Nitrification toxic effects

Nitrification is limited in most soils by the supply rate of NH4+ (40, 41). Competition exists between nitrifiers and vegetation, which may both be limited by the availability of NH4 +. This microbial demand for NH4 +, coupled with the high cation-exchange capacity of most temperate forest soils, leads to surface-water NH4+ concentrations that are usually undetectable. Nitrification rates may also be limited by inadequate microbial populations, lack of water, allelopathic effects (toxic effects produced by inhibitors manufactured by vegetation), or by low soil pH. 

What are the reported bad effects of nitrification The more important are (1) the greatly increased leachability of nitrites and nitrates in comparison with ammonia (2) the instability and reactivity of nitrites which may lead to volatile losses of nitrogen (3) the increase in soil acidity as a result of nitrate formation, especially where the nitrates are lost by leaching. With increase in acidity there may be toxic effects on plants produced by nitrites and aluminum and also excessive loss of mineral elements. 

Beg, S.A. et al. Effect of toxicants on biological nitrification for treatment of fertilizer industry wastewater. In Proceedings of 35th Industrial Waste Conference, Purdue University, Lafayette, BSf, 1980 Vol. 35, 826-834. 

In some cases, the effects of complex environmental mixtures could be accounted for in terms of concentration-additive effects of a few chemicals. In sediments of the German river Spittelwasser, which were contaminated by chemical industries in its vicinity, around 10 chemicals of a cocktail of several hundred compounds were found to explain the toxicity of the complex mixture to different aquatic organisms (Brack et al. 1999). The complex mixture of chemicals contained in motorway runoff proved toxic to a crustacean species (Gammarus pulex). Boxall and Maltby (1997) identified 3 polycyclic aromatic hydrocarbons (PAHs) as the cause of this toxicity. Subsequent laboratory experiments with reconstituted mixtures revealed that the toxicity of motorway runoff could indeed be traced to the combined concentration-additive effects of the 3 PAHs. Svenson et al. (2000) identified 4 fatty acids and 2 monoterpenes to be responsible for the inhibitory effects on the nitrification activity of the bacteria Nitrobacter in wastewater from a plant for drying wood-derived fuel. The toxicity of the synthetic mixture composed of 6 dominant toxicants agreed well with the toxicity of the original sample. 

On account of the high toxicity and considerable stability of phenols, these compounds lead to important problems in wastewater treatment. The biological treatment of water flows was inhibited by phenol at a concentration of 75 mg hydroquinone at a concentration of 15 mg 1 inhibited the biochemical treatment of wastewaters and the threshold concentration of the effect of 2,4-dinitrophenol on the biological treatment was found to be 20 mg 1 - m-aminophenol at a concentration of 1 mg 1 inhibited the BOD (biochemical oxygen demand) and nitrification of wastewaters. 

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