In marine waters, owing to high dilution factors and the episodic nature of inputs, contaminants are generally difficult to measure accurately. The analysis of contaminants in marine waters thus requires pre-concentration procedures (ie procedures that concentrate contaminants in the seawater to levels that can be detected by the analytical equipment) that can lead to sample contamination (eg from laboratory equipment that may contain contaminant residues) and are also labour intensive and hence costly. Marine sediments, however, are the ultimate sink for many contaminants and concentrations are usually several times higher than those found in the overlying water column. Although sediments are traditionally considered as an ultimate contaminant sink (ie efficiently sequestering contaminants so that they are unavailable to marine life), they can nevertheless act as a contaminant reservoir (ie contaminant source). Both marine benthic organisms that live in or on sediments (ie infauna and epifauna, respectively), and pelagic organisms are at risk from contaminated sediments. For example, sediment re-mobilisation can act as a non-point source and has the capacity to release contaminants causing adverse effects to aquatic organisms and potentially to human health through trophic transfer (movement of contaminants along the food chain).

Marine life also accumulates contaminants to higher concentrations than found in the water column through both the ingestion of food items previously exposed to contaminants and directly from the ambient water across permeable body surfaces (such as the gills). Further, tissue concentrations show the proportion of contaminant that was biologically available and give an indication of organism condition (health).

Although marine waters were considered for surveying under this Study, concentrations in sediment and tissue were believed to provide a more useful indication of concentrations of contaminants in the marine environment over time due to their role as "sinks" (sediment) or "processors" (tissue) of contaminants. Measuring contaminant concentrations in both sediment and biota are thus superior to analysing water samples for a number of reasons. For example, biota and sediments are passively exposed to any contaminants in the water and integrate contaminant inputs over time. Furthermore, periodic or snap-shot water monitoring can often be difficult to relate to contaminant inputs because unless the inputs are continuous (which is rare in aquatic environments) then water sampling alone can easily miss contamination episodes.