Sediment dredging is a major activity in the Netherlands, not only in the main rivers but also in ditches. The dredged material must meet certain objectives if it is to be disposed of in the adjacent soil. The IRIS (Integrated Risk Instrument for ditcheS) model has been developed to evaluate whether future levels of heavy metals will meet this standard. It describes the behaviour of organic and inorganic material as well as cadmium, copper, lead and zinc. A probabilistic approach dealt with the uncertainty of process parameters and emission fluxes. For uncertain and sensitive parameters Monte Carlo simulations were performed on values taken from a range. The simulations resulted in distributions for the model output variables. The model was calibrated and validated on field data in the 1990-1995 period and results showed the model to give an accurate fit to the data. Modelresults show that, at present, background loading, mainly consisting of fluxes from adjacent land, does not cause a reasonable chance of exceedance of the standards in sand- or clayditches. However, chances are very high that in peatditches concentrations will not meet standards especially in case of copper. In the latter case, additional sources will not change the probability of exceedance very much, whereas in clay and sand this particularly is the case. Again for copper, concentrations show the highest exceedance of standards. Most likely only a minor improvement might be possible the upcoming decades, because of the historical and present loading with fertilizers and/or manure and the substantial contribution from land in newly formed sediment.

Regional waters are being dredged once every 5 to 20 years to maintain the water discharge. The dredged material must meet certain objectives if it is to be disposed of in the adjacent soil. However, PAH levels exceed the sediment target value of 1.0 mg sum of PAH per kg dryweight of sediment in 60% of the ditches. In a preceeding study the present and future sediment quality has been investigated. In this study a probabilistic model was developed to investigate the effect of repeatedly distributing sediments on different categories of soil. When PAH concentration in sediment exceeds the target value up to a level of 10 mg.kg-1 (standard above which sediments must be deposited into a depot), only farm-land on sandy soils will show no exceedance of the target value for soils (equal to the target value for sediments). The other categories, farm-land on clay, grass-land on clay and grass-land on peat, show a considerable chance of exceedance of the target value. However, when being distributed, many of the sediments in which levels of PAH above the target value were measured, will cause no exceedance of the soil target value. For sand, clay and peat ditches respectively 100%, 63% and 74% of all measurements will lead to soil concentrations below the target value when being deposited on a regular basis. Decreasing atmospheric deposition will enlarge the possibility of distributing sediments without exceeding target values, especially in the case of farm-land on clay.

This study was carried out to assess the amounts of copper released by copper pipes used for drinking-water distribution into wastewater treatment plants, sewage sludge and surface water in the Netherlands. For the Netherlands as a whole, 57% of the copper load in wastewater treatment plants is attributed to copper pipes. Of this, an average of 77% ends up in sewage sludge in such concentrations as to hinder application of sewage sludge in agriculture. The remainder ends up in surface water where it is jointly responsible for the non-compliance of the Dutch surface-water standard for copper. Compliance can only be achieved by substantially reducting emissions. Corrosion control of drinking water contributes to reducing emissions, but this is not sufficient to meet the surface water standards. Little information was found on the contribution of water-heaters and of households compared to other users of drinking water.

CATS is an acronym for Contaminants in Aquatic and Terrestrial ecoSystems. CATS models have been developed for the prediction of fate and risks of toxicants. The aim of these models is to predict future risk levels of toxic substances for food webs. CATS-2 describes the behaviour of toxicants in sedimentation areas of main rivers in the Netherlands, such as Hollands Diep, Haringvliet and Ketelmeer. Bio-availability of toxicants to aquatic organisms is influenced by many biotic and abiotic characteristics of an ecosystem. Therefore, we integrated fate of toxicants in the abiotic environment with a food web model based on biomass cycling. Cycling of organic matter is the backbone of the model, acting as carrier for the toxicant. The food web consists of algae, zooplankton, bivalves, chironomid larvae, tubificid worms, whitefish, predatory fish, benthivorous fish, diving ducks and fish eating birds (Fig. 1). Cadmium and lindane (gamma-HCH) were selected to predict future risk levels in an example ecosystem, the Hollands Diep/Haringvliet area. Risk levels were calculated for two situations. First for the year 2000, with no additional clean-up of the river Rhine, and second for the year 2000 with additional clean-up according to the Rhine Action Programme. Model calculations predict that risks for both cadmium and lindane decrease, caused by the improvement of water quality in the River Rhine that feeds the area. The high cadmium load of the river Rhine in the past is responsible for high cadmium concentrations in the sediment. Even with additional clean up, sediment quality does not meet the Dutch quality objective of 2 mg/kg d.w. in the year 2000. Except for benthivorous fish, risks for the food web are low in the year 2000 indicating that in general the Rhine Action Plan is successful if its original emission-reduction goals can be achieved.

Watercourses have to be dredged once every 5 to 20 years to ensure suffcient depths for water inflow and outflow. Most of the resulting sediment is deposited on the adjacent land where polluting substances contribute to the emissions to the underlying soils. High level of PAHs (10 from VROM) in the sediment usually exceeds the sediment quality standard, putting the level of contamination in the watercourse mostly in class 2. From the survey on sediment quality in the area of the Hoogheemraadschap U.S.H.N. in Noord-Holland, regional differences in the quality of the sediment were observed. These differences could not be explained with local emissions. The sediment quality is a result of a combination of diffuse emissions. In this study, WABOGIS, the sediment quality was analysed with a geographical information system (GIS) to explain the differences in diffuse emissions. For all the local watercourses, the diffuse emissions from traffic, storm-water overflow or urbanisation are determined using geographical maps. Watercourses not influenced by these emissions are determined as delivering background pollution due to atmospheric deposition and surface runoff from surrounding soil. For background polluted locations with a sandy or clay soil, the sediment class is mostly 0 or 2, while peat soils lead to a class 2 sediment. Where there is an additional load, the greatest effect is seen in sandy soils. Locations where the combination of additional emissions determine the sediment quality mostly have a class 2 or 3 sediment.

The Dutch government has announced additional nitrogen measures on ca. 240,000 ha dry sandy soils in order to realise quality standards for nitrate in groundwater (i.e. 50 mg/l).The most important element of this additional policy is the introduction of lower levy-free surpluses for N for dry sandy areas. Here we estimate the effects of these additional measures. Provided the levy-free N surpluses are not exceeded, the area in which the nitrate standards will be met will increase from ca. 55% (present situation) to 75-85% of the total agricultural area in the Netherlands. The effect of the additional measures on the surface water quality will be small. However, it is questionable whether the levy-free N-surpluses wil be achieved in practise.

Dose-response functions were fitted on data from laboratory toxicity tests and were used to predict the response of functional groups in food webs. Direct effects of Chlorpyrifos (CPF), as observed in microcosm experiments, could be modelled adequately by incorporating dose-response functions in a CATS model. Indirect effects of CPF on functional groups, resulting from direct toxicity, could be predicted with the model too. The ecosystem response to toxicants was used to propose a quality standard called the Hazardous Concentration for Ecosystems (HCE). The HCE is based on both direct and indirect effects and is reached at a proposed 5% deviation of control biomass. The calculated HCEs for cadmium, Chlorpyrifos and DTDMAC are higher, but within two orders of magnitude of (proposed) Limit Values. The discrepancies are discussed.

Application of CATS models for regional assessment of bioaccumulation risks proved feasible. Case studies on heavy metals and organotin showed that initial concentrations, toxicant loading of the system and sorption coefficients strongly influence the prediction of bioaccumulation risks. Consistent quality objectives for soil, water and sediment allow a comparison between different ecosystems or regions. The evaluation of foodweb bioaccumulation for different toxicants is much less consistent since critical concentrations, NOECs etc. are not always available for the same organisms within food webs. Exceedance of quality objectives for food webs can be calculated on a routine basis by simplification of the procedure presented here.

Field studies in various polluted coastal areas in Europe and the United States of America clearly indicate a relation between pollution and the increase in prevalence of tumours and infectious diseases in fish. One of the chemicals of interest in the myriad of xenobiotics found in polluted waters and sediments is the organotin compound tributyltin (TBT), originating mainly from antifouling paints used on the hulls of ships. This report describes a study in which flounders (Platichthys flesus) were exposed to bis(tri-n-butyltin)oxide (TBTO) in the water under controlled laboratory conditions. The possible histopathological effects on several organs (gill, skin, eye, liver, mesonephros, ovary/testis, spleen, and gastrointestinal tract) were examined and morphometric analysis of the thymus was performed to assess the target organ(s) for TBTO in this fish species. Also the function of the non specific and specific resistance was studied using ex vivo/ in vitro immune function tests. Exposure of flounder to TBTO, in concentrations which are in the same order of magnitude as maximum TBT levels measured in the field (experiment: 17.3 mug TBT ; field: 7.2 mug TBT), caused mortality after 7-12 days, decreased the condition factor, resulted in gill lesions, and induced significant reduction of the non specific resistance. No marked effects on the relative thymus volume, or the specific immune system were noted after exposure to TBTO.

Speciation calculations were carried out on groundwater samples to shed more light on the chemical processes of rare earth elements (REE). These samples were taken from seven boreholes at several depths near the drinking water pumping station, Vierlingsbeek, The Netherlands. Complexation and precipitation reactions including inorganic and dissolved organic carbon (DOC) compounds, were taken into account. The REE speciation showed REE3+, REE(SO4)+, REE(CO3)+ and REE(DOC) to be the major species. Dissolution of REE-enriched solid phases probably does not account for the observed REEs in groundwater. This may be due to desorption of REEs on metal hydroxides. Multiple linear regression showed pH to be by far the most significant groundwater characteristic contributing to the variation in REE concentrations. Regression equations including only pH were derived to predict REE concentrations in groundwater.