<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="769" name="contamination and pollution" parent="1174" scope="Introduction of harmful substances into the environment by human action or natural processes."/><uf><usefor name="air pollution"><usewith><term thcode="2" code="65" name="atmospheric composition" parent="67" scope="Components of the mass of gases that surrounds a planet.  The earth's atmosphere consists of nitrogen, oxygen, and small portions of other gases."/></usewith></usefor><usefor name="effluent"/><usefor name="natural contaminants"/><usefor name="outfall"/><usefor name="pollution"/><usefor name="soil pollution"><usewith><term thcode="2" code="1080" name="soil resources" parent="777" scope="Natural resources of unconsolidated fragmented rock, humus, and mineral matter that cover the surface of the earth."/></usewith></usefor><usefor name="water pollution"><usewith><term thcode="2" code="1308" name="water resources" parent="777" scope="Stocks of water, the liquid derived from precipitation. A constituent of living matter and necessity for all life, it covers a large proportion of the earth's surface."/></usewith></usefor></uf><bt><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="2274" name="PFAS" parent="769" scope="Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemical compounds that are an emerging contaminant."/><term thcode="2" code="1723" name="industrial pollution" parent="769" scope="Introduction of harmful substances into the environment by manufacturing, power generation, mining, or material processing."/><term thcode="2" code="2269" name="microplastic contamination" parent="769" scope="Plastic particles less than 5 millimeters in diameter that come from a wide variety of sources, found in a variety of forms, including fibers, pellets/beads, foams, films, fragments, and tire particles, and reach aquatic environments through diverse pathways."/><term thcode="2" code="1363" name="nonpoint-source pollution" parent="769" scope="Contamination of the environment from sources spread widely across an area, not from a small number of identifiable locations."/><term thcode="2" code="879" name="pesticide and herbicide contamination" parent="769" scope="Pollution resulting from chemical agents applied to crops, rights of way, lawns, or residences to control weeds, insects, fungi, nematodes, rodents or other pests (pesticides) or kill undesirable plants (herbicides)."/><term thcode="2" code="1693" name="pharmaceutical contamination" parent="769" scope="Unintentional release of pharmaceutical compounds into the environment; work focuses on the effects of these compounds on organisms and water resources."/><term thcode="2" code="1180" name="toxic radionuclide contamination" parent="769" scope="Introduction into the environment of unstable isotopes of elements that undergo radioactive decay, emitting radiation that is harmful to organisms."/><term thcode="2" code="1181" name="toxic trace element contamination" parent="769" scope="Introduction into the environment of elements (such as arsenic, cadmium, lead, and mercury) which have a deleterious effect on living organisms when found naturally in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment."/></nt><rt><term thcode="2" code="320" name="ecotoxicology" parent="650" scope="Scientific study of causes, dispersal, and effects of contaminants on the environment."/><term thcode="2" code="531" name="hazards" parent="1174" scope="Potential dangers from both natural processes (e.g., earthquakes, floods, and climate change) and human impacts on the environment."/><term thcode="2" code="548" name="human impacts" parent="1174" scope="The effects, intentional or unintentional, beneficial or harmful, direct or indirect, which human activities have upon the environment and living things."/><term thcode="2" code="1293" name="waste treatment and disposal" parent="548" scope="The chemical and physical methods to recycle or dispose of materials which, without treatment, are deemed to have no further value or are too contaminated to be used."/><term thcode="2" code="1306" name="water quality" parent="1174" scope="The chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose."/></rt></descriptor>