Environmental Engineering Reference
In-Depth Information
4
Discussion
It has been demonstrated that the use of organic booster biocides in an-
tifouling paints on boats can lead to a significant presence in the coastal
environment, in both waters and sediments. Sources of booster biocides have
been identified as antifouling paints and agricultural and industrial inputs,
and their occurrence has been recorded at levels that may have significant im-
pacts on coastal and estuarial environments. Concentrations appear higher in
sediments, where anoxic conditions can lead to their persistence.
The complete ban on the use of TBT in antifouling paints on all ships could
result in an increase in the occurrence of booster biocides in the marine envi-
ronment, despite the subsequent restrictions on the use of a number of them.
A greater understanding of the long-term fate of these compounds in the en-
vironment is necessary to facilitate a more informed decision-making process
when regulating antifoulant use.
While the use of organotin-based antifouling formulations is to end, care
must be taken to avoid the substitution by other biocides which may be just
as damaging to the marine environment. This could be the case with a num-
ber of the replacement biocides, and, as has been demonstrated, levels of these
biocides in both waters and sediments could be high enough to warrant concern.
Although new antifoulants must be as effective against the fouling or-
ganisms as the organotins, they need to perform better in other areas, the
foremost of which is persistence. While toxicity to target organisms is re-
quired, persistence and sorptive behaviour must be minimised. The severity
of the problem of TBT lay in the combination of high toxicity and high per-
sistence in sediments, and some of the alternative biocides could demonstrate
environmental characteristics similar to those of TBT [90]. Booster biocides
must be licensed not to combine high toxicity with high persistence and in-
vestigating partitioning behaviour is instrumental in making this choice.
One of the lessons learned from the TBT experience is that policies should
be developed to regulate biocides on the basis of testing prior to licensing
rather than after the biocide has been used, and monitoring studies have sug-
gested that regulation is necessary. The results presented here show that several
booster biocides partition strongly to sediments. While this reduces the con-
centrations in the water and therefore the risk to aquatic organisms, it leads
to greater persistence of the compounds in the environment; hence, the risk
to sediment-dwelling organisms is increased. Monitoring should take place in
order to confirm the results of testing that takes place prior to licensing, rather
than as a substitute for this testing. It should be possible to predict in advance
whether a particular biocide will accumulate to a hazardous level in sediments
and to use this information when regulating its use. Although there is now evi-
dence on the levels of these biocides in waters, the lack of information on their
fate and behaviour makes accurate risk assessment difficult.
