On 13 January 2009, the long-awaited Priority Substances Directive (the "PSD") entered into force, imposing environmental quality standards for 33 priority substances discharged to water bodies. The PSD forms part of the drive to achieve good surface water chemical status as required by the Water Framework Directive (the "WFD").

The PSD fulfils part of the Commission's obligation under article 16 of the WFD to adopt specific measures for: (i) the progressive reduction of water pollution by pollutants that pose a significant risk to or via the aquatic environment (including to waters used for the abstraction of drinking water) and (ii) for the cessation or phasing-out of discharges, emissions and losses of those substances identified as priority hazardous substances.

Community-wide quality standards are laid down in the PSD for inland and other surface waters. (Groundwater impacts are governed by the separate old (1980) and new (2006) Groundwater Directives). The quality standards take 2 forms: annual average concentration limits (aimed at long-term impacts) and limits on the maximum allowable concentration permitted at any point in time (aimed at short-term impacts). The Commission is charged with keeping the standards under review taking into account technical and scientific progress and particularly new information thrown up by registration of chemicals under REACH regime.

For certain substances, member states will have the option to set alternative standards for pollutants contained in sediments and/or in living organisms rather than in the water itself. Member states are obliged to monitor the long-term trends for bio-accumulative substances and to take measures to prevent any significant increase in their concentrations.

The list of 33 substances was originally drawn up in 2001, a year after the WFD was agreed. Eleven were chosen immediately as priority hazardous substances. Following adoption of the PSD, emissions of priority hazardous substances will need to cease by the end of 2028. In the debates on the PSD, the environmental committee of the European Parliament initially sought to extend the number of priority substances from 33 to 64 but dropped its proposal as part of a compromise deal with the Council of Ministers. Instead, Annex III to the PSD contains a list of 13 further substances (including dioxins as a group) to be considered for possible identification as additional priority substances or priority hazardous substances as part of the four-yearly review to be carried out by the Commission under the WFD (the next one being due by January 2011).

However, the European Parliament did achieve a number of important amendments to the Commission's original proposal. One of these is to qualify the extent to which member states can designate mixing zones near discharge points in which the concentration of pollutants will exceed the PSD standards.

Mixing zones can only be designated where they do not have the knock on effect of causing the remainder of the water body to exceed the quality standards. The relevant river basin management plans (the majority of which are currently out for consultation in the UK) must include a description of the approach and methodology applied to define the zone, and identify measures to reduce the extent of the mixing zones in the future. Those measures are specifically allowed to include proposals to revise the limits on discharges to water contained in environmental permits already issued. Mixing zones must also be restricted to the proximity of the discharge, and be proportionate having regard to the concentrations of pollutants at the point of discharge and to the restrictions on discharges of pollutants imposed under other EU legislation and consents. Technical guidelines are to be adopted which should hopefully make it clear how these requirements are to be applied.

In July 2006, much to the consternation of environmental groups such as WWF, the Commission dropped plans for complementary EU-wide emission limits, despite this being a requirement of the WFD. The Commission's justification was that existing EU legislation is sufficient and that (influenced by objections raised during consultation on the proposal for the directive) a further set of harmonised emission limits would not be cost-effective. The existing legislation includes the REACH chemical registration regime, which includes identification of substances which either require pre-authorisation or have to be taken off the market altogether. However, that process is only in its infancy. Other limits are set under the pollution prevention and control and pesticides regimes. For now, the Commission is merely committed under the PSD to review the need for additional harmonised measures "such as" emissions controls as part of its review of progress under the WFD itself.

Member states have only until 13 July of next year to implement the PSD's requirements.

For a copy of the Priority Substances Directive click here.