"The deep sea is the world's largest ecosystem by volume and is assumed to have a high assimilative capacity. Natural events, such as the sinking of surface plant and animal material to the seabed, sediment slides, benthic storms and hydrothermal vents can contribute vast amounts of material, both organic and inorganic, to the deep ocean. In the past the deep sea has been used as a repository for sewage, dredge spoil and radioactive waste. In addition, there has been interest in the disposal of large man-made objects and, more recently, the disposal of industrially-produced carbon dioxide." So begins a paper in the journal Environmental Conservation. Noting that "some of the materials disposed of in the deep sea may have natural analogues," the paper examines "natural processes in the deep sea including the vertical flux of organic material, turbidity currents and benthic storms, natural gas emissions, hydrothermal vents, natural radionuclides and rocky substrata, and compares them with anthropogenic input including sewage disposal, dredge spoil, carbon dioxide disposal, chemical contamination and the disposal of radioactive waste, wrecks and rigs."

The review takes issue with many of the claims that material dumped in the deep sea is essentially the same as that which exists in a natural state. For example, with regard to radioactive waste and how it would impact natural background levels of radioactivity, the paper notes that the "levels of natural radioactivity at vents in the deep sea have existed over an evolutionary time, resulting in suitable adaptations that should not be present in non-vent deep-sea organisms. Radionuclides found naturally in the sea are at low levels whereas the low-level anthropogenic radioactive loading to date has been in a relatively concentrated form, for example in drums."

Similarly, the study dismisses the notion that deep seabed disposal of heavy metals is safe because the output of trace metals from anthropogenic sources is similar to that from hydrothermal vents, as "hydrothermal vent animals have adapted to the potentially toxic metal loads in hydrothermal fluids that would be lethal to non-vent organisms, whereas the trace metal load in the vast areas of the deep sea is very low and any increase in this load might have toxic effects." It notes that the "contamination of coastal waters is a vivid reminder of what uncontrolled release of contaminants can do to marine organisms and their ambient environment."

The paper concludes that "natural processes and their apparent anthropogenic counterparts are false analogies. It is imperative that both the natural processes in the deep sea and the impact of any waste disposal are understood before one of the least contaminated environments on Earth becomes contaminated."

December 2003