Copepod Nitocra Research Articles

Investigating Population-Level Toxicity of the Antidepressant Citalopram in Harpacticoid Copepods Using In Vivo Methods and Bioenergetics-Based Population Modeling.

Recent research has revealed various lethal and sublethal effects of the selective serotonin reuptake inhibitor citalopram hydrobromide on the harpacticoid copepod Nitocra spinipes. In the present study, an individual-based model (IBM) grounded in the dynamic energy budget (DEB) theory was developed to extrapolate said effects to the population level. Using a generic DEB-IBM as a template, the model was designed to be as simple as possible, keeping model components that are outside the scope of the core DEB theory to a minimum. To test the model, a 56-day population experiment was performed at 0, 100, and 1000 μg citalopram hydrobromide L-1 . In the experiment, the populations quickly reached a plateau in the control and at 100 μg L-1 , which was correctly reproduced by the model and could be explained by food limitations hindering further population growth. At 1000 μg L-1 , a clear mismatch occurred: Whereas in the experiment the population size increased beyond the supposed (food competition-induced) capacity, the model predicted a suppression of the population size. It is assumed that the IBM still misses important components addressing population density-regulating processes. Particularly crowding effects may have played an important role in the population experiment and should be further investigated to improve the model. Overall, the current DEB IBM for N. spinipes should be seen as a promising starting point for bioenergetics-based copepod population modeling, which-with further improvements-may become a valuable individual-to-population extrapolation tool in the future. Environ Toxicol Chem 2023;42:1094-1108. © 2023 SETAC.

Making Sense of Life-History Effects of the Antidepressant Citalopram in the Copepod Nitocra spinipes Using a Bioenergetics Model.

The global consumption of human antidepressants has steadily increased over the last years. The most widely prescribed antidepressants are the selective serotonin reuptake inhibitors (SSRIs), which have been linked to various life-history effects in nontarget organisms. We investigated the effects of the SSRI citalopram hydrobromide on the life history of the copepod Nitocra spinipes. Slight but significant developmental delay effects were observed at nominal concentrations of 0.1 and 1 µg/L, with stronger effects occurring at measured concentrations of 178 µg/L and above. At 77 µg/L and above, a significant increase in adult body length and offspring production/brood was found, although the time between brood releases remained unaffected. The pre-adult surviving fraction was significantly reduced (by 44%) at 765 µg/L. For a mechanistic evaluation of these observations, we used a bioenergetics model for N. spinipes based on the dynamic energy budget theory. Toxicokinetic and toxicodynamic submodels were used to dynamically simulate the chemical uptake and elimination, as well as dose-response relationships for hypothetical physiological modes of action and survival over time. Although none of the commonly invoked physiological modes of action, acting on assimilation, maintenance, growth, or offspring production, could explain the observed combination of effects, a newly proposed physiological mode of action acting on the process of maturation delivered correct predictions in terms of each effect's direction. The model fits could be further improved by allowing for a gentler concentration-effect slope and by adding an auxiliary physiological mode of action acting on the reproduction efficiency. The quantitative explanations provided in the present study offer a starting point for exploratory simulation studies investigating the effects of SSRIs at higher ecological levels. Environ Toxicol Chem 2021;40:1928-1939. © 2021 SETAC.

Variability in Toxicity of Plastic Leachates as a Function of Weathering and Polymer Type: A Screening Study with the Copepod Nitocra spinipes.

AbstractThe production and use of plastic over many decades has resulted in its accumulation in the world's oceans. Plastic debris poses a range of potential risks to the marine environment and its biota. Especially, the potential hazards of small plastic debris and chemicals associated with plastic have not been extensively studied. When buoyant plastic is exposed to ultraviolet radiation, it will slowly degrade and leach chemicals into surrounding waters. These leachates can include additives, sorbed organic pollutants, and degradation products of the plastic polymers. While most hazard assessments have focused on studying adverse effects due to the uptake of plastic, toxicity studies of the leachates of plastics are less common. To begin to address this knowledge gap, we studied the acute toxicity of leachates from diverse plastics in the harpacticoid copepod Nitocra spinipes. Our results show that leachates caused a higher toxicity after plastic was exposed to ultraviolet light compared to leaching in darkness. We observed differences in toxicity for different polymer types: polyvinyl chloride and polypropylene resulted in the most toxic leachates, while polystyrene and poly[ethylene terephthalate] were least toxic. Furthermore, we observed increased toxicity of leachates from some plastics that had been weathered in the real marine environment compared to matching new materials. Our results indicate that both weathering condition and polymer type influence the toxicity of plastic leachates.

Neonicotinoid Insecticides from a Marine Perspective: Acute and Chronic Copepod Testing and Derivation of Environmental Quality Standards.

Neonicotinoid insecticides have become of global concern for the aquatic environment. Harpacticoid copepods are among the organisms most sensitive to neonicotinoids. We exposed the brackish copepod Nitocra spinipes to 4 neonicotinoid insecticides (clothianidin, imidacloprid, thiacloprid, and thiamethoxam) to investigate acute toxicity on adults (96-h exposure) and effects on larval development (7-d exposure). We used these results in combination with publicly available ecotoxicity data to derive environmental quality standards (EQS). These EQS were ultimately used in a single-substance and mixture risk assessment for the Belgian part of the North Sea. Acute toxicity testing revealed that immobilization is a more sensitive endpoint than mortality, with 96-h median effect concentration (EC50) values of 6.9, 7.2, 25, and 120 µg L-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. In addition, the larval development tests resulted in 7-d no-observed-effect concentrations (NOECs) of 2.5, 2.7, 4.2, and >99 µg L-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. The derived saltwater annual average (AA-)EQS were 0.05, 0.0048, 0.002, and 0.016 µg L-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. Finally, the risk characterization revealed some exceedances of the AA-EQS in Belgian harbors for imidacloprid (number of exceedances, n = 2/4), for thiacloprid (n = 1/4), for thiamethoxam (n = 1/4), and for the mixture of the 4 neonicotinoids (n = 4/4), but not at the open sea. At the open sea site, the toxic unit sums relative to the AA-EQS were 0.72 and 0.22, suggesting no mixture risk, albeit with a relatively small margin of safety. Including short-term EC10 (96-h) values of N. spinipes for the AA-EQS derivation led to a refinement of the AA-EQS for clothianidin and thiamethoxam, suggesting their use for the AA-EQS derivation because one of the overarching goals of the definition of EQS is to protect species at the population level. Environ Toxicol Chem 2021;40:1353-1367. © 2021 SETAC.

Uptake and Egestion of Polyhydroxyalkanoate Microbeads in the Marine Copepod Nitocra lacustris pacifica

Uptake and Egestion of Polyhydroxyalkanoate Microbeads in the Marine Copepod Nitocra lacustris pacifica

Estimating inter-individual variability of dynamic energy budget model parameters for the copepod Nitocra spinipes from existing life-history data

The degree of biological variability within a population is an important factor for its ecological success. Yet, individual-based population models (IBMs) that utilize the Dynamic Energy Budget (DEB) theory as a mechanistic basis to simulate an individual's life history, largely rely on rule-of-thumb estimates of inter-individual variability of their parameter values. In this study, we explored how data from previous life-history experiments with the copepod Nitocra spinipes could be used to make realistic estimates of variability in DEB parameter values for this species. We specifically investigated to which one of 12 possible parameters variability should be added, and what shape and scale its probability distribution should have, to most accurately reproduce the experimental data's variation with model simulations. The best result was achieved by drawing the parameter ‘surface-area-specific maximum assimilation rate’ from a log-normal distribution with a standard deviation of 0.15 or by drawing the maturity thresholds for birth and puberty (assuming proportionality between the two) from a log-normal distribution with a standard deviation of 0.40. In both cases, the model not only accurately reproduced the variation observed in development time data (which had been used in the fitting process) but also gave adequate predictions of the variation observed in brood size data (which had not been used for fitting). Although the findings of this study apply to one species only, the methods presented here are a proof of principle for how the question of intra-specific variability in a DEB model, for any species, can be addressed in a simple, yet purposeful manner.

Chronic effects of fire suppressors on the reproduction of the copepod Nitocra sp.

Fire suppressors are widely used in firefighting and their chemical composition may present a mixture of perfluorochlorinated surfactants (PFCs), including the perfluorooctane sulfonate (PFOS) which has been internationally banned due to its classification as a persistent organic pollutant (POP). PFCs have been found in environmental matrices and soft tissues of organisms, but the potential effect of such compounds on marine organisms has been overlooked. Here, it was evaluated whether the chronic exposures (i.e., seven days) to the fire suppressors Ageofoam, Cold Fire, Kidde and Argus could affect the reproduction of the copepod Nitocra sp. The tested concentrations consisted of those recommended on the products’ manuals and those ranging between 0.0001% and 1%. For each compound, the effective concentrations to 50% exposed organisms (EC50) and the lowest observed effect concentrations (LOEC) were estimated. All the fire suppressors exhibited high toxicity, causing fecundity reduction. At the recommended dilutions, 100% lethality occurred for all compounds. The EC50 values ranged from 0.00817% - Ageofoam - to 0.03081% - Argus. The LOECs ranged from 0.001% - Ageofoam - to 0.1% - Argus and Kidde; and were much lower than the concentrations recommended for commercial use. The fire suppressors showed high toxicity to the copepod, reducing the reproduction rates, even in very low concentrations, suggesting that the release of such substances in the estuary caused severe effects to the environment. This assessment provides subsides to the environmental regulation of fire suppressors in Brazil, because these compounds do not have national regulations for their use and disposal.

Quantitative analysis of pellets on beaches of the São Paulo coast and associated non-ingested ecotoxicological effects on marine organisms

We evaluated the densities of plastic pellets on beaches along the coast of São Paulo State in Brazil in order to establish a relationship between their spatial distribution and their distance from the main source of pellets. We hypothesized that pellets would be concentrated close to their main source (in this case, the Port of Santos). We also tested whether beached pellets could induce toxicity in water and sediment samples, as well as whether pellet color, sample site (beach), and pellet density were correlated with toxicity. We observed a decreasing gradient of pellet density along the São Paulo coast, with higher densities detected within Santos Bay, which is close to the Port of Santos. Beached pellets induced water-based toxicity in the sea urchin Lytechinus variegatus and the copepod Nitocra sp. at high densities but were not capable of producing toxicity at environmentally realistic densities.

The draft genome of strain cCpun from biting midges confirms insect Cardinium are not a monophyletic group and reveals a novel gene family expansion in a symbiont.

BackgroundIt is estimated that 13% of arthropod species carry the heritable symbiont Cardinium hertigii. 16S rRNA and gyrB sequence divides this species into at least four groups (A–D), with the A group infecting a range of arthropods, the B group infecting nematode worms, the C group infecting Culicoides biting midges, and the D group associated with the marine copepod Nitocra spinipes. To date, genome sequence has only been available for strains from groups A and B, impeding general understanding of the evolutionary history of the radiation. We present a draft genome sequence for a C group Cardinium, motivated both by the paucity of genomic information outside of the A and B group, and the importance of Culicoides biting midge hosts as arbovirus vectors.MethodsWe reconstructed the genome of cCpun, a Cardinium strain from group C that naturally infects Culicoides punctatus, through Illumina sequencing of infected host specimens.ResultsThe draft genome presented has high completeness, with BUSCO scores comparable to closed group A Cardinium genomes. Phylogenomic analysis based on concatenated single copy core proteins do not support Cardinium from arthropod hosts as a monophyletic group, with nematode Cardinium strains nested within the two groups infecting arthropod hosts. Analysis of the genome of cCpun revealed expansion of a variety of gene families classically considered important in symbiosis (e.g., ankyrin domain containing genes), and one set—characterized by DUF1703 domains—not previously associated with symbiotic lifestyle. This protein group encodes putative secreted nucleases, and the cCpun genome carried at least 25 widely divergent paralogs, 24 of which shared a common ancestor in the C group. The genome revealed no evidence in support of B vitamin provisioning to its haematophagous host, and indeed suggests Cardinium may be a net importer of biotin.DiscussionThese data indicate strains of Cardinium within nematodes cluster within Cardinium strains found in insects. The draft genome of cCpun further produces new hypotheses as to the interaction of the symbiont with the midge host, in particular the biological role of DUF1703 nuclease proteins that are predicted as being secreted by cCpun. In contrast, the coding content of this genome provides no support for a role for the symbiont in provisioning the host with B vitamins.

Two dynamic energy budget models for the harpacticoid copepod Nitocra spinipes

The harpacticoid copepod Nitocra spinipes is a commonly used test species in ecotoxicological studies and subject of multiple international testing guidelines. While we strive for a better understanding of toxicant-induced effects in this species, physiological models rooted in the Dynamic Energy Budget (DEB) theory can help to explain such effects on the level of energy allocations within the organism. In previous works that aimed to capture the copepod life history in a DEB model, diverging assumptions on the growth pattern of copepods were made. While some authors presumed von Bertalanffy growth, others presumed an upcurving in length versus time due to metabolic acceleration. In this study we parametrized the two typified DEB models “abp” (metabolic acceleration from birth to puberty) and “sbp” (standard von Bertalanffy growth from birth to puberty) on life history data of N. spinipes. Besides using data from literature, we also measured additional length-at-time data to aid the parameter estimation. As the body proportions of N. spinipes changed continuously throughout its development, we used the square root of the top view area as a length measure to scale with the cube root of structural volume in length-to-volume conversions. Experimental data were predicted well with both models according to goodness of fit criteria. Despite a slightly better data fit in abp, we cannot rule out sbp as implausible. Overall, we expect both models to perform equally well in future applications. More detailed data on N. spinipes and closely related species are needed to support or reject the presumption of metabolic acceleration in the life history of copepods.

Temperature and food quantity effects on the harpacticoid copepod Nitocra spinipes: Combining in vivo bioassays with population modeling.

The harpacticoid copepod Nitocra spinipes has become a popular model species for toxicity testing over the past few decades. However, the combined influence of temperature and food shortage, two climate change-related stressors, has never been assessed in this species. Consequently, effects of three temperatures (15, 20 and 25°C) and six food regimes (between 0 and 5 × 105 algal cells/mL) on the life cycle of N. spinipes were examined in this study. Similarly to other copepod species, development times and brood sizes decreased with rising temperatures. Mortality was lowest in the 20°C temperature setup, indicating a close-by temperature optimum for this species. Decreasing food concentrations led to increased development times, higher mortality and a reduction in brood size. A sex ratio shift toward more females per male was observed for increasing temperatures, while no significant relationship with food concentration was found. Temperature and food functions for each endpoint were integrated into an existing individual-based population model for N. spinipes which in the future may serve as an extrapolation tool in environmental risk assessment. The model was able to accurately reproduce the experimental data in subsequent verification simulations. We suggest that temperature, food shortage, and potentially other climate change-related stressors should be considered in environmental risk assessment of chemicals to account for non-optimal exposure conditions that may occur in the field. Furthermore, we advocate combining in vivo bioassays with population modeling as a cost effective higher tier approach to assess such considerations.

해양생태독성평가를 위한 열대 요각류 Nitocra sp.의 이용 가능성

열대지역과 같은 특정지역에서 오염물질의 독성평가 시, 그 지역의 생태환경에 적합한 위해성평가를 위해서는 그 지방 고유의 생물에 대한 독성실험이 요구된다. 따라서 본 연구는 열대에서 분리한 열대 요각류 Nitocra sp.를 독성실험생물로 사용하기 위해 이들을 안정적으로 배양/유지하기 위한 최적배양환경조건과 해양생태독성평가 가능성을 조사하였다. 최적 배양환경요인으로 수온, 염분 및 먹이에 대해 조사하였으며 생태독성평가는 급성독성과 만성독성 실험으로 나누어 실시하였다. 최적배양조건 실험데이터의 통계분석을 위해 One-way ANOVA test를 실시하였다. 최적배양환경조건을 조사한 결과, Nitocra sp.는 수온 <TEX>$29^{\circ}C$</TEX>, 염분 24~34&#x2030;에서 먹이로 Tetraselmis suecica를 공급하였을 때, 비교적 빠른 발달기간과 높은 생존율을 보였다. 최적배양조건을 바탕으로 구리와 비소에 대한 독성평가를 실시한 결과, 구리와 비소의 각 노출농도에 따라 민감하게 잘 반응해서 반수치사농도 즉 <TEX>$LC_{50}$</TEX>값과 영향을 미치지 않는 농도인 NOEC값을 얻을 수 있었다. 만성독성시험 결과, 구리와 비소노출 모두, 성비와 생산력은 유의적인 차이가 없었던 반면, 발달기간과 생존율은 농도에 따라 반응을 보였기 때문에 종말점으로 사용이 가능한 것으로 나타났다. 본 연구를 종합해 보았을 때, 열대 요각류인 Nitocra sp.는 열대 해양독성물질 평가를 위한 생태독성실험생물로 사용이 가능할 것으로 판단되며 차후 다양한 독성물질의 평가에 활용이 기대된다. Indigenous species are needed for more accurate toxicity assessments in tropical regions. Thus, we determined not only the optimum culture conditions for stable maintenance of Nitocra sp. isolated from tropical regions but also the availability of copepods for marine ecotoxicological evaluation. Experiments on temperature, salinity, and diet as factors for optimum culture conditions as well as acute and chronic toxicity tests for ecotoxicological assessment were carried out. Data on optimum culture conditions were analyzed for statistically significant observations using one-way analysis of variance (ANOVA). Optimum temperature and salinity for Nitocra sp. were <TEX>$29^{\circ}C$</TEX> and 24~39&#x2030;, and Nitocra sp. fed Tetraselmis suecica had relatively faster development and higher survival than other microalga. Under optimum culture conditions, toxicity tests were carried out. The <TEX>$LC_{50}$</TEX> level and NOEC (no observed effect concentration) levels of copper and arsenic were calculated in the acute toxicity test. In the chronic test of Cu and As, developmental time and survival traits were usable endpoints for toxicity assessments. As a result, tropical copepod Nitocra sp. seems to be a potential candidate organism for marine ecotoxicological evaluation.

Passive dosing of triclosan in multigeneration tests with copepods – stable exposure concentrations and effects at the low μg/L range

Ecotoxicity testing is a crucial component of chemical risk assessment. Still, due to methodological difficulties related to controlling exposure concentrations over time, data on long-term effects of organic chemicals at low concentrations are limited. The aim of the present study was, therefore, to test the applicability of passive dosing to maintain stable concentrations of the organochlorine bacteriocide triclosan in the water phase during a 6-wk multigeneration population development test with the harpacticoid copepod Nitocra spinipes. Triclosan was loaded into silicone (1000 mg), which was used as passive dosing phase in the exposure vials. The distribution ratio for triclosan between silicone and water (Dsilicone-water ) was 10466 ± 1927. A population development test was conducted at 3 concentration levels of triclosan that were measured to be 3 μg/L to 5 μg/L, 7 μg/L to 11 μg/L and 16 μg/L to 26 μg/L. The results demonstrate that passive dosing is applicable for long-term ecotoxicity testing of organic chemicals, including during significant growth of the test organism population. Shifts in the demographic structure of the population during exposure suggest the most severe effects were exerted on juvenile development. Progressively lower development index values in the populations exposed to increasing triclosan concentrations suggest developmental retardation. The results further stress the need for chronic exposure during ecotoxicity testing in chemical risk assessment because even the most sensitive endpoint was not significant until after 7 d of exposure. Environ Toxicol Chem 2017;36:1254-1260. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Naupliar development ofNitocra karanovici(Copepoda, Harpacticoida)

All six naupliar stages of the harpacticoid copepod Nitocra karanovici are described. A key to the identification of the naupliar stages is provided. Stages can be distinguished by number of segments of the exopod of antenna 2, setation of the limbs including the bud of the caudal ramus, and presence and setation of the bud of maxilla 1. A particular naupliar character was found in the nauplii of N. karanovici that is in common for all Ameiridimorpha, except Ameiridae and otherwise not known from other Harpacticoida. This is a pair of bean-shaped, bare medial cuticular areas of the ventral body wall present in Parastenocarididae, Cylindropsyllidae, and as in Canthocamptus, Attheyella, Moraria, and Mesochra of the Canthocamptidae.

Slow Avoidance Response to Contaminated Sediments Elicits Sublethal Toxicity to Benthic Invertebrates

Advanced analytical techniques have identified the heterogeneity of sediments in aquatic environments which may impact the exposure of benthic organisms to contaminants. Acute and chronic toxicity associated with short, intermittent exposure to four field-collected contaminated sediments were assessed for the epi-benthic amphipod Melita plumulosa and the harpacticoid copepod Nitocra spinipes. Increasing the duration of exposure caused a decrease in survival of M. plumulosa and N. spinipes during 10-d bioassays. Increasing the frequency of exposure to a total exposure time >96-h resulted in a significant toxicity to M. plumulosa. Reproduction decreased for both species from exposure to contaminated sediment. For M. plumulosa, reproductive effects occurred for shorter exposures than the time taken to sense and avoid contaminant exposure. Thus, while avoidance behaviors may prevent acute lethality, slow responses may not prevent sublethal effects. Exposure of M. plumulosa to contaminated sediment appeared to cause a physiological change in females which reduced fecundity. This study indicates that sediment toxicity methods which utilize static continuous exposures may overestimate the toxicity that would occur at a field location. However, by preventing organisms from avoiding unfavorable sediments, these methods provide a precautionary assessment of possible effects, which is usually the aim of most assessments frameworks.

Reproductive performance, growth and development time of a tropical harpacticoid copepod, Nitocra affinis californica Lang, 1965 fed with different microalgal diets

This study examines the growth, reproductive performance and survival of a copepod Nitocra affinis californica Lang, 1965 fed with three microalgal food items singly (a diatom, C. calcitrans ; a green algae, N. oculata ; flagellated green algae, T. tetrathele) and in combinations (50% C.calcitrans +50% N. oculata; 50% C. calcitrans+50% T. tetrathele; 50% N. oculata+50% T.tetrathele; 50% C. calcitrans+25% N. oculata+25% T. tetrathele). The experiments were performed under controlled laboratory condition (30ppt salinity, temperature of 30°C, light intensity of 25μmolm−2s−1 and 12h light:12h dark cycle). Feeding densities were maintained at 106 cells ml−1 throughout the study. The highest (p<0.05) egg production was achieved by copepods fed with C. calcitrans and mixed algal diet (50% C. calcitrans+25% N. oculata+25% T. tetrathele) with mean values of 133.6±3.9 and 128.2±2.0 eggs female−1, respectively. Similarly, the highest (p<0.05) offspring production (132.0±3.8 offsprings female−1), survival from nauplii to adult (98.8±0.2) and maximum specific growth rate (K=0.43±0.0) was achieved with N. affinis californica fed C. calcitrans. The shortest (p<0.05) embryonic development time, time interval between egg sac, development time from nauplii to copepodid and copepodid to adult resulted from feeding with T. tetrathele. The longevity of the female N. affinis was found to be longest (p<0.05) when fed with mixed algal diet (42.2±0.7days) and combination of C. calcitrans+T. tetrathele (41.4±0.7days). The present study revealed that amongst the microalgae offered, C. calcitrans was the best food item as indicated by the highest reproductive capacity (eggs female−1 and offsprings female−1) of the N. affinis californica. Significantly higher nutritional values of C. calcitrans compared to other microalgae were probably responsible for the best reproductive and growth performance of N. affinis.

Antibiotic-Induced Change of Bacterial Communities Associated with the Copepod Nitocra spinipes

Environmental pressures, such as physical factors, diet and contaminants may affect interactions between microbial symbionts and their multicellular hosts. Despite obvious relevance, effects of antimicrobial contaminants on host-symbiont relations in non-target aquatic organisms are largely unknown. We show that exposure to antibiotics had negative effects on survival and juvenile development of the copepod Nitocra spinipes and caused significant alterations in copepod-associated bacterial communities. The significant positive correlations between indices of copepod development and bacterial diversity indicate that disruption of the microflora was likely to be an important factor behind retarded juvenile development in the experimental animals. Moreover, as evidenced by ribotype distribution in the bacterial clone libraries, the exposure to antibiotics caused a shift in dominance from Betaproteobacteria to Cardinium bacteria; the latter have been shown to cause reproductive manipulations in various terrestrial arthropods. Thus, in addition to providing evidence that the antibiotic-induced perturbation of the microbial community associates with reductions in fitness-related traits of the host, this study is the first record of a copepod serving as a host for endosymbiotic Cardinium. Taken together, our results suggest that (1) antimicrobial substances and possibly other stressors can affect micobiome and symbiont-mediated interactions in copepods and other hosts, and (2) Cardinium endosymbionts may occur in other copepods and affect reproduction of their hosts.

Performance and sensitivity of rapid sublethal sediment toxicity tests with the amphipod Melita plumulosa and copepod Nitocra spinipes

Sublethal whole-sediment toxicity tests are an important tool for assessing the potential effects of contaminated sediments. However, the longer duration required for evaluating potential chronic effects may increase endpoint variability and test costs compared to survival endpoints. In the present study we compare the performance and sensitivity to contaminants of 10-d sublethal sediment toxicity tests with the amphipod Melita plumulosa and harpacticoid copepod Nitocra spinipes. For both tests, sublethal effects were consistently observed when sediment contaminant concentrations exceeded sediment quality guideline (SQG) concentrations. The response of these bioassays in metal-contaminated sediments was shown to conform ideally with respect to the mean SQG quotient calculated on the basis of the Australian and New Zealand lower SQG trigger value, with toxicity being observed only in those sediments where the mean quotient exceeded one. Better predictions of nontoxicity were obtained when dilute acid-extractable rather than total metal concentrations were used. Using the upper SQG, toxicity frequently occurred at mean quotients below one. The effects were generally consistent with predictions from the acid-volatile sulfide and simultaneously extracted metal model. Effects on reproduction of M. plumulosa were detected for sediments that did not cause effects on survival and highlighted the environmental relevance and importance of using these sublethal endpoints. When using four replicates for M. plumulosa and five replicates for N. spinipes, the endpoint variability (standard error) was less than 10%. Variations in sediment particle size and organic carbon content did not affect endpoint variability. Both species are relatively easily cultured in the laboratory, and the estimated effort and cost of achieving the sublethal endpoints is 1.5 times that of the acute survival test endpoints.

Comparison of six sewage effluents treated with different treatment technologies—Population level responses in the harpacticoid copepod Nitocra spinipes

Since conventional treatment technologies may fail in removing many micro-pollutants, there is currently a focus on the potential of additional treatment technologies for improved sewage treatment. The aim of the present study was to evaluate six different effluents from Henriksdal Sewage Treatment Plant in Stockholm, Sweden. The effluents were; conventionally treated effluent (chemical phosphorous removal in combination with an activated sludge process, including biological nitrogen removal and a sand filter), with additional treatments individually added to the conventional treatment; active carbon filtration, ozonation at 5 mg l −1, ozonation at 15 mg l −1, ozonation at 5 mg l −1 + moving bed biofilm reactor and irradiation with ultraviolet radiation + hydrogen peroxide. The evaluation was done by characterizing and comparing the effluents using a Lefkovitch matrix model based on a life cycle test with the harpacticoid copepod Nitocra spinipes, combined with analysis of juvenile development and survival over time. The conventionally treated effluent resulted in the most negative effects, leading to the conclusion that all additional treatments in the present study created effluents with less negative impacts on the copepod populations. The ozone treatments with the low dose treatment in particular, resulted in the overall least negative effects. Moving bed biofilm reactor combined with ozone did not improve the quality of the effluent in the sense that slightly more negative effects on the population abundance were seen for this treatment technology compared to ozonation alone. The active carbon treatment had more negative effects than the ozone treatments, most of which could possibly be explained by removal of essential metal ions. The effluent which was treated with ultraviolet radiation + hydrogen peroxide resulted in few developmental and survival effects over time, but still showed negative effects on the population level. Matrix population modeling proved a useful tool for biologically characterizing and comparing the effluents. Basing the assessment either on the individual level data (development and survival over time or total reproductive output) or the population level data (lambda values and projected population abundances) would not have resulted in the same conclusions as combining both analyses. The juvenile development and survival over time allowed for closer monitoring of the important molting process, whereas the population modeling provided an integrated measure of potential effects at the population level. If the dilution of the effluent in the recipient is considered, the biological effects recorded in the present study were not of substantial significance for the copepod populations, regardless of treatment technology.

Are individual NOEC levels safe for mixtures? A study on mixture toxicity of brominated flame–retardants in the copepod Nitocra spinipes

In aquatic ecosystems organisms are exposed to mixtures of pollutants. Still, risk assessment focuses almost exclusively on effect characterization of individual substances. The main objective of the current study was therefore to study mixture toxicity of a common group of industrial substances, i.e., brominated flame–retardants (BFRs), in the harpacticoid copepod Nitocra spinipes. Initially, 10 BFRs with high hydrophobicity but otherwise varying chemical characteristics were selected based on multivariate chemical characterization and tested individually for effects on mortality and development using a partial life cycle test (six days) where silica gel is used as a carrier of the hydrophobic substances. Based on these findings, six of the 10 BFRs were mixed in a series of NOEC proportions (which were set to 0.008, 0.04, 0.2, 1, and five times the NOEC concentrations for each individual BFR), loaded on silica gel and tested in a full life cycle test (26 days). Significantly increased mortality was observed in N. spinipes after six and 26 days exposure at a NOEC proportion that equals the NOEC LDR value (×1) for each BFR in the mixture ( p = 0.0015 and p = 0.0105, respectively). At the NOEC × 5 proportion all animals were dead. None of the other NOEC proportions caused significant negative responses related to development and reproduction. This shows that low concentrations of individual substances can cause toxicity if exposed in mixtures, which highlights the need to consider mixture toxicity to a greater extent in regulatory work.