Temporal and spatial trends in heavy metal concentrations in the marine mussel Mytilus edulis from the Western Scheldt estuary (The Netherlands)

Abstract

Since the first North Sea Conference (1984, Bremen), all countries bordering the North Sea made commitments to reduce discharge of hazardous substances into the North Sea. From Belgium and The Netherlands, large reductions (upto 90%) in heavy metal emissions from land-based sources have been reported between 1985 and 2000. Recently, some studies in the Western Scheldt estuary (WS) have shown that total metal concentration in the water, sediments and suspended particles have decreased compared to levels in the 70s. However, data on aquatic organisms is still very limited and it is therefore difficult to confirm whether the reductions in pollution input and generally improving water quality in the WS have a corresponding impact on the levels of heavy metals in aquatic organisms. The current study measured metal concentrations in the soft tissues of mussels, Mytilus edulis (known to be good indicators of environmental metal pollution) during the period 1996-2002. Spatial (salinity and pollution gradients), temporal and seasonal variations were also studied. Results showed a down-stream decreasing trend for the metals studied (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) during all sampling campaigns. There was also a significant seasonal effect on tissue metal concentrations, with a peak observed around spring in both WS and the nearby less polluted Eastern Scheldt (ES). On temporal trends, a clear drop of metals in mussels was observed in the early 80s coinciding with the start of the efforts to reduce chemical pollution input into the North Sea. Since those early reductions, metal concentrations in mussels generally remained unchanged upto mid 90s. However, in recent times metal concentration in mussels have increased significantly, for example Cd in 2002 was almost 10 times the values in 1983 and similar to levels seen during the peak in the 70s. Other metals also increased in the 90s also reaching levels seen in the 70s. As there is no indication of recent increase in metal input into the estuary, we suggest that increased metal concentrations observed in mussels in recent years especially in the upper estuary are most likely a result of changes in physical and chemical speciation and metal bioavailability. Such changes may be caused by changes in some water quality parameters in the estuary (i.e. increased dissolved oxygen, concentration of organic matter), resulting in conditions that favour releases of sediment-bound metals into the water column. The relationship between metal content and season showed very similar annual profiles in the polluted WS and less polluted ES. Thus, seasonal variations in metal concentrations appear to be largely controlled by biological processes, while total body burdens are dependent on environmental levels and bioavailability.

Metal trace elements in mussels in Urubuqueçaba Island, Santos Bay, Brazil

“…Only Zn showed similarity to the results obtained in the present work (Vernocchi et al, 2007). Higher concentrations in colder months were also identified by Mubiana et al (2005) for M. edulis in the Netherlands, with Cd, Cr, Zn in the winter, and Fe, Mn, Ni, and Pb in the spring; the values for Mn and Ni are corroborated by those observed in the present work.…”

Spatial and Temporal Variation in Cadmium Body Loads of Four Intertidal Invertebrates from False Bay, South Africa

“…Mean Cd levels in all invertebrates from False Bay were greater than those found by Greenfield et al (2011) for Perna perna and Liu & Kueh (2005) for Perna viridus in Victoria Harbour, Hong Kong. However, all the maximum concentrations we measured in mussels from False Bay were below the metal concentrations recorded for mussels (Mytilus edulis) from the metal polluted Western Scheldt Estuary in The Netherlands (Mubiana et al 2005).…”

“…1) to obtain baseline information of Cd levels in intertidal invertebrates and their immediate surroundings. Seasonal effects are also critical in biomonitoring programmes (Mubiana et al 2005). However, little is known about the influence of seasonal changes on metal content in organisms of the intertidal zone in False Bay.…”

Comparison of trace metal bioavailabilities in European coastal waters using mussels from Mytilus edulis complex as biomonitors

“…It has been suggested that accumulated trace metals concentrations in bivalves vary significantly with season and body size (Casas et al 2004;Lobel and Wright 1982;Wallace et al 2003;Mubiana et al 2005), which occasionally requires correcting these effects before spatial comparisons are made on large scales. However, the influence of an animal's size (age) on soft tissue metal concentration appears to be ambiguous and can depend on local environmental conditions.…”