J.F. Postma

Distribution of Microcystins in a Lake Foodweb: No Evidence for Biomagnification

Microcystins, toxins produced by cyanobacteria, may play a role in fish kills, although their specific contribution remains unclear. A better understanding of the eco-toxicological effects of microcystins is hampered by a lack of analyses at different trophic levels in lake foodwebs. We present 3 years of monitoring data, and directly compare the transfer of microcystin in the foodweb starting with the uptake of (toxic) cyanobacteria by two different filter feeders: the cladoceran Daphnia galeata and the zebra mussel Dreissena polymorpha. Furthermore foodwebs are compared in years in which the colonial cyanobacterium Microcystis aeruginosa or the filamentous cyanobacterium Planktothrix agardhii dominated; there are implications in terms of the types and amount of microcystins produced and in the ingestion of cyanobacteria. Microcystin concentrations in the seston commonly reached levels where harmful effects on zooplankton are to be expected. Likewise, concentrations in zooplankton reached levels where intoxication of fish is likely. The food chain starting with Dreissena (consumed by roach and diving ducks) remained relatively free from microcystins. Liver damage, typical for exposure to microcystins, was observed in a large fraction of the populations of different fish species, although no relation with the amount of microcystin could be established. Microcystin levels were especially high in the livers of planktivorous fish, mainly smelt. This puts piscivorous birds at risk. We found no evidence for biomagnification of microcystins. Concentrations in filter feeders were always much below those in the seston, and yet vectorial transport to higher trophic levels took place. Concentrations of microcystin in smelt liver exceeded those in the diet of these fish, but it is incorrect to compare levels in a selected organ to those in a whole organism (zooplankton). The discussion focuses on the implications of detoxication and covalent binding of microcystin for the transfer of the toxin in the foodweb. It seems likely that microcystins are one, but not the sole, factor involved in fish kills during blooms of cyanobacteria.

Tenax extraction mimics benthic and terrestrial bioavailability of organic compounds

Biota to sediment accumulation factors (BSAFs) are widely used to describe the potential accumulation of organic contaminants in organisms. From field studies it is known that these BSAFs can vary dramatically between sediments of different origin, which is possibly explained by the variation in bioavailability of organic contaminants in sediments. In the present study it is shown that the variability in BSAF values for different sediment samples obtained at two Dutch freshwater sites could largely be explained by the variation in Tenax-extractable concentrations in these sediments. Variations of a factor of about 50 could be explained. The ratio between concentrations in biota and Tenax-extractable concentrations in sediment varied slightly between sediments and contaminant class, but was close to the theoretically expected value of 2. This is a strong indication that Tenax-extractable concentrations of contaminants in sediments are an excellent indicator of available concentrations.

Chronic toxicity of cadmium to Chironomus riparius (Diptera: Chironomidae) at different food levels.

The interacting effects of cadmium toxicity and food limitation on the midge, Chironomus riparius, were studied during chronic exposure in laboratory experiments. If the food was supplied ad libitum, both larval developmental time and mortality of the larvae were negatively affected by cadmium concentrations of 2.0–16.2 μg/L. The number of eggs deposited per female and the mean life span of the imagines were not affected by cadmium. Integration of these separate effects into a population growth rate showed a clear reduction with increasing cadmium concentrations. Food limitation of unexposed larvae at high population density reduced fitness, judged on all parameters studied and consequently reduced the population growth rate (up to 85%).The effects on larvae, which were exposed to both cadmium and food limitation, differed considerably from the response to the individual stress factors. Exposure to cadmium increased mortality among food-limited first and second instar larvae. Consequently, the amount of food available for each surviving larva increased. At the two lowest concentrations studied (2.0 and 5.6 μg Cd/L), these indirect positive effects of cadmium overruled the direct negative effects and caused an increase of the fitness of the food-limited exposed larvae compared to the food-limited, unexposed controls. At a concentration of 16.2 μg Cd/L, the negative effects of cadmium on food-limited midges balanced the positive effects of reduced food limitation. At this concentration, the population growth rate did not differ significantly from the food-limited control any more. It is concluded that the indirect positive effects of cadmium on food limitation could eliminate negative, direct effects of low cadmium concentrations on food-limited chironomid populations.

Alterations in Life-History Traits of Chironomus riparius (Diptera) Obtained from Metal Contaminated Rivers

Cadmium tolerance in field populations of the midge Chironomus riparius was studied by comparing the effects of chronic cadmium exposure on several life-history parameters using first generation, laboratory-reared animals. Differences between populations of C. riparius were therefore assumed to have a genetic basis. Field populations naturally exposed to metals were less sensitive to cadmium compared to unexposed populations, when larval development time and hatchability of the egg masses were measured. However, larval mortality still increased with cadmium exposure and no differences between exposed and unexposed populations were observed. Furthermore, life-history patterns differed between metal tolerant and nontolerant populations grown under control conditions. Metal tolerant populations were characterized by a high control mortality (50%) or an increased larval development time (with 30%). The results, therefore, indicated the presence of costs of tolerance, while a direct selection on certain life-history characteristics due to metal pollution was absent.

Site specific differentiation in metal tolerance in the midge, Chironomus riparius (Diptera: Chironomidae)

Metal tolerance in Chironomus riparius (Diptera) populations from contaminated streams was studied by comparing the effects of cadmium, zinc and iron on first generation laboratory reared midges. First instar larvae were exposed for four days, after which surviving larvae were counted and their length measured. Larvae from two highly polluted sites, kept under control conditions, grew substantially slower than those from other populations. All populations showed the same growth responses to increased zinc concentrations, but differences were found in the responses to both cadmium and iron. Since population differentiation was demonstrated in first generation laboratory animals, it is suggested that the differences between populations of C. riparius have a genetic basis.

Inter-laboratory comparison of five marine bioassays for evaluating the toxicity of dredged material

Four laboratories were compared to ascertain the reproducibility of test methods for five bioassays: the ten day whole sediment bioassay with the amphipod Corophium volutator, the fourteen day whole sediment bioassay with adult sea urchins Echinocardium cordatum, the Microtox solid phase bioassay with the bacterium Vibrio fischeri, the oyster larvae sediment elutriate bioassay using Crassostrea gigas and the sediment pore water bioassay with the rotifer Brachionus plicatilis. The bioassays were all conducted according to the standard operating procedures of the National Institute for Coastal and Marine Management/RIKZ and carried out with one control sediment and three moderately contaminated dredged materials from the Netherlands. Reference toxicant tests were also performed for every bioassay, to assess the condition of the test species. Reproducibility and inter-laboratory variability were evaluated by calculating coefficients of variation for the sediment bioassays and considering the ability of each laboratory to achieve the test acceptability criteria and to identify a number of confounding factors. The bioassays involving the amphipods and sea urchins had an acceptable inter-laboratory variability, with average coefficients of variation of 20% or less. The Microtox solid phase bioassay showed high reproducibility and the least variability among laboratories, with average coefficients of variation of 12%. In contrast, the results for percent net response in the oyster larvae bioassay were very variable and poorly reproducible: in three of the four sediments the coefficients of variation exceeded 100%. Two laboratories did not meet the test acceptability criterion for oyster embryo development in the control sediment. Survival in the rotifer bioassay also varied greatly among laboratories with average coefficients of variation of 48%. We conclude that the main sources of inter-laboratory variability were 1) individual differences in the skill and experience of laboratory technicians (for the amphipod, oyster larvae and rotifer bioassays); 2) the use of different batches of test organisms (sea urchin bioassay) and 3) the use of different dilution water (oyster larvae bioassay).

Environmental risk assessment on aquatic-terrestrial gradients in a freshwater tidal area

Environmental risk assessments are generally performed for either terrestrial or aquatic systems, while these systems sometimes exist in close proximity. The objective of this study is to compare environmental risks along gradients from aquatic to terrestrial conditions. The assessment involved chemical analysis (including bioavailable fractions), as well as bioassays and bioaccumulation experiments using aquatic and terrestrial organisms. The results demonstrate that sediments and soils from neighbouring aquatic and terrestrial systems may render different assessments in terms of environmental risks. Metal availability for oligochaetes appeared to be limited in the aquatic environment as compared to the terrestrial environment, while the reverse was observed for organic contaminants. This paper aims to illustrate the use of various assessment techniques within a framework to compare ecological risks in aquatic and terrestrial environments. The obtained results are useful when considering (a prioritisation of) remedial actions.

ENVIRONMENTAL MONITORING IN THE NORTH SEA BY COMBINING BIOMARKER STUDIES IN THE SEA STAR ASTERIAS RUBENS WITH SEDIMENT QUALITY ASSESSMENT BASED ON SEA URCHIN BIOASSAYS

Abstract A number of biomarker measurements in the sea star Asterias rubens and sediment pore water bioassays with the sea urchin species Paracentrotus lividus and Psammechinus miliaris were applied in North Sea field studies. On the basis of contaminant levels in the pyloric caeca of sea stars, several pollution gradients became apparent, running from rivers in the Netherlands, England and Germany into offshore parts of the North Sea. No pollution-related effects were observed on reproduction of Asterias rubens, while success of embryonic development was relatively low at all stations. Responses of biomarkers in sea stars were relatively low, nevertheless indicating effects in stations of coastal zones near the rivers Rhine, Scheldt, Tees/Tyne and Elbe. Sea stars from stations in coastal zones showed relatively high levels of P450 and the 418 nm peak known to be present most marine invertebrates. Inhibiting effects outweighed possible induction of microsomal cytochrome P450 activity. The station nearest to the Elbe estuary showed the strongest inhibition of BPH activity and AChE activity. DNA integrity was lower especially in stations near the Dutch coast and in the area near the Humber and the rivers Tees/Tyne. Sediment quality assessment showed strong toxicity for the sea urchin Psammechinus miliaris in pore water from sediments throughout the North Sea. Toxicity identification evaluation (TIE) procedures revealed that the effects in the sea urchin bioassays are partly due to the natural background levels of zinc in pore water. For some of the sediments collected, also other contaminants may contribute to the observed sediment toxicity. Together with sediment toxicity tests, the combined use of bioaccumulation measurements and biomarkers in sea stars can be used for risk assessment of polluted estuaries.