Low Level Contaminants Study

Early in 1999, the US Geological Survey with funding from the Estuary Partnership completed a study of contaminants using a relatively new technique known as the lipid bag or semi-permeable membrane device. The technique is designed specifically to measure organic compounds that not very soluble in water but are readily absorbed in body fats tissue (lipids). The lipid bag technique attempts to mimic nature using lipids suspended in the water column over time to evaluate the concentration of these toxins encountered by aquatic life.

Fish and wildlife populations in and near the Columbia River are exposed to wide variety of contaminants from both runoff and atmospheric deposition. Elevated levels of toxic contaminants have been found in the tissues of fish, river otters, mink, bald eagles and osprey in the Columbia River and have been correlated with reproductive abnormalities. These chemical compounds coming from industrial, agricultural, and residential use include organochlorine pesticides such as DDT and other organochlorine compounds including dioxins and PCBs. Atmospheric deposition from auto exhausts, wood stoves, and industrial sources also contribute contaminants to the system in the form of polycyclic aromatic hydrocarbons (PAHs). These compounds have a common trait, they have very low solubility in water but are readily sorbed by fatty tissues (lipids). They also have a tendency to bioaccumulate, that is, they concentrate in animal tissue and are passed up the food chain.

The US Geological Survey deployed the first set of sample devices during the 1997 low flow period and repeated the process in 1998 during high-flow conditions. Nine main-stem sites and seven tributary sites were used spanning approximately 700 miles of the Columbia River. Sediment samples from the streambed were also collected at 3 sites. The lipid bags were deployed in canisters, secured at each site by an anchor and a tether line to a fixed structure. Floats were used to ensure the canisters stayed suspended off the streambed. The sampling devices were left in the water for 35 days. All samples were analyzed by the USGS laboratories in Missouri.

Conclusions reached by the study:

• Mechanisms such as volatilization, dilution, and settling of suspended particles can act to significantly reduce concentrations of contaminants along the river's flow path if no new sources of contaminants occur.
• Elevated levels of contaminants in the Portland-Vancouver area are primarily from local rather than upstream sources.
• Elevated levels of many compounds tend to be diluted during periods of high discharge.
• The much higher flows of the main stem Columbia River considerably dilute elevated concentrations of contaminants entering from tributaries.
• The distribution of these compounds in streambed sediments is not necessarily indicative of their distribution in the water column.

Finally the study demonstrates that semi permeable membrane devices can be an effective way to measure patterns of contaminant occurrence at concentrations that are relevant to organisms associated with the river but are generally undetectable by conventional water-sampling techniques. This provides a new tool in the arsenal of methods available to scientists to track the impacts of contaminants in the environment.

Limited copies of the report entitled, "Investigation of the Distribution of Organochlorine and Polycyclic Aromatic Hydrocarbon Compounds in the Lower Columbia River Using Semipermeable Membrane Devices" Water-Resources Investigations Report 99-4051, USGS, are available from the Estuary Partnership.