During the last four to five decades, environmental impact assessments became the rule for many industrial and municipal developments in terrestrial and shallow water marine habitats. The experience gained allowed the advance of general procedures and the evolution of certain rules for the conduct of such assessments. However, this was not the case for anthropogenic interventions in the deep sea, which commenced only half a century ago.
The first large-scale use of the deep sea was the permanent storage (since 1946) of low-level radioactive wastes, with high numbers of waste containing barrels dumped between 1967 and 1982 in 4000–5300 metres depth into the northeast Atlantic Ocean (e.g. Holiday, 1984) and in smaller numbers in other deep-sea localities (see Thiel et al., 1998). Surface discharge of sewage sludge occurred in large amounts from 1986 to 1996 off the coast of New York and New Jersey above 2500 metres water depth (Bothner et al., 1994). The discharge impacts were monitored, but the results did not allow the prediction for other deep-sea endeavors such as metal ore resource mining.
It was in the mid-1960s that our view of polymetallic nodules changed from regarding them as curious ore concretions to considering them valuable resources for metals such as nickel, cobalt and copper, among others. In the 1970s, industrial nations that conducted exploration cruises, started to investigate potential mining areas and developed mining techniques for collecting polymetallic nodules from the seafloor. In the process, it became clear that an environmental impact assessment would be required to evaluate the consequences of a potential mining in the deep-sea.
The first ocean mining test, conducted on the Blake Plateau in the western Atlantic Ocean by Deepsea Ventures Inc. (Kaufman and Latimer, 1971), was already accompanied by a program to assess the impacts of deep-sea mining. Major environmental studies included the US Deep Ocean Mining Environmental Study (DOMES) in the eastern Pacific Ocean (e.g. Ozturgut et al., 1981) and the German Metalliferous Sediment Atlantis II (MESEDA) program in the Red Sea (Karbe et al., 1981; Thiel et al., 1986). Both assessments featured basic investigations in the potential mining regions and monitoring of technical pre-pilot mining tests in 1978 and 1979, respectively.
The outstanding results of MESEDA included the identification of weaknesses and deficiencies of the previous studies and lead to the conclusion that to compile the amount of collected data into an environmental risk assessment a different approach would be needed.