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Life or processes that require, or are not destroyed by, the presence of oxygen.

A life or process that occurs in, or is not destroyed by, the absence of oxygen.

Involving the impact of people on nature; induced, caused, or altered by the presence and activities of people, as in water and air pollution.

(1) Consisting of, relating to, or being in water; living or growing in, on, or near the water. (2) Taking place in or on the water. (3) An organism that lives in, on, or near the water.


(1) The bottom of lakes or oceans. (2) Referring to organisms that live on the bottom of water bodies.

Benthic organisms
Those organisms living at or near the bottom of a body of water. They include a number of types of organisms, such as bacteria, fungi, insect larvae and nymphs, snails, clams, and crayfish. They are useful as indicators of water quality.

The increase in concentration of a chemical in organisms that reside in environments contaminated with low concentrations of various organic compounds. Also used to describe the progressive increase in the amount of a chemical in an organism resulting from rates of absorption of a substance in excess of its metabolism and excretion.

Degree of ability to be absorbed and ready to interact in organism metabolism.

(1) The process by which an individual organism directly concentrates a substance from the surrounding air, water, or soil. (2) The increase in concentration of a chemical in an organism resulting from absorption levels exceeding the rate of metabolism and excretion.

Biologic monitoring (or biomonitoring)
Measuring hazardous substances in biologic materials (such as blood, hair, urine, or breath) to determine whether exposure has occurred. A blood test for lead is an example of biologic monitoring.

Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain.

Body Burden
The amount of a chemical stored in the body at a given time, especially a potential toxin in the body as the result of exposure.


Community Based Participatory Research (CBPR)
Community-based participatory research (CBPR) is a partnership approach to research that equitably involves, for example, community members, organizational representatives, and researchers in all aspects of the research process and in which all partners contribute expertise and share decision making and ownership.

The amount of a substance present in a certain amount of soil, water, air, food, blood, hair, urine, breath, or any other media. In water, concentrations are often reported in units of mass (such as milligrams or micrograms) per unit volume (such as liters) of water, or in units such as parts per million. In solid samples (such as soils or fish tissues), concentrations are often reported in units of mass (such as milligrams) per unit of mass of sample (such as kilograms), or in units such as parts per million.

A substance that is either present in an environment where it does not belong or is present at levels that might cause harmful (adverse) health effects.

Contamination (Water)
Impairment of the quality of water sources by sewage, industrial waste, or other matters to a degree which creates a hazard to public health. Also, the degradation of the natural quality of water as a result of human activities. There is no implication of any specific limits, since the degree of permissible contamination depends upon the intended end use, or uses, of the water.


Demethylation (of mercury)
The opposite of methylation, where methylmercury is converted into inorganic mercury.

Dissolved oxygen
Concentration of oxygen dissolved in water and readily available to fish and other aquatic organisms.

The amount of a substance to which a person is exposed over some time period. Dose is a measurement of exposure. Dose is often expressed as milligram (amount) per kilogram (a measure of body weight) per day (a measure of time) when people eat or drink contaminated water, food, or soil. In general, the greater the dose, the greater the likelihood of an effect. An "exposure dose" is how much of a substance is encountered in the environment. An "absorbed dose" is the amount of a substance that actually got into the body through the eyes, skin, stomach, intestines, or lungs.


The study of the inter-relationships of living things to one another and to the environment.

A community of animals, plants, and bacteria, and its interrelated physical and chemical environment. An ecosystem can be as small as a rotting log or a puddle of water, but current management efforts typically focus on larger landscape units, such as a mountain range, a river basin, or a watershed.

Environmental media
Soil, water, air, biota (plants and animals), or any other parts of the environment that can contain contaminants.

The warm upper layer of a body of water with thermal stratification, which extends down from the surface to the Thermocline, which forms the boundary between the warmer upper layers of the epilimnion and the colder waters of the lower depths, or hypolimnion. The epilimnion is less dense than the lower waters and is wind-circulated and essentially homothermous.

The degradation of water quality due to enrichment by nutrients, primarily nitrogen (N) and phosphorus (P), which results in excessive plant (principally algae) growth and decay.

Contact with a substance by swallowing, breathing, or touching the skin or eyes. Exposure may be short-term (acute exposure), of intermediate duration, or long-term (chronic exposure).

The degradation of water quality due to enrichment by nutrients, primarily nitrogen (N) and phosphorus (P), which results in excessive plant (principally algae) growth and decay.

Exposure assessment
Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed.

Exposure pathway
The route a substance takes from its source (where it began) to its end point (where it ends), and how people can come into contact with (or get exposed to) it.


Food frequency questionnaire
A survey designed to find out how frequently a person eats certain types of foods over a certain period of time.

Food chain
A succession of organisms in an ecological community that constitutes a continuation of food energy from one organism to another as each consumes a lower member and in turn is preyed upon by a higher member.

Food web
A complex of interrelated food chains in an ecological community.


Heavy Metals
Metals having a specific gravity of 5.0 or greater; generally toxic in relatively low concentrations to plant and animal life and tend to accumulate in the food chain. Examples include lead, mercury, cadmium, chromium, and arsenic.

chemical abbreviation for the element mercury.

The lowermost, non-circulating layer of cold water in a thermally stratified lake or reservoir that lies below the thermocline, remains perpetually cold and is usually deficient of oxygen.


Of or related to a substance that does not contain carbon atoms (with some exceptions, such as carbon dioxide, carbonates, methane).


Kilogram (kg)
A unit of mass, equivalent to 2.2 pounds.


The region along the shore of a non-flowing body of water.


Heavy metal that can accumulate in the environment and is highly toxic if breathed or swallowed.

Methylmercury (MeHg, or CH3Hg)
An organic compound that has known neurological toxicity effects that tend to biomagnify up the food chain in aquatic environments. Biomagnification is a biological process wherein a contaminant’s concentration increases at each level up the food chain, including humans. Thus, the availability of such contaminants, even in the seemingly insignificant parts per trillion range, often are ecologically important. Typically, methylmercury is formed by the action of certain bacteria on available supplies of inorganic mercury in stream-bottom sediments containing low concentrations of dissolved oxygen. However, the reverse process, or demethylation also is known to occur and this “detoxifying” of methylmercury is the subject of ongoing research

Milligrams per kilogram. See parts per million.

Milligrams per liter. A standard unit for expressing concentrations in water. See parts per million.


Nitrates represent a class of chemical compounds having the formula NO3. Nitrate salts are used as fertilizers to supply a nitrogen source for plant growth. Nitrate additions to surface waters can lead to excessive growth of aquatic plants.

Nutrient Pollution
Contamination of water resources by excessive inputs of nutrients. In surface waters, excess algal production is a major concern. Although natural sources of nutrients exist, major sources are typically anthropogenic (caused by human activities) and include point sources such as municipal sewage-treatment plants and industrial outflows, and non-point sources such as commercial fertilizers, animal waste, and combustion emissions.


Of or related to a substance that contains carbon atoms linked together by carbon-carbon bonds. All living matter is organic.

Organic carbon (OC)
A measure of organic matter present in aqueous solution, suspension, or bottom sediments. May be reported as dissolved organic carbon (DOC), suspended organic carbon (SOC), or total organic carbon (TOC).

Organic matter (OM)
Plant and animal residues, or substances made by living organisms. All are based upon carbon compounds.


Parts per million (ppm)
A unit of concentration, indicating the number of “parts” by weight of a substance per million parts of water, soil, fish tissue, etc. This unit is commonly used to represent pollutant concentrations, and levels of mercury in fish and hair samples are often reported in parts per million. In water, 1 ppm is equivalent to 1 mg/L (milligram per liter). In solid samples (soils, sediments, fish tissues), 1 ppm is equivalent to 1 mg/kg (milligram per kilogram).

An element that is essential to plant life but can contribute to eutrophication of water bodies.

ee parts per million

(Ecology) A group of organisms of the same species living together in an area. (Public health) A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age).


Reference dose (RfD)
An EPA estimate, with uncertainty or safety factors built in, of the daily lifetime dose of a substance that is unlikely to cause harm in humans.

Pertaining to the banks of a river, stream, waterway, or other, typically, flowing body of water as well as to plant and animal communities along such bodies of water. This term is also commonly used for other bodies of water, e.g., ponds, lakes, etc., although littoral is the more precise term for such stationary bodies of water.


A portion or piece of a whole. A selected subset of a population or subset of whatever is being studied. For example, in a study of people the sample is a number of people chosen from a larger population. An environmental sample (for example, a small amount of soil or water) might be collected to measure contamination in the environment at a specific location.

Sample size
The number of units chosen from a population or an environment.

Soil, sand, and minerals washed from the land into water, usually after rain.

Sulfate reducing bacteria
Microorganisms that are found in anaerobic water and sediments that are thought to be primarily responsible for methylation of inorganic mercury to methylmercury.

Surface water
Water on the surface of the earth, such as in lakes, rivers, streams, ponds, and springs.

A systematic collection of information or data. A survey can be conducted to collect information from a group of people or from the environment. Surveys of a group of people can be conducted by telephone, by mail, or in person. Some surveys are done by interviewing a group of people


A layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt. The intermediate summer or transition zone in lakes between the overlying epilimnion and the underlying hypolimnion, defined as that middle region of a thermally stratified lake or reservoir in which there is a rapid decrease in temperature with water depth.

Trace metals
A general term for metals found in small quantities (less than 1 milligram per liter – mg/l) in water, usually due to their insolubility or low natural abundance.


(1) An area that, because of topographic slope, contributes water to a specified surface water drainage system, such as a stream or river. An area confined by topographic divides that drains a given stream or river.


Agency for Toxic Substances & Disease Registry (ATSDR). Glossary of Terms.

Nevada Division of Water Resources, Department of Conservation and Natural Resources.
Water Words Dictionary: A Compilation of Technical Water, Water Quality, Environmental, and Water-Related Terms.

U.S. Environmental Protection Agency (US EPA). Terms of Environment: Glossary, Abbreviations and Acronyms.

Harvard School of Public Health LEAD Agency university of Oklahoma Health Sciences Center logo

National Institute of Environmental Health Sciences The Grand Lake Watershed Mercury Study is supported with funding from the National Institute of Environmental Health Sciences Grant No.1R21ES017941.

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