Descriptor 8 of the MSFD describes protection against the pollution of marine waters by chemical contaminants. The Descriptor is closely related to the activities under the Water Framework Directive (WFD) [2000/60/EU], which covers freshwaters and some marine waters.

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D8 Commission Decision (EU) 2017/848 of 17 May 2017
Concentrations of contaminants are at levels not giving rise to pollution effects.
Criteria
D8C1 – Primary: Within coastal and territorial waters, the concentrations of contaminants do not exceed the following threshold values: 
(a) for contaminants set out under point 1(a) of criteria elements, the values set in accordance with Directive 2000/60/EC;
(b) when contaminants under point (a) are measured in a matrix for which no value is set under Directive 2000/60/EC, the concentration of those contaminants in that matrix established by Member States through regional or subregional cooperation; 
(c) for additional contaminants selected under point 1(b) of criteria elements, the concentrations for a specified matrix (water, sediment or biota) which may give rise to pollution effects. Member States shall establish these concentrations through regional or subregional cooperation, considering their application within and beyond coastal and territorial waters. 
Beyond territorial waters, the concentrations of contaminants do not exceed the following threshold values: 
(a) for contaminants selected under point 2(a) of criteria elements, the values as applicable within coastal and territorial waters; 
(b) for contaminants selected under point 2(b) of criteria elements, the concentrations for a specified matrix (water, sediment or biota) which may give rise to pollution effects. Member States shall establish these concentrations through regional or subregional cooperation. 

D8C2 – Secondary: The health of species and the condition of habitats (such as their species composition and relative abundance at locations of chronic pollution) are not adversely affected due to contaminants including cumulative and synergetic effects. Member States shall establish those adverse effects and their threshold values through regional or subregional cooperation.

D8C3 – Primary: The spatial extent and duration of significant acute pollution events are minimized.

D8C4 – Secondary (to be used when a significant acute pollution event has occurred): The adverse effects of significant acute pollution events on the health of species and on the condition of habitats (such as their species composition and relative abundance) are minimized and, where possible, eliminated.
Glossary
According to the WFD, pollutants mean 'any substance liable to cause pollution'. The definition adds 'in particular those listed in Annex VIII'. In addition, in the WFD, hazardous substances are defined as "substances (i.e. chemical elements and compounds) or groups of substances that are toxic, persistent and liable to bio-accumulate, and other substances or groups of substances which give rise to an equivalent level of concern". This definition is in line with the definition of hazardous substances used in Regional Sea Conventions (RSCs), like OSPAR and HELCOM. Moreover, the WFD defines priority substances as "substances identified in accordance with Article 16(2) and listed in Annex X". Among these substances there are priority hazardous substances, which means substances identified in accordance with Article 16(3) and (6) for which measures have to be taken in accordance with Article 16(1) and (8).

As per Annex III of the MSFD, contaminants are synthetic compounds, non-synthetic substances and compounds, and radio-nuclides1. Therefore, the term "contaminant" relevant to the scope of Descriptor 8 of the MSFD encompasses hazardous substances, including priority substances and priority hazardous substances, but excludes three classes of pollutants from Annex VIII of the WFD, namely 'materials in suspension', 'substances which contribute to eutrophication (in particular, nitrates and phosphates)' and 'substances which have an unfavourable influence on the oxygen balance (and can be measured using parameters such as BOD, COD, etc.)'. These are covered under other Descriptors (namely 5).

Pollution effects are deleterious effects, such as harm to living resources and marine ecosystems, including loss of biodiversity, hazards to human health, the hindering of marine activities, including fishing, tourism and recreation and other legitimate uses of the sea, impairment of the quality for use of sea water and reduction of amenities or, in general, impairment of the sustainable use of marine goods and services, which result or are likely to result from the direct or indirect introduction into the marine environment, as a result of human activity, of substances or energy (MSFD Art 3.8).

Acute pollution events are events which can cause short time and severe pollution to the marine environment. They can be deliberate or accidental, e.g. illegal discharges and oil spills.

Environmental quality standards (EQS) are concentrations of pollutants which should not be exceeded in order to protect human health and the environment, as established in the context of the WFD, and thereby represent criteria for assessing whether Member States are in compliance (WFD Article 2, paragraph 24).