producing volatile compounds with strong inhibitory effects such as carbon disulfide and thiourea. in particular, thiophosphoryl triamide has been a notable addition where it has the dual purpose of inhibiting both the production of urease and nitrification. in a study of inhibitory effects of oxidation by the bacteria nitrosomonas europaea, the use of thioethers resulted in the oxidation of these compounds to sulfoxides, where the s atom is the primary site of oxidation by amo. this is most strongly correlated to the field of competitive inhibition. examples of n-heterocyclic molecules. n-heterocyclic compounds are also highly effective nitrification inhibitors and are often classified by their ring structure. the mode of action for these compounds is not well understood: while nitrapyrin, a widely used inhibitor and substrate of amo, is a weak mechanism-based inhibitor of said enzyme, the effects of said mechanism are unable to correlate directly with the compound's ability to inhibit nitrification. it is suggested that nitrapyrin acts against the monooxygenase enzyme within the bacteria, preventing growth and ch4/nh4 oxidation. compounds containing two or three adjacent ring n atoms (pyridazine, pyrazole, indazole) tend to have a significantly higher inhibition effect than compounds containing non-adjacent n atoms or singular ring n atoms (pyridine, pyrrole). this suggests that the presence of ring n atoms is directly correlated with the inhibition effect of this class of compounds. methane oxidation inhibition some enzymatic nitrification inhibitors, such as nitrapyrin, can also inhibit the oxidation of methane in methanotrophic bacteria. amo shows similar kinetic turnover rates to methane monooxygenase (mmo) found in methanotrophs, indicating that mmo is a similar catalyst to amo for the purpose of methane oxidation. furthermore, methanotrophic bacteria share many similarities to nh3 oxidizers such as nitrosomonas. the inhibitor profile of particulate forms of mmo (pmmo) shows similarity to the profile of amo, leading to similarity in properties between mmo in methanotrophs and amo in autotrophs. environmental concerns nitrification process tank at a sewage treatment plant nitrification inhibitors are also of interest from an environmental standpoint because of the production of nitrates and nitrous oxide from the process of nitrification. nitrous oxide (n2o), although its atmospheric concentration is much lower than that of co2, has a global warming potential of about 300 times greater than carbon dioxide and contributes 6% of planetary warming due to greenhouse gases. this compound is also notable for catalyzing the breakup of ozone in the stratosphere. nitrates, a toxic compound for wildlife and livestock and a product of nitrification, are also of concern. soil, consisting of polyanionic clays and silicates, generally has a net anionic charge. consequently, ammonium (nh4+) binds tightly to the soil but nitrate ions (no3−) do not. because nitrate is more mobile, it leaches into groundwater supplies through agricultural runoff. nitrates in groundwater can affect surface water concentrations, either through direct groundwater-surface water interactions (e.g., gaining stream reaches, springs), or from when it is extracted for surface use. as an example, much of the drinking water in the united states comes from groundwater, but most wastewater treatment plants discharge to surface water. wildlife such as amphibians, freshwater fish, and insects are sensitive to nitrate levels, and have been known to cause death and developmental anomalies in affected species. nitrate levels also contribute to eutrophication, a process in which large algal blooms reduce oxygen levels in bodies of water and lead to death in oxygen-consuming creatures due to anoxia. nitrification is also thought to contribute to the formation of photochemical smog, ground level ozone, acid rain, changes in species diversity, and other undesirable processes. in addition, nitrification inhibitors have also been shown to suppress the oxidation of methane (ch4), a potent greenhouse gas, to co2. both nitrapyrin and acetylene are shown to be especially strong suppressors of both processes, although the modes of action distinguishing them are unclear.