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4. English summary

Monitoring of organic contaminants in the aquatic environment is often limited to measurement of the concentration in biota or sediment. Typically, the concentration in the water phase is too low or the concentration varies with time, and the collection of a representative sample is not practically feasible. A technique where sample collection occur 1) in situ, 2) over an extended time scale, 3) with simultaneous pre-concentration of the contaminants in the sampler, and 4) without requirements of energy, has the characteristics of a possible alternative. These alternatives are described in the report based on a literature survey of the published methods on passive accumulating collectors (PACs) for the aquatic environment. The following issues are addressed: the types of PACs available, the range of compounds collected or tested, the applicability in environmental compartments and conditions, and the possibilities of comparison to concentrations in water, sediment or biota. A final evaluation relative to the usefulness for monitoring purposes is given.

For the purpose of this review a PAC was defined as an abiotic object capable of accumulating compounds against a concentration gradient without an energy source. A semipermeable barrier was not required, although most PACs have this feature. Due to the type of interaction or the barrier all the PACs accumulate compounds from the truly dissolved phase, i.e. not bound to dissolved or particulate matter.

The types of PACs available

Many passive sampling devices have been used only in a few studies and have not gained application in monitoring. The most successful PAC presently, is the semipermeable membrane device (SPMD), but the solvent-filled dialysis tubing has also been used in a number of studies and laboratories. Recently, a "Passive Sampler" based on similar proven principles has been presented and tested in a Round Robin exercise, but results have not yet been presented of in situ tests. The Empore disk and the solid phase micro extraction (SPME) methods are based directly on laboratory equipment, but do have potential in situ applicability.

The range of compounds collected or tested

The principle of the PACs is almost exclusively based on accumulation of the compound in a hydrophobic matrix, and obviously the majority of tested and detected compounds are non polar organics.

An abbreviated list of tested compounds comprise the groups of organochlorine pesticides, organophosphates, pyrethroids, selected urea derivates, triazines, aromatic hydrocarbons, alkyphenol compounds, halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons, chlorophenyls (PCB/PCT), chlorophenols, polyaromatic hydrocarbons (PAH), phosphate triesters, phthalates, anionic detergents (LAS), cationic detergents, organotin compounds, dioxins and furans, and various special compounds (e.g. non-nitro musk fragrances and algal metabolites).

Overview of published PAC methods that have been used or can be used in situ. Several sampling purposes are identified: determination of contamint concentration in the water (quantitative), qualitative or semi-quantitative determination of occurrence (screening), collection of material for toxicity tests (toxicity tests), determination of bioconcentration potential (bioconcentration)

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Generally, PACs have not been used in water for collection of volatiles (e.g. MTBE) or hydrophilic compounds such as the pesticides phenoxy acids, sulfonyl urea compounds, dithiocarbamates, carbamates, benzonitrils, halogenated carboxylic acids, or for aliphatic amines. These compounds are all on the Danish national monitoring programme for the aquatic environment. Although the ionic detergents have been tested with PACs, accumulation is not feasible.

Applicability in environmental compartments and conditions

There are no fundamental obstacles or technical difficulties in applying PACs in marine and fresh water environments. SPMDs have been exposed in a range of aqueous compartments: small streams and rivers, lakes, coastal zone and open sea, well water and waste water. Solvent-filled dialysis tubes have also been exposed in various compartments, but is a less robust construction. Several PACs have been used in terrestrial studies.

Comparison to water, sediment or biota concentration

PACs developed for quantitative or semi-quantitative use in situ are typically exposed from one to four weeks. During the exposure period contaminants are accumulated and contained within the PAC. The compounds are released only very slowly and the PACs can therefore be used as "guard dogs" for monitoring transient emissions.

Mathematical descriptions of uptake and release processes have been developed for SPMDs. For a range of compounds the necessary laboratory calibration data are available, which allow calculation of the water concentration of a compound from the concentration in the SPMDs. At oscillating concentrations in the aqueous phase the concentration calculated will be a time weighted average.

Some PACs (Empore disks) can be used for calculating the bioconcentration potential directly, and most will accumulate from the truly dissolved phase, which for many organisms is also the bioavailable phase. PACs are therefore often used in toxicity tests and for estimation of bioavailability.

PACs have been exposed in interstitial water of sediment in situ and in laboratory experiments. The exposure conditions are too complicated for direct calculation of the interstitial water concentration of contaminants, but PACs (presently the SPMDs), may be advantageous for screening purposes, since the detection limits for strongly hydrophobic compounds are superior to conventional water sample analysis.

Cost and quality

Only the SPMD is available commercially. An estimate of the cost shows comparable prices with conventional water sampling and most likely considerably lower cost compared to automatic in situ sampling. Only a few in situ data on accuracy and precision are available for PACs. Among PACs the SPMDs show the best performance data with relative standard deviations typical from 5-30% (the better data for the more hydrophobic compounds).

PAC usefulness in monitoring

PACs may be used for quantitative determination of specific compounds and for semi-quantitive screening for a range of compounds depending on the characteristics of the PACs. The PACs have been evaluated according to a number of national and international lists of priority pollutants.

PAC method ranked according to percentage of compounds on the list the method has potential for sampling semi-quantitatively(metals excluded). Rank: Good (>75%), Medium (25-75%), Poor (<25%)