This invention relates generally to fluid sampling and more particularly to methods of sampling toxin flux rates across the sediment/water interface at the ocean floor.
Sediment in many bays, harbors and coastal waters 1s contaminated with metal and organic toxins. These toxins are known to cause extensive biological harm to aquatic environments. As a result of the threat of biological harm, remedies for contamination due to toxins are continually being devised.
In order to effectuate a satisfactory remedy however, the source of contamination must first be identified. The remedial urgency (i.e. biological risk) relative to other contaminated sites must also be determined. With toxin sources identified and biological risk assessed, remedial resources can be efficiently allocated to remedy contamination caused by toxins.
Historically, industrial discharge, chemical spills, improper waste disposal and urban runoff have been the largest known toxin sources. These sources are relatively easy to pin point. It is now known, however, that a significant portion of aquatic contamination comes via pore water and particulate bound contaminate exchange in benthic sediment (i.e. soluble toxins are suspended and leached from underwater sediment into the aquatic environment).
Sedimentary (benthic) contamination is particularly troublesome to remedy because, unlike contamination caused by chemical spills and industrial discharge, the source is often difficult to pinpoint. Benthic contamination also creates a high level of biological risk for benthic organisms whose survival depends on the condition of the underwater sediment. Additionally, as toxins in the underwater sediment migrate across the sediment/water interface and into the aquatic environment, all aquatic organisms are put at risk of contamination. Due to the scope and seriousness of problems associated with benthic contamination, a myriad of approaches have been developed to measure toxin levels in benthic sediments.
One common approach has been to remove and transport a sediment sample to a laboratory for chemical and biological testing. This approach requires numerous samples and is thus time consuming, expensive and inefficient. Inaccuracy is caused by sediment removal prior to testing. More specifically, removal of a sample disturbs the sediment so that natural conditions present at the site may not be well preserved in the laboratory. Localized variables such as underwater pressure, temperature, salinity, pH, oxygen and light intensity effect sediment samples. As toxin levels and bioavailability directly depend on these localized variables, toxin levels and toxicity in laboratory test samples do not always coincide with those detected under natural conditions.
Besides inaccuracy, another problem associated with previous method of sediment testing is that it is not capable of yielding changes in toxin concentrations. Since several samples taken at a single point are required to determine change in toxin concentrations and the act of removing sediment samples disturbs nearby sediment, tiny changes in toxicant levels can not be ascertained with any useful degree of certainty.
Toxin concentration by itself is not indicative of the level of biological risk. To precisely determine biological risk, the biological uptake and accumulation of toxicant by marine life must be determined. Unfortunately, direct measurement of these factors is extraordinarily difficult. Indirect measurements, however, may be made. This is accomplished by measuring the amount of soluble toxins which leach through pore water, cross the sediment water boundary and enter the aquatic environment. This is called the benthic flux rate.
The benthic flux rate is the most accurate known indicator of the rate at which toxins are entering an aquatic environment from the sediment. The benthic flux rate is also useful in pinpointing the source of contamination by determining whether toxins are leaching from the sediments into the water or vice versa. Together with traditional monitoring and assessment techniques, these benthic flux measurements are effective for determining the source of and biological risk associated with contamination of benthic sediments.
In view of the inefficiency, inaccuracy and imprecision of the other sediment sampling methods and in accordance with this inventive concept, a need has become apparent for an improved method of benthic flux sampling which includes isolating a volume of water on the ocean floor in a closed chamber, measuring variables such as temperature, salinity, pH and dissolved oxygen concentration and maintaining appropriate oxygen levels to insure precise and accurate toxin concentration determination by periodic sampling to ascertain the benthic flux rate.