Report No DWI0662

Jun 1985

Under the EC Dangerous Substances Directive (76/464), Member States are required to reduce pollution of both fresh and salt waters, resulting from the discharge of List II substances, by the Environmental Quality Objective (EQO) approach. The Department of the Environment have commissioned WRc to recommend Environmental Quality Standards (EQSs) for selected List II substances. This report is one of a series of 16 produced in fulfilment of the contract.

Sources of ammonia are discussed and the chemistry of ammonia in water reviewed. Information is presented on the concentrations of ammonia in the environment, with emphasis on UK and European waters.

EQS values are recommended as appropriate for all the agreed uses of water (as discussed in TR 206). EQSs for the protection of fish and other aquatic organisms in both fresh and salt waters have been proposed on the basis of literature reviews, which are presented as separate Annexes. The recommended EQS values for all uses are summarised in an annotated Table and, for comparison, water quality standards from other countries are also tabulated.

Un-ionised ammonia is the most toxic form to aquatic organisms and as far as possible EQS values have been expressed in terms of un-ionised NH₃-N. The relation between un-ionised and total ammonia is dependent on pH, temperature and salinity, or ionic strength as indicated in the table provided (where total dissolved solids is the parameter used as a measure of ionic strength). The production of CO₂ by fish lowers the pH at the gill surface relative to the pH of the main waterbody changing the un-ionised ammonia concentration to which the fish is exposed. This effect is particularly important at pH values greater than 8.

As indicated in the report, monitoring for ammonia is widespread in the UK particularly in freshwaters. Extension of monitoring to saline waters may involve additional expenditure, although the extent of this depends on decisions yet to be taken about the frequency of surveillance and rate of improvement required.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.