Nitrate Toxicity

<h2 >Toxicity</h2>

<h3 >Toxicosis</h3>

<p ><b>Nitrate toxicosis</b> can occur through <a href="http://en.wikipedia.org/w/index.php?title=Enterohepatic_metabolism&action=edit&redlink=1" class="new" title="Enterohepatic metabolism (page does not exist)" >enterohepatic metabolism</a> of nitrate to nitrite being an intermediate.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-3" >[4]</a></sup> Nitrites <a href="http://en.wikipedia.org/wiki/Oxidize" title="Oxidize" class="mw-redirect" >oxidize</a> the <a href="http://en.wikipedia.org/wiki/Iron" title="Iron" >iron</a> atoms in <a href="http://en.wikipedia.org/wiki/Hemoglobin" title="Hemoglobin" >hemoglobin</a> from <a href="http://en.wikipedia.org/wiki/Ferrous" title="Ferrous" >ferrous</a> iron (2+) to<a href="http://en.wikipedia.org/wiki/Ferric" title="Ferric" >ferric</a> iron (3+), rendering it unable to carry oxygen.<sup id="cite_ref-Kim-shapiro2005_4-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-Kim-shapiro2005-4" >[5]</a></sup> This process can lead to generalized <a href="http://en.wikipedia.org/wiki/Hypoxia_(medical)" title="Hypoxia (medical)" >lack of oxygen</a> in organ tissue and a dangerous condition called <a href="http://en.wikipedia.org/wiki/Methemoglobinemia" title="Methemoglobinemia" >methemoglobinemia</a>. Although nitrite converts to <a href="http://en.wikipedia.org/wiki/Ammonia" title="Ammonia" >ammonia</a>, if there is more nitrite than can be converted, the animal slowly suffers from a lack of oxygen.<sup id="cite_ref-5" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-5" >[6]</a></sup>

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<h3 >Human health effects</h3>

<p >Humans are subject to nitrate toxicity, with <a href="http://en.wikipedia.org/wiki/Infant" title="Infant" >infants</a> being especially vulnerable to methemoglobinemia due to nitrate metabolizing <a href="http://en.wikipedia.org/wiki/Triglyceride" title="Triglyceride" >triglycerides</a> present at higher concentrations than at other stages of development. Methemoglobinemia in infants is known as <a href="http://en.wikipedia.org/wiki/Blue_baby_syndrome#Other_causes" title="Blue baby syndrome" >blue baby syndrome</a>. Although nitrates in drinking water were once thought to be a contributing factor, there are now significant scientific doubts as to whether there is a causal link.<sup id="cite_ref-6" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-6" >[7]</a></sup><sup id="cite_ref-7" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-7" >[8]</a></sup> Blue baby syndrome is now thought to be the product of a number of factors, which can include any factor which causes gastric upset, such as diarrhoeal infection, protein intolerance, heavy metal toxicity etc., with nitrates playing a minor role. Nitrates, if a factor in a specific case, would most often be ingested by infants in high nitrate drinking water. However, nitrate exposure may also occur if eating, for instance, vegetables containing high levels of nitrate. Lettuce may contain elevated nitrate under growth conditions such as reduced sunlight, undersupply of the essential micronutrients molybdenum (Mo) and iron (Fe), or high concentrations of nitrate due to reduced assimilation of nitrate in the plant. High levels of nitrate fertilization also contribute to elevated levels of nitrate in the harvested plant.<sup id="cite_ref-8" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-8" >[9]</a></sup></p>

<p>

Some adults can be more susceptible to the effects of nitrate than others. The <a href="http://en.wikipedia.org/wiki/Cytochrome_b5_reductase" title="Cytochrome b5 reductase" >methemoglobin reductase</a> <a href="http://en.wikipedia.org/wiki/Enzyme" title="Enzyme" >enzyme</a> may be under-produced or absent in certain people that have an inherited mutation.<sup id="cite_ref-doh_9-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-doh-9" >[10]</a></sup> Such individuals cannot break down methemoglobin as rapidly as those that do have the enzyme, leading to increased circulating levels of methemoglobin (the implication being that their blood is not as oxygen-rich). Those with insufficient stomach acid<sup id="cite_ref-doh_9-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-doh-9" >[10]</a></sup> (including some vegetarians and vegans) may also be at risk. It is the increased consumption of green, leafy vegetables that typically accompany these types of diets may lead to increased nitrate intake. A wide variety of medical conditions, including food allergies, asthma,<sup id="cite_ref-10" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-10" >[11]</a></sup> hepatitis, and gallstones may be linked with low stomach acid; these individuals may also be highly sensitive to the effects of nitrate.</p>

<p>

<a href="http://en.wikipedia.org/wiki/Methemoglobinemia" title="Methemoglobinemia" >Methemoglobinemia</a> can be treated with <a href="http://en.wikipedia.org/wiki/Methylene_blue" title="Methylene blue" >methylene blue</a>, which reduces ferric iron (3+) in affected blood cells back to ferrous iron (2+).<sup class="Template-Fact" >[<i><a href="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed" >citation needed</a></i>]</sup>

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<h3 >Marine toxicity</h3>

Sea surface nitrate from the <a href="http://en.wikipedia.org/wiki/World_Ocean_Atlas" title="World Ocean Atlas" >World Ocean Atlas</a>.</div>

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<p >In <a href="http://en.wikipedia.org/wiki/Freshwater" title="Freshwater" class="mw-redirect" >freshwater</a> or <a href="http://en.wikipedia.org/wiki/Estuary" title="Estuary" >estuarine</a> systems close to land, nitrate can reach high levels that can potentially cause the death of fish. While nitrate is much less toxic than ammonia or nitrite,<sup id="cite_ref-11" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-11" >[12]</a></sup> levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.<sup id="cite_ref-12" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-12" >[13]</a></sup> However, in light of inherent problems with past protocols on acute nitrate toxicity experiments, the extent of nitrate toxicity has been the subject of recent debate.<sup id="cite_ref-13" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-13" >[14]</a></sup></p>

<p>

In most cases of excess nitrate concentrations in aquatic systems, the primary source is <a href="http://en.wikipedia.org/wiki/Surface_runoff" title="Surface runoff" >surface runoff</a> from agricultural or <a href="http://en.wikipedia.org/wiki/Landscape" title="Landscape" >landscaped</a>areas that have received excess nitrate fertilizer. This is called <a href="http://en.wikipedia.org/wiki/Eutrophication" title="Eutrophication" >eutrophication</a> and can lead to algae blooms. As well as leading to water <a href="http://en.wikipedia.org/wiki/Hypoxia(environmental)" title="Hypoxia (environmental)" >anoxia</a> and <a href="http://en.wikipedia.org/wiki/Dead_zone(ecology)" title="Dead zone (ecology)" >dead zones</a>, these blooms may cause other changes to <a href="http://en.wikipedia.org/wiki/Ecosystem" title="Ecosystem" >ecosystem</a> function, favouring some groups of organisms over others. As a consequence, as nitrate forms a component of <a href="http://en.wikipedia.org/wiki/Total_dissolved_solids" title="Total dissolved solids" >total dissolved solids</a>, they are widely used as an indicator of <a href="http://en.wikipedia.org/wiki/Water_quality" title="Water quality" >water quality</a>.

Nitrate also is a by-product of <a href="http://en.wikipedia.org/wiki/Septic_tank" title="Septic tank" >septic systems</a>. To be specific, it is a naturally occurring chemical that is left after the breakdown or decomposition of animal or human waste. Water quality may also be affected through ground water resources that have a high number of septic systems in a watershed. Septics leach down into ground water resources or aquifers and supply nearby bodies of water. Lakes that rely on ground water are often affected by nitrification through this process.

Nitrate in drinking water at levels above the national standard poses an immediate threat to young children. Excessive levels can result in a condition known as "<a href="http://en.wikipedia.org/wiki/Blue_baby_syndrome" title="Blue baby syndrome" >blue baby syndrome</a>". If untreated, the condition can be fatal. Boiling water contaminated with nitrate increases the nitrate concentration and the potential risk.</p>

<h3 >Nitrate toxicity in livestock</h3>

<p >Nitrate poisoning is a concern for cattle producers primarily, but also for other ruminant growers. Nitrate is naturally consumed by growing plants; however when growth is interrupted, the roots of plants will continue to take up nitrate from soil, and unless new plant growth occurs, the nitrate will accumulate. Thus, harvesting after nitrate buildup results in a crop that is high in nitrates. Factors that can cause nitrate buildup in plants are frost, hail damage, drought, hot dry winds, pesticide damage, herbicide damage and any other plant stunting environmental causes.<sup id="cite_ref-14" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-14" >[15]</a></sup>

Symptoms of nitrate poisoning include increased heart rate and respiration; in advanced cases blood and tissue may turn a blue or brown color. Feed can be tested for nitrate; treatment consists of supplementing or substituting existing supplies with lower nitrate material. Safe levels of nitrate for various types of livestock are as follows:<sup id="cite_ref-15" class="reference" ><a href="http://en.wikipedia.org/wiki/Nitrates#cite_note-15" >[16]</a></sup></p>