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Are the Biotic Ligand Models (BLM) suitable for assessing the ecological risk of metals in Nordic freshwaters?

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Basic project information


Ecological risk assessment of surface waters requires monitoring of the presence of metals and toxic elements. The European Union Water Framework Directive (WFD) guides acceptable levels for priority substances, and therefore, sets environmental quality standards (EQS). These standards also affect the classification of water bodies and may induce mitigation actions.

Environmental Quality Standards (EQS) in the EU have up to now been measured as total or dissolved metal concentrations. This is because the dissolved metal concentration has previously been thought to be a better estimate of the bioavailable, hazardous fraction of a metal. However, other water chemistry factors strongly affect bioavailability of metals. Moreover, the EQS values are based on laboratory toxicity tests performed with fully dissociated inorganic metal salts. Under such test conditions, most of the metal is present as free ions and, thus most likely overestimate the test metal`s toxicity. In order to improve metal risk assessment, Biotic Ligand Models (BLMs) that connect metal toxicity, critical metal accumulation and bioavailability into a single concept have been developed.

The implementation of EU water framework directive has reached a critical turning point. Valid from the end of 2015 (e.g. Finland) the new directive amendment requires that the annual average concentrations for nickel Ni and Pb be reported as the bioavailable rather than dissolved concentration. The EU guide suggests applying the “user-friendly” BLMs to estimate the bioavailable fractions and local EQS values for Ni, Cu and Zn. Unfortunately, a significant fraction of investigated Nordic freshwaters had Ca2+ (75%), alkalinity (29%) and pH (22%) levels outside the calibration range of recommended BLMs. Nordic countries therefore need to decide which metals and which methods they will apply for the updated monitoring work. This may also need adjustment of the current EU models. It is important to note that the problem and solution do not only concern targets in Finland, Norway and Sweden but all soft and sour water bodies.

Objective and end results

The results from the project will help the Nordic countries to decide how to react to the requirements of the new Directive (2013/39/EU). The project will test current BLM models ability to assess Nordic waters in compliance with the new EU guidelines and result model adjustments/revisions if needed.


  1. The Nordic countries has a scientifically sound method to assess bioavailability based Environmental Quality Standards in soft and acidic surface waters.
  2. The implementation of the bioavailability based EQS is clear and well guided at all levels of end users.


Toxicity testing

The Environmental Quality Standards are based on toxicity tests performed with species at all levels of aquatic food web. Also, Biotic Ligand Models are adjusted with the toxicity data but the problem is that data with soft and acidic waters is scarce. This project will produce data performed with chronic, long lasting (days-weeks) toxicity tests with invertebrates and algae. Low pH and hardness will put test species close to their tolerance limits and native species will be applied. SYKE will concentrate on Daphnia longispina (water flea) and Lymnaea stagnalis (mollusc) and ACES on Pseudokirchneriella subcapitata (algae). The tested heavy metals will be copper (in ACES), nickel and zinc (in SYKE).

The test waters will cover typical qualities in the Nordic countries. One set of sample waters concentrate on the hardness range (Ca ≤ 1 to 11 mg/L) and other set for pH and associated DOC (pH 4 -7; DOC 2 – 40 mg/L).


Our associated partners have developed the “user-friendly” models and coordinate the work internationally. They will use “full” BLMs to estimate exposure concentrations and once the data is collected, test the fit of models and perform adjustments if needed.


A summary of the project results were presented in the Society of Toxicology and Chemistry Europe in Helsinki 26th-30th of May 2019 in a poster corner. The poster link.


The final meeting of the project was held in SYKE/Helsinki 14th of June 2019. There were attendants from the project team, industry and regulators in Finland. Sweden, Norway and Iceland. The following topics were discussed using power point presentations. The presentations are available from the project manager.

Project summary and conclusions

Implementation of the bioavailable EQSs in the Nordic countries

  • Practices in FI, SE, NO

Model developer’s selected short updates

  • The new EU CIS Guidance document “Implementation of the bioavailability based EQS for metals”
  • Implementation e.g. backgrounds, tiered approach
  • Choosing model: Bio-met or PNEC-Pro?
  • New model developments

Conclusions and future work needed in the Nordic countries/in soft waters

  • e.g. Baltic Sea and the bioavailable based EQSs?
  • Joint applications?

Additional information

Project manager Matti Leppänen, tel. +358 295 251 368,

Published 2016-06-03 at 14:30, updated 2019-07-02 at 14:58

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