Dynamics of metal adaptation in riverine chironomids

The ability of the non-biting midge Chironomus riparius to survive and reproduce in metal polluted lowland rivers facilitates the opportunity to study micro-evolutionary processes in situ. However, due to larval drift, adapted midge populations are subject to regular immigration of non-adapted specimens from clean upstream river reaches. To examine the influence of non-adapted genes in adapted midge populations on the level of metal adaptation, an upstream and downstream chironomid population were crossbred on eight separate occasions in the laboratory to mimic gene flow. Several life-history characteristics, indicating adaptation to metals, were followed seasonally in the parental strains as well as in the reciprocal crossings. Such crossings were done over a 14-month period and maternal effects were found to be absent, indicating a major genetic component for the increased metal tolerance in the exposed midge populations. Furthermore, results confirmed the presence of adaptation to metals in exposed chironomids. However, a rapid loss of metal adaptation in the first generation hybrid offspring was clearly demonstrated. Consequently, the large temporal variation in metal adaptation in midge populations from the river can be explained by the earlier reported seasonal variations in selection pressure and immigration rates from non-adapted sub-populations.     

First world-wide interlaboratory study on polybrominated diphenylethers (PBDEs)

The first world-wide interlaboratory study on PBDEs, organised between November 1999 and April 2000, involved five biological samples, two sediments and two standard solutions. These materials were sent to 26 participants in nine different countries. Results were returned from 18 laboratories. The results reported for BDE 47 were acceptable with a range of relative standard deviations (Rsd) of 17-40%. Results for the BDEs 99 (Rsd 25-77%), BDE 100 (Rsd 19-48%), 153 (Rsd 30-48%) and 154 (Rsd 25-43%) showed that a further improvement of these analyses is needed. The BDE 209 analysis is not under the control of the participating laboratories. The data reported for the biota samples were very variable and for the two sediments Rsd values of 48% and 78% were obtained. It is recommended that analysts pay more attention to the special requirements for the BDE 209 analysis such as avoiding exposure to intensive light and exposure for too long times to too high temperatures.     

Cyst-based toxicity tests X: comparison of the sensitivity of the acute Daphnia magna test and two crustacean microbiotests for chemicals and wastes

This paper statistically evaluates the sensitivity of the acute Daphnia magna bioassay in comparison to that of two crustacean microbiotests: the Streptoxkit F and Thamnotoxkit F, which make use of larvae of the anostracans Streptocephalus proboscideus and Thamnocephalus platyurus respectively, hatched from cysts. Regression equations were calculated for 146 data pairs, taken from 5 different studies dealing with the acute toxicity of pure chemicals, effluents, river sediments, solid wastes and monitoring wells, and sludges. All comparisons show that there is a significant relationship (p< 0.05) between the acute effects found with the D.magna and the two crustacean microbiotests; correlation coefficients ranged from 0.84 to 0.92.

In the majority of cases, effect ratios between the conventional D.magna and the microbiotests were within a factor 2 for both pure chemicals and environmental samples.

Variation coefficients for repeated tests on the reference chemical potassium dichromate indicate a good precision and hence a good degree of standardization of the microbiotest procedures. The evidence provided in this paper demonstrates that the new crustacean microbiotests can be used as low cost alternatives to the conventional D.magna acute assay.     

Prenatal detection of cystic fibrosis; comparative study of maltase and alkaline phosphatase activities in amniotic fluid

The potential value of microvillar enzymes in the prenatal diagnosis of cystic fibrosis (CF) has previously been demonstrated and is corroborated in the present comparative study. Maltase and alkaline phosphatase (ALP) activities were studied in the amniotic fluids of 57 pregnancies with a 1 in 4 risk for CF or with a known CF outcome and in 489 controls. A simple assay for maltase activity (MU-maltase) with the fluorogenic substate 4-methylumbelliferyl α-glucoside, offers great technical advantages and an at least equal detection rate of CF, when compared to the previously used test with maltose as substrate. Intestinal ALP was estimated either as phenylalanine inhibitable activity (PI-ALP) or as the proportions of residual activity in the presence of the inhibitors phenylalanine or homoarginine. MU-maltase and PI-ALP appeared the most successful methods: both tests were able to detect 14 of the 16 (88 per cent) pregnancies with fetal CF. Each of the two tests alone also allowed a correct prediction in 24 of the 25 pregnancies at risk but with normal outcome; however all 25 cases could be correctly predicted by a combined evaluation. It is suggested that more than one intestinal enzyme activity should be evaluated to allow optimal results in the prenatal monitoring of pregnancies at high risk for CF.     

Voluntary employee turnover: combining variables from the ‘traditional’ turnover literature with the theory of planned behavior

In this study we tried to answer the question of whether the three predictors from the theory of planned behavior provide a satisfactory explanation for intentions and behaviors in the context of voluntary employee turnover. We examined whether variables which have traditionally played a prominent role in the study of turnover, i.e., job satisfaction, organizational commitment, age, and tenure, were capable of explaining additional variance in turnover intentions and voluntary turnover. We conducted a longitudinal study in which 296 respondents serving as professionals in the Royal Netherlands Navy completed a questionnaire. Half a year later they were asked to answer a second identical questionnaire; data were obtained from 202 participants who answered all relevant questions in both questionnaires. Their actual behavior (staying versus leaving) was registered during a 2‐year period following the completion of the first questionnaire. Behavioral intentions proved to be the best predictor of turnover in which the effects of all other variables were accounted for. Job satisfaction and tenure explained a significant proportion of the variance in intentions after the effects of the predictors from the theory of planned behavior had been taken into account. The results are discussed in relation to theoretical, methodological, and practical issues. Copyright © 2004 John Wiley & Sons, Ltd.     

Enhancement of PAH biodegradation in soil by physicochemical pretreatment

The effects were studied of short-term heating of contaminated soil and its soaking in an organic solvent on the subsequent biodegradation of PAHs. In a clayey dredged sludge with a high organic-matter content (12%), heating at 120°C for one hour increased the degree of degradation after 21 days of an aged PAH contamination from 9.5 ± 0.7% to 27 ± 5%. Lower temperatures resulted in smaller increases. The observed increase in biodegradation is caused by either transfer of PAHs from sorption sites with low desorption rates to those with high ones or transformation of slow-sorption sites into fast-sorption ones. Soaking of the above sludge in a 4:1 (v/vj acetone-water mixture increased the degree of degradation from 9.5 ± 0.7% to 20.4 ± 1.4%, probably as a result of dissolution of the PAHs in the pore liquid during soaking. Thermal pretreatment of a contaminated sandy soil with a low organic-matter content showed no significant effect on the degradation of aged PAHs. Soaking of the sandy soil increased the degradation of only PAHs of high molecular weight, namely from 24 ± 5% to 48 ± 7%.     

Feeding current characteristics of three morphologically different bivalve suspension feeders, Crassostrea gigas, Mytilus edulis and Cerastoderma edule, in relation to food competition

Introduced Pacific oysters (Crassostrea gigas) have shown rapid expansion in the Oosterschelde estuary, while stocks of native bivalves declined slightly or remained stable. This indicates that they might have an advantage over native bivalve filter feeders. Hence, at the scale of individual bivalves, we studied whether this advantage occurs in optimizing food intake over native bivalves. We investigated feeding current characteristics, in which potential differences may ultimately lead to a differential food intake. We compared feeding currents of the invasive epibenthic non-siphonate Pacific oyster to those of two native bivalve suspension feeders: the epibenthic siphonate blue mussel Mytilus edulis and the endobenthic siphonate common cockle Cerastoderma edule. Inhalant flow fields were studied empirically using digital particle image velocimetry and particle tracking velocimetry. Exhalant jet speeds were modelled for a range of exhalant-aperture cross-sectional areas as determined in the laboratory and a range of filtration rates derived from literature. Significant differences were found in inhalant and exhalant current velocities and properties of the inhalant flow field (acceleration and distance of influence). At comparable body weight, inhalant current velocities were lower in C. gigas than in the other species. Modelled exhalant jets were higher in C. gigas, but oriented horizontally instead of vertically as in the other species. Despite these significant differences and apparent morphological differences between the three species, absolute differences in feeding current characteristics were small and are not expected to lead to significant differences in feeding efficiency.     

Impact of 100-Year Human Interventions on the Deltaic Coastal Zone of the Inner Thermaikos Gulf (Greece): A DPSIR Framework Analysis

The Axios River delta and the Inner Thermaikos Gulf coastal zone have experienced a long period of human interventions during the past 100 years. A post-evaluation of long run coastal zone changes under the Drivers-Pressures-State-Impacts-Response (DPSIR) conceptual framework is presented. The DPSIR approach is then used to project out into possible futures in order to connect with policy and management options proposed for the improvement of the current conditions and the achievement of sustainable development, in the coastal zone. Socio-economic driving forces with their origins in the end of the 19^th century have generated numerous pressures in the coastal environment that changed the state of the environment. In the first part of the last century, there was no coupling between change of state and policy. Due to increasing environmental awareness, a coupling became more apparent over the last thirty years. Human interventions include river route realignment, extensive drainage of the plains, irrigation network, roads and dam constructions. The consequences were positive for the economic development of the area, human health, and navigation for the port of Thessaloniki. In contrast, the manipulation and over-use of natural resources has led to a reduction of wetlands, biodiversity loss, stress on freshwater supplies, and subsidence of coastal areas, aquifer salinization, and rapid coastal erosion. Three plausible future scenarios are utilised in order to investigate the implications of this environmental change process and possible socio-economic consequences.     

Relation between forest vegetation, atmospheric deposition and site conditions at regional and European scales

Several monitoring programs have been set up to assess effects of atmospheric deposition on forest ecosystems. The aim of the present study was to evaluate effects on the understorey vegetation, based on the first round of a regional (the Netherlands) and a European forest monitoring program. A multivariate statistical analysis showed surprisingly similar results for both data sets; the vegetation appeared to be largely determined by the ‘traditional’ factors soil, climate, and tree species, but there was a small but statistically significant effect of atmospheric deposition. The effects of deposition include a slight shift towards nitrophytic species at high N deposition in the European network, and towards acidophytic species at high S-deposition in the Dutch network. The relatively small effect of atmospheric deposition is understandable in view of the very large natural variation in environmental conditions. Time series of both vegetation and environment are needed to assess deposition effects in detail.