Health and Environment

Nitrogen fertilizer not taken up by crops, or excess nitrogen excreted by livestock, can come with substantial costs to the environment and human health. Unlike the inert nitrogen gas (N2) abundant in our atmosphere, the nitrogen applied as synthetic fertilizer or excreted in manure and urine is biologically reactive (reactive nitrogen). This reactive nitrogen is transformed by microbes and moves easily through the soil, air or water. As it travels through these pathways it can lead to the contamination of water and air resources and negatively affect ecosystem and human health.

The California Nitrogen Assessment aims to evaluate the science on impacts of reactive nitrogen to California environments and the health of Californians. An important aspect of this evaluation is to analyze the uncertainty around some oft-cited claims of negative environmental and health impacts caused by reactive nitrogen.

Reactive Nitrogen & Water Pollution

Ground Water & Health

Nitrate, a reactive form of N, is the dominant form of nitrogen pollution in surface and groundwater.  Many communities rely on groundwater for drinking water, and the frequency of nitrate contamination in public drinking water supply wells is a significant human health concern.  Consuming water with high levels of nitrates may lead to significant health issues, including methemoglobinemia (also called blue-baby syndrome), certain types of cancer, and other chronic health issues caused by repeated ingestion of water with high levels of nitrates. The assessment will review the current state of knowledge on the health effects of nitrates in drinking water.

Surface Water & Environment

Surface water contamination with nitrate contamination does not generally occur in areas which supply drinking water.  However, surface water nitrogen pollution can have significant environmental consequences for aquatic and estuarine ecosystems such harmful algal blooms and “dead zones.” In California, the effects of surface water contamination are not as large as they are in other areas such as the Gulf of Mexico and the Chesapeake Bay. The assessment will seek to quantify the impact of nitrate runoff into surface water.

Reactive Nitrogen & Air Pollution

The production of gaseous forms (ammonia, nitrogen oxides, and nitrous oxide) of reactive N results in several human health and environmental concerns. 

Nitrogen Gases and Human Health

Ammonia (NH3) and nitrogen oxides (NOx) are both associated with particulate formation (PM 2.5) in the atmosphere. Animal agriculture is the largest source of ammonia to the atmosphere in California. Fossil fuel combustion is the major source of nitrogen oxides, and agricultural soils are a minor source. Nitrogen oxides also contribute to the formation of ground level ozone. Both PM 2.5 and ozone are associated with respiratory illness.

Environmental Impacts

The reactive nitrogen gases of ammonia (NH3) and nitrogen oxides (NOx) that are emitted to the atmosphere by human activity can be redeposited on nearby ecosystems with deleterious effects.The invasion of non-native species, loss of biodiversity, changes in fire regime, and surface water contamination have all been associated with atmospheric nitrogen deposition. (Weiss 2006, Fenn et al. 2003)

Nitrous oxide, (N2O), is associated with two other environmental problems.  First, nitrous oxide is a potent greenhouse gas, 300 times more potent than carbon dioxide.  Secondly, nitrous oxide is projected to become the dominant stratospheric ozone depleting gas with the elimination of CFCs. While there are several sources, agriculture accounts for roughly 70 percent of the total nitrous oxide emissions in California.