| Macromolecules
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| Very large, organic molecules such as proteins and nucleic acids that constitute the structural and functional parts of cells.
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| Macronutrient
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| A chemical substance needed by living organisms in large quantities (for example, carbon, oxygen, hydrogen, and nitrogen). Contrast with micronutrient.
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| MACT (maximum achievable control technology)
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| The best technologies available for reducing the output of especially toxic industrial pollutants.
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| Magma
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| Molten rock from deep in the earth’s interior; called lava when it spews from volcanic vents.
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| Magma
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| Molten rock beneath the earth’s crust.
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| Magnetic confinement
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| A technique for enclosing a nuclear fusion reaction in a powerful magnetic field inside a vacuum chamber.
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| Magnuson Act
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| An act passed in 1976 which extended the limits of jurisdiction over coastal waters and fisheries of the United States to 200 miles offshore.
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| Malignant tumor
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| A mass of cancerous cells that have left their site of origin, migrated through the body, invaded normal tissues, and are growing out of control.
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| Malnourishment
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| A nutritional imbalance caused by lack of specific dietary components or inability to absorb or utilize essential nutrient.
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| Malnutrition
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| The lack of essential nutrients such as vitamins, minerals, and amino acids. Malnutrition ranges from mild to severe and life-threatening.
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| Malthusian growth
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| A population explosion followed by a population crash; also called irruptive growth.
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| Man and biosphere (MAB) program
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| A design for nature preserves that divides protected areas into zones with different purposes. A highly protected core is surrounded by a buffer zone and peripheral regions in which multiple-use resource harvesting is permitted.
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| Manganese nodules
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| Nodular accumulations of manganese and other minerals such as iron and copper found on the ocean floor at depths of 300 to 6000 meters. Particularly abundant in the Pacific Ocean.
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| Mantle
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| A hot, pliable layer of rock that surrounds the earth’s core and underlies the cool, outer crust.
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| Marasmus
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| A widespread human protein deficiency disease caused by a diet low in calories and protein or imbalance in essential amino acids.
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| Marginal costs
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| The cost to produce one additional unit of a good or service.
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| Mariculture
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| Cultivation of fish and other aquatic organisms in salt water (estuaries and bays).
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| Marine
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| Living in or pertaining to the sea.
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| Market equilibrium
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| The dynamic balance between supply and demand under a given set of conditions in a “free” market (one with no monopolies or government interventions).
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| Marsh
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| Wetland without trees; in North America, this type of land is characterized by cattails and rushed.
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| Mass burn
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| Incineration of unsorted solid waste.
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| Mass number
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| The number that accompanies the chemical name or symbol of an element or isotope. It represents the number of neutrons and protons in the nucleus of the atom.
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| Material safety data sheets (MSDS)
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| Documents containing information on the reactivity and toxicity of chemicals that must accompany the shipping, storage, and handling of over 600 chemicals.
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| Materials recycling facility (MRF)
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| A processing plant where regionalized recycling is facilitated. Recyclable municipal solid waste, usually presorted, is prepared in bulk for the recycling market.
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| Matter
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| Anything that takes up space and has mass.
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| Mature community
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| A community that remain more or less the same over a long period of time. Climax stage of succession. Also called a climax community.
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| Mature ecosystem
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| An ecosystem in the climax stage of succession, characterized by high species diversity and high stability. Contrast with immature ecosystem.
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| Maximum suitable yield (MSY)
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| The maximum amount of a renewable resource that can be taken year after year without depleting the resource. It is the maximum rate of use or harvest that will be balanced by the regenerative capacity of the system -- for example, the maximum rate of tree cutting that can be balanced.
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| Measure of economic welfare
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| Proposed standard that takes into account the accumulated wealth of a nation.
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| Mediterranean climate areas
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| Specialized landscapes with warm, dry summers; cool, wet winters; many unique plant and animal adaptations; and many levels of endemism.
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| Megacity
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| See megalopolis.
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| Megalopolis
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| Also known as a megacity or supercity; megalopolis indicates an urban area with more than 10 million inhabitants.
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| Megawatt (MW)
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| Unit of electrical power equal to one thousand kilowatts or one million watts.
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| Meltdown
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| The event of a nuclear reactor's getting out of control or losing its cooling water so that it melts horn its own production of heat. The melted reactor would continue to produce heat and could melt its way out of the reactor vessel and eventually down into groundwater, where it would cause a violent eruption of steam that could spread radioactive materials over a wide area.
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| Mesosphere
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| The atmospheric layer above the stratosphere and below the thermosphere; the middle layer; temperatures are usually very low.
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| Mesothelioma
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| A tumor of the lining of the lung (pleura). Caused by asbestos.
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| Metabolism
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| All the energy and matter exchanges that occur within a living cell or organism collectively, the life processes.
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| Metalimnion
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| See thermocline.
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| Metamorphic rock
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| Igneous and sedimentary rocks modifies by heat, pressure, and chemical reactions.
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| Metastasis
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| Movement of cancer cells to another location where new tumors are formed.
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| Methane
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| A gas, CH4. It is the primary constituent of natural gas. It is also produced as a product of fermentation by microbes. Methane from ruminant animals is thought to be responsible for the rise in atmospheric methane, of concern because methane is one of the greenhouse gases.
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| Methane hydrate
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| Small bubbles or individual molecules of methane (natural gas) trapped in a crystalline matrix of frozen water.
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| Methylmercury
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| Water-soluble organic form of mercury formed by bacteria in aquatic ecosystems from inorganic (insoluble) mercury pollution. Able to undergo biological magnification.
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| Microbe
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| A term used to refer to any microscopic organism, primary bacteria, viruses, and protozoans.
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| Microclimate
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| The actual conditions experienced by an organism in its particular location. Owing to numerous factors such as shading, drainage, and sheltering, the microclimate may be quite distinct from the overall climate.
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| Microconsumers
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| Bacteria and single-celled fungi that are part of the decomposer food chain.
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| Microfiltration
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| A process for purifying water in which water is forced under very high pressure through a membrane that is fine enough to filter out ions and molecules in solution; used by small desalination plants to filter salt from seawater. Also called reverse osmosis.
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| Micro-hydro generators
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| Small power generators that can be used in low-level rivers to provide economical power for four to six homes, freeing them from dependence on large utilities and foreign energy supplies.
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| Microlending
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| 7he process of providing very small loans (usually $50-8500) to poor people to facilitate their starting a small enterprise to become economically self-sufficient.
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| Micronutrient
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| An element needed by organisms, but only in small quantities, such as copper, iron, and zinc. Contrast with macronutrient.
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| Microorganism
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| Any microscopic organism, particularly bacteria, viruses, and protozoans.
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| Midnight dumping
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| The wanton illicit dumping of materials, particularly hazardous wastes, frequently under the cover of darkness.
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| Migration
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| Movement of people across state and national boundaries to set up new residence. See immigration, emigration, in-migration, and out migration.
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| Milankovitch cycles
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| Periodic variations in tilt, eccentricity, and wobble in the earth’s orbit; milutin milankovitch suggested that it is responsible for cyclic weather changes.
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| Mill tailings
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| Residue from uranium processing plants. Spent uranium ore that is contaminated with radioactivity.
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| Milpa agriculture
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| An ancient farming system in which small patches of tropical forests are cleared and perennial polyculture agriculture practiced and is then followed by many years of fallow to restore the soil; also called swidden agriculture.
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| Minamata disease
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| A "disease" named for a fishing village in Japan where an "epidemic" was first observed. Symptoms, which included spastic movements, mental retardation, coma, death, and crippling birth defects in the next generation, were found to be the result of mercury poisoning.
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| Mineral
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| Any hard, brittle, stonelike material that occurs naturally in Earth's crust. All consist of various combinations of positive and negative ions held together by ionic bonds. Pure minerals, or crystals are one specific combination of elements. Common rocks are composed of mixtures of two or more minerals.
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| Mineralization
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| The process of gradual oxidation of the organic matter (humus) present in soil that leaves just the gritty mineral component of the soil.
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| Minimum tillage
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| Reduced plowing and cultivating of cropland between and during growing seasons to help reduce soil erosion and save energy. Also called conservation tillage.
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| Mitigation
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| Repairing or rehabilitating a damaged ecosystem or compensating for damage by providing a substitute or replacement area.
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| Mixed perennial polyculture
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| Growing a mixture of different perennial crop species (where the same plant persists for more than one year) together in the same plot; imitates the diversity of a natural system and is often more stable and more suitable for sustainable agriculture than monoculture of annual plants.
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| Mixture
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| Forms when there is no chemical bonding between the molecules of the elements involved. For example, air contains (is a mixture of) oxygen, nitrogen, and carbon dioxide.
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| Mobilization
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| In soil science, the bringing into solution of normally insoluble minerals. Presents a particular problem when the elements of such minerals have toxic effects.
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| Moderator
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| In a nuclear reactor, the moderator is any material that slows down neutrons from fission reactions so that they are traveling at the right speed to trigger another fission. Water and graphite represent two types of moderators.
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| Molecule
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| A specific union of two or more atoms. The smallest unit of a compound that still has the characteristics of that compound
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| Monitored, retrievable storage
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| Holding wastes in underground mines or secure surface facilities such as fry casks where they can be watched and repackaged, if necessary.
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| Monkey wrenching
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| Environmental sabotage such as driving large spikes in trees to protect them from loggers, vandalizing construction equipment, pulling up survey stakes for unwanted developments, and destroying billboards.
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| Monoculture agroforestry
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| Intensive planting of a single species; an efficient wood production approach, but one that encourages pests and disease infestations and conflicts with wildlife habitat or recreation uses.
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| Monoculture/Monocropping
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| The practice of growing the same crop over very wide areas, for example, thousands of square kilometers of wheat, and only wheat, grown in the Midwest.
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| Monsoon
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| A seasonal reversal of wind patterns caused by the different heating and cooling rate of the oceans and continents.
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| Montane coniferous forests
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| Coniferous forests of the mountains consisting of belts of different forest communities along an altitudinal gradient.
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| Montreal Protocol
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| An agreement made in 1987 by a large group of nations to cut back the production of chlorofluorocarbons by 50% by the year 2000 in order to protect the ozone shield. A 1990 amendment calls for the complete phase out of these chemicals by 2000 in developed nations and by 2010 in less-developed nations.
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| Moral agents
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| Beings capable of making distinctions between right and wrong and acting accordingly. Those whom we hold responsible for their actions.
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| Moral extensionism
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| Expansion of our understanding of inherent value or rights to persons, organisms, or things that might not be considered worthy of value or rights under some ethical philosophies.
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| Moral subjects
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| Beings that are not capable of distinguishing between right or wrong or that are not able to act on moral principles and yet are capable of being wronged by others. This category assumes some rights or inherent values in moral subjects that gives us duties or obligations towards them.
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| Morals
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| A set of ethical principles that guide our actions and relationships.
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| Morbidity
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| Illness or disease.
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| More-developed countries (MDC)
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| Industrialized nations characterized by high per capita incomes, low birth and death rates, low population growth rates, and high levels of industrialization and urbanization.
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| Mortality
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| Death rate in a population; the probability of dying.
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| MRF
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| Materials recycling facility.
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| Muellerian mimicry
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| Evolution of two species, both of which are unpalatable and, have poisonous stingers or some other defense mechanism, to resemble each other.
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| Mulch
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| Protective ground cover, including manure, wood chips, straw, seaweed, leaves, and other natural products, or synthetic materials, such as heavy paper or plastic, that protect the soul, save water, and prevent weed growth.
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| Multiple use
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| Many uses that occur simultaneously; used in forest management; limited to mutually compatible uses.
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| Municipal solid waste ~MSW)
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| The entirety of refuse or trash generated by a residential and business community. The refuse that a municipality is responsible for collecting and disposing of distinct from agricultural and industrial wastes.
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| Mutagenic
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| Causing mutations.
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| Mutagens
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| Agents, such as chemicals or radiation, that damage or alter genetic material (DNA) in cells.
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| Mutation
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| A random change in one or more genes of an organism. Mutations may occur spontaneously in nature, but their number and degree are vastly increased by exposure to radiation and/or certain chemicals. Mutation generally result in a physical deformity and/or metabolic malfunction.
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| Mutualism
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| A symbiotic relationship between individuals of two different species in which both species benefit from the association.
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| Mycelia
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| The threadlike feeding filaments of fungi.
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| Mycorrhiza, pl. mycorrhizae
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| The mycelia of certain fungi that grow symbiotically with the roots of some plants and provide for additional nutrient uptake.
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