The technical background to supporting the policy decisions on allocating phosphate-saturated soils and tackling the problems which these soils cause are presented here. Since 1987 the Dutch government has taken several steps to diminishing the problem of phosphate-saturated soils.New legislation will become available in 1998 for regulating the use of nutrients. The Ministries of Agriculture, Nature Management and Fisheries (LNV) and of Housing, Spatial Planning and the Environment (VROM) are planning to issue a general administrative order (GAO) to regulate phosphate use on phosphate-saturated soils. Several choices have to be made beforehand (1) Should the GAO cover the total agricultural area or should it be limited to, for example, the areas with known high historical loads? (2) What method should be used to identify phosphate-saturated soils? (3) Should management of all phosphate-saturated soils be restricted by the GAO or only the most polluted ones? (4) What level of net phosphorus export from the fields for which the GAO prescribes management restrictions should be implemented? Alternative answers to each of these questions have been formulated, with the pro's and cons for each given. Answers from the perspective of the GAO regulating farm management pertain to the national scale. The alternatives described can also be used for regulation limited to selected areas, such as those for nature conservation. In this case, methods described here can be used to select fields within the selected areas. In conclusion, several suggestions for future research are given, such as focusing on the effects in the long and medium term of soil phosphorus depletion on both agriculture and the environment. Although there are still questions to be answered, it has been made clear that the phosphorus status of most soils in the Netherlands at the moment is unnecessarily high from both the agricultural (plant production) and the environmental viewpoints.

A multi-stress model has been developed in the Netherlands on a national scale to forecast changes in plant species composition due to acidification, eutrophication and dessication. This model, called SMART-MOVE, consists of: a soil module (SMART2) used for calculating changes in groundwater level, pH and nutrient availability, and a vegetation module, consisting of regression equations that describe the relationships between the probability of occurrence and environmental factors. These environmental factors represent average Ellenberg indication values for pH, availability of water and nutrient availability. Salinity was also included since in large parts of the Netherlands salinity is of major importance for species composition. Essential input data for these modules, such as groundwater level and seepage flux, can be calculated with the National Groundwater Model, for example. In this study relationships were calculated between the Ellenberg indication values and the relevant soil factors: pH, average spring groundwater table, biomass production, nitrogen production, concentrations of several nutrients and chloride concentration for both terrestrial and aquatic systems. Where it was possible to use a sigmoid model, to cope with the original ordinal and limited scale of indication values, the explained variance increased by 5-10%. In the regression analyses, almost 7000 vegetation releves from a variety of ecosystems could be used, satisfying relationships with Ellenberg values were found for pH, average spring groundwater table and biomass and nitrogen production. These relationships are used to connect the soil module with the vegetation module and quantify the confidence of the model outcomes. Average Ellenberg indication values can be concluded to be succesful as estimates for the abiotic conditions in models like SMART-MOVE.

In this literature survey to assess the accumulation of micropollutants in activities regulated by General Administrative Order (GAO) of the Dutch Soil Protection Act, seven GAOs were considered. The main aim was to determine by means of a critical load approach if the annual accumulation of micropollutants from activities regulated by the GAOs would cause exceedance of the Dutch target value within a 100-year period. A secundary aim was to evaluate this critical load approach, as described and used in earlier RIVM studies. In this approach, the actual annual loads to soil (kg.ha-1.yr-1) from activities mentioned above are compared with critical loads for micropollutants. Critical loads are calculated using a model called SOACAS and represent the annual loads which will prevent the target value for soil being exceeded for a defined time period. The annual input of micropollutants is compared with these critical loads. To avoid accumulation of micropollutants in groundwater, a critical load is introduced to protect the soil water. In conclusion, additional policy measures will have to be generated to avoid accumulation of micropollutants exceeding Dutch target values for soil and groundwater. Sharp emission reduction is especially necessary for copper and zinc from pig manure. Recommendations considered for advanced research, monitoring and policy have been proposed for each of the GAOs.

The aim of this study was to support the policy on preventive soil protection with information concerning potential sources of local soil pollution. This study was an extension to earlier inventories on (potential) sources of soil pollution (e.g. industrial areas, landfills, oil-storage tanks). The emissions to soil were determined for eight potential sources and, following, potential soil concentrations in the top layer of the soil were estimated. Where possible these calculated concentrations were compared with measurements. The following sources were selected: public sewerage systems, pipelines (for oil products), roads and motorways, railways, tramways, galvanised power pylons, surface treatments and building activities. The study focused on heavy metals, pesticides, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, aromatic hydrocarbons and oil products.Conclusions have been made on (1) the contribution of the sources to the total emissions to the soil and (2) to the expected exceedance of the target values of pollutants in soil near sources mentioned. The contribution of the eight sources to the total emissions to soil is between 1 and 15% for heavy metals, about 41% for PAHs and maximally 15% for mineral oil. From the point of view of soil protection, the following sources and substances warrant further attention: emissions of chlorinated hydrocarbons from public sewerage systems ; emission and dispersion of lead, zinc, PAHs and oil along motorways ; emission of copper along railways and tramways ; potential leaching of PAH's and oil from railways ; emission of dichloromethane to the soil during the cleaning of buildings or removal of paint ; and copper, chromium and PAHs leaching from impregnated wood to the soil.

This report describes a procedure to develop a risk assessment methodology for contaminated sites with respect to the risk of dispersal in groundwater. The methodology was originally intended for landfills, but is for example also usable for risk assessment of contaminated industrial sites and sludge depots or to determine the priority of remediation. A Geographic Information System database can be constructed from available databases and preliminary modelling studies, which should then be ranked according to a fuzzy logic system, and incorporated into a Decision Support System. The final product, the Decision Support System, is a flexible instrument for making environmental policy decisions where the available data is vaguely defined and/or incomplete.

In general, pesticides which are liable to leach into groundwater at concentrations beyond the guideline concentration will not be authorised in the Netherlands. However, in the Long-term Crop Protection Plan adopted by the Dutch Government in 1991, it is stated that these pesticides can still be registered if the transformation rate in the saturated zone is sufficiently high. The transformation rate is considered to be 'sufficiently high' if the threshold concentration of 0.1 mg dm-3 is not exceeded at a depth of 10 m below the soil surface after a travel time of four years. The procedure for evaluating the behaviour of pesticides in the saturated zone will be discussed here, along with the secondary conditions for experimental research. In view of the absence of more precise knowledge on the behaviour of pesticides in the saturated zone, this procedure is considered the best achievable at the moment. The evaluation procedure is incorporated in the Decree on Environmental Criteria for Pesticides as an amendment to the Dutch Pesticide Act of 1962. The travel time of four years, as stated in the long-term crop protection plan, is adequate for the evaluation procedure; the travel time of water in the zone 1 to 10 m below the soil surface is always longer than four years, except for groundwater in the immediate vicinity of abstraction wells and a few sandy areas not in agricultural use.

A preliminary investigation was conducted on the occurrence of particular pesticides in the soil. The aim was to gain insight into the appearance and behaviour of pesticides in soil from the plough layer in order to support the admission policy. Seven pesticides were chosen for determination on the basis of their accumulation properties and their market share. Four pesticides were found in the plough layer: atrazine, fenpropimorph, parathion and simazine. The amounts measured did hardly exceed the detection limit, with the exception of atrazine which showed relatively high levels for a number of plots, but also a decline in time. Paraquat, pencycuron and pirimicarb could not be detected in any of the plots. The measured amounts correspond reasonably well with the amounts calculated with the simulation model PESTLA.

The aim of this Programming Study on 'Behaviour of Accumulated Contaminants in relation to Land Use Changes and Recoverability of Ecosystems' was to determine: 1) the available knowledge and 2) the short-, medium- and long-term research, needed to develop a risk assessment for the effects of mobilisation of nutrients and contaminants due to land-use changes from agriculture to nature or forest conservation. The most relevant changes in soil condition, which can take place after afforestation, are concluded to be acidification and increase in dissolved organic carbon. The development of wetlands can lead to decreases in redoxpotential and acidification. These changes in soil condition can result in mobilisation of phosphate and heavy metals. Risks from organic micropollutants are probably lower ; however, as yet not much is known about this. Increased contaminant mobility can lead to a decrease in decomposition, an increase in internal concentrations of toxicants in soil fauna and secondary poisoning of terrestrial fauna. The study also concludes that risk assessment for land-use changes will require integration of existing models. A 'quick-and-dirty' model integration is recommended as a 1 to 2-year research programme, along with research on existing nature-development projects to be used as model systems for medium-term research programmes. For long-term research priority will be given to monitoring, process research and model integration.

No Observed Effect Concentrations of species or processes are used to derive statistical sensitivity distributions. Hazardous Concentrations (HC5 and HC50) derived from these distributions define the ecotoxicological risk limits. The project 'Validation of Toxicity Data and Risk Limits for Soils' was set up to evaluate the ecological relevance of (1) laboratory toxicity data and (2) ecotoxicological risk limits, and to identify which factors introduce uncertainties. Toxic effects of zinc and other metals were studied on selected species (Trifolium pratense, Folsomia candida, Enchytraeus crypticus, Eisenia andrei) and on microbial degradation activities. Differences in bioavailability between soil types were found to be of prime importance in laboratory-to-field extrapolation of toxicity data. Studies with mixtures suggested that each contaminant should be taken into account in risk assessment. Variable exposure conditions appeared to modulate toxicity moderately. Toxic effects of zinc on community endpoints were determined at an experimental field plot and a heavy-metal contaminated field site using enchytraeids, nematodes and micro-organisms. No or weak responses were found at the HC5 level, while measurable effects were present at the HC50 level. This was confirmed by data from the literature. The scientific underpinning of HC values may be improved if toxicity-modulating factors such as bioavailability are taken into account in the interpretation of laboratory toxicity data and if long-term effects of contaminants are focused on.

Sorption isotherms for metals in soil obtained in the laboratory generally underpredict the observed metal content in the solid phase in the field. Isotherms based on in-situ data are therefore required. The aim of this study is to obtain field-based sorption isotherms for Cd, Cu, Pb and Zn as input for the heavy-metal accumulation model SOACAS. Two types of sorption isotherms were fitted using field data sets in this research: the Freundlich type, with one solid-phase fraction was fitted by Stepwise Linear Regression (LR), and a model with two solid phase mass fractions, a reactive fraction and a non-reactive fraction, was fitted with Nonlinear Least Squares Regression (NLSSR). From the results of the LR and the NLLSR fits of the Hoop-Janssen data set, the generally explained variance for the Zn models is shown to be the highest, followed by the Cd models. The explained variance of the Cu and Pb models is lower. The performance of the LR models and the NLLSR models is comparable. The NLLSR fits of the 2-phase isotherms of the Hoop-Janssen data set almost never include a statistically significant inert metal fraction. This implies that a 2-phase model can, in most cases, not be derived from this data set. The LR models derived from field data (this research) predicts the observed metal content in the solid phase in the field best compared with isotherms derived from batch data. The extension of the field partition data set and quality improvement is recommended for future research.