A variety of elements and organic compounds have entered the environment as a result of human activities. Such substances find their way to aquatic sediments from direct discharges to waterways, atmospheric emissions, and runoff. Some of these chemicals are known to harm fish or wildlife, either by direct toxicity, by reducing viability, or by limiting reproductive success. In aquatic systems, sediments become the eventual sink for most of these chemicals. Analyzing the sediments provides a first step in a chemical inventory that can lead to an assessment of potential biological impacts (Kennicutt and others, 1994).

Many elements (iron, aluminum, calcium, and others) enter the environment from the natural weathering of rock. Additional amounts of elements have been contributed by human activities such as mining, metals production and processing, fossil fuel combustion, municipal waste incineration, and transportationrelated sources. The environmental presence of some elements, such as lead and mercury, is almost entirely due to human activity. Lead is often associated with the use of leaded gasoline and from the manufacture and disposal of lead storage batteries. Mercury was used historically in a variety of industrial processes and as a pesticide. Nriagu and Pacyna (1998) concluded that human activity is the “most important element in the global biogeochemical cycling of the trace metals.”

The number of organic compounds in existence and their total production has more than tripled in the last century. Many of these compounds enter the environment directly as pesticides; others are inadvertently discharged. Some organic compounds have natural sources. Three general classes of organic compounds will be discussed: organochlorine compounds, polyaromatic hydrocarbons, and phthalates.

Almost all organochlorine compounds are manmade. Many are pesticides that were used widely in the 1950s–60s (DDT and chlordanes, for example). Use of most organochlorine pesticides was restricted or banned in the United States in the 1970s–80s. Polychlorinated biphenyls (PCBs) are also organochlorine compounds; they were used for a variety of applications, but most commonly as insulators in electrical transformers and other equipment. In general, organochlorine compounds degrade very slowly in the environment and therefore, are routinely found in environmental samples, despite the fact that they are no longer used in the United States. They are hydrophobic that is they do not dissolve readily in water and, in aquatic systems, are almost exclusively associated with sediments or tissue. Because these compounds cause a variety of adverse health effects in wildlife, the U.S. Environmental Protection Agency (USEPA) has listed many as priority pollutants. Organochlorine compounds also have been implicated as endocrine disrupters— chemicals that can interfere with the normal function of hormones.

Polyaromatic hydrocarbons (PAHs) are found in sediments throughout the world (Hites and others, 1980). Their presence is thought to be primarily anthropogenic. PAHs occur naturally in petroleum products and also are produced during combustion. They enter the environment from fuel spills, tar coatings, coal and other fossil fuel usage, road dust, and from the atmospheric deposition of combustion products (Prahl and others, 1984; Wakeham and others, 1980). Urban areas often have high concentrations of PAHs because of transportation-related sources (vehicle exhaust, paving materials, and releases of fuel or oil). Natural sources, such as forest fires, may contribute small amounts of PAHs. Several PAHs are known carcinogens (benzo[a]pyrene, for example); 16 are listed as USEPA priority pollutants.

Phthalate compounds are often associated with urban areas. They are used in a wide variety of industrial applications and in inks, adhesives, resins, and as plasticizers (chemicals that increase the flexibility of plastics). In aquatic systems, phthalates are found mostly in sediments where they degrade very slowly. Phthalates are thought to be endocrine disrupters; Jobling and others (1995) found that some phthalates were weakly estrogenic. USEPA considers some phthalates to be possible carcinogens.

This report describes the results of a reconnaissance survey of elements and organic compounds found in bed sediment and fish tissue in streams of the Tualatin River Basin. The basin is in northwestern Oregon to the west of the Portland metropolitan area (fig. 1). The Tualatin River flows for about 80 miles, draining an area of about 712 square miles, before it enters the Willamette River. Land use in the basin changes from mostly forested in the headwaters, to mixed forest and agriculture, to predominately urban. The basin supports a growing population of more than 350,000 people, most of whom live in lower parts of the basin. Water quality in the Tualatin River and its tributaries is expected to be affected by the increasing urbanization of the basin.