Assessment of the toxicity of mixtures of halogenated dibenzo-p-dioxins and dibenzofurans by use of toxicity equivalency factors (TEF)

In March 1988 the authors completed a report on the risk assessment of mixtures of halogenated dibenzo-p-dioxins and dibenzofurans at the request of the National Institute of Public Health and Environmental Protection in the Netherlands. Based on a study of the current knowledge of these compounds, a set of toxicity equivalency factors was proposed for use in such risk assessments. This paper presents the section of this report that deals with the literature on the effects of these compounds and the choice of toxicity equivalency factors. The uncertanties in the selection and application of toxicity equivalency factors are discussed.     

Response of zooxanthellae in symbiosis with the Mediterranean corals Cladocora caespitosa and Oculina patagonica to elevated temperatures

Scleractinian symbiotic corals living in the Ligurian Sea (NW Mediterranean Sea) have experienced warm summers during the last decade, with temperatures rapidly increasing, within a few days, to 3–4°C above the mean value of 24°C. The effect of elevated temperatures on the photosynthetic efficiency of zooxanthellae in symbiosis with temperate corals has not been well investigated. In this study, the corals, Cladocora caespitosa and Oculina patagonica were collected in the Ligurian Sea (44°N, 9°E), maintained during 2 weeks at the mean summer temperature of 24°C and then exposed during 48 h to temperatures of 24 (control), 27, 29 and 32°C. Chlorophyll (chl) fluorescence parameters [F _v/F _m, electron transport rate (ETR), non-photochemical quenching (NPQ)] were measured using pulse amplitude modulated (PAM) fluorimetry before, during the thermal increase, and after 1 and 7 days of recovery (corals maintained at 24°C). Zooxanthellae showed a broad tolerance to temperature increase, since their density remained unchanged and there was no significant reduction in their maximum quantum yield (F _v/F _m) or ETR up to 29°C. This temperature corresponded to a 5°C increase compared to the mean summer temperature (24°C) in the Ligurian Sea. At 32°C, there was a significant decrease in chl contents for both corals. This decrease was due to a reduction in the chl/zooxanthellae content. For C. caespitosa, there was also a decrease in ETR_max, not associated with a change in F _v/F _m or in the non-photochemical quenching (NPQ); for O. patagonica, both ETR_max and F _v/F _m significantly decreased, and NPQ_max showed a significant increase. Damages to the photosystem II appeared to be reversible in both corals, since F _v/F _m values returned to normal after 1 day at 24°C. Zooxanthellae in symbiosis with the Mediterranean corals investigated can therefore be considered as resistant to short-term increases in temperature, even well above the maximum temperatures experienced by these corals in summer.     

Toxicity and bioaccumulation of reduced TNT metabolites in the earthworm Eisenia andrei exposed to amended forest soil

Soils contaminated with 2,4,6-trinitrotoluene (TNT) and TNT primary reduction products have been found to be toxic to certain soil invertebrates, such as earthworms. The mechanism of toxicity of TNT and of its by-products is still not known. To ascertain if one of the TNT reduction products underlies TNT toxicity, we tested the toxicity and bioaccumulation of TNT reduction products. 2-Amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), 2,4-diamino-6-nitrotoluene (2,4-DANT) and 2,6-diamino-4-nitrotoluene (2,6-DANT) were tested separately in adult earthworms (Eisenia andrei) following a 14-d exposure to amended sandy loam forest soil. TNT, 4-ADNT, and 2-ADNT were lethal to earthworms (14-d LC(50) were: 580, 531 and 1088 micromol kg(-1), or 132, 105 and 215 mgkg(-1) dry soil, respectively) and gave the following order of toxicity: 4-ADNT>TNT>2-ADNT. Exposure to 2,4-DANT and to 2,6-DANT caused no mortality at 600 micromol kg(-1) or 100 mgkg(-1) dry soil. We found that all four TNT reduction products accumulated in earthworm tissues and 2-ADNT reached the highest levels at 3.0+/-0.3 micromol g(-1) tissue. The 14-d bioaccumulation factors were 5.1, 6.4, 5.1 and 3.2 for 2-ADNT, 4-ADNT, 2,4-DANT and 2,6-DANT, respectively. Results also suggest that some TNT metabolites are at least as toxic as TNT and should be considered when evaluating the overall toxicity of TNT-contaminated soil to earthworms.     

Removal of PCDD/F from incinerator flue gases by entrained-phase adsorption

The emission abatement of polychlorinated dioxins and furans (PCDD/F) Issued from municipal solid waste incineration is growing in importance because of more stringent emission standards and general concern about their toxic characteristics. These substances cannot be separated by conventional gas cleanup processes but are successfully removed through adsorption onto carbonaceous materials. The simplest technique is the entrained-phase injection of pulverized adsorbents in the flue gas, followed by fabric filter separation. The various related techniques are briefly reviewed here. Operating conditions and results obtained from Flemish MSWIs are given. The results illustrate the excellent overall removal efficiency. Furans are adsorbed to a slightly higher extent than dioxins. PCDD/F removal by carbonaceous adsorbents is thereafter modeled from first principles for the contribution of both entrained-phase (eta1) and cake filtration (eta2) to the overall efficiency (etaT). Application of the model equations and comparison of measured and predicted overall efficiencies for the Flemish municipal solid waste incinerators (MSWIs) demonstrate that the approach is meaningful and that the dominant parameters are the operating temperature, the dosage and activity of adsorbent, and the fraction of adsorbent in the filter cake. The model equations enable the MSWI operators to predict the adsorption efficiencies for any combination of operating parameters and to assess the sensitivity of the process to varying operating conditions.     

Observations on the biology of Donax trunculus and D. vittatus at Ile d'Oléron (French Atlantic coast)

Observations have been made on the biology of two species of the bivalve genus Donax, on two beaches, Vertbois and St. Trojan, on the Ile d'Oléron, French Atlantic coast. The two species displayed different vertical distribution: D. trunculus Linné in the intertidal; and D. vittatus (da Costa) between low-water spring tide (LWST) and 5 to 6m depth, with only the fringe of the population extending to the shore. D. trunculus also showed differential distribution by size or age, the youngest individuals being highest on the shore, and the oldest near LWST. The two species exhibited a similar pattern of seasonal recruitment and growth, but in both there were differences in growth characteristics between the two beaches, individuals at St. Trojan growing to a larger size than those at Vertbois. The mean pattern of mortality in the two areas was similar, and productivity per 100 recruits surviving to the first winter following settlement was greater at St. Trojan than at Vertbois. For D. trunculus the mean population density at Vertbois was higher and the production per unit area on the two beaches was similar. Production to biomass (B) and elimination to biomass (B) ratios were similar for the two beaches for both species, and while production was greater for D. trunculus at both beaches, the B and B ratios were higher for D. vittatus. Comparisons with other published data reveal that the rate of growth of D. trunculus is similar throughout its range from Brittany to the Mediterranean Sea, while that of D. vittatus shows more variation. In both species, there is a trend of increasing P/B and E/B ratios from north to south throughout the geographical range.     

Do bearing magnets affect the extent of deflection in clock-shifted homing pigeons?

When released after clock-shift, homing pigeons fail to orient towards the home direction but display a consistent deflection of their initial orientation due to the difference between the real sun azimuth and the computed azimuth according to the subjective time of each single bird. It has been reported that the size of the observed deflection is frequently smaller than expected and a discussion on the possible factors affecting the size of deflection has emerged. Some authors have proposed that the major factor in reducing the deflection after clock-shift is the simultaneous use of both the magnetic and the sun compasses, giving true and erroneous information, respectively, about the home direction. Therefore, a magnetic disturbance, by impeding the use of the geomagnetic information in determining the home direction, is presumed to increase the size of the deflection up to the levels of the expectation. To test this hypothesis, we released three groups of clock-shifted birds from unfamiliar locations (unmanipulated pigeons, pigeons bearing magnets on their head, and pigeons bearing magnets on their back) together with a group of unshifted control birds. As no difference in the orientation of the three groups emerged, we were not able to confirm the hypothesis of the role of the magnetic compass in reducing the expected deflection after clock-shift.Communicated by W. Wiltschko     

<Emphasis Type="Italic">Alexandrium catenella</Emphasis> (Dinophyceae), a toxic ribotype expanding in the NW Mediterranean Sea

The presence of the paralytic shellfish poisoning (PSP) dinoflagellate Alexandrium catenella in the north western (NW) Mediterranean Sea has been known since 1983. From this date on, the species has spread along the Spanish and Italian coastlines. Information concerning A. catenella isolates in the NW Mediterranean Sea was gained through phylogenetic studies. Twenty established toxic cultures of A. catenella taken from various NW Mediterranean Sea locations were analysed by nucleotide sequencing of the 5.8S rDNA and internal transcribed spacer regions. These rDNA ribosomal markers resulted useful in delineating the phylogenetic position of this species in the genus Alexandrium as well as in determining relationships between A. catenella isolates from different geographic areas. The phylogenetic position of the Mediterranean A. catenella ribotype, when compared to the “Alexandrium tamarense/catenella/fundyense species complex”, fits this species complex well. All the Mediterranean A. catenella isolates were constituted by only one genetic ribotype. By comparing the isolate sequences with those of other geographic areas, it revealed that the Mediterranean A. catenella ribotype was closely related to the A. catenella from Japan, Western Pacific Ocean. It was also evident that in temperate Japanese waters, a genetic variability was detected within A. catenella isolates; in fact, all strains resulted divergent showing as many as 15 mutational steps. The possibility that A. catenella has been recently introduced into the Mediterranean basin from temperate Asian areas is discussed.     

Comparison of spatial overlap between the polychaetes Nereis virens and Nephtys caeca in two intertidal estuarine environments

An intensive study of spatial overlap between the polychaetes Nereis virens (Sars) and Nephtys caeca (Fabricius) was conducted in 1992 on two tidal sand flats, which differ by their exposure to dominant winds and residual currents in the Lower St. Lawrence Estuary (Québec, Canada). Results showed that spatial overlap (Lloyd's index and spatial distribution) was higher among adults of both species at the lower tidal elevation of l'Anse-à-l'Orignal (north-east oriented). Results also suggest weaker interspecific interactions among juveniles of both species because of limited spatial overlap. In Baie-du-Ha!Ha! (south-west oriented), spatial overlap was greater than that observed in l'Anse-à-l'Orignal and appeared important in adults as well as in juveniles. Levins' directional measure of competition indicated an asymmetric spatial overlap between N. virens and N. caeca in Baie-du-Ha!Ha! and a symmetric overlap in l'Anse-à-l'Orignal. The intraspecific encounter values, estimated from Lloyd's mathematical expression, were significantly higher than values of interspecific interactions only in l'Anse-à-l'Orignal. Moreover, no vertical stratification was found inside the sediment, with no effect of the densities and individual body weights of the polychaetes. Juveniles of both species mainly inhabited the organic-rich upper portion of the sediments (0 to 12 cm), while adults colonised greater depths (>25 cm) where organic matter content was lower. A complementary field experiment was conducted in 1993 to investigate interspecific interactions (predation and competition) existing between N. virens and N. caeca. Results from this experiment depend on which species was first-introduced and showed an important variation in mortality rates between allopatric and sympatric conditions. The influence of competition and predation on the structure of these populations is also discussed in relation to their spatial overlap.     

Raising groundwater differentially affects mineralization and plant species abundance in dune slacks.

The experience with restoring high water levels (i.e., rewetting) within restoration ecology is limited, and information on changes in soil nutrient supply is scarce. A reduction in nutrient supply is needed to restore the desired oligotrophic vegetation. We determined the effects of restoration of high water levels on decomposition and net carbon (C), nitrogen (N), and phosphorus (P) mineralization rates in wet dune slacks and its consequences for the relative abundance of eutrophic vs. oligotrophic species in the vegetation. This was done by analyzing these variables for valleys that experienced a large groundwater rise vs. valleys that had a small groundwater rise but the same current water level. In addition, the influences of underlying factors (waterlogging, vegetation dieback, and soil dynamics prior to groundwater rise) were separated in a transplantation experiment. Short-term effects of large groundwater rise were a massive dieback of vegetation, increased thickness of the fermentation layer, increased microbial decomposition activity, increased C mineralization, and decreased net N mineralization. Net P mineralization was not affected. The relative abundance of oligotrophic vs. eutrophic species was greater at large groundwater rise. Changes in decomposition and mineralization by large groundwater rise were, however, not caused by the vegetation dieback, but due to previous soil conditions. Soils experiencing waterlogged conditions for 3-4 years or more prior to large groundwater rise had lower C and higher net N mineralization rates at waterlogged conditions than soils that had experienced aerobic conditions, presumably due to differences in labile soil C contents. Contrary to expectations induced by previously determined nutrient pulses and measured vegetation dieback, large groundwater rise resulted in lower soil nutrient supply rates and more oligotrophic vegetation. If these trends continue on the longer term, restoration of high water levels may be effective in restoration ecology to establish oligotrophic, wet vegetation in dune slacks.     

An approach to deal with uncertainty in energy and environmental planning: the MARKAL case

This paper presents a new concept to include uncertainty management in energy and environmental planning models developed in algebraic modeling languages. SETSTOCH is a tool for linking algebraic modeling languages with specialized stochastic programming solvers. Its main role is to retrieve from the modeling language a dynamically ordered core model (baseline scenario) that is sent automatically to the stochastic solver. The case presented herein concerns such a study realized with the IEAMARKAL model used by many research teams around the world.