Sludge disposal at Sea. Chemical monitoring at sludge disposal sites at the Belgian continental shelf (BAGGER)

Every year, large amounts of dredged sediments (sludge) are first examined to see if they meet strict quality criteria and then they are disposed of at sea. Dredging of marine sediments is done to secure naval passage in ports and channels as well as for capital dredging work. This long-term project, an assignment from the Belgian government, monitors sludge disposal sites on the Belgian continental shelf by looking at possible chemical and/or toxic effects. In a parallel study, the biological impact of sludge in the same zones is measured. This combination guarantees a thorough monitoring of the quality of the marine environment.

For each sludge disposal site, 3 areas are defined: the sludge disposal site, the area nearby the disposal site, and reference zones located further from the disposal site. At these zones, sediment and biota samples are taken twice per year and the concentrations of chemical compounds such as polychlorinated biphenyls, polycyclic aromatic hydrocarbons and heavy metals are measured. New emerging contaminants are also taken into consideration as well as pollution by plastic and marine litter. Toxicity evaluation is based on toxicity experiments and the evaluation of fish diseases.

Since 1979, relevant chemical parameters are monitored at sludge disposal sites as well as reference zones. This monitoring strategy allows to identify spatial effects as well as time trends of the chemical quality at and around disposal sites and to evaluate the quality of the marine environment. Follow-up and synthesis reports are made semiannually and every 5 years, respectively, and advice is given to policy makers regarding sludge disposal in the marine environment. Results are also publicized through scientific publications and presentations at symposiums.