Is Dredging the Real Problem? The Need for Elimination of Contaminants at Source
Presented during:
CEDA Dredging Days 2001 - Dredging Seen. Perspectives - From The Outside Looking In, Amsterdam
Authors:
M. Besieux
Abstract: Dumping of dredged materials,particularly those arising from harbours or industrialized estuaries,accounts for substantial inputs of contaminants to the wider marineenvironment. For example, as has been calculated from someharbours, dredged sediments dumped from this harbours contain asubstantial amount of the antifoulant TBT. Other than the heavymetals, PCBs and in some cases TBT, relatively few contaminants areroutinely reported for dredged material dumped at sea, thoughundoubtedly such materials represent substantial reservoirs ofcomplex mixtures of contaminants.
Dredging and disposal of harbour andestuarine sediments is consequently often viewed as a “dirty”activity. Such a view fails to recognize, however, that contaminantloads arise as a consequence of other human activities, generallybeyond the immediate control of the harbour authorities. Although inmany cases the bulk of contamination may be historic, ongoing inputsremain significant for many persistent chemicals, inputs of TBT fromongoing use in antifouling paints being a good example. The economiccosts of handling contaminated dredged materials are very high; thehidden environmental costs are impossible to determine.
The dumping of dredged material isregulated under the London Convention (LC) 1972 and regionally withinthe North East Atlantic region under the OSPAR Convention. Guidancefor management of dredged materials adopted under the LC acknowledgesthe key management goal of addressing upstream sources ofcontamination. Practical measures to address such sources remain,however, largely outside the remit of dumping conventions. Someregional measures (e.g. OSPAR hazardous substances strategy, EC WaterFramework Directive) might ultimately lead to upstream control orelimination of some hazardous substances, though legally enforceablemeasures will inevitably take time to formulate and implement.
In the mean time, harbour authoritiesand other actors involved in the management of dredged material haveboth a clear interest, and role to play, in encouraging moreresponsible practice with respect to the manufacture, use and releaseof chemicals. Co-ordinated action by the dredging community could,for example, contribute positively to ensuring that those involved inthe manufacture and use of organotin paints abide by the deadlines ofthe new IMO Convention on Harmful Antifoulants.