Environmental Engineering Reference
In-Depth Information
marinas and mooring areas are significantly higher than those in coastal
sites, indicating that the major source of Irgarol is antifouling paints on
boats [76]. Concentrations in estuarine sediments vary little vertically, in-
dicating a homogenous, reworked sediment probably due to bioturbation
or disturbance by activities such as dredging, tide energy or waves. Cer-
tain sites, for example boatyards, are dredged at least once a year and the
sediment is likely to have been disturbed [41]. Sediment contamination
with Irgarol was found to be related to high concentrations in the water
column [45].
Concentrations of Irgarol reported in the Blackwater estuary (ranging
from 0.15-0.68 ppb in water and 3.3-222 ppb in sediment) are similar to
values previously reported for water but are significantly higher for sedi-
ments [41]. Because water is the primary medium for the exposure of most
aquatic organisms to these types of biocides, almost all studies have been
carried out to determine concentrations of Irgarol in waters and not in sedi-
ments. In addition, because few data exist on the partitioning of Irgarol in
the aquatic environment, it is difficult to determine if the observed lower
concentrations in waters in comparison with sediments are associated with
Irgarol's preference towards sorptive partitioning. For example, this could
be attributed to the tidal exchange with uncontaminated waters. It has been
suggested, however, that partitioning onto settled or suspended particulate
matter may prove to be a critical process in determining the compound's
fate [45].
Information regarding the persistence of Irgarol in the aquatic environ-
ment is limited. Generally, degradation of Irgarol seems to be slow but is
more likely to occur in water than in sediment as a consequence of pho-
todegradation. Irgarol is not biodegradable in seawater; it has been recorded
that no degradation occurs in 8 weeks [48]. Solar irradiation degrades more
than 80% of Irgarol in water after 15 weeks [81]. In sediments, it has been
shown that degradation is slow even under aerobic conditions, with half-
lives of 100 and 200 days for marine and freshwater sediment, respectively,
and is considerably slower for anaerobic conditions [44]. Given the toxic-
ity of Irgarol there may be cause for concern that leaching of Irgarol from
boats in marinas may have effects on receiving water communities. Con-
centrations recorded after the boating season in waters (0.15-0.68 ppb) may
inhibit the growth rate and photosynthetic activity of several species. For ex-
ample the growth of
Enteromorpha intestinalis
, a species known to carpet
the surface of the mudflats in the Blackwater estuary [82], would probably
be inhibited under the concentrations of Irgarol observed in the Blackwa-
ter study [41]. The no-effect concentration for this species has been reported
at 0.022 ppb, with a 72-h EC
50
of 2.5 ppb [46]. The concentrations of Irgarol
found are not high enough to have acute toxic effects directly on higher
species, but its chronic effects at lower concentrations are unknown and dif-
ficult to determine.
