Ecological risk evaluation of ammonia nitrogen pollution in China based on the ecological grey water footprint model

The biosafety criteria of ammonia nitrogen (NH₃-N) exhibit uncertainties, posing challenges to the assessment of the hazard of social NH₃-N load to aquatic ecosystem. To evaluate this ecological hazard in China, an ecological grey water footprint (E-GWF) model is designed based on the uncertainty analysis theory. In the E-GWF model, the acute toxicity is quantified via short-term E-GWF (E-GWF_s) and acute risk (AR), while its chronic toxicity is quantified via long-term E-GWF (E-GWF_l) and chronic risk (CR). Results show the following. (i) Compared with the conventional GWF, the E-GWF performs better in the uncertainty analysis of the biosafety threshold, and it is more effective in ecological risk evaluation and environment planning. (ii) The E-GWF_s and E-GWF_l of NH₃-N in China are 309.4 and 2382.5 billion m³, respectively. Regions with large E-GWF are concentrated in the east and south, while regions with small E-GWF are concentrated in the north and west. (iii) The ecological risks of NH₃-N in Shanghai City, Tianjin City, Ningxia Province, Hebei Province, Jiangsu Province, Shanxi Province, and Shandong Province belong to the "High" grade. The ecological risks of NH₃-N in Tibet and Qinghai Province belong to the "Negligible" grade. (iv) The ecological risk of NH₃-N in China is mostly determined by industrial and domestic pollution. (v) To control the risk within allowable grades, the social NH₃-N pollution load of China should be decreased to 988.7 kilotons.