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To survey the conformity and quality of results among laboratories for microplastics determination worldwide, an international laboratory intercomparison and development exercise was organized. The 34 participants were requested to determine the polymer type and number or mass of polymer particles in 12 samples, i.e. six samples containing of pre-production pellets, five dissolvable soda tablets containing different (smaller) polymer particles and one blank soda tablet. A novel method for providing the test materials in aluminium strips was used. Thirty laboratories (88%) submitted data using their own method of choice, resulting in a variety of identification and quantification methods (n = 7). The majority of the labs (53-100%) correctly identified the type of polymer in all samples but one. The performance of the laboratories in quantifying and weighing the pellets was very good. The analysis of the number of the particles in the soda tablets varied considerably between laboratories (29-91%). The results of this study highlight the complexity of microplastics analysis and the need for harmonization of both reporting format and methods. Continued development and assessment of the comparability among analytical methods and laboratories are urgently needed to support monitoring programmes, research and decision-making.

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Policymakers are often dissatisfied by the lack of what they consider useful information to support water management. Analysis of this 'water information gap' shows that this is caused by a lack of proper communication between information users and information producers. To improve this communication the process of specification of information needs has been structured. Earlier experiences showed that this not only entailed developing a structure to manage the process, but also developing a structure to guide the breakdown of policy objectives into information needs. Such a structure to organise the problem supports policy makers and monitoring specialists in their communication. This paper describes three pilot projects where the DPSIR indicator framework was used to organise the problem. It is concluded that the DPSIR framework is useful for improving the communication between information users and information producers and is helpful in breaking down policy objectives into information needs in a structured way. The structured approach in this way assists in narrowing the water information gap. Use of the DPSIR framework however leads to a bias towards water management problems and does not provide for all the relevant information needs.

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The metaphor of the water information gap is used to describe the discontent between information users and information producers about the use of and need for specific information. This paper describes the rugby-ball methodology for specification of information needs that was developed on the basis of an analysis of the water information gap and insights from the literature on policy- and decision-analysis, problem-structuring, and information management. The methodology consists of a process-architecture to manage the process of assessing information needs and a structure to organise the information needs related to water policy objectives. The methodology was developed and enhanced through a Reflection-in-Action process in which interaction between ideas and practice leads to improved results. The paper describes the methodology and its development, and concludes both on the development process and on the abilities of the methodology to narrow the water information gap.

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There is mutual dissatisfaction among policy makers and monitoring specialists about producing what is considered useful information for policy development, implementation and evaluation. Insufficient or inappropriate communication between information users and producers is considered to be a main cause for this water information gap. This paper tests the rugby-ball methodology that has been designed to bridge the gap. The rugby-ball methodology consist of a five step plan that helps policy makers and monitoring specialists to communicate in a proper way and to come to a joint process of defining information needs. The methodology is first tested in a study to assess the information needs for the 4th National Policy Document on Water Management in the Netherlands. From the study it is concluded that the rugby-ball methodology is an important step in bridging the water information gap by better defining what useful information is. The methodology is also improved on the basis of this study by including a structure to support the breakdown of policy objectives into information needs.

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A hydrological model was constructed with the commercially available modelling environment ECoS for the calculation of mixing plots of dissolved pesticide concentrations in the Scheldt Estuary. The model was based on a one-dimensional advection-dispersion equation and dispersion coefficients were calculated from measured salinity profiles. The model could correctly predict the movement of water masses within the estuary. Nominal flushing times of the estuary were calculated with the fraction-of-freshwater method and ranged between 25 and 95 days, depending on the freshwater discharge. Model calculations demonstrated that the application-related time profiles of pesticide input may well induce curvature in the calculated estuarine mixing plot even if the pesticide behaves conservatively. Calculated mixing plots were compared with experimental data and good agreement was obtained between the measurements and the conservative mixing plot of atrazine. For metolachlor an additional direct emission had to be modelled to explain the differences between the experimental data and the conservative mixing plot. For dichlorvos and simazine. on the other hand, an estuarine loss constant had to be included in the model. Using a least-squares procedure the estuarine loss constants for dichlorvos and simazine were estimated at half-lives of five and 26 days, respectively. Because mixing plots were strongly influenced by the time profiles of pesticide input, standard procedures in which net fluxes are calculated from mixing plots, were not applicable. Therefore, net fluxes were calculated with a newly developed procedure in which the estuarine loss constants and the estuarine flushing time were combined. For the non-conservative compounds dichlorvos and simazine, the net fluxes to the North Sea were found to be 96 and 64%, respectively, lower than the gross fluxes transported by the River Scheldt.

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As part of the Fluxes of Agrochemicals into the Marine Environment (FAME) project, the gross fluxes of selected pesticides (i.e. the herbicides atrazine, simazine, alachlor and metolachlor, the atrazine degradation product desethylatrazine, the insecticide dichlorvos and the antifouling agent Irgarol 1051) transported by the river Scheldt and the Canal Ghent-Terneuzen were determined from March 1995 through February 1997. In general, the observed temporal trends were related to the application period of the pesticides, except for metolachlor for which elevated concentrations were observed in the winter of 1995-1996. Relatively large gross fluxes were found for desethylatrazine compared with its parent compound. A study on the estuarine behaviour of pesticides showed distinct differences between the compound classes. The mixing plots of the organophosphorus insecticides dichlorvos and diazinon revealed clear evidence of estuarine loss processes which agrees with their low DT50 values reported for water/sediment systems, their relatively high Henry's law constants and, for diazinon, its relatively high Koc value. The mixing plots of the acetanilides alachlor and metolachlor were strongly influenced by an additional direct emission into the estuary, which was evident from a maximum in dissolved concentration near a salinity of 10@1000. An apparent conservative behaviour was observed for the triazine compounds atrazine and Irgarol 1051. This was in contrast to simazine, which showed an apparent non-conservative behaviour. However, the time profiles of the riverine concentrations of simazine did not exclude that the observed curvature was solely caused by estuarine losses; therefore, additional modelling is required. In a follow-up study a suitable hydrological model of the Scheldt estuary was constructed; the results will be presented in a forthcoming paper (Steen, R.J.C.A., Evers, E.H.G., Van Hattum, B., Cofino, W.P. and Brinkman, U.A.Th. Net fluxes of pesticides from the Scheldt estuary into the North Sea: a model approach. Environmental Pollution, submitted.

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The aim of this paper is to analyze the potential of indicators for integrated river basin management and to develop a set of indicators for the management of transboundary river basins. An indicator, comprising a variable or some aggregation of variables, describes a system or process such that it has significance beyond the face value of its components. Integrated river basin management takes into account policies and measures for the multifunctional use of rivers on a catchment scale and associated institutional changes. Indicators are useful instruments for this process for two reasons. Firstly, they meet the information need of policy- and decision-makers. Secondly, indicators can be used to structure the definition and description of information needs and collection of information between the different international, institutional, and sectoral management levels. The development of indicators involves a number of steps: definition of aim, construction of conceptual model, selection of variables, comparison with selection criteria, database assessment, and indicator selection. In this paper these steps are discussed and specified for integrated river basin management. This results in a set of indicators describing the pressure to the river, the state of the river ecosystem, the impact to goods and services provided by the river, and the societal response. The proposed set of indicators measured at a river basin scale provides integrated information on the use and supply of goods and services, underlying cause-effect relationships and possible trade-offs and their spatial distribution (e.g., upstream versus downstream). Furthermore, we propose a division of tasks and responsibilities for river basin management with regard to the development of indicators, data collection, and their application in decision-making.

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A method is developed for the determination of polar pesticides and their transformation products [atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachlor] in surface, estuarine and sea water samples at the low ng/l level. Solid-phase extraction is combined off-line with column liquid chromatography-electrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridges and graphitized carbon black extraction disks, is evaluated. The influence of the organic solvent used in gradient LC, as well as the amount of co-extracted humic material on the ESI process is studied. The eluotropic strength of the organic solvent was found to have a distinct effect on the sensitivity of ESI-MS if coupled with LC gradient separations. Methanol gave much better results than acetonitrile and phenylurea compounds are more susceptible to solvent changes than triazines. Co-extracted humic material causes signal suppression in ESI-MS-MS detection. The degree of suppression depends upon the sample pH and the nature of the samples, i.e., surface or estuarine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, with the exception of DPU (8 ng/l). The applicability of the procedure was demonstrated by analyzing surface and estuarine water.

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An analytical procedure was developed that enables routine analysis of four estrogenic hormones in concentrations below 1 ng/l in surface water and waste water. The recovery was 88-98% with a limit of detection of 0.1-2.4 ng/l depending on the compound and the matrix measured. This method was used to determine the occurrence of 17 beta-estradiol, 17 alpha-estradiol, estrone and 17 alpha-ethinylestradiol in the aquatic environment in The Netherlands. The data show that estrogenic hormones can be detected at low concentrations (up to 6 ng/l) at some locations in surface water. In selected effluents of waste water treatment plants estrone and 17 beta-estradiol were detected in concentrations in the ng/l range. Concentrations of 17 alpha-estradiol and the contraceptive 17 alpha-ethinylestradiol were in most of these samples below the limit of detection. Hormone glucuronides were not detected in most surface water and effluents.

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Bioaccumulation of non-, mono-, and di-ortho-substituted chlorobiphenyls (CBs) was investigated in four species of mustelids (weasel, stoat, polecat, and otter) and their preys, from a restricted area in the northern part of The Netherlands. Diets of these mustelids ranged from terrestrial (weasel, stoat, and polecat) to aquatic (otter). Diet-specific biomagnification factors (BMFs), CB in diet relative to CB in mustelids, were calculated for the sum of 28 congeners (SigmaCB), for the sum of the toxic equivalent concentration (SigmaTEQ) and on an individual congener basis. Biotransformation was studied in relation to structural CB properties (vicinal H-atom substitution). In addition, the methylsulphonyl CB-metabolites were determined. The concentration of SigmaCB on lipid weight basis increased in the order weasel < stoat < polecat < otter. On the basis of SigmaTEQ, the order changed to weasel < polecat < stoat < otter. Most of the differences in BMFs between the CBs could be explained by the vicinal H-atom structure-activity rules. For all mustelids, the lowest BMFs were found for congeners with vicinal H-atoms in the meta, para position. Indications were found that all mustelid species can metabolize these congeners. For some of the CBs, their methylsulphonyl-CB metabolites were determined and found to be present in concentrations up to 350-fold higher than those of the parent compounds. In addition, the non-ortho CBs 126 and 169 are selectively retained in the liver of weasel, stoat, and otter. These CBs had the highest BMFs of all congeners. However, rather surprisingly, in polecat the highest BMFs were found for di-ortho-substituted CBs. This animal was able to metabolize all congeners with vicinal H-atoms in the ortho and meta position (non- and mono-ortho CBs). The information concerning the differences in bioaccumulation of CBs for closely related mustelid species increased the understanding of reported differences in PCB toxicity between mink and ferrets, and suggest that weasel, stoat, and otter are at least as sensitive to CBs as are mink, while polecats are less sensitive. As otter is exposed to much higher concentrations of CBs trough their diet than weasel and stoat, the toxic threat of CBs will be the greatest for this animal.

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An extensive study on the presence of nine organotin compounds (OTs) in a freshwater foodweb was made, using newly developed analytical procedures in order to obtain insight in accumulation and degradation processes. Tributyltin (TBT), Triphenyltin (TPT) and their degradation products were detected. Zebra mussels, eel, roach, bream, pike, perch, and pike perch and cormorant showed high OT body concentrations. At the lower trophic levels, phenyltin concentrations were higher in benthic species while butyltin concentrations were higher in pelagic species. This indicates that TBT is passed on primarily via the water, while TPT is passed on to a larger extent via the sediment. At the higher trophic levels, net bioaccumulation of TPT was greater than that of TBT, resulting in relatively higher TPT concentrations. High concentrations of biodegradation products of TBT, but not of TPT, were found in the livers of fish and birds, which indicates that TBT is more easily metabolized than TPT. A comparison with literature data of fish lethal body concentrations revealed that fish in the field may be endangered. With birds, the highest concentrations of OTs were present in liver and kidney and not in subcutaneous fat, which confirms that OTs accumulate via different mechanisms than traditional lipophilic compounds. As a whole the OT concentrations found in the foodweb may be considered to be quite alarming.

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