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nitrite

Definition

A compound which contains nitrogen bound to two oxygen atoms. It is the first step in the oxidation of the ammonia excreted by aquatic organisms as the endproduct of the protein metabolism. Nitrite inhibits the uptake of oxygen by haemoglobin and is thus toxic to fish. Crustaceans are affected to a lesser extent as haemocyanin is only partially inhibited. pH modulates nitrite toxicity, and the presence of monovalent ions (chlorides or bicarbonates) strongly reduces nitrite toxicity. For a given concentration, therefore, nitrite is usually more toxic in fresh water than in brackish or sea water. Nitrite is the ionic form of nitric acid which is a very weak acid. The equilibrium is pH-dependent. Low pH values and low temperatures shift the equilibrium towards nitric acid. The reaction equation may be written as HNO2 <--> H+ + NO-2.

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