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MARINE RISK ASSESSMENT
Readily degradable 2) 15 15 50
Readily degradable, but failing 10-d window 50 50 150
Inherently degradable 3) 150 150 ∞
Persistent ∞ ∞ ∞
Notes to Table 24:
1) Half-lives from Table 7.
2) Pass level >70% DOC removal or > 60% ThOD in 28 days. Not applicable for freshwater.
3) A half-life of 150 days may be used only for those inherently degradable substances that are quickly mineralised in the MITI II or the
Zahn Wellens Test (cf. TGD Chapter 2.3.6). The half-life of 150 days is not fully scientifically justifiable (cf. TGD Chapter 2.3.6), but
reflects a “guesstimate consensus” between a number of experts.
4) Also including shallow marine water closest to the coastline
5) The half-lives mentioned under this heading are normally to be used in the regional assessment (coastal model) as described in
Section 4.2.5.
The half-lives for the marine environments that are described in Table 24 are provisional
recommendations, which should be reconsidered, when sufficient data for degradation of
different substances in screening tests and simulation tests have been evaluated. The basis for the
recommendation is the assumption that the degradation of xenobiotics in freshwater and
estuarine waters in general can be described by similar degradation rates, whereas the
degradation rates are lower in other marine environments more distant from the coastline (Here
the half-life is suggested to be increased by a factor of three relative to estuaries for readily
biodegradable substances and even more for more slowly degradable substances, see Table 24).
4.2.4 Local Assessment
4.2.4.1 Introduction
Usually releases to the environment stem from a point source leading to a locally high
environmental concentration of the substance. The highest risk resulting from discharges,
emissions and losses of a chemical into the environment is expected to be at this local scale close
to the point of emission. It should be recognised that this might not always be the case and that
other local high concentrations can arise some distance from the point of an emission due to
marine currents, transport and deposition of sediments etc. Where this is considered possible for
a local emission, specific modelling or measurements may be necessary. Since the aquatic
concentrations are highest at the point of emission, risks may be adequately assessed, at this
local scale, using the existing methodologies.
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