Potential risks of the nitrification inhibitors Nitrapyrin and DMPP: A review on non-target effects on microorganisms and environmental fate in agricultural soil

Reducing nitrous oxide (N2O) emissions from agricultural fields is central for achieving the EU target to reduce greenhouse gas (GHG) emissions by at least 55 % before 2030. A major source of anthropogenic N2O is microbial nitrification to nitrate (NO3-) of excess ammonium (NH4+) from fertilizer applications. Chemical nitrification inhibitors (NIs), such as nitrapyrin and DMPP, present a promising approach to curb N2O emissions and NO3- leaching. Despite growing knowledge of effects of NIs on nitrifying microorganisms, their environmental fate including leaching to groundwater and non-target impacts on microbial diversity and soil ecological functions remain unclear. This review compiles research on the mode of action, non-target effects, and environmental fate of nitrapyrin and DMPP. The exact inhibitory mechanism is not fully resolved, though Cu2+ chelation is a likely the primary mode of action. Early evidence also suggested potential impacts on methane (CH4) oxidation. Nitrapyrin is considered to have low leachability and degrades rapidly in soils low in organic matter, however, it is found in freshwater suggesting it can be transported through other environments. DMPP, with its higher water solubility, may pose an even greater risk of leaching, yet its environmental fate remains poorly understood. To avoid environmental consequences from large-scale NI use, further research is needed on their persistence, transport, and specificity. State-of-art omics techniques—such as total RNA analysis—should be applied to detect non-target effects and provide comprehensive environmental risk assessments.