Metals, metalloids, and radionuclides all are trace elements that occur naturally in the Earth's crust. In small quantities many trace elements are essential for health in all living organisms, but some trace elements can be toxic or cause cancer, and some can bioaccumulate. The USGS investigates where and how trace elements make their way into our Nation's surface water and groundwater.
Featured: 3-D Models of As and Mn in the Glacial Aquifer System
New 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured: Updated Information on the Nation's Groundwater Quality
Three new USGS fact sheets update information on groundwater quality in the nation's most heavily used aquifers. Metals are among the constituents that most frequently exceed human-health benchmarks.
Trace elements are simply elements present in minute amounts in the environment. Trace elements include metals, such as lead and iron; metalloids, such as arsenic; and radionclides (radioactive elements), such as radium and radon. Trace elements in our Nation's streams, rivers, and groundwater have natural and manmade sources. Rock weathering, soil erosion, and dissolution of water-soluble salts are examples of natural sources of trace elements. Many human activities also contribute trace elements to the environment—mining, urban runoff, industrial emissions, and nuclear reactions are just some of the many manmade sources. Trace elements tend to concentrate in sediment, but also can dissolve to some degree in water, and can present a risk to human and aquatic health.
► Learn about trace elements in groundwater in Principal Aquifers of the United States, our invisible, vital resource.
METALS
Many people might not realize that most elements are metals. Metals tend to be shiny, they make good conductors, and they're malleable and ductile. Most corrode when exposed to sea water or air, and lose electrons during reactions. We're familiar with many metals, for example gold, silver, lead, zinc, chromium, cadmium, and mercury. It's less obvious that other elements—beryllium, sodium, and lithium, for example—are metals too. Although manmade metal objects surround us each day, metals represent only a minute proportion of the elements in the Earth's crust.
There is no agreed-upon definition of "heavy metals," but heavy metals generally are considered to be those metals with a high density. Gold, silver, tin, copper, zinc, and iron are well-known examples of heavy metals. Some heavy metals, like iron and zinc, are essential nutrients at low concentrations but toxic at high concentrations. Other non-essential heavy metals, like cadmium, mercury, and lead, are toxic even at relatively low concentrations.
A "metalloid" has properties intermediate between metals and non-metals. From a water-quality point of view, arsenic is perhaps the metalloid of most concern. Other metalloids include boron and silicon, and carbon and some other trace elements are sometimes classified as metalloids.
Metals in water used for drinking and in sediment can present a risk to human and aquatic health. Various concentration benchmarks have been developed that indicate the concentration above which a metal is a health concern.
RADIONUCLIDES
Radionuclides (radiocative elements) also are trace elementa. Radionuclides in our environment are produced by minerals in the Earth’s crust, by cosmic rays hitting atoms in the Earth’s atmosphere, and by human activities. Radionuclides occur naturally in many rocks and minerals and therefore occur frequently groundwater. The most common examples of radionuclides in groundwater are uranium, radium, and radon.
► Learn more about radionuclides and water quality.
OTHER TRACE ELEMENTS
A small number of trace elements, such as selenium, are neither metals nor radionuclides. Selenium occurs naturally in sedimentary rocks, shales, coal and phosphate deposits, and soils. Application of irrigation water, which contains dissolved oxygen, can caused selenium to be released from sediment into groundwater, particularly in arid areas. This processes has been documented in the shallow Denver Basin aquifer in Colorado and in parts of the West where selenium occurs in rocks and sediments. Selenium in groundwater can discharge into streams, where it can bioaccumulate in the aquatic food chain. Chronic exposure in fish and aquatic invertebrates can cause reproductive impairments.
TRACE ELEMENTS AND DRINKING WATER
Concentrations of trace elements are more likely to be a problem in groundwater than in surface water, unless the area is impacted by mining. That’s because when groundwater moves through the rocks and sediments that make up an aquifer, some of the minerals in or adhered to those rocks and sediment are released into the water. Groundwater that has been in an aquifer a long time has had more time to interact with aquifer materials than groundwater that has recharged recently. Additionally, geochemical conditions, such as pH and redox, change as groundwater slowly moves along a flowpath from recharge to discharge—those geochemical conditions can affect whether metals are released into the groundwater.
Groundwater age is just one of the factors that can affect the concentration of trace elements. Other factors include climate and, geology, and human actions. Climate4 plays a role because in regions where precipitation is low and evaporation rates are high, there is less water to dilute the products of rock weathering. Geology plays a role because the metals available for leaching into groundwater depend on types of minerals present in the rocks and sediment. Finally, human actions such as irrigation and pumping can affect concentrations of trace elements in groundwater, often by changing the geochemical conditions, such as pH and redox conditions, within the aquifer.
Metals reported to widely occur at concentrations above drinking-water benchmarks in untreated groundwater from some aquifers include manganese and the metalloid arsenic. Other metals, like iron, might not be present at levels that are a health risk, but can be a nuisance by making water unpleasant to drink or by staining fixtures. Levels of metals can be lowered through treatment. Water from public-supply wells is required to be tested by the well operator on a routine basis to help assure that the water provided to consumers meets Federal and State water-quality standards, which exist for many but not all metals. Routine testing of water from domestic (private) wells is not required, and it is up to the homeowner or private-well owner to test, maintain, and treat the water from their well. The best way to know the water quality of a domestic well is to have it tested.
In areas impacted by mining, acid runoff dissolves heavy metals, such as copper, lead, and mercury, into groundwater or surface water. Acidic, metal-laden drainage from abandoned coal mines can have substantial effects on aquatic resources. Problems that can be associated with mine drainage include contaminated drinking water, disrupted growth and reproduction of aquatic plants and animals, and the corroding effects of the acid on parts of infrastructures such as bridges.
Corrosive water can contribute to elevated concentrations of metals in drinking water, but in this case the metals come from within the water distribution system, such as pipes used for plumbing. Naturally corrosive water is not dangerous to consume in itself, but if plumbing materials contain lead or copper, corrosive water can cause these metals to leach into the water supply. Both surface water and groundwater can be corrosive. Many factors contribute to corrosivity, including elevated concentrations of chloride and other dissolved solids, pH out of neutral range, elevated concentrations of suspended solids, and low alkalinity.
METALS IN LAKE SEDIMENTS—RECONSTRUCTING CONTAMINANT TRENDS
Metals tend to adhere to sediment; they can be carried by suspended sediment in streams and rivers to lakes and reservoirs, where the sediment and metals settle to the bottom. The history of metal contamination in a watershed is recorded in the lake sediment, and by collecting and analyzing cores of that sediment the watershed's contamination history can be reconstructed.
Trends in metals, as recorded in sediment cores, reflect legislation, regulation, and changing demographics and industrial practices in the United States. For example, sediment cores clearly indicate the peak in the use of leaded gasoline in the late 1960s and early 1970s. A study of metals trends in 35 reservoirs and lakes across the U.S. found decreasing trends in both lead and chromium in most lakes, and increasing trends in few or no lakes. Sediment cores can also record trends in metals associated with local sources such as mining and smelters. In urban areas, fluvial sources (urban runoff and streams) contribute far greater fluxes of metals than do atmospheric sources.
► Learn more about metals and lake sediment cores.
ADDITIONAL RESOURCES
- Toxic Metals (Occupational Safety and Health Administration)
- Metals (Food and Drug Administration)
- Potential Well Water Contaminants (U.S. Environmental Protection Agency)
Follow the links to web pages on topics related to trace elements and water quality.
Radionuclides
Chloride, Salinity, and Dissolved Solids
Arsenic and Drinking Water
Mercury
Corrosivity
Water-Quality Benchmarks for Contaminants
Groundwater Quality—Current Conditions and Changes Through Time
Predicting Groundwater Quality in Unmonitored Areas
Water-Quality Trends From Lake Cores
Oxidation/Reduction (Redox)
Sediment-Associated Contaminants
Trace Elements in Streams Near the Stibnite Mining Area
Below are news stories associated with trace elements and water quality.
Contaminants present in many parts of the Glacial aquifer system
Are you one of 30 million Americans whose drinking-water supply relies on groundwater from the glacial aquifer system? A new USGS study assesses the quality of untreated groundwater from this critical water resource, which underlies parts of 25 northern U.S. states.
- Overview
Metals, metalloids, and radionuclides all are trace elements that occur naturally in the Earth's crust. In small quantities many trace elements are essential for health in all living organisms, but some trace elements can be toxic or cause cancer, and some can bioaccumulate. The USGS investigates where and how trace elements make their way into our Nation's surface water and groundwater.
Featured: 3-D Models of As and Mn in the Glacial Aquifer System
New 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured: Updated Information on the Nation's Groundwater Quality
Three new USGS fact sheets update information on groundwater quality in the nation's most heavily used aquifers. Metals are among the constituents that most frequently exceed human-health benchmarks.
Trace elements are simply elements present in minute amounts in the environment. Trace elements include metals, such as lead and iron; metalloids, such as arsenic; and radionclides (radioactive elements), such as radium and radon. Trace elements in our Nation's streams, rivers, and groundwater have natural and manmade sources. Rock weathering, soil erosion, and dissolution of water-soluble salts are examples of natural sources of trace elements. Many human activities also contribute trace elements to the environment—mining, urban runoff, industrial emissions, and nuclear reactions are just some of the many manmade sources. Trace elements tend to concentrate in sediment, but also can dissolve to some degree in water, and can present a risk to human and aquatic health.
► Learn about trace elements in groundwater in Principal Aquifers of the United States, our invisible, vital resource.
METALS
Many people might not realize that most elements are metals. Metals tend to be shiny, they make good conductors, and they're malleable and ductile. Most corrode when exposed to sea water or air, and lose electrons during reactions. We're familiar with many metals, for example gold, silver, lead, zinc, chromium, cadmium, and mercury. It's less obvious that other elements—beryllium, sodium, and lithium, for example—are metals too. Although manmade metal objects surround us each day, metals represent only a minute proportion of the elements in the Earth's crust.
There is no agreed-upon definition of "heavy metals," but heavy metals generally are considered to be those metals with a high density. Gold, silver, tin, copper, zinc, and iron are well-known examples of heavy metals. Some heavy metals, like iron and zinc, are essential nutrients at low concentrations but toxic at high concentrations. Other non-essential heavy metals, like cadmium, mercury, and lead, are toxic even at relatively low concentrations.
A "metalloid" has properties intermediate between metals and non-metals. From a water-quality point of view, arsenic is perhaps the metalloid of most concern. Other metalloids include boron and silicon, and carbon and some other trace elements are sometimes classified as metalloids.
Metals in water used for drinking and in sediment can present a risk to human and aquatic health. Various concentration benchmarks have been developed that indicate the concentration above which a metal is a health concern.
RADIONUCLIDES
Radionuclides (radiocative elements) also are trace elementa. Radionuclides in our environment are produced by minerals in the Earth’s crust, by cosmic rays hitting atoms in the Earth’s atmosphere, and by human activities. Radionuclides occur naturally in many rocks and minerals and therefore occur frequently groundwater. The most common examples of radionuclides in groundwater are uranium, radium, and radon.
► Learn more about radionuclides and water quality.
OTHER TRACE ELEMENTS
A small number of trace elements, such as selenium, are neither metals nor radionuclides. Selenium occurs naturally in sedimentary rocks, shales, coal and phosphate deposits, and soils. Application of irrigation water, which contains dissolved oxygen, can caused selenium to be released from sediment into groundwater, particularly in arid areas. This processes has been documented in the shallow Denver Basin aquifer in Colorado and in parts of the West where selenium occurs in rocks and sediments. Selenium in groundwater can discharge into streams, where it can bioaccumulate in the aquatic food chain. Chronic exposure in fish and aquatic invertebrates can cause reproductive impairments.
TRACE ELEMENTS AND DRINKING WATER
Concentrations of trace elements are more likely to be a problem in groundwater than in surface water, unless the area is impacted by mining. That’s because when groundwater moves through the rocks and sediments that make up an aquifer, some of the minerals in or adhered to those rocks and sediment are released into the water. Groundwater that has been in an aquifer a long time has had more time to interact with aquifer materials than groundwater that has recharged recently. Additionally, geochemical conditions, such as pH and redox, change as groundwater slowly moves along a flowpath from recharge to discharge—those geochemical conditions can affect whether metals are released into the groundwater.
Groundwater age is just one of the factors that can affect the concentration of trace elements. Other factors include climate and, geology, and human actions. Climate4 plays a role because in regions where precipitation is low and evaporation rates are high, there is less water to dilute the products of rock weathering. Geology plays a role because the metals available for leaching into groundwater depend on types of minerals present in the rocks and sediment. Finally, human actions such as irrigation and pumping can affect concentrations of trace elements in groundwater, often by changing the geochemical conditions, such as pH and redox conditions, within the aquifer.
Metals reported to widely occur at concentrations above drinking-water benchmarks in untreated groundwater from some aquifers include manganese and the metalloid arsenic. Other metals, like iron, might not be present at levels that are a health risk, but can be a nuisance by making water unpleasant to drink or by staining fixtures. Levels of metals can be lowered through treatment. Water from public-supply wells is required to be tested by the well operator on a routine basis to help assure that the water provided to consumers meets Federal and State water-quality standards, which exist for many but not all metals. Routine testing of water from domestic (private) wells is not required, and it is up to the homeowner or private-well owner to test, maintain, and treat the water from their well. The best way to know the water quality of a domestic well is to have it tested.
In areas impacted by mining, acid runoff dissolves heavy metals, such as copper, lead, and mercury, into groundwater or surface water. Acidic, metal-laden drainage from abandoned coal mines can have substantial effects on aquatic resources. Problems that can be associated with mine drainage include contaminated drinking water, disrupted growth and reproduction of aquatic plants and animals, and the corroding effects of the acid on parts of infrastructures such as bridges.
Corrosive water can contribute to elevated concentrations of metals in drinking water, but in this case the metals come from within the water distribution system, such as pipes used for plumbing. Naturally corrosive water is not dangerous to consume in itself, but if plumbing materials contain lead or copper, corrosive water can cause these metals to leach into the water supply. Both surface water and groundwater can be corrosive. Many factors contribute to corrosivity, including elevated concentrations of chloride and other dissolved solids, pH out of neutral range, elevated concentrations of suspended solids, and low alkalinity.
METALS IN LAKE SEDIMENTS—RECONSTRUCTING CONTAMINANT TRENDS
Sources/Usage: Public Domain.Researchers cut slices of sediment from a lake-sediment core for analysis. By analyzing concentrations of sediment-associated contaminants from the bottom of the core to the top, the history of that contaminant in the watershed can be reconstructed. Metals tend to adhere to sediment; they can be carried by suspended sediment in streams and rivers to lakes and reservoirs, where the sediment and metals settle to the bottom. The history of metal contamination in a watershed is recorded in the lake sediment, and by collecting and analyzing cores of that sediment the watershed's contamination history can be reconstructed.
Trends in metals, as recorded in sediment cores, reflect legislation, regulation, and changing demographics and industrial practices in the United States. For example, sediment cores clearly indicate the peak in the use of leaded gasoline in the late 1960s and early 1970s. A study of metals trends in 35 reservoirs and lakes across the U.S. found decreasing trends in both lead and chromium in most lakes, and increasing trends in few or no lakes. Sediment cores can also record trends in metals associated with local sources such as mining and smelters. In urban areas, fluvial sources (urban runoff and streams) contribute far greater fluxes of metals than do atmospheric sources.
► Learn more about metals and lake sediment cores.
ADDITIONAL RESOURCES
- Toxic Metals (Occupational Safety and Health Administration)
- Metals (Food and Drug Administration)
- Potential Well Water Contaminants (U.S. Environmental Protection Agency)
- Science
Follow the links to web pages on topics related to trace elements and water quality.
Radionuclides
Many people might be surprised to learn that drinking-water sources, especially groundwater, can contain radioactive elements (radionuclides). Radionuclides in water can be a concern for human health because several are toxic or carcinogenic. Other radionuclides are useful tools for determining the age of groundwater in an aquifer or of sediment deposited at the bottom of a water body.Chloride, Salinity, and Dissolved Solids
All natural waters contain some dissolved solids (salinity) from contact with soils, rocks, and other natural materials. Too much, though, and dissolved solids can impair water use. Unpleasant taste, high water-treatment costs, mineral accumulation in plumbing, staining, corrosion, and restricted use for irrigation are among the problems associated with elevated concentrations of dissolved solids.Arsenic and Drinking Water
Arsenic is a naturally occurring element, but long-term exposure can cause cancer in people. There has been a substantial amount of research done to address arsenic in groundwater and drinking-water supplies around the country. The USGS studies local and national sources of arsenic to help health officials better manage our water resources.Mercury
Mercury is a potent neurotoxin that can affect the human nervous system. Eating fish contaminated with mercury can cause serious harm to people and wildlife.Corrosivity
Corrosivity describes how aggressive water is at corroding pipes and fixtures. Corrosive water can cause lead and copper in pipes to leach into drinking water and can eventually cause leaks in plumbing. Surface water and groundwater, both sources of drinking water, can potentially be corrosive.Water-Quality Benchmarks for Contaminants
How does the water quality measure up? It all depends on what the water will be used for and what contaminants are of interest. Water-quality benchmarks are designed to protect drinking water, recreation, aquatic life, and wildlife. Here you’ll find links to some of the most widely used sets of water, sediment, and fish tissue benchmarks and general guidance about their interpretation.Groundwater Quality—Current Conditions and Changes Through Time
Is groundwater the source of your drinking water? The USGS is assessing the quality of groundwater used for public supply using newly collected data along with existing water-quality data. Learn more about this invisible, vital resource so many of us depend on.Predicting Groundwater Quality in Unmonitored Areas
Groundwater provides nearly one-half of the Nation’s drinking water, and sustains the steady flow of streams and rivers and the ecological systems that depend on that flow. Unless we drill a well, how can we know the quality of the groundwater below? Learn about how the USGS is using sophisticated techniques to predict groundwater quality and view national maps of groundwater quality.Water-Quality Trends From Lake Cores
Sediment cores let us look back in time at the contaminant history of a watershed. Learn about what lake and reservoir sediment cores tell us about trends in metals, organochlorine pesticides, polycyclic aromatic hydrocarbons, and other sediment-related contaminants.Oxidation/Reduction (Redox)
The redox state of groundwater—whether the groundwater is oxic (oxidized) or anoxic (reduced)—has profound implications for groundwater quality. Knowing the redox conditions of groundwater can help determine whether it contains elevated levels of many contaminants, including arsenic, nitrate, and even some manmade contaminants.Sediment-Associated Contaminants
Stream, river, and lake bed sediment are reservoirs for many contaminants. These contaminants include some “legacy” contaminants, like DDT, PCBs, and chlordane, and chemicals currently in use, like the insecticide bifenthrin and many flame retardants. Learn about techniques used to study sediment-associated contaminants and their importance to aquatic biota.Trace Elements in Streams Near the Stibnite Mining Area
Mining of stibnite (antimony sulfide), tungsten, gold, silver, and mercury near the town of Stibnite in central Idaho has left a legacy of trace element contamination in the East Fork of the South Fork of the Salmon River (EFSFSR) and its tributaries. Concentrations of arsenic, antimony, and mercury frequently exceed human health criteria and may impact threatened or endangered salmonid species... - Data
- Publications
- News
Below are news stories associated with trace elements and water quality.
Contaminants present in many parts of the Glacial aquifer system
Are you one of 30 million Americans whose drinking-water supply relies on groundwater from the glacial aquifer system? A new USGS study assesses the quality of untreated groundwater from this critical water resource, which underlies parts of 25 northern U.S. states.