{
"@context": "http://schema.org/", "@type": "WebPage", "additionalType": "Topic", "url": "https://www.usgs.gov/mission-areas/water-resources/science/sediment-associated-contaminants", "headline": "Sediment-Associated Contaminants", "datePublished": "September 17, 2018", "author": [ { "@type": "Person", "name": "Barbara J Mahler", "url": "https://www.usgs.gov/staff-profiles/barbara-j-mahler", "identifier": { "@type": "PropertyValue", "propertyID": "orcid", "value": "0000-0002-9150-9552" } } ], "description": [ { "@type": "TextObject", "text": "Importance to Stream EcologyThe USGS Regional Stream Quality Assessment (RSQA) is assessing the importance of a wide-range of stressors to aquatic ecosystems in small streams, including sediment-associated contaminants. The assessment includes evaluation of toxicity of stream sediment in urban, agricultural, and undeveloped settings to aquatic organisms. For example, the pesticide bifenthrin in sediment was found to reduce the abundance of insect larvae and to affect the timing of the metamorphosis of those larvae to adult insects." }, { "@type": "TextObject", "text": "Sediment-associated contaminants are of particular concern for aquatic organisms that live in the bed sediment of streams, rivers, and lakes\u2014referred to as benthic organisms. Dragonfly larvae, for example, live in sediment, as do the larvae of many other insects. Mollusks, such as mussels and clams, crustaceans, such as crayfish, and many fish and amphibians live in, on, or near the sediment, or consume smaller organisms that do, and therefore sensitive to the contaminants associated with that sediment." }, { "@type": "TextObject", "text": "Pesticides in biofilms may be a better predictor than sediment of potential adverse effects on the community of organisms that live on and in the streambed, reports a new study by the USGS Regional Stream Quality Assessment." }, { "@type": "TextObject", "text": "Many contaminants adhere, or \u201csorb\u201d, to sediment rather than readily dissolving in water. Once sorbed, these chemicals can persist in the sediment for years, long after they are no longer detectable in water. These types of chemicals, sometimes referred to as \u201chydrophobic\u201d (\"water fearing\u201d), include many legacy contaminants, like DDT, PCBs, and chlordane, that were banned decades ago but are still found in lake and stream bed sediment, sometimes at concentrations high enough to be a risk to aquatic organisms. Other hydrophobic contaminants are being released into the environment, like the pesticide bifenthrin, flame retardant chemicals, and polycyclic aromatic hydrocarbons (PAHs). Most metals, such as lead, zinc, and cadmium, also concentrate in sediment rather than water." }, { "@type": "TextObject", "text": "At what concentration is a sediment-associated contaminant likely to be toxic? Sediment benchmarks provide two levels: the concentration below which the sediment is unlikely to be toxic (the threshold effects concentration, or TEC) and the concentration above which the sediment is likely to be toxic (the probable effects concentration, or PEC). These benchmarks provide a handy context to evaluate the potential toxicity of sediment-associated contaminants." }, { "@type": "TextObject", "text": "Trends in Sediment-Associated ContaminantsThe fact that some contaminants adhere to sediment offers a unique opportunity to track how their concentrations have changed over time. Sediment cores\u2014essentially long tubes of mud pulled from a lake or reservoir\u2014allow us to look back in time at contaminant trends in a watershed. Concentrations at the top of the core reflect recent inputs of contaminants, and concentrations farther down the core reflect older and older inputs." }, { "@type": "TextObject", "text": "Sediment cores have allowed us to see the effectiveness of bans on some chemicals, such as DDT, with their concentrations decreasing toward the top of the core. Sediment cores also allow us to identify concerns about chemicals, such as PAHs, whose concentrations increase toward the top of the core." }, { "@type": "TextObject", "text": "Although we typically think of suspended sediment as being associated with surface water\u2014streams, rivers, and lakes\u2014suspended sediment and the contaminants associated with it can also be transported with groundwater through the subsurface conduits found in karst aquifers." }, { "@type": "TextObject", "text": "Contaminant Transport on Suspended SedimentNot all contaminated sediment is bed sediment. Hydrophobic contaminants\u2014contaminants that do not dissolve in water\u2014can bind to sediment as well and be transported down streams and rivers, ultimately to be deposited in the bed sediment of a downstream lake or the ocean. By measuring contaminants on suspended sediment in conjunction with flow, the loads and yields of hydrophobic contaminants can be estimated. Stormwater is a particularly important source of contaminants sorbed to and transported by suspended sediment." }, { "@type": "TextObject", "text": "Stream, river, and lake bed sediment are reservoirs for many contaminants. These contaminants include some \u201clegacy\u201d 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." }, { "@type": "TextObject", "text": "Dirt, sand, and other particulate material on parking lots and streets is washing off into urban streams, reports a new study by the U.S. Geological Survey Regional Stream Quality Assessment. Learn about important implications for water quality." } ], "funder": { "@type": "Organization", "name": "Water Resources Mission Area", "url": "https://www.usgs.gov/mission-areas/water-resources" }, "about": [ { "@type": "Thing", "name": "Soil Moisture and Permafrost" }, { "@type": "Thing", "name": "Stormwater" }, { "@type": "Thing", "name": "Environmental Health" }, { "@type": "Thing", "name": "Karst, Sinkholes, and Land Subsidence" }, { "@type": "Thing", "name": "Geology" }, { "@type": "Thing", "name": "Advanced Capabilities and Research" }, { "@type": "Thing", "name": "Science Technology" }, { "@type": "Thing", "name": "Aquatic Biology and Ecosystems" }, { "@type": "Thing", "name": "Ecosystem Health" }, { "@type": "Thing", "name": "Plant and Animal Communities" }, { "@type": "Thing", "name": "Groundwater, Aquifers, Wells, and Springs" }, { "@type": "Thing", "name": "Energy" }, { "@type": "Thing", "name": "Streams and Rivers" }, { "@type": "Thing", "name": "Lakes and Reservoirs" }, { "@type": "Thing", "name": "Information Systems" }, { "@type": "Thing", "name": "Methods and Analysis" }, { "@type": "Thing", "name": "Contaminant Transport Modeling" }, { "@type": "Thing", "name": "Water" }, { "@type": "Thing", "name": "Erosion and Sedimentation" }, { "@type": "Thing", "name": "Pollution (Chemical and Biological)" }, { "@type": "Thing", "name": "Measuring and Monitoring Water" }, { "@type": "Thing", "name": "Common Water Issues" }, { "@type": "Thing", "name": "Water Quality" }, { "@type": "Thing", "name": "Microbiology" } ]
}