Temporal trends in soft tissue metal levels in the periwinkle Littorina littorea along the Scheldt estuary, The Netherlands

Is metal pollution a threat to the continued survival of the starfish in False Bay, South Africa?

Urbanisation and industrial development in the catchment area of False Bay in South Africa are increasing and concern was raised about the effect of environmental pollutants on intertidal fauna such as starfish. The aim of the present study was to obtain initial descriptive baseline data over several seasons during 2000–2001 of metal concentrations in water, sediment and body samples of the chosen cushion starfish Parvulastra exigua (Lamarck, 1816) that occurs widely in the intertidal zone of False Bay. Concentrations of cadmium, copper, lead, nickel and zinc were measured in samples of the cushion starfish, water and sediment at five localities along the coast of False Bay. The samples were chemically analysed for metals by atomic spectrophotometry. The highest individually measured concentrations of cadmium (Cd) in starfish and sediment were found in the northern coastal region between Strand and Muizenberg where most industrial activity and human settlement occur. Large variation in concentrations of all metals occurred between localities and seasons. The mean concentrations of Cd and Pb in water and sediment were in a few instances slightly higher than the recommended levels or target values of the South African marine water and sediment quality norms but still lower than those in various developed countries. Indications are that the bay was at the time of this study still less contaminated by metals in comparison with the coastal waters of various other countries. The accumulation of nonessential metals such as cadmium and lead in both sediment and bodies of starfish was nevertheless such that it can be assumed that environmental concentrations in some parts of the bay could over time build up to levels that are detrimental to the species as well as their predators. This study provided evidence that the cushion starfish in False Bay is exposed to several metals of which some are potentially hazardous since they tend to gradually accumulate in animal bodies. Risk assessment, however, requires additional information about the causal relationship between exposure and biological effects at the cellular, organismic and population levels before informed decisions can be made whether the threat to starfish is such that intervention is required.

Effect of metal accumulation on metallothionein level and condition of the periwinkle Littorina littorea along the Scheldt estuary (the Netherlands)

Metal (i.e. Ag, As, Ca, Cd, Co, Cu, Mn, Pb and Zn) and metallothionein (MT) concentrations in the soft tissue of Littorina littorea were measured along the heavily polluted Western Scheldt (WS) and relatively clean Eastern Scheldt (ES) estuary. Along the WS metal and MT levels in periwinkles reflected the known downstream decreasing pollution gradient. Surprisingly in ES animals As, Mn and Zn concentrations decreased from east to west reflecting past pollution. Compared to the WS metal concentrations of ES periwinkles were significantly lower and both estuaries were maximally discriminated from each other based on their Cd soft tissue concentration using a canonical discriminant analysis. Furthermore, no overall difference was found in MT levels among animals from both estuaries. Using previously obtained condition data (i.e. dry/wet weight ratio and lipid content) the relation between soft tissue metal concentration (i.e. Cd, Cu and Zn) and fitness indicators (i.e. MT and condition data) was examined using a canonical correlation analysis. Periwinkles with a high metal load (i.e. Cd and Zn) also had high MT levels but were in a relatively poor condition.

Metal exposure and biological responses in resident and transplanted blue mussels (Mytilus edulis) from the Scheldt estuary

The Western Scheldt river and estuary is known to be highly polluted as it receives industrial, agricultural and domestic effluents from one of the most populated and industrialised zones in Europe. Aquatic organisms are exposed to pollutants, specifically metals that are present in different environmental phases, e.g. dissolved, suspended material or sediment phases. The objective of this study was to study the relationship that exists between environmental metal levels, the degree of metal uptake by aquatic organisms with the concomitant biological responses. For this purpose the bivalve mollusk, Mytilus edulis, was selected as bioaccumulation indicator organism. Environmental (water and sediment) and mussel samples were collected during the late winter (March 2000) from sampling sites in the Scheldt estuary. Sites were selected to represent a salinity gradient from the mouth of the estuary to the furthest distribution area of mussels upstream in the system. Together with standard water quality parameters (e.g. salinity, dissolved oxygen, dissolved organic carbon, etc.) concentrations of twelve metals were analysed in the water (dissolved and suspended matter) and sediments. Levels of these metals were also measured in the soft tissue of M. edulis, together with concomitant biomarker responses in resident mussel populations at each site. The biomarkers that were included in this study were condition index, scope for growth, survival in air, cell membrane stability, DNA damage, and metallothioneins. Data were subjected to multivariate statistical analysis. The physico-chemical parameters and metals in the environmental samples clustered the sites to reflect the distribution based on the salinity gradient. Bioaccumulation results revealed increased metal uptake along a pollution gradient with the highest metal bioaccumulation occurring at the upstream most sites and therefore closest to the in the industrial activities. However, the biomarker responses clustered the sites in a manner that reflected the influence of combination of internal exposure (bioaccumulation) and external exposure (physico-chemical conditions). These differences in biomarker responses clearly demonstrated were attributed to abiotic factors other than metal pollution alone e.g. localized short-term increases in increased suspended sediment concentrations and decreased dissolved oxygen concentrations.

Effects of environmental stress on the condition of Littorina littorea along the Scheldt estuary (The Netherlands)

The condition of the periwinkle Littorina littorea, expressed in terms of its shell morphology, reproductive impairment (i.e. female sterility/intersex, male penis shedding), trematode infestation load, lipid reserves and dry/wet weight ratio, was determined in function of environmental stress along the polluted Western and relatively clean Eastern Scheldt estuary (The Netherlands). The upstream increasing pollution and decreasing salinity levels along the Western Scheldt estuary (Fig. 1) are reflected in the dry/wet weight ratio and lipid content of the periwinkles. Compared to the Eastern Scheldt, female intersex (i.e. indicator of TBT pollution) and sterility occurred more frequently in the Western Scheldt estuary, while male penis shedding was even restricted to the latter estuary. The highest population intersex and sterility incidence was found near the harbour of Vlissingen and reflects potential nautical activities. The number of trematode infested periwinkles did not differ between both estuaries, although local sampling site differences were detected within each estuary, reflecting the complex interactions that exist among parasites, hosts and the local environment. Finally, both estuaries were maximally discriminated from each other based on the shell weight of the periwinkles using a canonical discriminant analysis. Periwinkles with the heaviest shells were found in the Western Scheldt estuary and may reflect growth rate or structural population differences caused by the less favourable living conditions in the Western Scheldt estuary.