What do fertilisers and gunpowder have in common?

During the summer holiday, my family and I visited a large cave in the Malaysia. The cave was a famous tourist attraction as there were thousands of bats living in the cave. As we walked along the elevated walkway in the cave, the guide began to talk about the history of the cave. He said that in the past, people used to collect guano in the cave. As he said that, the guide shined his flashlight on the cave floor, and I realised that I could not see it at all, as it was covered in a thick layer of bat feces. The guide then explained that people collected guano for fertiliser and even used it to make fireworks. After he said that, I thought why would people want to go all the way to a cave just to collect bat droppings for fertiliser, and how can bat droppings be used to make fireworks. When I returned to Shanghai, I decided to do some research to find out what chemical properties of guano made it such a valuable fertiliser and how could it be used to make fireworks.

Based on my research, I found that the reason why guano could be both a fertiliser and a component in explosive is because of the rich amounts of various nitrates (NO3)in it. Nitrates are polyatomic ions that have a trigonal planar structure, with the nitrogen atom as the central atom.
As mentioned earlier, guano was valued as an extremely efficient fertiliser because of the high amounts of nitrates in it. (Wikipedia). Nitrates contain nitrogen, which is an extremely important element for not only plant life but also other organisms as well because it is the main component of amino acids and nucleic acids, which is used to make DNA and other essential proteins. However, the element nitrogen itself cannot be broken down and used by plants as nitrogen molecules are held together by extremely strong triple bonds. Therefore, nitrogen has to be reduced into various nitrates. This is why nitrates have a negative charge to indicate a gain of electrons. Plants get these nitrates naturally from the soil. By adding fertilisers such as guano, the nitrate concentration of the soil increases, therefore increasing plant growth. These nitrates include potassium nitrate  KNO3   , sodium nitrate NaNO3 and others. However, though guano used to be mined and collected in the past, today these nitrates are produced synthetically. For example, potassium nitrate is produced when sodium nitrate and potassium chloride are reacted together in a decomposition reaction.

NaNO3 (aq) + KCl (aq) → NaCl (aq) + KNO3 (aq)

Sodium nitrate is produced in a acid-base reaction with nitric acid and soda ash

2 HNO3 + Na2CO3 → 2 NaNO3 + H2O + CO2

However, while fertilisers containing nitrates greatly promote agricultural growth, the excessive use of them has a negative impact on the environment. When the excess fertilsers get washed away into freshwater lakes and rivers, eutrophication occurs, in which there is an excessive growth of algae. The algae deplete the surrounding waters of oxygen, killing the marine life in it (Schindler, David, Vallentyne, Joh R, 2004).

As to the reason why guano is used to make fireworks, the answer is because nitrates are powerful oxidisers (Earl, 1978). Oxidisers are essential in explosives as it provides the oxygen needed to fuel the explosion (Earl, 1978). This is because as mentioned earlier nitrates are reduced fro nitrogen. As we have recently learnt, oxidizing agents are often the ones that had been reduced. Nitrates are often used as oxidisers because of the energy released from the triple bonds of nitrogen.

From my research on guano I realised how chemistry can be used to benefit and harm society. Using chemistry to isolate and mass produce nitrates in synthetic fertilsers from guano boosts agricultural production. However, these fertisers pollute the environment. Understanding the chemical properties of nitrates lead to the development of powerful explosives that can be used for peaceful purposes such as mining or harmful purposes such as terrorism. In conclusion, knowledge in chemistry can be used to benefit our lives and also identify potential threats.

Reference

Earl, Brian (1978), Cornish Explosives, Cornwall: The Trevithick Society

Schindler, David and Vallentyne, John R. (2004) Over fertilization of the World’s Freshwaters and Estuaries, University of Alberta Press

http://en.wikipedia.org/wiki/Guano

One thought on “What do fertilisers and gunpowder have in common?

  1. Upon reading Nick’s post, I was particularly attentive to the chemical equations involving sodium and potassium nitrate. I then immediately remembered from our Food Chemistry unit in class, that both of these substances are not only used in fertilizers and gunpowder, but also as food preservatives! Nick’s post really got me thinking about the versatility of chemical substances and their unexpected prevalence in our daily lives. So, I set out to investigate sodium and potassium nitrate and nitrite, and their food-preserving properties. Preliminary research exposed me to the heavy controversy over the danger of nitrates and nitrites, and from there I was able to formulate my research question: What are the effects of consuming nitrates and nitrites as preservatives in food, and to what extent are these two substances dangerous to our health?

    My first source of information, was naturally the IB Chemistry Options textbook I had on hand. Reading the table of information about food preservatives, it stated that the function of nitrates and nitrites as food additives was to “stabilize flavor, give color to meat, prevent rancidity, protect against botulism pathogens.” Sodium and potassium nitrate and nitrite are particularly useful for curing meats such as “salami, hot dogs, pepperoni salami, bologna, bacon, and SPAM” (Derry et al., 2009). At this point, what really bothered me was that the textbook consistently presented nitrates and nitrites together and did not distinguish between them – so I turned to the Internet and tried to find out what the difference between the two was.

    Nitrates (NO3-), when consumed, are reduced to nitrites (NO2-) by bacteria present in the mouth and digestive system (Butler & Feelisch, 2008). Typically, when oxygen is abundant, bacterial microorganisms use oxygen in aerobic respiration as their terminal electron acceptor; however, when nitrates are more abundant in the gut than oxygen, these microbes instead use nitrate as their electron acceptor in place of oxygen, reducing nitrate into nitrite. The following equation illustrates this reduction taking place:

    NO3- + 2e- + 2H+ –> NO2- + H2O

    (Paustian, 2000)

    This presence of nitrites (NO2-) seems to be the main source of controversy regarding the dangerous nature of these two substances. Surprisingly, processed meats are not the only source of this compound; a typical person consumes 80% of his or her nitrite from vegetables such as spinach, lettuce, and broccoli, and 13% from “swallowed saliva” (Yoquinto, 2011). It seems that nitrites are an integral part of our body’s fuel and our metabolic processes – what made them so worrisome among consumers and health policymakers? My understanding of nitrites was becoming increasingly perplexing.

    According to a journal published for the American Society for Nutrition, dietary nitrites in food are produced endogenously by the body upon consumption of nitrates and are “associated with an increased risk of gastrointestinal cancer, and in infants, methemoglobinemia” (Hord et al., 2009). From here, my research developed a new focus, and I began to look at the relationship between nitrites and the two concerns: methemoglobinemia and cancer.

    First, methemoglobinemia is colloquially known as “blue baby syndrome,” and is a condition that occurs when the converted nitrite reacts with the iron in hemoglobin to produce methemoglobin. Unlike hemoglobin, methemoglobin does not facilitate the transport of oxygen to body tissue, preventing the proper functioning of our body’s organs (Ohio Department of Health, 2006). A condition most commonly found in infants, methemoglobinemia can lead to cyanosis (turning a blue color) due to the lack of oxygen in the blood. Other sources confirmed the hypothesis that nitrites contributed to methemoglobinemia – an article from Medscape stated that “organic and inorganic nitrates and nitrites are common causes” of acquired methemoglobinemia (Denshaw-Burke, 2013). Even a study conducted in the 1950s found that infants who consumed well water contaminated with nitrates led to the development of methemoglobin (Powlson et al., 2008).

    However, reading on in the same journal article, I found that this study had numerous limitations. In another experiment isolating nitrates as the factor causing methemoglobinemia in babies, researchers found that the condition was caused by an intestinal infection that resulted from “fecal bacteria” rather than high levels of nitrites in their food and water (Powlson et al., 2008). Furthermore, toxicologists have noted that while “several cases of methemoglobinemia have been reported in infants in the US using water containing nitrate at levels higher than the current maximum contaminant level (MCL) of 45 ppm (mg/liter) nitrate,” a “definite conclusion on the cause and effect relationship cannot be drawn” (Fan & Steinberg, 1996). Like most of the debated issues of the scientific arena, the controversy can be attributed to the uncertainty of the experiments testing nitrates’ effect on methemoglobinemia. I was limited by my inability to access Powlson et al.’s full study, and therefore could not find specific explanations proposed by the study that refuted the role of nitrates as a cause of methemoglobinemia. Searching further, however, I found another study that claims that “nitrate alone does not cause methemoglobinemia,” on the grounds that the few studies exposing children and adult subjects to high nitrate and nitrite levels did not produce the disease (Cornblath & Hartmann, 1948, as cited in Hord et al., 2009). So, it seemed to me that other factors, such as the “fecal bacteria” in the digestive tract, could be an additional cause of the condition.

    The second concern about nitrate toxicity is its ability to contribute to gastrointestinal cancer. This linkage was mainly magnified by the discovery that consumed nitrites have the ability to “react with secondary amines or N-alkylamides to generate carcinogenic N-nitroso compounds (NOCs)” (Mensinga et al., 2003, as cited in Hord et al., 2009). These NOCs have been shown to be carcinogenic in animal studies, but their cancer-causing properties in humans have yet to be confirmed (Hord et al., 2009). In addition, antioxidants such as sodium ascorbate (vitamin C) can “inhibit” the reaction between secondary amines and nitrites that produce such NOCs, which is why bacon and other cured meats are accompanied by these antioxidants during preservation (Rao et al., 1982, as cited in Hord et al., 2009). Here, I was able to refer to my understanding of natural sources of antioxidants in vegetables to address my previous confusion about the abundant existence of nitrates in our diet. Despite their high nitrate concentration, these green leafy vegetables contain high levels of antioxidants that prevent the development of carcinogenic compounds, counteracting the potential cancerous effect of NOCs. This information fit with what I knew about antioxidants, and cleared up a lot about the innocuous presence of nitrites in vegetables.

    Moreover, scientists have uncovered that inorganic nitrite and nitrate could even have therapeutic properties, citing their potential for aiding in vasodilation (decreasing blood pressure), interacting with blood and tissues, and preventing against ischemia injuries (Butler & Feelisch, 2008).

    Looking back at my investigation, I took a step back from the science and, naturally, could not help considering the ToK side of this debate and the major implications. To me, perceptional bias and linguistics seemed to serve as a barrier to society’s objective interpretation of scientific information. I say this because I myself am guilty of it – when I know that sodium nitrate is used as a “preservative” or “food additive,” my immediate reaction is, “hmmmm, I should avoid that” even when it may in reality be rather harmless and only toxic at extreme levels. Linguistically, and especially in relation to food ingredients, chemical terminology just does not seem to click with consumers. Of course, there are obvious exceptions to this, such as when manufacturers use scientific facts to praise a product as part of their commercial endeavors. But from personal experience, I know that any knowledge of incomprehensible scientific names on the bottom of an ingredients list is a big disincentive for health-conscious people. Evaluating the finding that nitrites cause cancer, I realized that simply the words “carcinogenic” and “cancer” were enough to scare people from ever consuming ham or lunch meat again, even though the formation of cancer-causing nitrosamines has been shown only to occur under certain conditions and in certain people. Or, remembering that I always saw “nitrates and nitrites” presented together whenever their toxicity was discussed, even though only one of them was the true culprit for potential danger, showed me the need for scientific literacy and motivated me to not simply accept whatever information was handed to me.

    So it seems that language and expectancy bias has prevented me from seeing a full picture – but when I was able to overcome this underlying obstacle I found myself more knowledgable and tolerant of the various scientific perspectives regarding nitrites. After all, I can’t deny that both sides of the argument have contributed significantly to the drive for further and more comprehensive research for the wellbeing and safety of consumers like me.

    Sources:

    Derry, L., Clark, F., Ellis, J., Jeffery, F., Jordan, C., Ellett, B., & O’Shea, P. (2009). Chemistry for use with the IB diploma programme: Options. Port Melbourne, Victoria: Pearson Education Australia.

    Butler, A. R., Feelisch, M. (2008). Therapeutic uses of inorganic nitrite and nitrate. Circulation, doi: 10.1161/​CIRCULATIONAHA.107.753814

    Paustian, T. (2000, July 5). Anaerobic respiration. Retrieved from http://dwb.unl.edu/Teacher/NSF/C11/C11Links/www.bact.wisc.edu/microtextbook/metabolism/RespAnaer.html

    Hord, N. G., Tang, Y., & Bryan, N. S. (2009). Food sources of nitrates and nitrites: The physiologic context for potential health benefits. The American Journal of Clinical Nutrition, 90(1), 1-10. doi: 10.3945/​ajcn.2008.27131

    Yoquinto, L. (2011, December 30). The truth about nitrites in lunch meat. Retrieved from http://www.livescience.com/36057-truth-nitrites-lunch-meat-preservatives.html

    Ohio Department of Health, Bureau of Environmental Health. (2006). Nitrates and nitrites nitrates: Answers to frequently asked health questions. Retrieved from website: http://www.odh.ohio.gov/~/media/ODH/ASSETS/Files/eh/water/factsheet/nitrates.ashx

    Denshaw-Burke, M. et al. (2013, June 3). Methemoglobinemia. Retrieved from http://emedicine.medscape.com/article/204178-overview

    Powlson, D. S., et al. (2008). When does nitrate become a risk for humans?. Journal f Environmental Quality, 37(2), 291-295. doi: 10.2134/jeq2007.0177

    Fan, A. M., & Steinberg, V. E. (1996). Health implications of nitrate and nitrite in drinking water: an update on methemoglobinemia occurrence and reproductive and developmental toxicity. Regulatory Toxicology and Pharmacology: RTP, 23(1), 35-43. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/8628918

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