Nitrification and urease inhibitors (NUIs) in soil and water: Environmental fate, distribution, and risk assessment

Nitrogen (N) fertilisers play a key role in food security by providing essential nutrients that enhance crop growth. However, excessive applications of N fertilisers can lead to N loss from the soil, resulting in potential air and water pollution. Nitrification inhibitors (NIs) and urease inhibitors (UIs) are chemical compounds with the potential to reduce ammonia loss, nitrous oxide emissions and nitrate leaching while improving N use efficiency. However, questions relating to potential risks to the environment and food chain have been raised. Therefore, it is crucial to understand the environmental fate and distribution of nitrification and urease inhibitors (NUIs) to help protect the long-term ecological balance and assess potential concerns regarding human health. This review examined the availability of NUIs in the European market and related government strategies, further highlighting the potential rise in demand for NUIs and their subsequent potential release into the environment. For NBPT, a relatively short half-life of up to 5 days has been observed. On the other hand, NIs like DCD exhibited significantly varied half-lives from days to months, primarily affected by multiple soil characteristics (e.g., temperature), thus highlighting the myriad of risk factors at play. This review details existing knowledge on potential degradation, leaching, and runoff of NUIs in soil to assist risk assessors and policymakers, helping identify potential exposure pathways and supporting the estimates of environmental concentrations for environmental and human receptors.