(b) Measuring Methods: Estimates of oil discharges from various sources on land
and at sea are normally made indirectly. For ship accidents, the amount of oil lost is
estimated as the difference between the amount carried and the amount retained after
the accident. For oil fingerprinted as bilge water, the expected bilge load, known from
ships that discharge their waste oil legally, is also estimated. Only in a few cases has
the amount of oil discharged into the marine environment been monitored on a regular
basis (e.g. discharge of oil from refineries). For some regions, aerial surveillance is
available. (c) Limitations of the Indicator: Accidental or routine discharges are, in many
cases, not accounted for. In general, available data sets are very limited, as oil is
discharged from many different sources. In many countries, oil discharges are not
included in national environmental monitoring programmes. It therefore is not
possible at present to develop realistic estimates showing actual input and time series
to illustrate real trends. (d) Alternative Definitions/Indicators: Because of current limitations on discharge
data, an alternative definition could be based on the amount of oil input to marine and
coastal environments by the major sources, namely the oil lost by offshore activities,
the oil discharged by coastal refineries and spills from shipping. Such an approach
excludes input from riverine and atmospheric deposition. The indicator can be disaggregated into two sub-indicators: (i) oil discharges from
land-based and offshore installations and (ii) accidental oil discharges, legal oil spills
and illegal spills from ships at sea.
ASSESSMENT OF DATA (a) Data Needed to Compile the Indicator: Estimates of oil input to coastal areas
and seas from the main sources of oil disposal.
