Table of Contents

  • In the waste water treatment process in sewage treatment plants, sewage sludge is produced as a by-product. The sludge contains nitrogen and phosphorus that originate from the waste water. In addition to these nutrients, sludge also contains micronutrients and organic matter. Many of these substances are required for the production of food and they can be recycled by using sludge as a fertiliser on farm lands.

  • Sludge from municipal waste water treatment plants is rich in phosphorus. The use of sludge as a fertilizer on agricultural land may decrease the need for mineral fertilizers and may contribute to more efficient recycling of nutrients. However, sewage sludge also contains numerous organic pollutants. There is a general concern that using sludge on agricultural land contributes to environmental pollution and may cause negative effects on human health and the environment. The major goals of this report was to assess this aspect by 1) reviewing current levels of organic pollutants in sludge form the Nordic countries; 2) assessing whether these levels may change as a consequence of recent chemicals legislation; 3) evaluate the potential for environmental pollution and risks, by suggesting effect based limit values (EBLs) for sludge on agricultural land; 4) discussing the suitability of applying these EBLs as limit values.

  • Large amounts of sludge are produced annually in municipal waste water treatment plants. The sludge is rich in nutrients and using sludge as a fertilizer in e.g. agriculture may contribute to closing the societal nutrient fluxes and to diminishing the need for mineral fertilizers. However, municipal sludge also contains toxic pollutants. The occurrence of metals such as copper and lead in sludge is well known since decades. During the past decade or so, numerous organic pollutants have been detected ubiquitously in sludge. Widespread usage of sludge in agriculture and elsewhere may therefore contribute to a contamination of large land areas and to toxics exposure in the ecosystem and to humans. It is therefore of general interest that nutrient recycling by sludge application is safe, i.e. that it does not pose risks for ecosystems, for human health or for pollutant accumulation in the soil environment.

  • The evaluative step is critically dependent on pertinent data on current levels of organic pollutants in sludge in the nordic countries. Data on sewage sludge has been compiled by using open sources (databases and reports) and scientic papers. National experts were also contacted in all nordic countries in order to identify all available data. It is assumed that all studies from which data were compiled used sufficient QA/QS on the analytical methods used. Quality check in this study was constrained to identifying obvious outliers in datasets.

  • An overview of available data for those substances that are prioritised in the report is shown in table 11. The full reference and a fuller description of data are given in appendice 1, that also includes a short summary of other organic compounds that have been detected in sludge during the last years. The concentrations of PAH, PCB, alkylphenols, phthalates and LAS are summarised below, with comments on:

  • The major sources of the selected chemicals to the WWTP are described based on information found in available publications. Information on production and use patterns of the selected chemicals are in combination with the physical and chemical properties of the chemical groups used for the identification of sources leading to emissions and contaminations of sludge in WWTP.

  • The long-term accumulation of organic pollutants in soil, following sludge amendment, is discussed in this chapter. The first section gives a brief review of case studies where sludge-treated soils have been monitored for organic pollutants. In the second section, the impact of sludge amendment on long-term accumulation of persistent organics in soils is discussed based on mass-balance modelling. The relative importance of atmospheric deposition and sludge amendment is illustrated. Calculated levels in soil are compared to background soil concentrations.

  • Derivation of effect based levels in sludge is based on the critical soil concentration for soil living plants and animals, birds and for human exposure from root vegetables (table 16). The latter values were calculated according to methods described in chapter 2.3. Due to lack of toxicity data, critical soil concentrations for soil organisms and plants could not be calculated for all substances that were considered.

  • Limit values are used to protect human health and the environment, and are generally based on scientific principles. However, limit values may also be used as a driving force to obtain political or ethical principals. Limit values may well be an effective way to control soil contamination from sludge. However, limit values should be justified. Strict or liberal limitations can both cause criticism and give unexpected consequences regarding use of sludge as resource. Protection of soil and waters from contamination is important. It is also important to look at different soil usage, i.e. whether it concerns food production or parks, green areas, city gardens, urban areas, forests or land reclamation. This chapter contains a discussion on the suitability and constraints of risk based limit values for organic pollutants. Finally some aspects of monitoring programmes for organic pollutants in sludge are also discussed. An overview of the current Nordic regulations for use of sludge is given in appendice 5.

  • Data on the levels of organic pollutants in sewage sludge from the Nordic countries have been compiled. Data have been sought through contacts with national authorities, in open reports and in the scientific literature. All organic substances for which sludge data were found were compiled. However, the descriptive analysis is restricted to the substances included in the report from VKM (2009), except for the pharmaceuticals which are not treated in this report. The substances are listed in table A1. PAHs are evaluated both as single substances and as different groupings such as ΣPAH16.

  • The calculations of guide values are based on the modelling performed by VKM (2009). The principles, equations and adjustments used are presented in chapter 2. Values of different substance specific parameters are listed in table A2. In some cases other values than those used by VKM were used. Arguments are given in the following.

  • The tables show the critical concentrations in sludge (mg/kg dw) for the different endpoints considered.

  • The main goal for making regulations as limit values and to restrict discharges is to protect human health and the environment. Contamination of agricultural soil is basically caused by different types of fertilisers, pesticides and by diffuse emissions from atmospheric deposition. Sludge is a fingerprint of the different substances we all are exposed to in our daily life, and the pollution by organic contaminants in the waste water system can be regarded as diffuse emissions. There are different management traditions and approaches to protect soil and to identify contaminated soils and some of this management system should be considered before making a proposal for limit values for organic contaminants in sludge.

  • The current Nordic regulations for sludge usage on agricultural land have two purposes: to allow efficient reuse of nutrients and to minimize the impact of metals on the agricultural ecosystems. This chapter aims at illustrating these current regulations.