engleski

Application of passive sampling technique (DGT) for monitoring of trace metals in nautically active areas

One of the major pollution sources to coastal waters are harbors and marinas. Despite usually very low concentrations of metals in natural waters (trace metals - TM), some of them are listed as “priority” (Hg, Cd, Pb, Ni) or “other” pollutants (Cu, Zn). Monitoring of their (bioavailable) concentrations should be regularly performed in natural waters. Passive sampling is a promising approach of TM monitoring. The main advantage of diffusive gradient in thin films (DGT) technique is its ability for in-situ pre-concentration of TM, providing time weighted average (TWA) concentration of labile (reactive) TM, which are considered as potentially bioavailable/toxic. For this study representative sites within the Šibenik bay and the Rijeka harbour were selected. These sites were submitted to seasonal or permanent anthropogenic pressure by boat traffic (e.g. antifouling paints, sacrificial anode). In summer periods, a significant increase of TM concentrations (especially Cu) was evidenced in surface (brackish) layer in the Šibenik bay, which is attributed to an increased nautical traffic releasing metals from anti-fouling paints. As expected, highest concentrations of TM were found in nautical marinas and the Šibenik harbor. The fraction of DGT-labile TM, which reflects their chemical speciation (primarily, their binding to natural organic ligands), ranged from > 90% for Cd, to < 20% for Cu. Very good agreement between the vertical profiles of DGT-labile and dissolved TM concentrations suggests that the DGT technique can be successfully used for monitoring of potentially bioavailable TM concentrations. Due to the rare grab sampling (only once in 2 weeks) and inability to have composite sampling over the DGT-deployment period (2 weeks), no correlation between DGT-labile and dissolved concentrations of TM was obtained for study in the Rijeka harbor. This demonstrates the “problem” of grab sampling methodology and shows the dynamics of TM in the Rijeka harbor. In overall, results showed that there is no apparent continuous anthropogenic pollution of seawater in the Rijeka Harbor and that determined concentrations of TM were lower than prescribed by Regulation on water quality standards in Croatia (NN 89/2010).

Passive sampling; DGT; trace metals; Šibenik bay; Rijeka harbour

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