Editorial Feature

Optical Methods for Detecting Nitrogen in Water

Nitrogen is a vital element for plant and animal growth. An overabundance of the substance, however, is linked with adverse effects on the health of humans, animals, and our ecosystems.

nitrogen, water

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Excess nitrate can enter our water systems as a direct result of fertilizer use. Additionally, some nitrate enters the water from the atmosphere where it accumulates after being deposited by cars and other sources. In the US alone, 3 million tons of nitrogen enter the water from the atmosphere each year.

Scientific research has focused on understanding how exposure to too much nitrogen can impact the health of babies. As a result, we understand that excessive exposure to the substance can alter how the blood carries oxygen, which can lead to methemoglobinemia (blue baby syndrome) a serious illness that can result in death.

The effects of drinking water high in nitrates have been less extensively studied in adults, however, a growing body of research is revealing potential links between nitrate exposure and symptoms such as abdominal cramps, increased heart rate, headaches, and nausea. It has also been suggested that those who consume water high in nitrates may be at an increased risk of cancer, particularly gastric cancer.

Therefore, it is important to establish effective and efficient methods to detect nitrogen within water. Here, we discuss current methods of nitrogen detection, including newer optical methods, and give an overview of how the technology may develop in the future.

Current Technology and Recent Developments

Numerous detection methods have been established to measure levels of nitrogen in water sources. Many spectrophotometric methods and ion-selective electrode methods have been developed as well as colorimetry, potentiometry, spectrophotometry, spectrofluorimetry, chromatography.

Additionally, sensors are being developed for situ passive monitoring of soil nitrogen to monitor and manage a major source of water nitrogen.

More recently, developments have been made in optical detection, electrochemical detection, and biological enzyme detection systems for nitrogen in water.

In terms of optical detection, the development of an ultraviolet optical fiber sensor has been particularly groundbreaking in this field. In 2015, a team based in Malaysia successfully created a novel ultraviolet optical fiber sensor able to determine levels of nitrate and nitrite in water samples. 

The process leveraged the unique absorptivity spectra of nitrate and nitrite. The team showed that the absorbance of light at these specific wavelengths had a linear relationship with the concentration of nitrate and nitrite in the water samples. The method was proven to be effective and unhampered by the presence of other chemical species in the water. This technology is now being further developed for widespread adoption as we discuss below.

Future Directions of Nitrogen Detection

A paper published in 2021 explores a novel optical method of detecting nitrogen in water. The study, published in the journal Sensors, proposed a method based on identifying the spectral fingerprint of water sources to determine the content of nitrogen.

When water contains high levels of nitrogen, it causes the release of ammonia from monochloramine, which is then converted into nitrite and nitrate via oxidation. As the process occurs, the spectral fingerprint of the water changes. Therefore, the team of scientists working in Australia established a method of assessing water nitrification status by isolating the nitrate and nitrite absorbance fingerprints from the total spectra.

Following this, a machine learning model was developed to link the spectral features of pure nitrate and nitrite with specific concentrations. Data collected from the study proved that the novel method could reliably detect and quantify nitrate and nitrite levels in water, however, further development is needed before the technique can be widely implemented.

It is possible that in several years, optical methods of detecting nitrogen in water will be implemented across the globe to monitor nitrogen levels in various water sources. They might be used to ensure that concentrations of nitrogen are kept to safe levels in drinking water. These methods may also be adapted to test the water in natural settings to protect the environment from dangerous levels of nitrogen that have been proven to harm ecosystems.

Future directions of optical nitrogen detection systems will also focus on the development of portable sensors to promote the widespread adoption and versatility of nitrogen monitoring systems. Ultraviolet fiber sensors are being developed into portable systems that can fit into smartphones.

In a paper published in 2021, scientists based in South Africa explain how they developed a smartphone-based nitrate sensor that can accurately measure the concentration of nitrates in water samples. Their tests demonstrated that the UV spectrum absorbance analysis was successfully performed through their platform of a smartphone combined with a scintillator. They showed that the results obtained via their smartphone technology were comparable to those obtained in laboratory experiments.

The novel technology is a low-cost and portable device that offers high measurement accuracy and sensitivity. It is likely that will begin to see the benefits of widespread adoption of such technology in the coming years.

References and Further Reading

Hossain, S., Cook, D., Chow, C. and Hewa, G., 2021. Development of an Optical Method to Monitor Nitrification in Drinking Water. Sensors, 21(22), p.7525. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8618176/

Ingles, J., Louw, T. and Booysen, M., 2021. Water quality assessment using a portable UV optical absorbance nitrate sensor with a scintillator and smartphone camera. Water SA https://www.researchgate.net/publication/348341738_Water_quality_assessment_using_a_portable_UV_optical_absorbance_nitrate_sensor_with_a_scintillator_and_smartphone_camera

Li, D., Xu, X., Li, Z., Wang, T. and Wang, C., 2020. Detection methods of ammonia nitrogen in water: A review. TrAC Trends in Analytical Chemistry, 127, p.115890. https://www.sciencedirect.com/science/article/abs/pii/S0165993620301199

Moo, Y., Matjafri, M., Lim, H. and Tan, C., 2016. New development of optical fibre sensor for determination of nitrate and nitrite in water. Optik, 127(3), pp.1312-1319. https://www.sciencedirect.com/science/article/abs/pii/S0030402615011286

Ward, M., Jones, R., Brender, J., de Kok, T., Weyer, P., Nolan, B., Villanueva, C. and van Breda, S., 2018. Drinking Water Nitrate and Human Health: An Updated Review. International Journal of Environmental Research and Public Health, 15(7), p.1557. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6068531/

 

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Sarah Moore

Written by

Sarah Moore

After studying Psychology and then Neuroscience, Sarah quickly found her enjoyment for researching and writing research papers; turning to a passion to connect ideas with people through writing.

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