Author
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Follett, Jennifer |
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Follett, Ronald |
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Submitted to: Elsevier
Publication Type: Book / Chapter Publication Acceptance Date: 10/10/2007 Publication Date: 7/14/2008 Citation: Follett, J.R., Follett, R.F. 2008. Relationship of environmental nitrogen metabolism to human health. Chapter 4. pp 71-104, J.L. Hatfield and R.F. Follett (eds). Nitrogen in the Environment; Sources, Problems, and Management. 2nd editiion. Elsevier Sci Pubs. Interpretive Summary: The need by humans to produce and consume food and other agricultural products is increasing. This need is directly related to increasing World populations, demands for goods and services, and expectations. Proteins are an essential component of the human diet because, unlike plants, humans are unable to utilize more simple forms of N and rely on food sources for protein. Although humans may not be able to utilize simpler forms of N for normal physiological functions such as energy and synthesis of proteins, they are exposed to and capable of absorbing other forms of N such as nitrate (NO3-) and nitrite (NO2-) and even N-Nitroso Compounds (NOC). These compounds can have serious health effects on humans. In addition to the effect of N-containing compounds on humans it is important to consider the impact of humans to N loading into the environment. We estimate the total intake and loss of N by humans in the US to be in the range of 0.8-1.0 million MT/year indicating that N excretion by humans has a large potential to impact the environment. Such impacts on the environment by N from humans are just as important to consider as those from livestock wastes, inefficient fertilizer-N use, or from other N sources. It is especially important to recognize the potentially serious environmental effects that may occur as the human population continues to grow. Technical Abstract: The need by humans to produce and consume food and other agricultural products is increasing. This need is directly related to increasing World populations, demands for goods and services, and expectations. Nitrogen (N) is contained in all of the amino acids and proteins in the foods consumed by humans. The use of N to produce food and other products is generally increasing as human needs increase. Proteins are an essential component of the human diet because, unlike plants, humans are unable to utilize more simple forms of N and rely on food sources for protein which can then be digested to amino acids and used for protein synthesis in the body. Estimation of protein requirements for humans depends both on the content of essential amino acids and digestibility of the protein. Although humans may not be able to utilize simpler forms of N for normal physiological functions such as energy and synthesis of proteins, they are exposed to and capable of absorbing other forms of N such as nitrate (NO3-) and nitrite(NO2-) and even N-Nitroso Compounds (NOC). Nitrate can be obtained from plant sources as well as from contaminated drinking water and is easily absorbed by the intestine. Nitrate itself is not generally considered as a health risk but may become a concern due to its conversion to NO2-. The main health risk associated with NO3- consumption is methemoglobinemia due to the conversion of NO3- to NO2-, which in turn can interact with hemoglobin leading to formation of methemoglobin, leading to oxygen deprivation of the cells. Secondary and related deleterious effects of exposure to NO3- include increased respiratory infections, inhibition of iodine uptake by the thyroid, and possible reproductive problems. Although concerns about NO3- and NO2- have been focused mainly on harmful effects there is growing acceptance for the beneficial effects of the related compound nitric oxide (NO). Nitric oxide is a free radical gas that acts as a messenger molecule for regulation of several systems including blood vessel dilation, hormonal and neurotransmission functions. Nitrosamines and nitrosamindes are in the group of N-containing substances identified as NOC substances. These compounds are important to consider in the human diet since they are capable of participating in DNA alkylation and appear to be among the most potent and broad acting carcinogens known. In addition to the effect of N-containing compounds on humans it is important to consider the impact of humans to N loading into the environment. We estimate the total intake and loss of N by humans in the US to be in the range of 0.8-1.0 million MT/year indicating that N excretion by humans has a large potential to impact the environment. Such impacts on the environment by N from humans are just as important to consider as those from livestock wastes, inefficient fertilizer-N use, or from other N sources. It is especially important to recognize the potentially serious environmental effects that may occur as the human population continues to grow. |
