Green Alga Selenastrum Capricornutum Research Articles

A new supported TiO2 film deposited on stainless steel for the photocatalytic degradation of contaminants of emerging concern

A new supported catalyst composed of a nanostructured TiO2 film deposited on a stainless steel mesh (nanoTiO2-SS) using the Metal Organic Chemical Vapour Deposition (MOCVD) technique was evaluated for the photocatalytic degradation of a mixture of contaminants of emerging concern. Results showed that under the oxidative conditions tested, the nanoTiO2-SS catalyst demonstrated an efficiency in degrading the target contaminants higher than that observed under direct photolysis and photocatalysis using the conventional TiO2 Degussa P25 catalyst at the same amount of TiO2 participating to the photocatalysis. Specifically, the rate of removal of warfarin and trimethoprim obtained with the new catalyst was found twice the one observed by using TiO2 Degussa P25 and approximately 1.6 times faster for metoprolol, carbamazepine and gemfibrozil. An evaluation of the electrical energy per order magnitude of removal (EE/O) confirmed the enhanced performance of the new catalyst (24.3–31.8kWhm−3 rather than 32.8–39.3kWhm−3 for conventional TiO2) and that the performance is compound-dependent. Toxicity testing revealed that some assays are suitable for the investigation of bioactivity of treated waters containing contaminants of emerging concern at μgL−1 level. Specifically, the AMES Fluctuation Test, Fish Embryo Acute Toxicity Test and Green alga Selenastrum capricornutum test provided valuable results for an environmental impact assessment. On the other hand, the Daphnia magna and Vibrio fischeri acute toxicity tests were not sensitive enough to detect bioactivity in the samples analysed without prior pre-concentration.

Measuring the effects of food availability on Lake Superior Diporeia consumption rates using radiolabeled algae

Abstract Within the Lake Superior benthic macroinvertebrate community, Diporeia spp. are the most abundant organisms and account for the largest proportion of biomass. As detritivores that feed on organic material in surficial sediments, Diporeia play a major role in transferring energy and nutrients to higher trophic level consumers and are favored prey for Lake Whitefish and other benthivorous fish species. The objective of this study is to quantify and model the response of the Diporeia consumption rate to changes in food availability. Diporeia were introduced to microcosms containing various concentrations of 14 C-labeled green algae ( Selenastrum capricornutum ) and incubated for 24 hours. Consumption was calculated as the radioisotope content of each animal divided by the specific activity of the labeled algae. A hyperbolic (Michaelis–Menten) function was fit to the data, yielding a maximum consumption rate of 1.76 ± 0.4 SE mg C/g DW/d. The predicted consumption rate corresponding to average Lake Superior algal carbon fluxes was 0.08 ± 0.15 mg C/g DW/d. For the observed range of carbon fluxes to benthic habitats in the Great Lakes, the relationship between consumption and food supply is well described by a linear function, with consumption rates ranging from 0.08–0.38 mg C/g DW/d. The parameter estimates presented here may act as inputs for a bioenergetics model used to predict Diporeia growth and production in Lake Superior.

Toxicity of waters from the St. Lawrence River at Massena Area-of-Concern to the plankton species Selenastrum capricornutum and Ceriodaphnia dubia

In 1972, the US and Canada committed to restore the chemical, physical, and biological integrity of the Great Lakes Ecosystem under the first Great Lakes Water Quality Agreement. During subsequent amendments, part of the St. Lawrence River at Massena NY, and segments of three tributaries, were designated as one Area of Concern (AOC) due to various beneficial use impairments (BUIs). Plankton beneficial use was designated impaired within this AOC because phytoplankton and zooplankton population data were unavailable or needed “further assessment”. Contaminated sediments from industrial waste disposal have been largely remediated, thus, the plankton BUI may currently be obsolete. The St. Lawrence River at Massena AOC remedial action plan established two criteria which may be used to assess the plankton BUI; the second states that, “in the absence of community structure data, plankton bioassays confirm no toxicity impact in ambient waters”. This study was implemented during 2011 to determine whether this criterion was achieved. Acute toxicity and chronic toxicity of local waters were quantified seasonally using standardized bioassays with green alga Selenastrum capricornutum and water flea Ceriodaphnia dubia to test the hypothesis that waters from sites within the AOC were no more toxic than were waters from adjacent reference sites. The results of univariate and multivariate analyses confirm that ambient waters from most AOC sites (and seasons) were not toxic to both species. Assuming both test species represent natural plankton assemblages, the quality of surface waters throughout most of this AOC should not seriously impair the health of resident plankton communities.

Ionic liquids as lubricants or lubrication additives: An ecotoxicity and biodegradability assessment

This paper reports on the (eco)toxicity and biodegradability of ionic liquids considered for application as lubricants or lubrication additives. Ammonium- and pyrrolidinium-based cations combined with methylsulphate, methylsulphonate and/or (CF3SO2)2N− anions were investigated in tests to determine their aquatic toxicity using water fleas Daphnia magna, green algae Selenastrum capricornutum and marine bacteria (Vibrio fischeri). Additional test systems with an isolated enzyme (acetylcholinesterase) and isolated leukaemia cells from rats (IPC-81) were used to assess the biological activity of the ionic liquids. These compounds generally exhibit low acute toxicity and biological activity. Their biodegradability was screened according to OECD test procedures 301 B and 301 F. For choline and methoxy-choline ionic liquids ready biodegradability was observed within 5 or 10d, respectively. Some of the compounds selected have a considerable potential to contribute to the development of more sustainable products and processes.

Impacts of Nonpoint-Source Pollution on the Structure of Diatom Assemblages, Whole-Stream Oxygen Metabolism, and Growth of Selenastrum capricornutum in the Red River Watershed of North-Central Tennessee

Assessments of stream biology are prerequisites to developing watershed management plans to improve ecological integrity. We sampled six streams in the Red River Watershed of North-Central Tennessee to evaluate the effects of non-point source pollution on diatom assemblages, primary production, and potential for excessive algal growth. We used diatom indices to assess the structure of diatom assemblages, changes of oxygen concentrations to evaluate primary production, and growth dynamics of the green alga Selenastrum capricornutum to evaluate the potential for excessive algal growth. The three most abundant diatom taxa collected were Nitzschia linearis (16%), Navicula reichardtiana (15%), and Navicula tripunctata (7%). Habitat impairment in all six streams is indicated by: (1) high Siltation Index values for diatom assemblages which indicate loss of biotic integrity as a result of excessive sediments from erosion, (2) high rates of whole-stream oxygen metabolism characteristic of eutrophic conditions, (3) low ratios of whole-stream gross primary production to respiration distinctive of heterotroph-dominated habitats often associated with poor quality water, and (4) high carrying capacities for Selenastrum capricornutum indicative of nutrient enrichment. High values of the Trophic Diatom Index and low values of the Pollution Tolerance Index of diatom assemblages at five of the six stream sites signify impairment due to eutrophication. The results reveal the impacts of excessive sediments and nutrient enrichment on the structure of diatom assemblages, oxygen dynamics, and potential for excessive algal growth in streams of the Red River Watershed.

Evaluation of the toxicity of Streptomyces aburaviensis (R9) extract towards various agricultural pests

The dichloromethane extract of culture filtrate from Streptomyces aburaviensis R9 was evaluated using various rapid bioassays to determine potential inhibitory effects towards phytopathogenic fungi (Colletotrichum acutatum, C. fragariae, C. gloeosoprioids, Botrytis cinerea, Fusarium oxysporum, Phomopsis viticola and P. obscurans), fish bacterial pathogens (Edwardsiella ictaluri and Flavobacterium columnare), a green alga (Selenastrum capricornutum), plant seeds [Bent grass (Agrostis sp.) monocot and lettuce (Lactuca sativa) dicot] and 2-methylisoborneol (MIB)-producing cyanobacteria (Planktothrix perornata and Pseudanabaena sp.). The dichloromethane extract showed selective inhibition against the cyanobacterium P. perornata, with a lowest-complete-inhibition concentration (LCIC) of 10 mg/L and lowest-observed-effect concentration (LOEC) of 10 mg/L while LCIC and LOEC values were 100 mg/L when tested against S. capricornutum. This extract also showed slight meristematic cytogenic necrosis at 200 mg/L towards germinated seeds of both test plants. The compounds were not very toxic towards the channel catfish (Ictalurus punctatus) pathogenic bacteria E. ictaluri and F. columnare. Preliminary evaluation of the extract toward C. acutatum, C. fragariae and C. gloeosoprioids using TLC bioautography revealed moderate activity. However, further evaluation of the extract using a microtiter plate bioassay determined that inhibition was strongest against C. acutatum and C. fragariae, though this inhibitory activity diminished at 72 hours and was moderately less active than the commercial fungicides azoxystrobin and captan when comparing 1 - 100 mg/L levels at 48 hours.

In Vitro Evaluation of the Antimicrobial Agent AquaFrin as a Bactericide and Selective Algicide for Use in Channel Catfish Aquaculture

AbstractProducers of pond‐raised channel catfish Ictalurus punctatus in the southeastern United States can experience huge economic losses due to enteric septicemia of catfish (ESC) and columnaris disease and to the presence of certain odor‐producing cyanobacteria in production ponds that result in “off‐flavor” channel catfish. AquaFrin (lauryl methyl pyrifrin), a product currently being evaluated for commercial use, belongs to a class of porphyrins that have been shown to be very effective as antibacterial agents. As a preliminary step to assess the potential use of AquaFrin as a therapeutant against ESC and columnaris, we used a rapid bioassay to evaluate AquaFrin for antibacterial activity against the Gram‐negative bacterium Edwardsiella ictaluri (etiological agent of ESC), two genotypes of the Gram‐negative bacterium Flavobacterium columnare (etiological agent of columnaris disease), and the representative Gram‐positive bacterium Staphylococcus aureus (American Type Culture Collection 29213) for comparison. In addition, we performed a bioassay‐directed evaluation of AquaFrin for selective toxicity toward the musty cyanobacterium Planktothrix perornata. AquaFrin was found to possess antibacterial activity toward all tested bacteria and yielded the following minimal inhibitory concentration results: 0.5 mg/L for F. columnare isolate ALM‐00‐173, 1.0 mg/L for F. columnare isolate BioMed, 0.1 mg/L for S. aureus, and 9.8 mg/L for E. ictaluri. The range of 96‐h 50% inhibition concentrations (0.07–0.2 mg/L) for AquaFrin toward P. perornata and the green alga Selenastrum capricornutum indicates strong potential for its use as a broad‐spectrum algicide.

Comparative phytotoxicity of methylated and inorganic arsenic- and antimony species to Lemna minor, Wolffia arrhiza and Selenastrum capricornutum

The alkylation of metalloids through the transfer of methyl groups is an important factor in the biogeochemical cycling of elements like arsenic and antimony. In the environment, many different organic and inorganic forms of these elements can therefore be found in soils, sediments or organisms. Studies that compare the ecotoxicity of these different chemical species however are rare. Therefore, this study aimed to generate toxicity data on two scarcely studied organic compounds of arsenic and antimony, as well as to compare their toxicity to the inorganic species, which are studied so far to a higher extent, in order to improve the environmental effect assessment of these elements. To this purpose, bioassays were performed in which three different aquatic organisms (the floating water plants Lemna minor and Wolffia arrhiza and the green alga Selenastrum capricornutum) were exposed to a concentration series of 3 different arsenic species (sodium arsenite — As(III), sodium arsenate — As(V), and monomethylarsonous diiodide — MMAs(III)) and three different antimony species (antimony potassium tartrate hydrate — Sb(III), potassium hexahydroxoantimonate — Sb(V), trimethylantimony(V) bromide — TMSb(V). The observed effect concentrations demonstrated that the inorganic (III)- and (V)-valent species of arsenic were clearly more toxic than the corresponding antimony species. The highest overall toxicity has been shown by MMAs(III) followed by the inorganic As(III). The highest toxicity of the three tested antimony species has been observed for TMSb(V). The observed differences in effect levels stress the importance once more that speciation must not be ignored in toxicity studies.

Effects of metals on biosorption and biodegradation of mixed polycyclic aromatic hydrocarbons by a freshwater green alga Selenastrum capricornutum

The effects of metals (cadmium, zinc, copper and nickel in a mixture) on biosorption and biodegradation of five mixed polycyclic aromatic hydrocarbons (PAHs), namely fluorene (FLU), phenanthrene (PHE), fluoranthrene (FLA), pyrene (PYR) and benzo[a]pyrene (BAP), by Selenastrum capricornutum were investigated. Exposure to metals significantly influenced the interactions between cells and PAHs and, such impact was PAH species dependent. For low molecular weight PAHs (FLU and PHE), both metal dosage and exposure time posed a significant, positive effect on their removal, with up to 99% of FLU and 89% of PHE were removed from the medium in seven days, which was mainly due to the cellular degradation induced by metal stress. For high molecular weight PAHs (FLA, PYR and BAP), the presence of metals did not affect the removal efficiency, but the uptake in the ethyl acetate-extractable fraction of the biomass was increased.

Acute aquatic toxicity of western juniper (Juniperus occidentalis) foliage and Port Orford cedar (Chamaecyparis lawsoniana) heartwood oils

Recently, interest has developed for using essential oils from Western juniper (Juniperus occidentalis) foliage and Port Orford cedar (Chamaecyparis lawsoniana) heartwood in commercial products such as pest repellents and cosmetics. In order to gauge the relative toxicological risk that these oils pose to freshwater and marine organisms, the acute aquatic toxicity of these oils was evaluated using OPPTS guidelines to the cladoceran Daphnia magna, the rainbow trout Oncorhynchus mykiss and the green alga Selenastrum capricornutum. For western juniper foliage oil, no toxicity was exhibited toward D. magna or O. mykiss, even at 5.0 mg/L (the highest concentration tested and limit of solubility). For toxicity to S. capricornutum using algal cell density, the 72 and 96 h EC50 value was 1.7 mg/L and the no observable effect concentration (NOEC) was 0.63 mg/L. For Port Orford cedar heartwood oil, no toxicity was exhibited toward O. mykiss or S. capricornutum, even at 5.0 mg/L (the highest concentration tested and limit of solubility). The 48-h D. magna EC50 value was 1.9 mg/L; the NOEC values for algal cell density were 1.25 mg/L (72 h) and 0.63 mg/L (96 h). In summary, this study shows that western juniper foliage and Port Orford cedar heartwood oils demonstrate little to no risk to aquatic organisms.

Algicide Constituents from Swinglea glutinosa

Oscillatoria perornata, a cyanobacterium (blue-green alga), common in catfish production ponds in the southeastern United States, produces the monoterpene 2-methylisoborneol (MIB), which is absorbed into catfish flesh and imparts a "musty" taste, rendering them unpalatable and unmarketable. Algicides that are currently in the commercial market to control O. perornata have broad-spectrum toxicity toward other beneficial phytoplankton, such as the green alga Selenastrum capricornutum, as well as low biodegradability. As part of our continuing efforts to search for natural-product-based algicides, the ethyl acetate extract of the roots of Swinglea glutinosa was investigated. This report describes isolation and structure elucidation of one novel coumarin, two known coumarins, and nine acridone alkaloids from S. glutinosa root extracts and the evaluation of these compounds for algicidal activity against O. perornata.

Antimicrobial Activity of Stilbene Derivatives

Certain species of cyanobacteria are responsible for fish “off-flavor” that causes annual losses of up to $60 million for U.S. catfish farmers. The “musty” and “earthy” flavor of the fish flesh is caused by the absorption of the cyanobacterial metabolites 2-methylisobroneol (MIB) and geosmin, respectively. Edwardsiella ictaluri and Flavobacterium columnare are the causative bacteria for the two most common diseases in pond-raised channel catfish referred to as enteric septicemia of catfish and columnaris, respectively. In an attempt to find a solution to control problems caused by these undesirable pathogenic bacteria and cyanobacteria, more than 20 natural and synthetic stilbenes were tested for activity against these microorganisms. Both cis and trans isomers of 4-(3,5-dimethoxystyryl)aniline demonstrated moderate toxicity against the MIB-producing cyanobacterium Oscillatoria perornata and were also found to be selectively toxic compared to their activity against the green alga Selenastrum capricornutum. Resveratrol showed slight activity against E. ictaluri and F. columnare based upon minimum inhibitory concentration.

Growth and physiological responses of freshwater green alga Selenastrum capricornutum to allelochemical ethyl 2-methyl acetoacetate (EMA) under different initial algal densities

Most natural algicides including macrophytic allelochemicals are known to selectively inhibit algal growth. The investigations on the modes of action about the species-specific algicides are little. In this study, the effects of allelochemical ethyl 2-methyl acetoacetate (EMA) identified from reed ( Phragmites communis) on the growth, physiological, and biochemical processes of green alga Selenastrum capricornutum were investigated. The results showed that EMA had multiple effects on the growth of S. capricornutum under different initial algal densities (IADs). The algal growth was inhibited by EMA at low IADs, but stimulated at high IADs. Further, the potential modes of action of EMA on S. capricornutum were explored from ultrastructure, metabolic activity, reactive oxygen species level, and lipid peroxidation to trace the microenvironment changes in the algal cells. Damage in cell structure occurred at low IAD, but cells were well developed with increased metabolic activity at high IAD. The reactive oxygen species (ROS) levels were increased under both conditions. The increase of ROS level was acute at low IAD but slow at high IAD. EMA caused significant lipid peroxidation, i.e. oxidative damage on membrane lipids at low IAD but not at high IAD. Based on these results, the initial algal density is considered an important factor to influence algal growth and physiological and biochemical responses to EMA, the effects of EMA on S. capricornutum may be “hormesis-like”, and different ROS increase ratio may be directly related with different responses of S. capricornutum to EMA.

EFFECT OF IMIDAZOLIUM-BASED IONIC LIQUIDS ON THE PHOTOSYNTHETIC ACTIVITY AND GROWTH RATE OF SELENASTRUM CAPRICORNUTUM

Ionic liquids (ILs) are low-melting organic salts that are being researched intensively as possible environmentally friendly replacements for volatile organic solvents. Despite their nonmeasurable vapor pressure, some quantities of ILs soon will be present in effluent discharges because solubility of ILs in water is small, but far from negligible. Therefore, it is important to understand how ILs will influence aquatic ecosystems. In the present study, the toxic effects of imidazolium-based ILs (1-butyl-3-methylimidazolium cation associated with bromide [BMIM] [Br] and tetrafluoroborate [BMIM] [BF4]) to the freshwater green alga Selenastrum capricornutum were investigated. Two approaches were followed to quantify toxicity of these compounds: Analyses of photosynthetic activity and cell proliferation. The obtained data showed that the relative declines of growth rates generally were more pronounced than those of photosynthetic activity. The ecotoxicity of a range of common organic solvents also was examined. It was revealed that both imidazolium-based ILs studied were some orders of magnitude more toxic than methanol, isopropanol, and dimethylformamide. In addition, with respect to IL incorporating perfluorinated anion, EC50 values (concentrations which lead to a 50% reduction of the exposed organisms relative to control) of the previously prepared stock solution were significantly lower compared to those of the freshly made one. This might be due to hydrolytic effects of [BMIM][BF4] leading to fluoride formation, which was confirmed by ion chromatography analysis. This indicates that, after ILs are discharged into the aqueous system, they can become more toxic than expected by laboratory data with fresh ILs.

Small‐scale fluid motion mediates growth and nutrient uptake of Selenastrum capricornutum

Summary1. A fluid‐flow reactor using submersible speakers was constructed to generate small‐scale fluid motion similar to conditions measured in open water environments; flow was quantified by particle image velocimetry. Additionally a Couette‐type rotating cylinder was used to generate shear flows; flow was quantified using an optical hotwire probe and torque measurements. Growth rates of the green alga Selenastrum capricornutum were determined from changes in cell counts and viability was tested using the fluorogenic probe fluoresceine diacetate.2. Evidence that fluid motion directly affects growth rates was obtained as a significant difference between growth in a moving versus non‐moving fluid. A near 2‐fold increase in growth rate was achieved for an energy dissipation rate of ɛ = 10−7 m2 s−3; a rate common in lakes and oceans. The onset of the viability equilibrium, identified as the day of the test period when the number of active cells equalled non‐active cells, was delayed by 2 days for moving fluid conditions as compared with a non‐moving fluid.3. Nutrient uptake was determined by a decrease in the bulk fluid concentration and cellular phosphorus concentration was also estimated. The thickness of the diffusive sublayer surrounding a cell, a zone dominated by molecular diffusion, was estimated. Increasing fluid motion was found to decrease the thickness of this layer. The Sherwood number (ratio of total mass flux to molecular mass flux) showed that advective flux surrounding cells dominated molecular diffusion flux with regard to Péclet numbers (ratio of advective transport to molecular diffusion transport). Fluid motion facilitated uptake rates and resulted in increased growth rates, compared with no‐flow conditions. The rate‐of‐rotation and the rate‐of‐strain in a moving fluid equally mediated the diffusive sublayer thickness surrounding the cells. Our study demonstrates that small‐scale fluid motion mediates algal growth kinetics and therefore should be included in predictive models for algal blooms.

Chemical Constituents of the Aquatic Plant Schoenoplectus lacustris: Evaluation of Phytotoxic Effects on the Green Alga Selenastrum capricornutum

Forty-nine secondary metabolites were isolated from aqueous and alcoholic extracts of the aquatic plant Shoenoplectus lacustris. All compounds were characterized based on spectroscopic data. Eleven free and glycosylated low-molecular polyphenols, 17 cinnamic acid and dihydrocinnamic acid derivatives, 11 flavonoids, and 10 C13 nor-isoprenoids were identified. The structure of the new compound, 1-benzoyl-glycerol-2-alpha-L-arabinopyranoside, was elucidated by 2D NMR experiments (COSY, HSQC, HMBC, NOESY). To evaluate potential phytotoxic effects, all compounds were tested on the green alga Selenastrum capricornutum, a unicellular organism commonly used in tests of toxicity as a bioindicator of eutrophic sites. The most active compound was (-)-catechin, showing an inhibition similar to that of the algaecide CuSO4.

Use of Selenastrum Capricornutum Growth Inhibition Test for Testing Toxicity of Metal Ions in Soil and Water

ABSTRACTThe unicellular green alga Selenastrum capricornutum (Rhapidocelis subcapitata) growth inhibition assay was applied to the toxicity testing of water, suspensions of heavy-metal-polluted clinker and waste ore pile. The ISO 8692:2004 standard test procedure was followed, and growth rate inhibition indexes were determined. Despite high concentrations of zinc in water (38.47 mg/L of Zn), exceeding by approximately 400-fold the EC50 value for S. capricornutum (0.1 mg Zn/L), 72-h algal growth in the soil extracts was inhibited with 50% in comparison with growth in the standard control ISO mineral medium. Cell dead of algae was observed by clinker leacheates contained up to 796 mg Cu/L. Decreasing of inhibition effect and rate of cell dead could not be explained by supplementary nitrogen, phosphorous, and carbonate leached from the waste ore pile and clinker.

Algicidal and antifungal compounds from the roots of Ruta graveolens and synthesis of their analogs

Bioassay-guided fractionation of the ethyl acetate extract of Ruta graveolens roots yielded rutacridone epoxide with potent selective algicidal activity towards the 2-methyl-isoborneol (MIB)-producing blue-green alga Oscillatoria perornata, with relatively little effect on the green alga Selenastrum capricornutum. The diol-analog of rutacridone epoxide, gravacridondiol, which was also present in the same extract, had significantly less activity towards O. perornata. Rutacridone epoxide also showed significantly higher activity than commercial fungicides captan and benomyl in our micro-bioassay against the agriculturally important pathogenic fungi Colletotrichum fragariae, C. gloeosporioides, C. acutatum, and Botrytis cineara and Fusarium oxysporium. Rutacridone epoxide is reported as a direct-acting mutagen, precluding its use as an agrochemical. In order to understand the structure–activity relationships and to develop new potential biocides without toxicity and mutagenicity, some analogs containing the (2-methyloxiranyl)-dihydrobenzofuran moiety with an epoxide were synthesized and tested. None of the synthetic analogs showed comparable activities to rutacridone epoxide. The absolute stereochemistry of rutacridone was determined to be 2′(R) and that of rutacridone epoxide to be 2′(R), 3′(R) by CD and NMR analysis.

Phytotoxic and Antifungal Compounds from Two Apiaceae Species, Lomatium californicum and Ligusticum hultenii, Rich Sources of Z-ligustilide and Apiol, Respectively

The seeds of two Apiaceae species, Ligusticum hultenii and Lomatium californicum, were investigated. Preliminary bioassays indicated that methylene chloride extracts of seeds of both species contained selective phytotoxic activity against monocots and antifungal activity against Colletotrichum fragariae. Active constituents were isolated by bioassay-guided fractionation, and the structures were elucidated by NMR and GC-MS as apiol and Z-ligustilide, isolated from L. hultenii and L. californicum, respectively. Apiol and Z-ligustilide had I50 values of about 80 and 600 microM, respectively, for inhibition of the growth of Lemna paucicostata. The methylene chloride (CH2Cl2) extracts of the seeds and the isolated and purified compounds were tested against the 2-methylisobomeol-producing cyanobacterium (blue-green alga) Oscillatoria perornata, and the green alga Selenastrum capricornutum. The CH2Cl2 extracts of both Apiaceae species and apiol were weakly toxic to both species of phytoplankton, while Z-ligustilide was toxic to both with a lowest complete inhibitory concentration (LCIC) of 53 microM. Seeds of L. californicum and L. hultenii were found to be rich sources of Z-ligustilide (97 mg/g of dry seed) and apiol (40 mg/g of dry seed), respectively.

Preliminary ecotoxicological characterization of a new energetic substance, CL-20

A new energetic substance hexanitrohexaazaisowurtzitane (or CL-20) was tested for its toxicities to various ecological receptors. CL-20 (ε-polymorph) was amended to soil or deionized water to construct concentration gradients. Results of Microtox (15-min contact) and 96-h algae growth inhibition tests indicate that CL-20 showed no adverse effects on the bioluminescence of marine bacteria Vibrio fischeri and the cell density of freshwater green algae Selenastrum capricornutum respectively, up to its water solubility (ca. 3.6 mg l −1). CL-20 and its possible biotransformation products did not inhibit seed germination and early seedling (16–19 d) growth of alfalfa ( Medicago sativa) and perennial ryegrass ( Lolium perenne) up to 10 000 mg kg −1 in a Sassafras sandy loam soil (SSL). Indigenous soil microorganisms in SSL and a garden soil were exposed to CL-20 for one or two weeks before dehydrogenase activity (DHA) or potential nitrification activity (PNA) were assayed. Results indicate that up to 10 000 mg kg −1 soil of CL-20 had no statistically significant effects on microbial communities measured as DHA or on the ammonium oxidizing bacteria determined as PNA in both soils. Data indicates that CL-20 was not acutely toxic to the species or microbial communities tested and that further studies are required to address the potential long-term environmental impact of CL-20 and its possible degradation products.