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EU agency: action needed on ‘cocktail effect’ in water bodies

General - River © Dmitry Naumov -

Extra measures are needed to tackle the presence of ‘cocktail effect’ chemicals in European water bodies, the European Environmental Agency has concluded.

In its report Chemicals in European Waters, the EEA said action on a number of priority substances in lakes and rivers "seem to have been effective" in preventing their entry into surface waters, but there are more chemicals in the environment "about which we know little".

These priority substances include dichloromethane, trichloroethylene, 1,2-dichloroethane (EDC), refrigerant carbon tetrachloride and degreaser tetrachloroethylene.

Challenges remain in effectively dealing with mercury and brominated flame retardants, and with many harmful chemicals which have not been prioritised for monitoring under the EU Water Framework Directive, the report said.

Combined threat

Even though they are individually present at "harmless concentration", substances like mercury can combine with "natural salts, organic compounds, nutrients from sewage and other waste water and chemicals coming from air emissions", the report said.  

One key concern is that the detection of "several hundred organic chemicals" at low concentrations in a single freshwater body is "common" but the level of risk is "insufficiently understood".

The EU’s Water Framework Directive (WFD) sets concentration limits for certain single pollutants presenting "a significant risk to or via the aquatic environment". However, the EEA said, this single-substance assessment does not match the variety and "complexity" of water composition.

The issue was raised in 2009 by the European Council in its conclusions on combination effects. It stressed that most EU legislation is built on a chemical-by-chemical assessment approach, and that further action to address combination effects of chemicals is required.

The EEA’s State of Water report published in July last year found 46% of surface water bodies failed to achieve a "good chemical status". Only 38% of monitored lakes and rivers do not present excessive concentrations of priority substances, while 16% have an unknown chemical status, it said.

Other substances whose presence in large quantities' causes concerns include polybrominated diphenylethers – widely used as flame retardants in the 1990s and 2000s – and polycyclic aromatic hydrocarbons (PAHs), carcinogenic substances produced by burning organic matter.

The way ahead

Existing EU rules provide a flexible approach for water management "but do not reflect recent scientific developments in the assessment of mixtures", the EEA said.

Its report calls for more robust reporting on data of chemical emissions and improvements to monitoring, modelling and reporting of diffuse sources of pollution. This is to ensure the subject is "correctly understood and measures can be appropriately targeted".

Authorities should also:

  • move beyond priority substances by implementing methods to assess risks represented by mixtures in the aquatic environment "effectively";
  • improve emissions data by collecting and streamlining them under "consistent and comparable approaches"; and
  • develop safer alternatives to harmful chemicals.

Some EU countries are already addressing cocktail effects. The Danish National Food Institute, for instance, has created a section on its chemical portal on research into cocktail effects of chemicals.

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