[Rikko]

Nitrite disrupts multiple physiological functions in aquatic animals. Jensen Frank B Institute of Biology, University of Southern Denmark, Campusvej 55, DK-5230 M Odense, Denmark. fbj@biology.sdu.uk Comparative biochemistry and physiology. Part A, Molecular & integrative physiology (2003 May), 135(1), 9-24.

Abstract

Nitrite is a potential problem in aquatic environments. Freshwater fish actively take up nitrite across the gills, leading to high internal concentrations. Seawater fish are less susceptible but do take up nitrite across intestine and gills. Nitrite has multiple physiological effects. Its uptake is at the expense of chloride, leading to chloride depletion. Nitrite also activates efflux of potassium from skeletal muscle and erythrocytes, disturbing intracellular and extracellular K(+) levels. Nitrite transfer across the erythrocytic membrane leads to oxidation of haemoglobin to methaemoglobin (metHb), compromising blood O(2) transport. Other haem proteins are also oxidised. Hyperventilation is observed, and eventually tissue O(2) shortage becomes reflected in elevated lactate concentrations. Heart rate increases rapidly, before any significant elevations in metHb or extracellular potassium occur. This suggests nitrite-induced vasodilation (possibly via nitric oxide generated from nitrite) that is countered by increased cardiac pumping to re-establish blood pressure. Nitrite can form and/or mimic nitric oxide and thereby interfere with processes regulated by this local hormone. Steroid hormone synthesis may be inhibited, while changes in ammonia and urea levels and excretion rates reflect an influence of nitrite on nitrogen metabolism. Detoxification of nitrite occurs via endogenous oxidation to nitrate, and elimination of nitrite takes place both via gills and urine. The susceptibility to nitrite varies between species and in some cases also within species. Rainbow trout fall into two groups with regard to susceptibility and physiological response. These two groups are not related to sex but show significant different nitrite uptake rates.

from http://www.reefcentral.com/forums/sh...hreadid=384359

There we go. They did one experiment and finally killed a shrimp at 109ppm nitrite. 19 ppm for chinook salmon fry. In the nastiest FW tank I've ever had the joy of water testing, I've never seen it exceed 4ppm. I'm sure it's possible, but unlikely to happen.

Another long-winded thread by Randy: http://reefcentral.com/forums/showth...=nitrite+toxic

Originally Posted by Randy Holmes-Farley

Consequently, there seems little new evidence that nitrite is especially toxic. Without pronouncing anything dramatic, I probably would not worry about it in your tank, especially since it may just be a testing error.