Amendment of soils with metal-rich sludge: Potential water toxicity due to metal release via over-time slaking.

Industrial metal-rich sludge can improve soil properties, but it is potentially toxic to soils and adjacent aquatic systems. The soil-sludge-water interactions influence metals bioavailability over time, a phenomenon mostly regulated by the still debatable "sludge physical protection" or "sludge delayed release" hypotheses. The present study aimed to investigate: (1) whether sludge increases soil aggregate stability against slaking, (2) which hypothesis mostly regulates metal release from soils to water and (3) the ecotoxicity of the metals released during soil slaking for aquatic organisms. Under a realistic field scale, soils amended with an industrial sludge or spiked with equivalent metal solutions (of Cr, Cu, Ni, Zn) were collected over three months to test soil aggregate stability, the ecotoxicity of the slaking water and metal contents in soil and water. The "sludge physical protection" was verified for all metals, though for Cu the "sludge delayed release" hypothesis appears plausible after three months. Soil amendment with sludge did not lead to effects on the growth of the microalga Raphidocelis subcapitata, contrarily to the observed for the metal-spiked soil. Criteria regulating soils sludge-amendment management should thus include doses not hazardous to biota, and not only metal threshold levels.

Ecological risk assessment of the Paraíba River estuary (Brazil): Plan for a tier 1 screening phase for the ecotoxicological line of evidence.

The knowledge produced in temperate regions is still used today to evaluate environmental problems in the tropics, without taking into consideration environmental differences, such as local conditions, the sensitivity and ecology of species, and exposure routes of contaminants, essential for understanding and determining the fate and toxicity of chemicals. Considering that Environmental Risk Assessment (ERA) studies for tropical systems are scarce and need to be adjusted, the present study aims at contributing to the awareness and development of tropical ecotoxicology. The estuary of the Paraíba River in Northeast Brazil was selected as a model study-case, as it is a large estuary, subjected to a heavy human pressure due to the numerous social, economic and industrial activities. The present study describes the framework for the problem formulation phase of the ERA process; it first includes a detailed integration of the scientific information available on the study area, to then derive the conceptual model, and finally present the analysis plan for the tier 1 screening phase. The latter is designed to be fundamentally supported by the ecotoxicological line of evidence, to ascertain, without delay, where and why there are environmental problems (i.e., adverse biological effects); ecotoxicological tools developed in temperate climates will be optimized to assess water quality in a tropical system. In addition to its intrinsic value for protecting the study area, the results of the present study are expected to provide an important baseline for conducting ERA in similar tropical aquatic systems across the globe.

Appraisal on the role of passive sampling for more integrative frameworks on the environmental risk assessment of contaminants.

Over time multiple lines of research have been integrated as important components of evidence for assessing the ecological quality status of water bodies within the framework of Environmental Risk Assessment (ERA) approaches. One of the most used integrative approaches is the triad which combines, based on the weight-of-evidence, three lines of research, the chemical (to identify what is causing the effect), the ecological (to identify the effects at the ecosystem level) and the ecotoxicological (to ascertain the causes of ecological damage), with the agreement between the different lines of risk evidence increasing the confidence in the management decisions. Although the triad approach has proven greatly strategic in ERA processes, new assessment (and monitoring) integrative and effective tools are most welcome. In this regard, the present study is an appraisal on the boost that passive sampling, by allowing to increase information reliability, can give within each of the triad lines of evidence, for more integrative ERA frameworks. In parallel to this appraisal, examples of works that used passive samplers within the triad are presented providing support for the use of these devices in a complementary form to generate holistic information for ERA and ease the process of decision-making.

Evaluating formulation and storage of Arthrobacter aurescens strain TC1 as a bioremediation tool for terbuthylazine contaminated soils: Efficacy on abatement of aquatic ecotoxicity.

Recently, a bioremediation tool consisting of freshly grown cells of the Arthrobacter aurescens strain TC1 proved successful in the cleanup of terbuthylazine (TBA) contaminated soil, with potential to prevent TBA dispersal via the soil-water pathway. The present work aimed at examining the feasibility of preparing and formulating bioaugmentation bacterial cells in advance which retain adequate viability and herbicide-degrading activity during storage and transport to contaminated sites. Three different types of formulation of A. aurescens TC1 cells were performed, namely cell paste, lyophilized, and adsorbed onto the mineral carrier vermiculite. Vermiculite-based cell material and cell paste offered survival rates significantly higher (≥78% of cells recovered viable, when compared to the initial numbers) than lyophilized cells (≥65%) after storage at 4 °C for up to a maximum period of 30 days. Inocula prepared from the three types of formulated and stored cells supported adequate levels of herbicide-biodegradation activity, ultimately allowing an almost complete removal of TBA from either liquid buffer or soil. In soil microcosms, the efficacy of bioremediation of TBA-contaminated soil in terms of decontamination (%) based on the ecotoxicity assessment of soil eluates towards a freshwater microalga was found to differ within formulations in the order: lyophilized cells (~100% efficacy at the end of one or two weeks of bioremediation treatment with an initial inoculum of ~2.5 × 107 viable cells/g of soil; similar to fresh cells) > vermiculite-adsorbed cells (81% with ~2.4 × 108 cells/g) > cell paste (68% with ~2.4 × 108 cells/g). The limitations and advantages of each type of bacterial formulation, together with the prediction of their applicability in the field are discussed.

Long-term effects of the fungicide pyrimethanil on aquatic primary producers in macrophyte-dominated outdoor mesocosms in two European ecoregions.

Even though empirical data supporting sound ecoregion-specific ecotoxicological evaluations are still scarce, the differences of environmental (including climatic) conditions in specific ecoregions are already currently being regulated for environmental risk assessment of pesticides in Europe. To shed new light on the ecotoxicological effects of pesticides on aquatic communities across ecoregions, the model pollutant pyrimethanil (fungicide) was tested in an outdoor mesocosm study with macrophyte-dominated communities in the European "South" (Portugal) and "Centre" (Germany) regulatory zones. Phytoplankton indicators monitored over 12 months indicated a low risk of the fungicide (0.73 or 0.77 mg pyrimethanil L-1, single application) to phytoplankton functioning; as expected since exposure simulated worst-case scenarios. However, the growth of key structural macroalgae and macrophytes was affected by the fungicide and negative effects occurred, especially in the Central zone experiment. Such effects were not detected earlier than approximately nine months post single pyrimethanil application. The presence or absence of such extremely long-lasting/delayed pyrimethanil effects depended on species, competitive situation, and ecoregion-specific physico-chemical environment. The present findings suggest that a better understanding of both direct and indirect effects of fungicide pollution on aquatic flora in two European ecoregions helps to consolidate the environmental risk assessment of pesticides in specific regulatory zones.

Stressor-driven emigration and recolonisation patterns in disturbed habitats.

Although essential to conservation, little is known about how stress intensity can provoke emigration from disturbed habitats and allow recolonisation of those same environments. To demonstrate the applicability of laboratory experiments, we tested two hypotheses empirically using zebrafish response to artificially polluted environments that exhibited a linear gradient of stressor (acid mine drainage) levels. We hypothesized that emigration is distance-independent but time-correlated (spacelessness hypothesis). Additionally, we hypothesized that stressor-driven emigration could predict the extent of population growth in recovering habitats (avoidance-recolonisation hypothesis). For example, if half the organisms emigrate at a given stressor level, then the remainder should be able to recolonise a habitat experiencing the same stressor intensity. Comparisons of the small-scale experiment with a larger-scale simulation suggested that controlled laboratory results can be extrapolated to field populations (although time to perceive the contamination gradient may pose differential individual effects) because AC50 (median avoidance concentration) values of an acid mine drainage sample (AMD) were not statistically different when fish were exposed to the same gradient in 3-m long [0.50% (0.43-0.57)] or 30-m long [0.73% (0.30-2.2)] systems. Regarding the avoidance-recolonisation hypothesis, the number of recolonisers was inversely proportional to the number of avoiders (ACx = RC100-x). In particular, the similar distribution of fish along the 0-3% AMD gradient in both avoidance and recolonisation experiments resulted in identical AC50 and RC50 values: 0.55% (0.34-0.87) and 0.55% (0.45-0.67) AMD, respectively. The inclusion of avoidance and recolonisation responses in the environmental risk assessments provides a novel perspective of risk based on the emigration of organisms and contributes to the understanding and prediction of biological invasions and ecosystem recovery after restoration.

Stress-driven emigration in complex field scenarios of habitat disturbance: The heterogeneous multi-habitat assay system (HeMHAS).

Lines of evidence used in ecological risk assessment (ERA) are essentially three: chemistry, biology and ecotoxicology. Until now, the fundamental assumption made when measuring ecological risks is that organisms are forcedly exposed to stressors. However, when organisms can avoid disturbed habitats by escaping to less stressful areas, the assumption that exposure is mandatory to pose risk may not match field disturbance scenarios. A non-forced exposure approach using a linear free-choice multi-compartmented system has been proposed previously as a complementary tool to assess the effects on organisms' spatial avoidance/preference responses. Yet, the linearity of the latter system limits avoidance measurements to one spatial dimension. A novel, heterogeneous multi-habitat assay system (HeMHAS) consisting of 18 connected circular compartments (3 compartments on a vertical axis in each one of 6 zones on a longitudinal axis; a 2D system) is put forward here to be used in heterogeneous-habitat selection studies, as it makes it possible to assess the ability of organisms to detect contamination and other stressors and select more favorable habitats. In the present study, the avoidance to copper by zebrafish (Danio rerio) was tested after exposing organisms to a copper gradient in the HeMHAS and compared with that in the linear system. Avoidance occurred for all copper concentrations: 43% in the lowest (21 µg·L-1) to 72% in the highest (221 µg·L-1). Results obtained within the HeMHAS (AC50: 60 µg·L-1) were statistically (p = 0.72) similar to avoidance of copper by D. rerio in the linear non-forced system (AC50: 89 µg·L-1). In summary, the simulation of a copper gradient in the HeMHAS (2D system) allowed to assess the potential repellency of copper to zebrafish and to corroborate the ability of organisms to detect and avoid potentially toxic concentrations.

A novel approach to assessing environmental disturbance based on habitat selection by zebra fish as a model organism.

Aquatic ecotoxicity assays used to assess ecological risk assume that organisms living in a contaminated habitat are forcedly exposed to the contamination. This assumption neglects the ability of organisms to detect and avoid contamination by moving towards less disturbed habitats, as long as connectivity exists. In fluvial systems, many environmental parameters vary spatially and thus condition organisms' habitat selection. We assessed the preference of zebra fish (Danio rerio) when exposed to water samples from two western Ecuadorian rivers with apparently distinct disturbance levels: Pescadillo River (highly disturbed) and Oro River (moderately disturbed). Using a non-forced exposure system in which water samples from each river were arranged according to their spatial sequence in the field and connected to allow individuals to move freely among samples, we assayed habitat selection by D. rerio to assess environmental disturbance in the two rivers. Fish exposed to Pescadillo River samples preferred downstream samples near the confluence zone with the Oro River. Fish exposed to Oro River samples preferred upstream waters. When exposed to samples from both rivers simultaneously, fish exhibited the same pattern of habitat selection by preferring the Oro River samples. Given that the rivers are connected, preference for the Oro River enabled us to predict a depression in fish populations in the Pescadillo River. Although these findings indicate higher disturbance levels in the Pescadillo River, none of the physical-chemical variables measured was significantly correlated with the preference pattern towards the Oro River. Non-linear spatial patterns of habitat preference suggest that other environmental parameters like urban or agricultural contaminants play an important role in the model organism's habitat selection in these rivers. The non-forced exposure system represents a habitat selection-based approach that can serve as a valuable tool to unravel the factors that dictate organisms' spatial distribution in connected ecosystems.

Habitat fragmentation caused by contaminants: Atrazine as a chemical barrier isolating fish populations.

Information on how atrazine can affect the spatial distribution of organisms is non-existent. As this effect has been observed for some other contaminants, we hypothesized that atrazine-containing leachates/discharges could trigger spatial avoidance by the fish Poecilia reticulata and form a chemical barrier isolating upstream and downstream populations. Firstly, guppies were exposed to an atrazine gradient in a non-forced exposure system, in which organisms moved freely among the concentrations, to assess their ability to avoid atrazine. Secondly, a chemical barrier formed by atrazine, separating two clean habitats (extremities of the non-forced system), was simulated to assess whether the presence of the contaminant could prevent guppies from migrating to the other side of the system. Fish were able to avoid atrazine contamination at environmentally relevant concentrations (0.02 µg L-1), below those described to cause sub-lethal effects. The AC50 (atrazine concentration causing avoidance to 50% of the population) was 0.065 µg L-1. The chemical barrier formed by atrazine at 150 µg L-1 (concentration that should produce an avoidance around 82%) caused a reduction in the migratory potential of the fish by 47%; while the chemical barrier at 1058 µg L-1 (concentration that produces torpidity) caused a reduction in the migratory potential of the fish by 91%. Contamination by atrazine, besides driving the spatial distribution of fish populations, has potential to act as a chemical barrier by isolating fish populations. This study includes a novel approach to be integrated in environmental risk assessment schemes to assess high-tier contamination effects such as habitat fragmentation and population displacement and isolation.

Attractiveness of food and avoidance from contamination as conflicting stimuli to habitat selection by fish.

Habitat selection by fish is the outcome of a choice between different stimuli. Typically, the presence of food tends to attract organisms, while contamination triggers an avoidance response to prevent toxic effects. Given that both food and contaminants are not homogeneously distributed in the environment and that food can be available in contaminated zones, a key question has been put forward in the present study: does a higher availability of food in contaminated areas interfere in the avoidance response to contaminants regardless of the contamination level? Tilapia fry (Oreochromis sp.; 2.5-3.0 cm and 0.5-0.8 g) were exposed to two different effluent samples, diluted along a free-choice, non-forced exposure system simulating a contamination gradient. Initially, avoidance to the effluents was checked during a one hour exposure. Afterwards, food was added to the system so that the availability of food increased with the increase in the level of contamination, and the avoidance response to contamination was checked during another hour. Results clearly showed a concentration-dependent avoidance response for both effluents during the first hour (i.e., with no food). However, in presence of the food, the avoidance pattern was altered: organisms were propelled to intermittently move towards contaminated areas where food availability was higher. The incursions were taken regardless of the potential risk linked to the toxic effects. In conclusion, even when the risk of toxicity was imminent, tilapia fry were more intensively stimulated by the attractiveness of the food than by repulsion to the contamination.

Active and passive spatial avoidance by aquatic organisms from environmental stressors: A complementary perspective and a critical review.

Spatial avoidance is a mechanism by which many organisms prevent their exposure to environmental stressors, namely chemical contaminants. Numerous studies on active avoidance and drift by aquatic organisms, as well as the main approaches used to measure both responses, were reviewed. We put forward a particular recommendation regarding methodological approaches: active avoidance should preferably be evaluated under a dilution gradient in a multi-compartmented system instead of in a bi-compartmented system. Available data on spatial avoidance from contamination indicate that emigration can occur at even lower contaminant concentrations than sub-individual noxious effects (assessed with the traditional forced-exposure assays), challenging the widely accepted paradigm in ecotoxicology that contaminant-driven adverse consequences at the population level result from a time delayed cascade of sequentially linked biochemical, cellular, physiological, and finally whole organism deleterious effects. Therefore, contaminants should not be viewed solely as potential toxicants at the individual level, but also as potential disturbers of habitats, by making the latter, at least partially, unsuited to accommodate life. Also, exposure to contamination is needed to trigger avoidance, but uptake is not mandatory, which demands the concept of exposure to be expanded, to include also the mere perception of the stressor. Since emigration eventually leads to local population extinction, and thus to severe implications for ecosystem structure and functioning, we then recommend that avoidance data be incorporated in environmental risk assessment schemes.

Effects of the fungicide pyrimethanil on biofilm and organic matter processing in outdoor lentic mesocosms.

The effect of the fungicide pyrimethanil (0.7 mg L(−1)) on biofilm development and alder leaf litter decomposition in aquatic ecosystems was assessed in outdoor lentic mesocosms immediately and 274 days after pyrimethanil application. Pyrimethanil decreased ergosterol concentrations (an indicator of fungal biomass) and the abundance and richness of the macroinvertebrate community associated with decomposing leaves. However, because neither fungi nor macroinvertebrates were main factors contributing to decomposition in this particular system, organic matter processing rates were not affected. After 274 days, pyrimethanil concentration in the water column was ≤0.004 mg L(−1) but richness, biomass and composition of the invertebrate community associated with decomposing leaf-litter still showed the effect. The comparison of ergosterol (a molecule existing on both algae and fungal cell membranes), with chlorophyll (an indicator of algal biomass) associated with biofilm suggests that pyrimethanil may decrease fungal biomass and alter the relative abundance of algae and fungi on biofilm developing in control- and treated-mesocosms.

Evaluation of Arthrobacter aurescens Strain TC1 as Bioaugmentation Bacterium in Soils Contaminated with the Herbicidal Substance Terbuthylazine.

In the last years the chloro-s-triazine active substance terbuthylazine has been increasingly used as an herbicide and may leave residues in the environment which can be of concern. The present study aimed at developing a bioaugmentation tool based on the soil bacterium Arthrobacter aurescens strain TC1 for the remediation of terbuthylazine contaminated soils and at examining its efficacy for both soil and aquatic compartments. First, the feasibility of growing the bioaugmentation bacterium inocula on simple sole nitrogen sources (ammonium and nitrate) instead of atrazine, while still maintaining its efficiency to biodegrade terbuthylazine was shown. In sequence, the successful and quick (3 days) bioremediation efficacy of ammonium-grown A. aurescens TC1 cells was proven in a natural soil freshly spiked or four-months aged with commercial terbuthylazine at a dose 10× higher than the recommended in corn cultivation, to mimic spill situations. Ecotoxicity assessment of the soil eluates towards a freshwater microalga supported the effectiveness of the bioaugmentation tool. Obtained results highlight the potential to decontaminate soil while minimizing terbuthylazine from reaching aquatic compartments via the soil-water pathway. The usefulness of this bioaugmentation tool to provide rapid environment decontamination is particularly relevant in the event of accidental high herbicide contamination. Its limitations and advantages are discussed.

Ecological Risk Assessment of a Metal-Contaminated Area in the Tropics. Tier II: Detailed Assessment.

This study presents data on the detailed evaluation (tier 2) of a site-specific ecological risk assessment (ssERA) in a former smelter area contaminated with metals (Santo Amaro, Bahia, Brazil). Combining information from three lines of evidence (LoE), chemical (ChemLoE), ecotoxicological (EcotoxLoE) and ecological (EcoLoE), in the Triad approach, integrated risk values were calculated to rank sites and confirm the potential risk disclosed with tier 1. Risk values were calculated for the habitat and for the retention functions in each sampling point. Habitat function included the ChemLoE calculated from total metal concentrations. The EcotoxLoE was based on reproduction tests with terrestrial invertebrates (Folsomia candida, Enchytraeus crypticus, Eisenia andrei), shoot length and plant biomass (Avena sativa, Brassica rapa). For the EcoLoE, ecological parameters (microbial parameters, soil invertebrate community, litter breakdown) were used to derive risk values. Retention function included the ChemLoE, calculated from extractable metal concentrations, and the EcotoxLoE based on eluate tests with aquatic organisms (Daphnia magna reproduction and Pseudokirchneriella subcapitata growth). Results related to the habitat function indicated that the metal residues are sufficient to cause risk to biota, while the low metal levels in extracts and the general lack of toxicity in aquatic tests indicated a high soil retention capacity in most sampling points. Integrated risk of tier 2 showed the same trend of tier 1, suggesting the need to proceed with remediation actions. The high risk levels were related to direct toxicity to organisms and indirect effects, such as failure in the establishment of vegetation and the consequent loss of habitat quality for microorganisms and soil fauna. This study shed some light on the selection of tools for the tier 2 of an ssERA in tropical metal-contaminated sites, focusing on ecological receptors at risk and using available chemical methods, ecological surveys and ecotoxicity tests.

A short-term sublethal toxicity assay with zebra fish based on preying rate and its integration with mortality.

Contaminant-induced feeding inhibition has direct and immediate consequences at higher levels of biological organization, by depressing the population consumption and thus hampering ecosystem functioning (e.g. grazing, organic matter decomposition). Thus, similarly to lethality and avoidance, feeding is mechanistically linked to ecosystem processes and is therefore an unequivocal ecologically meaningful response. The objective of the present study was to develop a short-term assay with the small freshwater fish Danio rerio, based on feeding. For this, a methodology to easily and precisely quantify feeding was first optimized: each fish was allowed to prey on ten live Daphnia magna juveniles, for 1h, just before the end of a 48-h exposure test period. Secondly, copper sensitivity of feeding relatively to survival and growth was evaluated. At the growth EC20 (40 µg L(-1)), feeding was inhibited by 53%, and at the feeding EC50 (36 µg L(-1)), mortality was negligible (1.3%). Integrating feeding and survival revealed a 97% depression in the population consumption at the LC50 (61 µg L(-1)). Thirdly, the influence of pH, conductivity and hardness on the feeding background variability was assessed by assaying waters collected at eight reference sites and was found to be negligible, within tested ranges. Fourthly, feeding assays with natural waters contaminated with acid mine drainage confirmed the integration of lethality and feeding to be pertinent at estimating contaminant effects at higher levels of biological organization.

Suitability of a Saccharomyces cerevisiae-based assay to assess the toxicity of pyrimethanil sprayed soils via surface runoff: comparison with standard aquatic and soil toxicity assays.

The present study is aimed at evaluating whether a gene expression assay with the microbial eukaryotic model Saccharomyces cerevisiae could be used as a suitable warning tool for the rapid preliminary screening of potential toxic effects on organisms due to scenarios of soil and water contamination with pyrimethanil. The assay consisted of measuring changes in the expression of the selected pyrimethanil-responsive genes ARG3 and ARG5,6 in a standardized yeast population. Evaluation was held by assessing the toxicity of surface runoff, a major route of pesticide exposure in aquatic systems due to non-point-source pollution, which was simulated with a pyrimethanil formulation at a semifield scale mimicking worst-case scenarios of soil contamination (e.g. accident or improper disposal). Yeast cells 2-h exposure to the runoff samples led to a significant 2-fold increase in the expression of both indicator genes. These results were compared with those from assays with organisms relevant for the aquatic and soil compartments, namely the nematode Caenorhabditis elegans (reproduction), the freshwater cladoceran Daphnia magna (survival and reproduction), the benthic midge Chironomus riparius (growth), and the soil invertebrates Folsomia candida and Enchytraeus crypticus (survival and reproduction). Under the experimental conditions used to simulate accidental discharges into soil, runoff waters were highly toxic to the standard test organisms, except for C. elegans. Overall, results point out the usefulness of the yeast assay to provide a rapid preview of the toxicity level in preliminary screenings of environmental samples in situations of inadvertent high pesticide contamination. Advantages and limitations of this novel method are discussed.

Unraveling the interactive effects of climate change and oil contamination on laboratory-simulated estuarine benthic communities.

There is growing concern that modifications to the global environment such as ocean acidification and increased ultraviolet radiation may interact with anthropogenic pollutants to adversely affect the future marine environment. Despite this, little is known about the nature of the potential risks posed by such interactions. Here, we performed a multifactorial microcosm experiment to assess the impact of ocean acidification, ultraviolet B (UV-B) radiation and oil hydrocarbon contamination on sediment chemistry, the microbial community (composition and function) and biochemical marker response of selected indicator species. We found that increased ocean acidification and oil contamination in the absence of UV-B will significantly alter bacterial composition by, among other things, greatly reducing the relative abundance of Desulfobacterales, known to be important oil hydrocarbon degraders. Along with changes in bacterial composition, we identified concomitant shifts in the composition of oil hydrocarbons in the sediment and an increase in oxidative stress effects on our indicator species. Interestingly, our study identifies UV-B as a critical component in the interaction between these factors, as its presence alleviates harmful effects caused by the combination of reduced pH and oil pollution. The model system used here shows that the interactive effect of reduced pH and oil contamination can adversely affect the structure and functioning of sediment benthic communities, with the potential to exacerbate the toxicity of oil hydrocarbons in marine ecosystems.

A short-term laboratory and in situ sediment assay based on the postexposure feeding of the estuarine isopod Cyathura carinata.

In situ assays based on feeding depression have been proposed as sublethal assays able to assess immediate contaminant effects on key ecosystem functions, long before effects on life-history traits can be detected. The in situ peculiarities provide more realistic exposure scenarios than laboratory-controlled conditions, which is particularly relevant for estuarine ecosystems where environmental conditions are highly variable. In this context, we developed a short-term cost-effective in situ assay based on the postexposure feeding of the estuarine species, Cyathura carinata, through the following steps: i) develop a methodology to quantify feeding under laboratory conditions; ii) quantify the sensitivity of the postexposure feeding response under laboratory conditions; iii) deploy the in situ assay at various field sites covering different environmental variables in a reference estuary and degrees of contamination in a contaminated estuary to, respectively, derive a model to predict postexposure feeding rates across sites varying in environmental variables and evaluate the potential of this in situ tool to assess sediment contamination in estuaries. A quantity of 100 defrosted nauplii of Artemia franciscana per isopod given during a short period of 30 min in darkness was adequate to allow estimating precise postexposure feeding rates. Laboratory toxicity tests showed the high sensitivity of postexposure feeding to Cd as a sublethal endpoint for C. carinata (7-fold lower than the corresponding 48-h LC50). However, this species appears to be able to face high concentrations of non-essential metals as Cd, with 96-h LC50 values (37 mg Cd/L) higher than values reported for other isopods, and among the highest concentrations reported for saltwater invertebrates. Results of in situ deployments at reference sites indicated that sediment with size fraction between 63-125 µm (very fine sand) influences feeding rates. The in situ assay across contaminated sites was able to discriminate between unpolluted and polluted estuaries, and also to detect degrees of toxicity among sampling sites within an estuary, after statistically adjusting feeding rates on the basis of the proportion of the sediment very fine sand influencing baseline feeding rates. The in situ postexposure feeding assay with C. carinata was found to be, therefore, a potential useful cost-effective tool for estuarine sediment toxicity assessments.

Contaminants as habitat disturbers: PAH-driven drift by Andean paramo stream insects.

Contaminants can behave as toxicants, when toxic effects are observed in organisms, as well as habitat disturbers and fragmentors, by triggering avoidance responses and generating less- or uninhabited zones. Drift by stream insects has long been considered a mechanism to avoid contamination by moving to most favorable habitats. Given that exploration and transportation of crude oil represent a threat for surrounding ecosystems, the key goal of the present study was to assess the ability of autochthonous groups of aquatic insects from the Ecuadorian paramo streams to avoid by drift different concentrations of polycyclic aromatic hydrocarbons (PAH) contained in the soluble fraction of locally transported crude oil. In the laboratory, different groups of insects were exposed to PAH for 12h. Three different assays, which varied in taxa and origin of the organisms, concentrations of PAH (0.6-38.8µgL(-1)), and environment settings (different levels of refuge and flow) were performed. For Anomalocosmoecus palugillensis (Limnephilidae), drift was a major cause of population decline in low concentration treatments but at higher concentrations mortality dominated. PAH was highly lethal, even at lower concentrations, for Chironomidae, Grypopterygidae (Claudioperla sp.) and Hydrobiosidae (Atopsyche sp.), and, therefore, no conclusion about drift can be drawn for these insects. Contamination by PAH showed to be a threat for benthic aquatic insects from Ecuadorian paramo streams as it can cause a population decline due to avoidance by drift and mortality.