The group of chemicals typically regarded as pollutants encompasses a large array of compounds, and is generally divided into chemical compounds and metals. Estimates of the number of chemicals produced anthropogenically range as high as 100,000 (Menditto & Turrio-Baldassarri 1999 in Hale & La Guardia 2002, Islam & Tanaka 2004); however, assessments of the toxicity and bioaccumulative nature of these are limited. Most research has included only a few classes of compounds, notably the halogenated hydrocarbons, a limited number of metals, and polyaromatic and non-aromatic hydrocarbons (Reijnders 1994, Hale & La Guardia 2002). Because these compounds resist degradation, and can be transported atmospherically and oceanographically from source points to remote areas, they will continue to persist in the environment, and reach a long-term global equilibrium rather than decline (Iwata et al. 1993, Tanabe et al. 1994). There are also concerns that climate change may be altering contaminant pathways and exposure (Wöhrnschimmel et al. 2013, McKinney et al. 2015).
Most pollutants identified in marine animals are incorporated into tissues via dietary intake, with many accumulating through the food web (Islam & Tanaka 2004). Consequently, animals feeding at high trophic levels tend to have higher tissue concentrations than those feeding at lower trophic levels (Aguilar et al. 1999). Various pollutants have been reported to be associated with deleterious effects on the immune, endocrine and nervous systems of marine animals, disrupting growth, development, sexual differentiation and resistance to disease (e.g. Reijnders 1994, Skaare et al. 2000, Tanabe 2002, Hammer et al. 2012). However, direct associations between contaminants and these effects are few, and most studies lack substantive evidence of sublethal effects because of numerous physiological and environmental confounding factors. This limits the ability to quantify the direct and indirect pressures that pollutants may be exerting on the marine environment.
Coordinated, ongoing monitoring of pollutants in the marine environment outside estuarine and enclosed embayment environments on a national scale is lacking (see further details on coastal river, and estuary and nutrient pollution in the Coasts report). Most reporting is ad hoc, and limited to measurements of the concentrations of contaminants in the tissues of various species (e.g. Haynes & Johnson 2000, Evans 2001, Evans et al. 2003, Templeman & Kingsford 2010, Brodie et al. 2012, Weijs et al. 2013) or modelling studies (GBRMPA 2014a). Most pollutant data, particularly from outside the Great Barrier Reef region, are now dated, and contemporary information is required concerning the distribution and impact of pollutants in the marine environment. Several fish species are monitored for concentrations of a small number of metals, polychlorinated biphenyls and other chemicals as part of the (Standard 1.4.1), which produces guidelines on the consumption of these fish. Because of the ad hoc nature of most assessments, establishing trends in the concentrations of pollutants in the marine environment is not possible.