The Lorenz Curve: A Proper Framework to Define Satisfactory Measures of Symbol Dominance, Symbol Diversity, and Information Entropy.

Novel measures of symbol dominance (dC1 and dC2), symbol diversity (DC1 = N (1 - dC1) and DC2 = N (1 - dC2)), and information entropy (HC1 = log2 DC1 and HC2 = log2 DC2) are derived from Lorenz-consistent statistics that I had previously proposed to quantify dominance and diversity in ecology. Here, dC1 refers to the average absolute difference between the relative abundances of dominant and subordinate symbols, with its value being equivalent to the maximum vertical distance from the Lorenz curve to the 45-degree line of equiprobability; dC2 refers to the average absolute difference between all pairs of relative symbol abundances, with its value being equivalent to twice the area between the Lorenz curve and the 45-degree line of equiprobability; N is the number of different symbols or maximum expected diversity. These Lorenz-consistent statistics are compared with statistics based on Shannon's entropy and Rényi's second-order entropy to show that the former have better mathematical behavior than the latter. The use of dC1, DC1, and HC1 is particularly recommended, as only changes in the allocation of relative abundance between dominant (pd > 1/N) and subordinate (ps < 1/N) symbols are of real relevance for probability distributions to achieve the reference distribution (pi = 1/N) or to deviate from it.

Responses of aquatic macrophytes to anthropogenic pressures: comparison between macrophyte metrics and indices.

Macrophyte responses to anthropogenic pressures in two rivers of Central Spain were assessed to check if simple metrics can exhibit a greater discriminatory and explanatory power than complex indices at small spatial scales. Field surveys were undertaken during the summer of 2014 (Duraton River) and the spring of 2015 (Tajuña River). Aquatic macrophytes were sampled using a sampling square (45 × 45 cm). In the middle Duraton River, macrophytes responded positively to the presence of a hydropower dam and a small weir, with Myriophyllum spicatum and Potamogeton pectinatus being relatively favored. Index of Macrophytes (IM) was better than Macroscopic Aquatic Vegetation Index (MAVI) and Fluvial Macrophyte Index (FMI) in detecting these responses, showing positive and significant correlations with total coverage, species richness, and species diversity. In the upper Tajuña River, macrophytes responded both negatively and positively to the occurrence of a trout farm effluent and a small weir, with Leptodictyum riparium and Veronica anagallis-aquatica being relatively favored. Although IM, MAVI, and FMI detected both negative and positive responses, correlations of IM with total coverage, species richness, and species diversity were higher. Species evenness was not sensitive enough to detect either positive or negative responses of aquatic macrophytes along the study areas. Overall, traditional and simple metrics (species composition, total coverage, species richness, species diversity) exhibited a greater discriminatory and explanatory power than more recent and complex indices (IM, MAVI, FMI) when assessing responses of aquatic macrophytes to anthropogenic pressures at impacted specific sites.

Ecotoxicological assessment of the impact of fluoride (F-) and turbidity on the freshwater snail Physella acuta in a polluted river receiving an industrial effluent.

We carried out field studies and laboratory experiments to assess the impact of fluoride (F-) and turbidity on the freshwater snail Physella acuta in a polluted river receiving an industrial effluent (the middle Duraton River, Central Spain). Fluoride concentrations and turbidity levels significantly increased downstream from the industrial effluent (with the highest values being 0.6 mg F-/L and 55.2 nephelometric turbidity unit). In addition, higher deposition of fine inorganic matter was evident at polluted sampling sites. Conversely, the abundance of P. acuta significantly declined (until its virtual disappearance) downstream from the industrial effluent. Toxicity bioassays showed that P. acuta is a relatively tolerant invertebrate species to fluoride toxicity, with estimated safe concentrations (expressed as LC0.10 values for infinite hours of exposure) for juvenile and adult snails being 2.4 and 3.7 mg F-/L, respectively. Furthermore, juvenile snails (more sensitive than adult snails) did not show significant alterations in their behavior through 15 days of exposure to 2.6 mg F-/L: mean values of the proportion of test snails located on the water surface habitat, as well as mean values of the sliding movement rate (velocity) of test snails, never showed significant differences when comparing control and treatment glass vessels. It is concluded that instream habitat degradation, derived from increased turbidity levels, might be a major cause for significant reductions in the abundance of P. acuta downstream from the industrial effluent. The presence of the competing gastropod Ancylus fluviatilis could also affect negatively the recovery of P. acuta abundance.

Development of a Low-Cost Ecotoxicological Bioassay Based on the Feeding Behaviour of the Aquatic Snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca).

Conventional acute tests are not suited to assess the effects of toxicants, because they do not use the concentrations that are usually found in natural ecosystems. By contrast, nonlethal realistic concentrations may cause deleterious effects on animal fitness as a consequence of behaviour impairment. Behaviour is a good integrative variable of complex biochemical and physiological processes. Therefore, bioassays based on behaviour are a useful tool in ecotoxicology. In this study, two bioassays were conducted: (1) acute bioassay (48 h) of acetone on the aquatic snail Potamopyrgus antipodarum, and (2) video-recording behavioural bioassay with pulse exposures to acetone to assess its effects on feeding behaviour. In the latter, animals were exposed to three pulses of acetone (24 h each) with 6 days of postexposure after each pulse. This design allowed us to assess the degree of feeding behaviour recovery after exposure and the effects of repeated pulses. Our results show that postexposure periods have an important effect on the recovery of normal feeding behaviour and that this developed bioassay is an ecotoxicological tool with a relatively low-cost and a short-time consuming. The application of this new tool to different ecotoxicological requirements is discussed.

Ammonia toxicity to the freshwater planarian Polycelis felina: contrasting effects of continuous versus discontinuous exposures.

Aquatic animals can be exposed to fluctuating concentrations of toxicants. In fact, for some toxicants (i.e., pesticides, ammonia), discontinuous exposure is more environmentally relevant than constant exposure. Responses of aquatic animals to each type of exposure may be different. However, despite the high ecological relevance of behaviour, there is still scarce information on the effects of discontinuous exposure on behaviour. Our study focused on the assessment of unionized ammonia toxicity on the behaviour of a freshwater planarian under continuous exposure (3 days of exposure and 18 days of recovery) versus discontinuous exposure (3 pulses of 1 day with 6 days of recovery between pulses = total 3 days of exposure and 18 days of recovery). Behaviour was assessed as locomotion activity. Bioassays with continuous and discontinuous exposure were performed with one control and five unionized ammonia concentrations (0.14-0.35 mg N-NH3/L). Unionized ammonia in continuous exposure caused less impact on behaviour than equivalent concentrations provided in a discontinuous exposure. By contrast, continuous exposures caused more impact on survival. The discontinuous exposure may allow detoxification during recovery periods, thus increasing the probability of survival in the next pulse. Under continuous exposure, the mortality threshold could be exceeded, and animals could die in greater proportion during exposure as well as the recovery period. We conclude that behavioural activity was a sensitive endpoint to assess the contrasting effects of continuous versus discontinuous exposure and that the response of planarians to discontinuous exposure is different to its response to continuous exposure.

Ecotoxicological assessment of the impact of nitrate (NO(3)(¯)) on the European endangered white-clawed crayfish Austropotamobius italicus (Faxon).

Field studies and laboratory experiments were conducted to assess the impact of elevated nitrate (NO(3)(¯)) concentrations on the European endangered white-clawed crayfish Austropotamobius italicus (Faxon) in the Henares River Basin (Central Spain), within an area that is vulnerable to nitrate pollution. Two sampling surveys were carried out in the summer of 2009 and 2011 to collect freshwater crayfish at eight sampling sites along this vulnerable area. The invasive read-swamp crayfish Procambarus clarkii (Girard) was the only collected crayfish species. Nitrate toxicity experiments however showed that A. italicus is one of the most tolerant species to nitrate toxicity. Although the food consumption was the most sensitive endpoint to nitrate toxicity (followed by the escape response and mortality), the no-observed-effect concentration (NOEC) for this endpoint after 14 days of exposure to nitrate was as high as 100mg NO(3)(¯)N/l, with some crayfish being still alive after fourteen days of exposure to a nominal nitrate concentration of 800mg NO(3)(-)N/l. Besides, a safe concentration of nitrate for A. italicus, along with its respective 95% confidence limits, were estimated to be 68.5 (22.4-187) mg (NO(3)(¯)N/l. Overall we conclude that elevated nitrate concentrations would not be responsible for the absence of white-clawed crayfish in the Henares River Basin. Other environmental factors, particularly the presence of P. clarkii and its fungal pathogen, would be major causes.

Assessment of drift as a recovery endpoint in aquatic snails exposed to ammonia.

Pollutants are an important factor that causes among others drift (i.e. downstream transport of aquatic organisms in the current) in aquatic invertebrates. However, drift response is taxon-specific, which necessitates the investigation of a wide variety of taxa. Additionally, no information on the effects of the common toxicant ammonia on this endpoint is available. Our study focuses on the effects of exposure and post-exposure to ammonia on the drift of the common aquatic mollusc: Potamopyrgus antipodarum (Hydrobiidae, Mollusca). The effects of ammonia were tested using percentage of drift and stay time (i.e. time that animals stay without dislodging), which were monitored during 2 days of exposure and 2 days of post-exposure in a laboratory stream microcosm. Drift was observed at concentration 4.3 times lower than the LC50 48 h to this species. Our results show that ammonia increases the percentage of drift and caused a reduction in stay time of the exposed animals, both endpoints recover to their normal values after 24 h of post-exposure to ammonia.

The impact of an industrial effluent on the water quality, submersed macrophytes and benthic macroinvertebrates in a dammed river of Central Spain.

This research was conducted in the middle Duratón River (Central Spain), in the vicinity of Burgomillodo Reservoir. An industrial effluent enters the river 300 m downstream from the dam. Fluoride and turbidity levels significantly increased downstream from the effluent, these levels being to some extent affected by differential water releases from the dam. The community of submersed macrophytes exhibited slighter responses and, accordingly, lower discriminatory power than the community of benthic macroinvertebrates, this indicating that metrics and indices based on macroinvertebrates may be more suitable for the biological monitoring of water pollution and habitat degradation in dammed rivers receiving industrial effluents. However, in relation to fluoride bioaccumulation at the organism level, macrophytes (Fontinalis antipyretica and Potamogeton pectinatus) were as suitable bioindicators of fluoride pollution as macroinvertebrates (Ancylus fluviatilis and Pacifastacus leniusculus). Fluoride bioaccumulation in both hard and soft tissues of these aquatic organisms could be used as suitable bioindicator of fluoride pollution (even lower than 1 mg F(-)L(-1)) in freshwater ecosystems. Echinogammarus calvus exhibited a great sensitivity to the toxicity of fluoride ions, with a 96 h LC50 of 7.5 mg F(-)L(-1) and an estimated safe concentration of 0.56 mg F(-)L(-1). The great capacity of E. calvus to take up and retain fluoride during exposures to fluoride ions would be a major cause of its great sensitivity to fluoride toxicity. It is concluded that the observed fluoride pollution might be partly responsible for the absence of this native amphipod downstream from the industrial effluent.

Reproductive traits and population structure of Astyanax aeneus (Characiformes: Characidae) from a subtropical river in Mexico.

Champotón River is an unknown area within the Mesoamerican hotspot in Southestern México. Reproductive traits and population structure of Astyanax aeneus were analyzed along an environmental gradient of the upper, middle and lower sections of the river, where diverse environmental factors were recorded. For this, nets were cast for 1 h at each site and A. aeneus were collected from all sections with sweep nets (5 and 10 m long by 5 m deep, 0.03m mesh size) and a casting net (0.05m mesh size). At each study site and campaign, a total of 80 specimens (in average) were collected and were fixed in 10% formaldehyde for further analysis. Population structure by size was analyzed for each study site, based on the relative frequencies by standard length classes. The length-weight relationship was determined, and the identification of gonadal developmental stages, reproductive period, size at first sexual maturity, relative fecundity, sex ratio and somatic indexes (gonadosomatic, hepatosomatic and Fulton's condition factor) were also assessed. Seven size classes were found in the upper and middle sections, and nine downstream, with seasonal and spatial pattern in size-class frequency distribution. Size at first maturity was 45.7mm for females and 40.8mm for males. The maximum relative fecundity was recorded at the downstream site and was positively correlated with body weight and standard length. Sex ratio (1.8:1 males: females) differed significantly from expected values (1:1). Gonadosomatic index scores indicated that the reproductive period of this species in the Champot6n River was from April to July, during the warm and wet season. Hepatosomatic index was negatively correlated with the Gonadosomatic index, evidencing transfer of energy from the liver towards gamete production. This strategy enabled A. aeneus to maintain robustness during the study period with tiny changes in condition factor. A. aeneus in the Champotón River, as opposed to South American river congeneric species of similar size, shows early sexual maturity, a short reproductive period with high gonadosomatic index values, and high fecundity, a trade-off for the short reproductive period. Spatio-temporal segregation was evident: breeders congregate downstream, while juveniles prefer the upper reaches. This pattern allows A. aenus to be successful in a river with high frequency of hurricanes.

Reproductive traits and population structure of Astyanax aeneus (Characiformes: Characidae) from a subtropical river in Mexico / Rasgos reproductivos y estructura de la población de Astyanax aeneus (Characiformes: Characidae) de un río subtropical en México

Champotón River is an unknown area within the Mesoamerican hotspot in Southestern México. Reproductive traits and population structure of Astyanax aeneus were analyzed along an environmental gradient of the upper, middle and lower sections of the river, where diverse environmental factors were recorded. For this, nets were cast for 1h at each site and A. aeneus were collected from all sections with sweep nets (5 and 10m long by 5m deep, 0.03m mesh size) and a casting net (0.05m mesh size). At each study site and campaign, a total of 80 specimens (in average) were collected and were fixed in 10% formaldehyde for further analysis. Population structure by size was analyzed for each study site, based on the relative frequencies by standard length classes. The length-weight relationship was determined, and the identification of gonadal developmental stages, reproductive period, size at first sexual maturity, relative fecundity, sex ratio and somatic indexes (gonadosomatic, hepatosomatic and Fulton’s condition factor) were also assessed. Seven size classes were found in the upper and middle sections, and nine downstream, with seasonal and spatial pattern in size-class frequency distribution. Size at first maturity was 45.7mm for females and 40.8mm for males. The maximum relative fecundity was recorded at the downstream site and was positively correlated with body weight and standard length. Sex ratio (1.8:1 males: females) differed significantly from expected values (1:1). Gonadosomatic index scores indicated that the reproductive period of this species in the Champotón River was from April to July, during the warm and wet season. Hepatosomatic index was negatively correlated with the Gonadosomatic index, evidencing transfer of energy from the liver towards gamete production. This strategy enabled A. aeneus to maintain robustness during the study period with tiny changes in condition factor. A. aeneus in the Champotón River, as opposed to South American river congeneric species of similar size, shows early sexual maturity, a short reproductive period with high gonadosomatic index values, and high fecundity, a trade-off for the short reproductive period. Spatio-temporal segregation was evident: breeders congregate down- stream, while juveniles prefer the upper reaches. This pattern allows A. aenus to be successful in a river with high frequency of hurricanes.

El Río Champotón es un área de desconocimiento científico dentro del hotspot de Mesoamérica en el sureste de México. Las características reproductivas y la estructura de la población de Astyanax aeneus fueron analizadas a lo largo de un gradiente ambiental en la porción dulceacuícola del río. Se estudiaron tres sitios: en la parte alta del río San Juan Carpizo, en la porción media San Antonio del Río y río abajo en Ulumal, en cinco períodos entre 2007 y 2008. Se registraron diversos factores ambientales en cada sitio de estudio. Los ejemplares de A. aeneus se recolectaron con redes de arrastre de 5 y 10m de largo por 5m de profundidad (0.03m malla) y atarraya (con luz de malla de 0.05m). Las redes fueron lanzadas durante 1 hora en cada sitio. En cada visita se recolectaron un promedio de 80 especímenes en cada sitio de estudio que se preservaron en formaldehído al 10% para su posterior análisis. Para cada sitio de estudio se analizó la estructura de la población por talla, con base en las frecuencias relativas de las clases de longitud estándar. Se determinó la relación peso-talla, se identificaron las etapas del desarrollo gonadal, la época reproductiva, el tamaño de primera madurez sexual, la fecundidad absoluta y relativa, la proporción de sexos y los índices somáticos (gonadosomático, hepatosomático y el factor de condición de Fulton). Se obtuvieron siete clases de talla en la parte alta y media del río y nueve río abajo, con un patrón de distribución estacional y espacial en las frecuencias de clase de tallas. La talla de primera madurez fue de 45.7mm en hembras y 40.8mm en machos. La máxima fecundidad absoluta se registró río abajo y se correlacionó positivamente con el peso corporal y la longitud estándar. La proporción de sexos (1.8:1 machos: hembras) difiere significativamente de los valores esperados (1:1). Los resultados del índice gonadosomático (IGS) indican que el período reproductivo en el Río Champotón es en julio, durante la temporada húmeda y cálida. El índice hepatosomático se correlacionó negativamente con el IGS, evidenciando la transferencia de energía desde el hígado hacia la producción de gametos. Esta estrategia permitió que A. aeneus mantuviera una condición robusta durante el periodo de estudio con pequeños cambios en el factor de condición. Nuestros resultados indican que A. aeneus en el río Champotón, a diferencia de otras especies del mismo género y de la misma talla en ríos de Sudamérica, presenta una maduración sexual precoz, una temporada reproductiva corta con elevados valores del IGS, y una elevada fecundidad, lo que compensa la temporada de reproducción corta. También se percibe una tendencia a la segregación espacial y temporal: los reproductores se congregan aguas abajo y los juveniles prefieren las partes más altas. Este patrón permite a A. aeneus tener éxito en un río con una alta frecuencia de huracanes.

Fluoride bioaccumulation and toxic effects on the survival and behavior of the endangered white-clawed crayfish Austropotamobius pallipes (Lereboullet).

Laboratory experiments were performed to examine the toxic effects of fluoride (F(-)) on the survival and behavior of white-clawed crayfish (Austropotamobius pallipes). Body fluoride contents (bioaccumulation) of test crayfish were also examined. No significant differences between male and female crayfish regarding mortality, escape (tail-flip) response, and fluoride bioaccumulation were detected. For mortality, 48-, 72-, 96-, 120-, 144-, 168-, and 192-h median lethal concentrations (LC50) were estimated to be 93.0, 55.3, 42.7, 36.5, 32.9, 30.6, and 28.9 mg F(-)/l, respectively. For the escape response, 48-, 72-, 96-, 120-, 144-, 168- and 192-h median effective concentrations (EC50) were estimated to be 18.4, 11.1, 8.6, 7.4, 6.7, 6.2 and 5.9 mg F(-)/l, respectively. Average food consumption in test crayfish tended to decrease with increasing water fluoride concentration with a 192-h lowest-observed effect concentration of 10.7 mg F(-)/l. These results indicate that the escape response was the most sensitive end point to fluoride toxicity followed by food consumption and mortality. Fluoride bioaccumulation in test crayfish increased with increasing water fluoride concentration and exposure time. The exoskeleton accumulated more fluoride than muscle. A comparison of the obtained results with previous data for other freshwater invertebrates shows that white-clawed crayfish are relatively tolerant to fluoride toxicity. We conclude that fluoride pollution in freshwater ecosystems should not be viewed as an important risk factor contributing to the catastrophic decrease of A. pallipes in many European countries. Our results indicate that fluoride bioaccumulation in A. pallipes might be used as a bioindicator of fluoride pollution in freshwater ecosystems where it is present.

Nitrate causes deleterious effects on the behaviour and reproduction of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca).

Nitrate (NO3 (-)) is present in aquatic ecosystems as a natural component of the nitrogen cycle. However, in the last decades, several human activities are the causes of the rising amounts of organic matter and inorganic nitrogen nutrients in aquatic ecosystems, causing notable increase of nitrate above background natural levels. In spite of the toxicity of nitrate to aquatic animals, there are relatively few studies on the chronic toxicity of this compound to invertebrates. The aim of our study is to assess the effect of chronic (35 days) exposure to nitrate on the behaviour (velocity of movement) and reproduction (number of newborns) of the aquatic snail Potamopyrgus antipodarum. Four actual concentrations of nitrate were used (21.4, 44.9, 81.8 and 156.1 mg N-NO3 (-)/L). In each treatment, 12 animals were individually monitored for velocity (weekly) and newborn production (every 3-4 days). Velocity was recorded using quantitative video monitoring. Our results showed that nitrate did not cause mortality, but it reduced the velocity of movement (at 44.9, 81.8 and 156.1 mg N-NO3 (-)/L) and number of live newborns (in all tested concentrations). Reproductive impairment was caused at realistic nitrate concentrations which is relevant to the risk assessment of this compound. Our study contributes to the knowledge of the chronic effects of nitrate on the behaviour and reproduction of an aquatic snail.

A video-based tracking analysis to assess the chronic toxic effects of fluoride ion on the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca).

Short-term lethal bioassays are not suited for assessing the real effects of pollutants in natural ecosystems, as their concentrations are usually unrealistic under an ecological point of view. By contrast, chronic bioassays are more realistic for assessing effects on aquatic animals, especially when behavioural endpoints are used. These endpoints are a good link between physiological and ecological effects. Among behavioural bioassays, those based on automated image analysis following video-recording have the advantage of being quantitative and non-subjective tests. The present study focuses on the assessment of chronic (63 days) effects of fluoride ion (F⁻) on the survival, proportion of affected animals (dead plus immobile animals) and several behavioural endpoints (monitored by video-recording and image analysis system) of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca). The bioassay consisted of one control and three actual fluoride concentrations (4.68, 18.6, and 37.1 mg F⁻/L) with 12 replicates in each treatment. The endpoints were monitored every 7 day of continuous exposure to fluoride ion. The highest fluoride concentrations killed all animals at the end of the bioassay. By contrast no animals died in the lowest fluoride treatment, but snails showed several alterations of behaviour: increase heterogeneity of velocity among successive recording periods, increase of the time to escape from a marked circle, and reduction of the heterogeneity in the utilization of space. Therefore, most of the behavioural endpoints were sensitive to environmentally realistic non-lethal fluoride concentrations, being useful parameters for ecological risk assessment. The ecological relevance of these findings is discussed.

The freshwater planarian Polycelis felina as a sensitive species to assess the long-term toxicity of ammonia.

Behavioural endpoints are a good link between physiological and ecological effects. However long-term behavioural endpoints are not uniformly studied over all different organism groups. For example behaviour has been scarcely studied in planarians. Unionized ammonia (NH(3)) is one of the most widespread pollutants in developed countries, and is known to alter animal behaviour. In this study a long-term (30 d) bioassay was conducted to assess the effect of this pollutant on survival and behavioural activity (e.g. locomotion activity) of the freshwater planarian Polycelis felina. One control and three environmentally-realistic concentrations of unionized ammonia (treatments of 0.02, 0.05, and 0.09 mg N-NH(3) L(-1)) were used in quintuplicate. The behaviour of planarians was measured after 0, 10, 20 and 30 d of ammonia exposure. Mortality was recorded every 2 d. Unionized ammonia increased mortality in the two highest NH(3) concentrations and the locomotory activity was depressed in all treatments after 20 d of exposure. Behavioural effect was observed at concentrations 20 times lower than the short-term LC50 for this species. Previous studies proposed safe concentrations of unionized ammonia of 0.01-0.10 mg N-NH(3) L(-1) to aquatic ecosystems, but our study has shown that these concentrations will affect planarians. Because planarians play a key role in streams (as predator/scavenger), safe concentrations should be below 0.02 mg N-NH(3) L(-1) to protect this species in the freshwater community. Our results can contribute to improve the knowledge about ammonia toxicity to freshwater ecosystems, we recommend that safe concentrations of unionized ammonia should be based on very sensitive species.

Contrasting sensitivities to fluoride toxicity between juveniles and adults of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca).

In contrast to aquatic vertebrates, there is scarce available information on the contrasting tolerance to fluoride of different life stages and/or sizes of aquatic invertebrates. The purpose of this study was to assess the likely differences in sensitivity between juveniles and adults of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) to short-term (4 days) toxicity of fluoride ion (F(-)). LC50 and EC50 values for juveniles were significantly lower than those for adults at 24, 48, 72 and 96 h. Based on our results, the use of fluoride data of bioassays with juveniles should provide more protective water quality criteria than data from adult stage.

Subchronic toxic effects of fluoride ion on the survival and behaviour of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca).

Short-term bioassays usually assess lethal effects of pollutants in animals, whereas subchronic bioassays are more suited for assessing effects on animal behaviour. Among them, videotaped bioassays are an improvement in the behavioural monitoring because they are easily and cheaply implemented. The present study focuses on the assessment of subchronic (14-day) effects of fluoride ion on the survival, proportion of dead plus immobile animals, and velocity (monitored by a videotaping and image analysis system) of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca). One control and three nominal fluoride concentrations (5, 20, and 40 mg F(-)/l [actual mean concentrations of 5.2, 17.5, and 37.0 mg F(-)/l, respectively]) were used. Each treatment (including the control) was replicated 12 times. Mortality, number of dead plus immobile animals, and velocity were monitored after 0, 7, and 14 days of exposure. After 14 days, animals exposed to 40 mg F(-)/l showed higher mortality, number of dead, and immobile individuals than control animals. Snails exposed to 5 and 20 mg F(-)/l were not affected by fluoride ion regarding these endpoints. In contrast, snails exposed to 20 mg F(-)/l for 7 and 14 days showed lower velocity than control animals. Therefore, velocity was sensitive to environmental fluoride concentrations and as such is a useful parameter for ecologic risk assessment. In addition, videotaping allowed us to detect behavioural patrons in velocity at very short exposures (seconds) during the monitoring process by showing that the velocity of snails must be monitored at least during the course of several minutes. We conclude that in P. antipodarum, velocity is a more sensitive endpoint than the classic mortality and immobility endpoints.

Fluoride toxicity and bioaccumulation in the invasive amphipod Dikerogammarus villosus (Sowinsky, 1894): a laboratory study.

The tolerance of the invasive amphipod Dikerogammarus villosus to fluoride (F⁻) toxicity was examined via laboratory experiments. 96-h LC50 and 240-h NOEC values were estimated to be 5.8 and 0.95 mg F⁻/L, respectively. Average whole-body fluoride content in control amphipods was 27.6 µg F⁻/g dry weight, whereas in exposed amphipods it ranged from 3,637 to 16,994 µg F⁻/g dry weight. All these results indicate that D. villosus is a very sensitive species to fluoride toxicity. Overall it is concluded that the potential risk of invasion for D. villosus in either natural or polluted freshwater ecosystems, exhibiting relatively high fluoride levels (at least ten-fold higher than the average freshwater background level of 0.15 mg F⁻/L), must be low.

Effects of pulse duration and post-exposure period on the nitrite toxicity to a freshwater amphipod.

This research assesses the effects of nitrite pulses and post-exposure periods after nitrite exposures on the survival of the freshwater amphipod Eulimnogammarus toletanus. A toxicity bioassay was performed using three different nitrite concentrations (0.5, 5.0 and 10.0 mg/L NO(2)-N), four pulse exposures (1, 8, 24 and 48 h) for each nitrite concentration, and four post-exposure times until to complete 96 h (i.e., 95, 88, 72 and 48 h, respectively). Our results showed a significant effect of nitrite concentrations, pulses and post-exposure times on the mortality of E. toletanus. The cumulative mortality at the end of pulse and that at the end of post-exposure time (delayed mortality) were different. We conclude that due to the high frequency of intermittent pollution in aquatic ecosystems it is necessary to incorporate the post-exposure effects into the traditional toxicological parameters to achieve a more realistic assessment of toxicants, especially at very short-term exposures.