Micronutrients are essential chemicals required by

organisms An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been pr ...

in small quantities to perform various biogeochemical processes and regulate physiological functions of cells and

organs In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to a ...

. By enabling these processes, micronutrients support the health of organisms throughout life. For humans, micronutrients typically take one of three forms:

vitamins Vitamins are organic molecules (or a set of closely related molecules called vitamers) that are essential to an organism in small quantities for proper metabolic function. Essential nutrients cannot be synthesized in the organism in suff ...

trace elements __NOTOC__ A trace element is a chemical element of a minute quantity, a trace amount, especially used in referring to a micronutrient, but is also used to refer to minor elements in the composition of a rock, or other chemical substance. In nutri ...

, and dietary minerals. Human micronutrient requirements are in amounts generally less than 100

milligrams The kilogram (also spelled kilogramme) is the base unit of mass in the International System of Units (SI), equal to one thousand grams. It has the unit symbol kg. The word "kilogram" is formed from the combination of the metric prefix kilo- (m ...

per day, whereas

macronutrients A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

are required in gram quantities daily. Deficiencies in micronutrient intake commonly result in

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is a deficiency, excess, or imbalance of energy, protein and other nutrients which adversely affects the body's tissues a ...

. In ecosystems, micronutrients most commonly take the form of

such as iron, strontium, and manganese. Micronutrient abundance in the environment greatly influences

biogeochemical cycles A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cyc ...

at the microbial level which large ecological communities rely on to survive. For example, marine primary producers are reliant upon bioavailable dissolved

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

for

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. Secondary and tertiary producers in oceans are therefore also reliant on the presence of sufficient dissolved iron concentrations. Role of marine animals in the cycling of iron in the Southern Ocean

Role of marine animals in the cycling of iron in the Southern Ocean

Naturally, micronutrients are transferred between reservoirs through processes like fluvial transport, aeolian processes, ocean circulation, volcanism, and biological uptake/transfer. Anthropogenic activities also alter the abundance of micronutrients in ecosystems. Industrial and agricultural practices can release trace metals into the atmosphere, waterways, and soils and deforestation can lead to higher trace metal-containing-dust transport into oceans.

Natural abundances of micronutrients

The natural abundance of elements is dependent on their atomic number based on the process of

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

such that elements with higher atomic numbers are typically less abundant than elements with low atomic numbers. Most micronutrients are

with high atomic numbers, meaning they exist naturally in low concentrations. Notable exceptions to this rule are

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

(atomic no. 5),

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

(atomic no. 25), and iron (atomic no. 26).

Primary producers An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds, which can be used by other organisms. Autotrophs produce complex organic compounds (such as carbohydrates, fats, and proteins) us ...

are the main contributors to the incorporation of micronutrients into a community's chemical inventory.

Consumers A consumer is a person or a group who intends to order, or use purchased goods, products, or services primarily for personal, social, family, household and similar needs, who is not directly related to entrepreneurial or business activities. Th ...

within an ecosystem are limited to the micronutrients in the tissue of the primary producers which they eat. Primary producers obtain their micronutrients from their surrounding abiotic environment and the recycling of organic matter in soils. For example, grasses take in iron from soils which animals rely upon for

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

production.

Sources and transport of micronutrients

Natural cycling

The original source of most nutrients, including micronutrients, is the geological reservoir, also called the slow pool. Micronutrients trapped in rocks and minerals must first be broken down through physical or chemical weathering before they can enter the fast pool, meaning they cycle between reservoirs on shorter timescales. Micronutrients can physically exchange between reservoirs in various ways such as from terrestrial soils to oceans via aeolian transport or fluvial transport, from oceans to

marine sediments Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either have their origins in soil and rocks and have been transported from the land to the sea ...

via deposition of organic matter, and from sediments to the geologic reservoir via

lithification Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...

. Alternatively, micronutrients can exit the geologic reservoir through tectonic processes such as through

volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

hydrothermal vents Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hots ...

Anthropogenic influences

Anthropogenic industry unintentionally injects micronutrients into various ecosystems across the globe. The addition of micronutrients into ecosystems can have both positive and negative impacts. In the face of climate change, the fertilization of oceans with iron has been proposed as a method of

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. It plays a crucial role in Climate change mitigation, limiting climate change by reducing the amount of Carbon dioxide in Earth's atmosphere, carbon dioxide in the atmosphe ...

; however, elevated levels of iron in high nutrient, low chlorophyll regions of the ocean can cause the production of

harmful algal blooms A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

which are toxic to both humans and marine life. Similarly, in lakes, isolated seas, and coastal bays or gulfs, addition of micronutrients can cause

eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

leading to hypoxia, decreasing ecosystem health. Micronutrients are released into ecosystems from many anthropogenic activities.

Fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

combustion releases micronutrients such as Zn, Fe, Ni, and Cu into the atmosphere, surrounding soils, and nearby waterways. Agricultural fertilizer runoff contains many micronutrients like Fe, Mn, Zn, Cu, Co, B, Mo and Ni. Fertilizer runoff injects these micronutrients into groundwater, soils, and waterways.

Deforestation Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...

decreases soil compaction, resulting in increased aeolian transport of dust containing micronutrients, especially Fe. Industrial mining produces

tailings In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material ...

which contaminates runoff. The improper treatment of mining tailings can result in the leakage of micronutrients into groundwater, soils, and nearby waterways.

Human micronutrient deficiencies

Inadequate intake of essential nutrients predisposes humans to various

chronic diseases A chronic condition (also known as chronic disease or chronic illness) is a health condition or disease that is persistent or otherwise long-lasting in its effects or a disease that comes with time. The term ''chronic'' is often applied when the ...

, with some 50% of American adults having one or more preventable disease. In the United States, foods poor in micronutrient content and high in

food energy Food energy is chemical energy that animals and humans derive from food to sustain their metabolism and muscular activity. Most animals derive most of their energy from aerobic respiration, namely combining the carbohydrates, fats, and protein ...

make up some 27% of daily

calorie The calorie is a unit of energy that originated from the caloric theory of heat. The large calorie, food calorie, dietary calorie, kilocalorie, or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter o ...

intake. One US national survey (National Health and Nutrition Examination Survey 2003-2006) found that persons with high sugar intake consumed fewer micronutrients, especially

A, C, and E, and magnesium. Various strategies have been employed to combat micronutrient deficiencies:

Salt iodization

Salt iodization is a strategy for addressing

iodine deficiency Iodine deficiency is a lack of the trace element iodine, an essential nutrient in the diet. It may result in metabolic problems such as goiter, sometimes as an endemic goiter as well as congenital iodine deficiency syndrome due to untreated ...

, which is a cause of mental health problems. In 1990, less than 20 percent of households in developing countries had adequate iodine in their diet.Flour Fortification Initiative, GAIN, Micronutrient Initiative, USAID, The

World Bank The World Bank is an international financial institution that provides loans and Grant (money), grants to the governments of Least developed countries, low- and Developing country, middle-income countries for the purposes of economic development ...

, UNICEF, ''Investing in the future: a united call to action on vitamin and mineral deficiencies'', p. 19. By 1994, international partnerships had formed in a global campaign for Universal Salt Iodization. By 2008, it was estimated that 72 percent of households in developing countries included iodized salt in their diets, and the number of countries in which iodine deficiency disorders were a public health concern reduced by more than half from 110 to 47 countries.

Vitamin A supplementation

Vitamin A Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinyl esters, and several provitamin (precursor) carotenoids, most not ...

deficiency is a major factor in causing

blindness Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficul ...

worldwide, particularly among children. Global vitamin A supplementation efforts have targeted 103 priority countries. Flour fortification has become an increasingly common method by which vitamin A can be added to diets thus reducing deficiencies.

Zinc

Zinc is a necessary micronutrient which the human body uses to fight infections and childhood diarrhea. Collectively, zinc deficiencies are responsible for 4% of child morbidity and mortality, as of 2013. Fortification of staple foods such as breads may improve serum zinc levels in the human population, increasing immune strength. Zinc fortification has also been considered for reducing effects cognition, though the effectiveness is still under research.

Plant micronutrient needs

Plants rely on micronutrients to build many essential proteins. In fact, every process that supports the growth of a plant is mediated by some protein which contains one of the many micronutrients. For example, Mn is an essential micronutrient for many plants because it builds the structure of photosystem II which splits water molecules to harness energy from electrons. Inadequate micronutrient uptake can result in deficiencies and even mortality in extreme cases. Alternatively, elevated concentrations of micronutrients in soils can result in toxicity. Examples of Plant Micronutrient Deficiencies *

Chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

, a condition where a plant cannot produce sufficient chlorophyll. A lack in copper, iron, manganese, or zinc can cause chlorosis. * Boron deficiency, a condition where a plant's ability to reproduce, grow, and create stem cells is inhibited. * Molybdenum deficiency, a condition where a buildup in nitrate because of a lack of nitrogenase production causes leaf yellowing, necrosis, and premature germination.

References

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