Human urea production, an ignored factor in the nitrogen debate.

Abstract

A public debate idealing with nitrogen (N) emissions is ongoing. Government reports use models in which the major N producers are agriculture and industry. Flemish NOx emission amounted to 26.4 kt N accompanied by an ammonia emission of 34.0 kt N. Major sources of Flemish N emission are agriculture (59% of total emission) and transport (21%); 95 percent of the ammonia emission is reported to come from agriculture. In this government's view, it looks like Flanders is unpopulated. In Flanders, 6,800,000 inhabitants show an average urea production of 20 g/day, or 3.65 kg N/year. This urea production eventually ends up in wastewaters as ammonia. Human urea production represents the grand total of 24.8 kl N/year. However, this contribution is made invisible in the statistics. Flemish reports mention a grand total of 33 kt/year, so Flemish numbers appear to be incomplete. Human production has not been taken into account. When calculating human N excretion in Flanders, 24.8 kt N/12.322 km2 is obtained, corresponding to an additional N load of ± 20 kg/ha. Implementing human N excretion into the calculation thoroughly changes the situation: adding human N production results in peak loads of 40 kg N/ha. The human nitrogen input is comparable with the heavily criticized contribution by agriculture. Policy should take into account the real size of the problem and not selectively focus on partial problems.