays on salmonids that few changes occur in mortality after 5 to 7 d, and that resistance might begin to develop within fish after this period of time, presumably due to improvement in the efficiency of the hemoglobin reductase system.

 

[toosie]

AvalancheDave, Cool! Thanks! Not until a pH of 3.35 does it reach a 1:1 ratio. I guess that makes sense even ammonia has to reach a high pH before it reaches a 1:1 ratio (I don't remember what pH that is), but it doesn't have to reach even close to that ratio to be highly toxic. But the article does say for nitrite..."The effect of pH on nitrite toxicity within the natural pH range appears to be minute." Interesting info for sure!

However...the info below...am I blind? It doesn't state the nitrite level, only the 96hours vs more days? I assume this is info you two have been hashing through on another thread, so I am likely just missing something. Perhaps it's purely on a need to know basis. . I guess I could look up the original paper...but nah. I think I'll watch from the sidelines.

Nevermind. The Lewis and Morris 1986 paper (don't you ever read these?) that you (Skavatar) originally cited has the answer:

 

[Skavatar]

the discussion of nitrites in aquarium water is for either fish in cycles (newbies that don't know about the nitrogen cycle, like I was when I started fish keeping) or for nitrite spikes, like improperly recharging Purigen, like I did once when I started using Purigen).

AvalancheDave
so they're saying nitrite is not lethal until atleast 20ppm, and up to around 100ppm depending on the species. Therefore any fish deaths during an aquarium hobbyist's nitrite spike 4-8ppm was absolutely 100% not a result of the nitrite spike.
And then they're saying any fish who survived the initial nitrite poisoning can adapt (build resistance) to the nitrite poisoning b/c they have a hemoglobin reductase system and that any treatments hobbyists used was irrelevant such as using salt or sodium dithionite, etc.

 

[Cichlidude]

Darn! Off to the store to buy more popcorn...

 

[toosie]

Darn! Off to the store to buy more popcorn...

I just hope they can shake hands and be friends when it's all said and done. Nothing wrong with a good healthy debate, with strong views on both sides. Just hope they remember to keep the gloves on. Hmmm, what round are we on?

 

[MissRuthless]

Nevermind. The Lewis and Morris 1986 paper (don't you ever read these?) that you (Skavatar) originally cited has the answer:

It seems quite important to point out that all the fish referenced in this quote are quite large - chinook salmon are the largest species weighing up to 75 lbs, cutthroat and rainbow trout both regularly exceed 20 lbs full grown, channel cats are one of the biggest catfish species... and beyond being much bigger, they are all pretty tough fish. I wouldn’t imagine their tolerance for nitrite to be remotely comparable to tiny aquarium fish honestly.

Also worth noting that the quote speaks of a *possibility* of a “degree of acclimation over long intervals” - not only do we know that sudden changes in water chemistry tend to be more fatal than long-term subpar conditions, but the study apparently shows it by stating that mortalities lessen after days to over a week - this is much longer than any accidental nitrite spike in an established tank will last unless something is terribly wrong and no one notices, and IMO it would be very bad logic to base one’s water change schedule on during a fish-in cycle. Taking from this information the idea that 4-8ppm nitrite spikes have never killed an aquarium fish (this is an astronomical amount for a home aquarium - standard liquid tests don’t even read up to 20+ppm, API’s test stops at 5) is a severe misunderstanding of the facts stated.

 

[Skavatar]

standard liquid tests don’t even read up to 20+ppm, API’s test stops at 5) is a severe misunderstanding of the facts stated.

the way to determine higher levels of X is to dilute with tap water or bottled water that is 0,0,0.

Both my fish in cycle nitrite phase and the nitrite spike lasted 3 weeks. When the API nitrite test was dark purple 5ppm. I filled the test tube with half tank water and half tap water. The result was lighter than 5ppm, but still higher than 2ppm. I then did a 1/3 dilution, 1/3 tank water and 2/3 tap water. The test color was very close to 2ppm, just a tad darker. Since the test is so imprecise, jumping from 2ppm to 5ppm, I estimated the nitrite to be more than 6 but less than 9, and settled on 8ppm.

 

[MissRuthless]

That’s pretty smart. Not something most people would think to do, and I hate to say it but I know plenty who aren’t capable of thinking up or working out an equation like that at all - median intelligence ain’t what it used to be lol. But my point was this - the test isn’t meant for the user to need to repeatedly dilute the sample to get a proper reading. Some people who know far, far more about fishkeeping than either you or I, or maybe anyone on this forum, decided that 5ppm was a generous upper limit for the range of nitrite most customers need to detect. I personally have never heard of an aquarium with upwards of 20ppm; not to claim it’s impossible, but highly unlikely and would require severe neglect or purposeful pollution to achieve.

You seem to have ignored my entire post outside of that one sentence though...

 

[Skavatar]

I agreed with your post. just explaining how I knew I had 8ppm nitrite even though the test only tested up to 5ppm

 

[AvalancheDave]

However...the info below...am I blind? It doesn't state the nitrite level, only the 96hours vs more days? I assume this is info you two have been hashing through on another thread, so I am likely just missing something. Perhaps it's purely on a need to know basis. . I guess I could look up the original paper...but nah. I think I'll watch from the sidelines.

The question is how do you determine safe nitrite levels from 24- or 96-hr LC50 (those values are in tables in the paper). A lot of this paper is about ratios (don't blame me, Skavatar was the one who chose it) and in addressing the question it refers to papers who have done testing beyond 96-hrs.

so they're saying nitrite is not lethal until atleast 20ppm, and up to around 100ppm depending on the species. Therefore any fish deaths during an aquarium hobbyist's nitrite spike 4-8ppm was absolutely 100% not a result of the nitrite spike.
And then they're saying any fish who survived the initial nitrite poisoning can adapt (build resistance) to the nitrite poisoning b/c they have a hemoglobin reductase system and that any treatments hobbyists used was irrelevant such as using salt or sodium dithionite, etc.

Nitrite toxicity is highly dependent on chloride levels or, more specifically, the chloride:nitrite ratio. That's why one or more control groups are needed before any conclusions can be drawn. Otherwise, chloride levels would need to be known and the nitrite level would have to be far into the toxic range.

It seems quite important to point out that all the fish referenced in this quote are quite large - chinook salmon are the largest species weighing up to 75 lbs, cutthroat and rainbow trout both regularly exceed 20 lbs full grown, channel cats are one of the biggest catfish species... and beyond being much bigger, they are all pretty tough fish. I wouldn’t imagine their tolerance for nitrite to be remotely comparable to tiny aquarium fish honestly.

Did you miss the part about the salmon being 1 and 11 grams? Within the same species, smaller/younger fish appear to be more tolerant of nitrite.



Kroupova 2005

Between species, it's not the adult size of the fish that matters. Salmonids as a group are consistently sensitive whereas other taxa vary.





Kroupova 2005




Kroupova 2016




Kroupova 2016

Tropical aquarium fish are every bit as tolerant of nitrite and more compared to salmonids and channel catfish.



SerezlI 2016

This was at 10 mg/L chloride. The numbers will be even higher at the 20-22 mg/L chloride level in the Lewis paper. Remember that 6.28 mg/L nitrite-nitrogen is 20.6 mg/L nitrite.

Also worth noting that the quote speaks of a *possibility* of a “degree of acclimation over long intervals” - not only do we know that sudden changes in water chemistry tend to be more fatal than long-term subpar conditions, but the study apparently shows it by stating that mortalities lessen after days to over a week - this is much longer than any accidental nitrite spike in an established tank will last unless something is terribly wrong and no one notices, and IMO it would be very bad logic to base one’s water change schedule on during a fish-in cycle. Taking from this information the idea that 4-8ppm nitrite spikes have never killed an aquarium fish (this is an astronomical amount for a home aquarium - standard liquid tests don’t even read up to 20+ppm, API’s test stops at 5) is a severe misunderstanding of the facts stated.

Kroupova 2005






Kroupova 2016

 

[david1978]

Most of this is way beyond my pay grade.

 

[smee82]

Most of this is way beyond my pay grade.

I was just thinking I don't get paid enough to work it all out.

 

[david1978]

Darn! Off to the store to buy more popcorn...

I ran out of popcorn. Switched to tide pods.

 

[Skavatar]

looks like I forgot to link my information on one of Prime's sulfur compounds that has been shown by medical research to reverse the effects of Nitrite poisoning aka Methemoglobin aka brown blood disease, post #32
What's The Difference Between Seachem Prime And Water Conditioner? | Cleaning and Maintenance Forum | 406714

i'm going to start documenting the negative effects of nitrite by fellow Fishlore members; aka "anecdotal evidence."

even at 0 ammonia, .5ppm Nitrite, 10 nitrate, plus an air stone, her fish are gasping/breathing heavily
Help - All My Fish Are Suddenly Breathing Really Heavily

Help - .5 Nitrite After Cleaning Filter

at 0 Ammonia, .5 Nitrite, 20 Nitrate, her guppies are suddenly hanging out at the surface.

 

[aoiumi]

So, after reading this a few times, some things I think should be pointed out:

This isn't just about what level will kill fish, but what level will cause them to deviate from normal behavior. I'll admit, I didn't really understand some of the papers, but they seem to only talk of whether the fish survived - not whether it showed normal behavior. I'd also expect that they were using healthy fish.

I also saw that chloride levels can affect toxicity. I know I'm not testing for chloride, and I'd doubt many other people are either.

Now, some theories can be drawn from this.

Perhaps most fish will show abnormal behavior when exposed to even low levels of nitrites, and deaths at low levels only happen to unhealthy fish.
If this was true we would expect ill fish to be the first to succumb, particularly fish that already had problems carrying oxygen. Gill problems seems the most likely culprit in this case, but there may be other things I'm not aware of that would decrease the amount of oxygen in a fish.

Extrapolating from above, perhaps PRIME really does protect from nitrites, and therefore although healthy fish are not in danger at relatively low levels of nitrites, they stop showing abnormal behavior when PRIME is introduced. Again, the ill fish that might have died are, in fact, saved.
If this was true, we would expect fish to stop showing abnormal behavior when PRIME is introduced, and would expect ill fish to die without PRIME, and live with PRIME.

Now onto chloride. I don't know much about it, but the simple fact that there are things aquarists aren't testing for that can have an impact on nitrite toxicity adds another element, an uncontrolled variable, and while I could wax poetic all that really needs to be said is that uncontrolled variables are a pain. Unless there's a way to easily know the amount of chloride in a tank, everything about nitrites will have an air of mystery for much longer than it probably should.

 

[Momgoose56]

So, after reading this a few times, some things I think should be pointed out:

This isn't just about what level will kill fish, but what level will cause them to deviate from normal behavior. I'll admit, I didn't really understand some of the papers, but they seem to only talk of whether the fish survived - not whether it showed normal behavior. I'd also expect that they were using healthy fish.

I also saw that chloride levels can affect toxicity. I know I'm not testing for chloride, and I'd doubt many other people are either.

Now, some theories can be drawn from this.

Perhaps most fish will show abnormal behavior when exposed to even low levels of nitrites, and deaths at low levels only happen to unhealthy fish.
If this was true we would expect ill fish to be the first to succumb, particularly fish that already had problems carrying oxygen. Gill problems seems the most likely culprit in this case, but there may be other things I'm not aware of that would decrease the amount of oxygen in a fish.

Extrapolating from above, perhaps PRIME really does protect from nitrites, and therefore although healthy fish are not in danger at relatively low levels of nitrites, they stop showing abnormal behavior when PRIME is introduced. Again, the ill fish that might have died are, in fact, saved.
If this was true, we would expect fish to stop showing abnormal behavior when PRIME is introduced, and would expect ill fish to die without PRIME, and live with PRIME.

Now onto chloride. I don't know much about it, but the simple fact that there are things aquarists aren't testing for that can have an impact on nitrite toxicity adds another element, an uncontrolled variable, and while I could wax poetic all that really needs to be said is that uncontrolled variables are a pain. Unless there's a way to easily know the amount of chloride in a tank, everything about nitrites will have an air of mystery for much longer than it probably should.

One of the treatments and/or remedies for high nitrites in a tank where water changes (to reduce nitrite levels) aren't possible is the addition of plain table salt (sodium chloride-NaCl) to the tank to ameliorate symptoms.