A chronic bioassay with the estuarine amphipod Corophium volutator: test method description and confounding factors

Methods of conducting a chronic sediment toxicity test with the estuarine amphipod Corophium volutator are described. They consist of a 49-day exposure, after which mortality, growth and reproduction are determined. Pilot experiments were used to optimize test design parameters such as temperature, duration, feeding and refreshing regimes, and effects of indigenous organisms. By way of further validation, the present study focused on the effects of four different parameters: oxygen saturation, salinity, ammonium and nitrite. These confounding factors might play an important role especially if the test is used for risk assessment of field-contaminated sediments. It is concluded that the present experimental design is well suited for chronic sediment exposures with C. volutator. The test can be performed at a broad range of salinity values, provided that controls are performed at the same salinity. Results further demonstrate that with the endpoints growth and reproduction this chronic test procedure is a factor 7-18 more sensitive to ammonium and nitrate than the standardized acute bioassay (endpoint mortality).     

Direct comparison of amphipod sensitivities to dredged sediments from Spanish ports

The sensitivity of the benthic amphipod species Ampelisca brevicornis and Corophium volutator to dredged sediments was compared through simultaneous testing on the standard 10 days sediment toxicity test. The results of mortality obtained for 22 harbor sediments sampled at several Spanish ports were studied together with the physico-chemical characteristics of the samples to obtain the incidence of toxicity in terms of dredged material categories and to identify possible differences in the amphipod mortality results when using one or another test species. The results showed a similar incidence of toxicity for medium-high and highly contaminated sediments for both amphipod species, similar to that obtained through the comparison of the chemical concentrations measured in sediments with the single limit values used in Spain for dredged material characterization and management. On the contrary, C. volutator presented a higher mortality and a higher incidence of toxicity when exposed to low and medium-low contaminated sediments, which may have been caused by the lower sensitivity of A. brevicornis when exposed to sediments from its natural environment. When compared to other amphipod species used for whole sediment toxicity assessment, both amphipod species used in this study reported slightly higher sensitivities although these differences could have been associated to the different set of chemical compounds considered when characterizing the sediment samples. In this sense, the amphipod mortality results were better predicted through the use of mean quotients than just by comparing the measured chemical concentrations with the single limit values used in Spain, which indicates that the toxic response of both species was caused by the cocktail of contaminants present in the sediments. Finally, the correlation analysis identified a higher association between A. brevicornis mortality and the metallic contaminants while C. volutator was more correlated with the organic micro-pollutants. Despite these differences, the results indicate that Ampelisca brevicornis can be used as test organism for dredged material characterization when enough individuals of other recommended species such as Corophium volutator are not available.     

Development and application of long-term sublethal whole sediment tests with Arenicola marina and Corophium volutator using Ivermectin as the test compound

Short-term whole sediment tests using the amphipod Corophium volutator and the polychaete Arenicola marina are now routinely used in Europe to assess the acute toxicity of marine sediments. However, there is still a need to develop longer-term assays which measure effects on sublethal endpoints that are more relevant to predicting impacts at the population level. The effect of increasing exposure times and measuring additional endpoints such as growth, on the sensitivity of these assays was investigated. The test compound used was the chemotherapeutant Ivermectin (IVM), used in aquaculture to treat sea lice infestations. IVM was found to be acutely toxic to both test organisms. Extending the lugworm test to 100 days increased sensitivity of survival by a factor of three; a significant reduction in casting rate was observed at concentrations an order of magnitude lower. This assay shows potential for detecting the sublethal effects of low concentrations of sediment contaminants. Increasing the exposure time did not seem to affect the sensitivity of the amphipod, but further method development is required.     

Cyst-based toxicity tests. XI. Influence of the type of food on the intrinsic growth rate of the rotifer Brachionus calyciflorus in short-chronic toxicity tests

As important members of zooplankton communities worldwide, rotifers are used extensively in ecotoxicological research. Chronic rotifer tests are, however, dependent on live algal food which adds to the complexity, the variability and the costs of these bioassays. To bypass the former problem, experiments have been undertaken with the freshwater rotifer Brachionus calyciflorus, to determine their intrinsic growth rate (r) when fed for 48 h on a mixture of green algae (Raphidocelis subcapitata recently renamed Pseudokirchneriella subcapitata) obtained from algal beads stored for different periods of time, and other inert foods. All tests have been performed in disposable multiwells, in 1 ml cups each inoculated with 1 rotifer freshly hatched from dried cysts. The majority of the growth tests was performed in eight replicates. The investigations revealed that microalgae from algal beads stored for up to one year, in darkness, at 4 degrees C, supplemented with dried blue-green algae (Spirulina) gave satisfactory rotifer reproduction. The intrinsic growth rates of the rotifers, were, however, dependent on the storage time of the algal beads; the highests r's (0.7-0.8) were obtained with algae from beads not older than four months. Growth tests with combinations of P. subcapitata and other inert feeds revealed that the enrichment food Selco used in aquaculture, also gave the same reproductive output as the combination microalgae/Spirulina. A rotifer growth experiment with 18 replicates showed that the variation coefficient is below 20% when the tests comprise eight replicates. This study demonstrated that microalgae from beads, supplemented by other inert food, open the door for a practical and cost-effective short-chronic rotifer test, which is totally independent of the culturing of both the test species and its live food.     

Influence of temperature and time on phosphorus removal in swine manure during batch aeration

This study was conducted to investigate the effects of temperature and time on the mechanisms of phosphorus removal in swine manure during aeration. Removal of soluble orthophosphates significantly increased with aeration time and temperature. Successive significant ortho-P removals were observed between days one and nine but no significant additional removals were recorded thereafter. Removals were significantly higher at temperatures of 20 and 25 degrees C than at temperatures of 5, 10, and 15 degrees C and ranged between 22.9 to 31.0%. Insoluble inorganic phosphorus also changed significantly with aeration time and temperature and with a similar trend as soluble orthophosphates. The pH of the manure explained 92 and 87% of the content of insoluble inorganic phosphorus at lower temperatures (5, 10, 15 degrees C) and at higher temperatures (20, and 25 degrees C), respectively. Organic phosphorus and aerobes growth patterns were similar to that of soluble orthophosphates removal. The rapid growth of aerobes was most probably the principal factor behind a rapid soluble ortho-P removal above 15 degrees C. The contribution of inorganic phosphates to the removal of soluble orthophosphates was approximately 61% while that due to organic P was approximately 35%. Precipitation was found to be the principal mechanism governing removal of soluble ortho-P in swine manure during aeration treatments.     

Environmental physiology of the mole crab Emerita asiatica, at a power plant discharge area on the east coast of India

Cage experiments at the discharge area of Madras Atomic Power Station (MAPS) facilitated studies of thermal tolerance in Emerita asiatica. At the laboratory, oxygen consumption at various temperatures and varying salinities was also investigated. In the field 100% mortality of crabs was recorded at the Condenser Cooling Water Pumps (CCWP) discharge site compared to no mortality at the Processed Sea Water Pumps (PSWP) site. This observation implicated temperature as a stress factor at the CCWP outfall, because other factors, including residual chlorine and water velocity, were the same at the PSWP and CCWP sites. Laboratory experiments on tolerance revealed that 38.5 degrees C was lethal to mole crabs. The time taken for 100% mortality decreased as the temperature increased from 35 to 40 degrees C. Oxygen metabolism showed a progressive increase with temperature from 29 to 36 degrees C, and declined at 37 degrees C. The influence of salinity on oxygen consumption was marginal at salinities of 20 to 35 per thousand but, when reduced to 15 per thousand, the oxygen consumption declined. The present study thus indicates that temperature could be the lethal factor, determining the distribution of mole crabs near the power station, where water temperature can exceed 40 degrees C.     

Effect of carbon dioxide concentration on biomass production and partitioning in Betula pubescens Ehrh. seedlings at different ozone and temperature regimes

Seedlings of Betula pubescens were grown at two CO(2) concentrations, in combination with either two O(3) concentrations or two air temperatures, during 34-35 days at 24 h day(-1) photoperiod in growth chambers placed in a greenhouse. Increasing the CO(2) concentration from 350 to 560 micromol mol(-1) at 17 degrees C air temperature increased the dry weight of the main leaves, main stem, branches and root. The mean relative growth rate (RGR) was increased 10% by CO(2) enrichment, while increasing the O(3) concentration from 7 to 62 nmol mol(-1) decreased the RGR by 9%. The relative biomass distribution between the different plant components was not significantly affected by the CO(2) concentration irrespective of the O(3) concentration. No significant interactions between CO(2) and O(3) concentration were found except on leaf size, which was stimulated more by elevated CO(2) concentration at high, compared to low, O(3) levels. In another experiment, elevated CO(2) (700 micromol mol(-1)) significantly increased the dry weight of the different plant components, and more at 20 degrees C than at 15 degrees C. Raising the CO(2) concentration increased the RGR by 5 and 10% at 15 and 20 degrees C, respectively. CO(2) enrichment increased the branch dry weight relatively more than the dry weight of the other plant parts. Increasing the CO(2) concentration or temperature increased the plant height and stem diameter, however, no interactions between CO(2) and temperature were found.     

Bacterial responses to temperature during aeration of pig slurry

The temperature effect on total anaerobic and aerobic bacterial growth in pig slurry was studied using low level batch aeration treatments. Five bioreactors were built using Plexiglas tubes to perform five temperature treatments (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C). An airflow rate of 0.129 L/min/L manure was used to aerate manure contained in all reactors. Data showed that temperature had a profound impact on the aerobic counts in pig slurry during the aeration process. When the temperature increased from 15 degrees C to 25 degrees C, the average oxidation-reduction potential decreased from +40 mV to -60 mV, accompanied by a 75% reduction of aerobic bacteria in the manure. At 25 degrees C, the anaerobic counts were consistently higher than aerobic counts for most of days. A quadratic relationship was observed between the aerobic counts and the oxidation-reduction potential with a correlation coefficient of 0.8374. To reduce odor generation potential, the oxidation-reduction potential in the manure should be maintained at +35 mV or higher.     

Effect of temperature and dissolved oxygen on the growth kinetics of Pseudomonas putida F1 growing on benzene and toluene

Batch experiments were conducted to determine the effect of temperature and dissolved oxygen concentration on the rates of growth and substrate (benzene and toluene) degradation by the toluene degrading strain, Pseudomonas putida F1. Over a range of temperature from 15 to 35 degrees C the maximum specific growth rate followed the Topiwala-Sinclair relationship when either benzene or toluene served as the sole carbon and energy source. Oxygen limited growth followed Monod saturation kinetics with the specific growth rate given as a function of the dissolved oxygen concentration. The oxygen half-saturation coefficient was found to be approximately 1 mg/l regardless of whether benzene or toluene was the substrate. Similar experiments with Burkholderia (Ralstonia) pickettii PKO1 for grown on toluene revealed an oxygen half-saturation coefficient of 0.7 mg/l.     

Transfer of the fungicide vinclozolin from treated to untreated plants via volatilization

Head lettuce plantlets (Lactuca sativa L. var. capitata) were potted, treated with vinclozolin at the six-leaf stage according to application standards and allowed to dry for 24 h. The potted plantlets were then placed in either growth chambers with controlled temperature (20 and 25 degrees C, respectively) or in a greenhouse (approximately 12 degrees C), together with untreated spinach (Spinacia oleracea L.) and standardized grass cultures (Lolium multiflorum Lam. ssp.) While the treated lettuce pots remained in the respective growing compartments until the end of the experiments, spinach and grass were exposed to the compartment air for 24 h and their shoot material was analyzed for vinclozolin by GC-ECD and GC-high resolution mass spectrometry. Exposure and analysis of untreated spinach and grass were carried out at two- or three-day intervals during the course of the experiments. Also, air samples were taken from the compartments at intervals and analyzed for vinclozolin. Maximum vinclozolin concentration in the growth chamber air was about 330 ng m(-3) while vinclozolin contamination of the untreated plants ranged from 50 to 200 microg kg(-1) FW (fresh weight). In the greenhouse atmospheric vinclozolin concentration reached approximately 15 ngm(-3) and maximum contamination of spinach and grass were 30-40 microg kg(-1) FW. Our data clearly show that unintended contamination of plants growing in the vicinity of vinclozolin-treated plants can occur even if the fungicide layer is completely dry. Implications for safety testing and food plants are discussed.     

Effects of temperature on mineralisation of petroleum in contaminated Antarctic terrestrial sediments

Although petroleum contamination has been identified at many Antarctic research stations, and is recognized as posing a significant threat to the Antarctic environment, full-scale in situ remediation has not yet been used in Antarctica. This is partly because it has been assumed that temperatures are too low for effective biodegradation. To test this, the effects of temperature on the hydrocarbon mineralisation rate in Antarctic terrestrial sediments were quantified. 14C-labelled octadecane was added to nutrient amended microcosms that were incubated over a range of temperatures between -2 and 42 degrees C. We found a positive correlation between temperature and mineralisation rate, with the fastest rates occurring in samples incubated at the highest temperatures. At temperatures below or near the freezing point of water there was a virtual absence of mineralisation. High temperatures (37 and 42 degrees C) and the temperatures just above the freezing point of water (4 degrees C) showed an initial mineralisation lag period, then a sharp increase in the mineralisation rate before a protracted plateau phase. Mineralisation at temperatures between 10 and 28 degrees C had no initial lag phase. The high rate of mineralisation at 37 and 42 degrees C was surprising, as most continental Antarctic microorganisms described thus far have an optimal temperature for growth of between 20 and 30 degrees C and a maximal growth temperature <37 degrees C. The main implications for bioremediation in Antarctica from this study are that a high-temperature treatment would yield the most rapid biodegradation of the contaminant. However, in situ biodegradation using nutrients and other amendments is still possible at soil temperatures that occur naturally in summer at the Antarctic site we studies (Casey Station 66 degrees 17(') S, 110 degrees 32(') E), although treatment times could be excessively long.     

Degradation of phenol and cresols at low temperatures using a suspended-carrier biofilm process

Degradation of phenol and o-, m- and p-cresol at a concentration of 150 mg l(-1) of each compound was studied in a suspended-carrier biofilm process consisting of two aerobic stages. The fungus Mortierella sarnyensis Mil'ko dominated the microflora in the first reactor, while bacteria dominated in the second reactor. The process was studied at 4, 7, 11 and 15 degrees C. The results from the experiments showed the process to be relatively efficient even at 4 degrees C. The degradation rate was 33% of that at 15 degrees C for o-cresol. Both phenol and the cresols were degraded in the first reactor and a new peak appeared in the HPLC-chromatograms indicating the formation of one or more intermediate compounds in the first stage. These compounds were however degraded to below the detection limit in the second reactor. Small new peaks appeared in the chromatograms of the outlet from the second reactor at the maximum loading rates.     

Degradation of [14C]isofenphos in soil in the laboratory under different soil pH's, temperatures, and moistures

The effects of three soil pH's, three soil temperatures, and three soil moistures on [14C]isofenphos degradation were investigated. All three factors interacted strongly and significantly affected the persistence of isofenphos as well as the formation of the degradation products (p less than 1%). Isofenphos degradation was greatest at the higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C (except under alkaline pH's), medium moisture 25% greater than 30% greater than 15%, and in both alkaline (pH = 8) and acidic soils (pH = 6) compared with neutral soil (pH = 7). Isofenphos oxon formation was greatest at higher temperatures 35 degrees C compared with 25 degrees C and 15 degrees C, in acidic soil greater than neutral soil greater than alkaline soil, and under high moisture (30%) compared with the 15% and 22.5% moistures. The formation of soil-bound residues was greatest at higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C, higher moisture 30% compared with 15% and 22.5%, and in alkaline soil compared with neutral and acidic soils.     

Control of bacterial growth in water using synthesized inorganic disinfectant

Chlorine is a popular method for controlling bacterial growth in cooling towers. However, there are several drawbacks such as the difficulties in maintaining the disinfection efficacy particularly at high temperature and pH. In order to overcome these difficulties, an inorganic disinfectant based on silver and copper, which is called EEKO-BALL (commercial name), was recently developed. EEKO-BALL is made from specific ceramics and coating materials. This study was performed to evaluate the efficacy of EEKO-BALL and compare it with that of silver (Ag+) and copper (Cu2+) ions. In addition, a field study was undertaken to investigate the control of bacterial growth in several cooling tower systems. The results showed that the contact time required for inactivating 99% of E. coli was 15 min in the EEKO-BALL stock solution at 25 degrees C, pH 7.3, with 0.05 mgl(-1) Ag and 0.05 mgl(-1) Cu. EEKO-BALL was approximately four times more effective than silver and copper ions in inactivating E. coli at 25 degrees C, pH 7.3. The control of bacterial growth in the cooling towers was found to be effective, lasting more than two months after a one-time installation of the EEKO-BALL. Overall, this study suggests that EEKO-BALL can effectively work as an inorganic disinfectant for bacterial growth control.     

The effect of ageing on the toxicity of zinc for the potworm Enchytraeus albidus.

Different extractable zinc fractions and the ecotoxicity of zinc in Enchytraeus albidus were assessed using freshly spiked artificial soils and spiked soils which had been aged for 8 weeks. Standard artificial Organization for Economic Cooperation and Development (OECD)-soils were aged in four different ways: (1) storing at 20 degrees C; (2) percolation followed by storing at 20 degrees C; (3) alternately heating at 60 degrees C and storing at 20 degrees C; and (4) alternately freezing at -20 degrees C and storing at 20 degrees C. Ageing had no clear influence on the pore water concentration, the water soluble and the calcium chloride extractable fraction of zinc in the artificial soils. Similarly, the 21d LC50 and the 42d EC50(reproduction) for E. albidus were not influenced by the different treatments. This absence of zinc fixation in the artificial soil during ageing was probably due to the use of kaolinite clay in OECD-soil.     

Production of male neonates in four cladoceran species exposed to a juvenile hormone analog, fenoxycarb

Previous studies have found that exposure of a cyclic parthenogen, the water flea Daphnia magna (Cladocera, Crustacea), to juvenile hormones and their analogs results in the production of neonates of male sex at concentration-dependent rates. We conducted reproduction experiments in four different species (Moina macrocopa, M. micrura, Ceriodaphnia dubia and C. reticulata) of cladoceran to test for the first time whether the occurrence of this phenomenon after exposure of the parent to such hormones is a generalized phenomenon. In the presence of a juvenile hormone analog, fenoxycarb, all four species produced male neonates and showed reduced rates of reproduction. The estimated median effective concentration (EC50) for the production of male neonates varied with species, ranging from 0.60 x 10(3) to 9.3 x 10(3) ng/l. Although there was a wide range of sensitivity to fenoxycarb, the production of male neonates in all four species demonstrates that this phenomenon is a common response to juvenile hormone analogs and further suggests that these hormones are capable of initiating sexual reproduction in cladocerans, most of which exhibit cyclic parthenogenesis.     

Dissipation of the herbicide clopyralid in an allophanic soil: laboratory and field studies

Soil dissipation of the herbicide clopyralid (3,6-dichloropicolinic acid) was measured in laboratory incubations and in field plots under different management regimes. In laboratory studies, soil was spiked with commercial grade liquid formulation of clopyralid (Versatill, 300 g a.i. L(-1) soluble concentrate) @ 0.8 microg a.i. g(-1) dry soil and the soil water content was maintained at 60% of water holding capacity of the soil. Treatments included incubation at 10 degrees C, 20 degrees C, 30 degrees C, day/night cycles (25/15 degrees C) and sterilized soil (20 degrees C). Furthermore, a field study was conducted at the Waikato Research Orchard near Hamilton, New Zealand starting in November 2000 to measure dissipation rates of clopyralid under differing agricultural situations. The management regimes were: permanent pasture, permanent pasture shielded from direct sunlight, bare ground, and bare ground shielded from direct sunlight. Clopyralid was sprayed in dilute solution @ 600 g a.i. ha(-1) on to field plots. Herbicide residue concentrations in soil samples taken at regular intervals after application were determined by gas chromatograph with electron capture detector. The laboratory experiments showed that dissipation rate of clopyralid was markedly faster in non-sterilized soil (20 degrees C), with a half-life (t1/2) of 7.3 d, than in sterilized soil (20 degrees C) with t1/2 of 57.8 d, demonstrating the importance of micro-organisms in the breakdown process. Higher temperatures led to more rapid dissipation of clopyralid (t1/2, 4.1 d at 30 degrees C vs 46.2 d at 10 degrees C). Dissipation was also faster in the day/night (25/15 degrees C) treatment (t1/2, 5.4 d), which could be partly due to activation of soil microbes by temperature fluctuations. In the field experiment, decomposition of clopyralid was much slower in the shaded plots under pasture (t1/2, 71.5 d) and bare ground (t1/2, 23.9 d) than in the unshaded pasture (t1/2, 5.0 d) and bare ground plots (t1/2, 12.9 d). These studies suggest that environmental factors such as temperature, soil water content, shading, and different management practices would have considerable influence on rate of clopyralid dissipation.     

Screening of physical-chemical methods for removal of organic material, nitrogen and toxicity from low strength landfill leachates

Physical-chemical methods have been suggested for the treatment of low strength municipal landfill leachates. Therefore, applicability of nanofiltration and air stripping were screened in laboratory-scale for the removal of organic matter, ammonia, and toxicity from low strength leachates (NH4-N 74-220 mg/l, chemical oxygen demand (COD) 190-920 mg O2/l, EC50 = 2-17% for Raphidocelis subcapitata). Ozonation was studied as well, but with the emphasis on enhancing biodegradability of leachates. Nanofiltration (25 degrees C) removed 52-66% of COD and 27-50% of ammonia, the latter indicating that ammonia may in part have been present as ammonium salt complexes. Biological pretreatment enhanced the overall COD removal. Air stripping (24 h at pH 11) resulted in 89% and 64% ammonia removal at 20 and 6 degrees C, respectively, the stripping rate remaining below 10 mg N/l h. COD removals of 4-21% were obtained in stripping. Ozonation (20 degrees C) increased the concentration of rapidly biodegradable COD (RBCOD), but the proportion of RBCOD of total COD was still below 20% indicating poor biological treatability. The effect of the different treatments on leachate toxicity was assessed with the Daphnia acute toxicity test (Daphnia magna) and algal growth inhibition test (Raphidcocelis subcapitata). None of the methods was effective in toxicity removal. By way of comparison, treatment in a full-scale biological plant decreased leachate toxicity to half of the initial value. Although leachate toxicity significantly correlated with COD and ammonia in untreated and treated leachate, in some stripping and ozonation experiments toxicity was increased in spite of COD and ammonia removals.     

A new protocol to measure the effects of toxicants on daphnid-algae interactions

Inhibition of zooplankton grazing by toxicants present at sublethal concentrations in freshwater ecosystems can lead to uncontrolled algal growth and consequently exacerbate eutrophication problems. Short-term measurements of cladoceran grazing inhibition have been reported for some toxicants, but these studies do not mimic the actual interactions between microalgae, daphnids and toxicants, since algal growth is not allowed. On the opposite, algal blooms in complex microcosm or mesocosm assays have been interpreted as consequences on zooplankton, but effects on grazing, survival, growth or reproduction could not be easily discriminated. In this study, a simple assay with daphnids and microalgae is proposed to measure effects on grazing in dynamic conditions (algal growth over 6 days), and applied to copper and lindane. In the same time, direct effects on algal growth can be shown and taken into account. Results are compared with daphnid response measured with different endpoints (immobilization test and static grazing assay). For both toxicants, effects at sublethal concentrations were demonstrated. Copper impaired daphnid grazing at 10 microg/l (60% inhibition) in the 48 h-static test and 15 microg/l (40% inhibition) in the 6 day-dynamic test, whereas 48 h-EC50 for daphnid mobility was 47 microg/l. The EC50s for lindane were 50 microg/l for daphnid grazing (48 h-static and 6 day-dynamic tests) and 383 microg/l for the immobilization test (48 h).     

Effects of ionic strength on the production of short chain volatile hydrocarbons by Dunaliella salina (Teodoresco)

The effect of ionic strength on the production of short chain volatile hydrocarbons was studied in cultures of Dunaliella salina. Axenic cultures of D. salina were grown at three different ionic strengths 0.5, 2 and 3 M of NaCl in Johnson (J/1) culture medium [Journal of Bacteriology 95 (1968) 1461] under the following laboratory growth conditions: a 12:12 h photoperiod, 300 micromolm(-2)s(-1) of photosynthetic active radiation (PAR) provided by a fluorescent lamp of 40 W combined with a 100 W incandescent lamp at 20 +/- 1 degrees C at pH 7.5. C1 to C5 hydrocarbons were detected using a head space technique and GC-FID. Cell numbers and growth rate was greatest at 2 M NaCl 4.3 x 10(6) cellml(-1) after a 15 days period of culture. Maximum hydrocarbon production was measured in the concentration of 0.5 NaCl with lower production rates in the more concentrated solutions. The principal hydrocarbon was pentane at 0.5 M but was ethane in 2 and 3 M solutions. Production rates for individual compounds ranged between 0.13 and 22 x 10(-15) microgCcell(-1)h(-1). It is suggested that the ability to produce and release volatile organic compounds of D. salina is related to osmotic conditions established by the ionic strength of growth solution.