Randall J. Bernot

Assessing the factors responsible for ionic liquid toxicity to aquatic organisms via quantitative structure–property relationship modeling

Using previously published toxicity data as well as a small set of heretofore-unpublished results, quantitative structure–property relationship models are developed to assess the factors that govern the toxicity of a range of different ionic liquids to two aquatic organisms (Vibrio fischeri and Daphnia magna). With at most four molecular descriptors, log10 EC50 and log10 LC50 data are reproduced with an R2 of 0.78–0.88. Besides the well-established link between toxicity and alkyl chain length on imidazolium, pyridinium and quaternary ammonium-based ionic liquids, the models predict that toxicity increases slightly with the number of nitrogen atoms in an aromatic cation ring. All other things being equal, toxicity is expected to show the trend with cation type of ammonium < pyridinium < imidazolium < triazolium < tetrazolium. In addition, toxicity is expected to decrease with ring methylation as well as with an increase in the number of negatively charged atoms on the cation. The anion plays a secondary role in toxicity for the compounds studied here, although the presence of positively charged atoms on the anion are predicted to slightly increase toxicity.

Acute and chronic toxicity of imidazolium‐based ionic liquids on Daphnia magna

Room-temperature ionic liquids (ILs) are considered to be green chemicals that may replace volatile organic solvents currently used by industry. However, IL effects on aquatic organisms and ecosystems are currently unknown. We studied the acute effects of imidazolium-based ILs on survival of the crustacean Daphnia magna and their chronic effects on number of first-brood neonates, total number of neonates, and average brood size. Lethal concentrations of imidazolium ILs with various anions (X-) ranged from a median lethal concentration (LC50) of 8.03 to 19.91 mg L(-1), whereas salts with a sodium cation (Na+ X-) were more than an order of magnitude higher (NaPF6 LC50, 9,344.81 mg L(-1); NaBF4 LC50, 4765.75 mg L(-1)). Thus, toxicity appeared to be related to the imidazolium cation and not to the various anions (e.g., Cl-, Br-, PF6-, and BF4-). The toxicity of imidazolium-based ILs is comparable to that of chemicals currently used in manufacturing and disinfection processes (e.g., ammonia and phenol), indicating that these green chemicals may be more harmful to aquatic organisms than current volatile organic solvents. We conducted 21-d chronic bioassays of individual D. magna exposed to nonlethal IL concentrations at constant food-resource levels. Daphnia magna produced significantly fewer total neonates, first-brood neonates, and average neonates when exposed to lower concentrations (0.3 mg L(-1)) of imidazolium-based ILs than in the presence of Na-based salts at higher concentrations (400 mg L(-1)). Such reductions in the reproductive output of Daphnia populations could cascade through natural freshwater ecosystems. The present study provides baseline information needed to assess the potential hazard that some ILs may pose should they be released into freshwater ecosystems.

EFFECTS OF IONIC LIQUIDS ON THE SURVIVAL, MOVEMENT, AND FEEDING BEHAVIOR OF THE FRESHWATER SNAIL,PHYSA ACUTA

Room-temperature ionic liquids (ILs) are being promoted as environmentally friendly alternatives to volatile organic solvents currently used by industry. Because ILs are novel and not yet in widespread use, their potential impact on aquatic organisms is unclear. We studied the effects of several ILs on the survivorship and behavior (movement and feeding rates) of the freshwater pulmonate snail, Physa acuta. Median lethal concentrations (LC50s) of ILs with imidazolium- and pyridinium-based cations and Br- and PF6- as anions ranged from 1 to 325 mg/L. Toxicity was greatest for ILs with eight-carbon alkyl chains attached to both imidazolium and pyridinium rings and declined with shorter alkyl chains, indicating a positive relationship between alkyl chain length and toxicity. Compared to controls, snails moved more slowly when exposed to butyl- and hexyl-cation ILs at 1 to 3% of LC50 concentrations but were not affected at higher IL concentrations (4-10% of LC50), which is characteristic of U-shaped dose-response curves. Snail movement was not affected by ILs with octyl alkyl groups. Grazing patterns, however, indicated that snails grazed less at higher IL concentrations. Physa acuta egestion rates were reduced in the presence of ILs at 3 to 10% of LC50 concentrations. Thus, nonlethal IL concentrations affected P. acuta behaviors, potentially impacting individual fitness and food web interactions. These results provide initial information needed to assess the potential hazards of ILs should they reach freshwater ecosystems.

Predator identity and consumer behavior: differential effects of fish and crayfish on the habitat use of a freshwater snail

Abstract Predators can alter the outcome of ecological interactions among other members of the food web through their effects on prey behavior. While it is well known that animals often alter their behavior with the imposition of predation risk, we know less about how other features of predators may affect prey behavior. For example, relatively few studies have addressed the effects of predator identity on prey behavior, but such knowledge is crucial to understanding food web interactions. This study contrasts the behavioral responses of the freshwater snail Physellagyrina to fish and crayfish predators. Snails were placed in experimental mesocosms containing caged fish and crayfish, so the only communication between experimental snails and their predators was via non-visual cues. The caged fish and crayfish were fed an equal number of snails, thereby simulating equal prey mortality rates. In the presence of fish, the experimental snails moved under cover, which confers safety from fish predators. However, in the presence of crayfish, snails avoided benthic cover and moved to the water surface. Thus, two species of predators, exerting the same level of mortality on prey, induced very different behavioral responses. We predict that these contrasting behavioral responses to predation risk have important consequences for the interactions between snails and their periphyton resources.

Predator identity and trait-mediated indirect effects in a littoral food web

Perturbations to the density of a species can be propagated to distant members of a food web via shifts in the density or the traits (i.e. behavior) of intermediary species. Predators with differing foraging modes may have different effects on prey behavior, and these effects may be transmitted differently through food webs. Here we test the hypothesis that shifts in the type of predator present in a food web indirectly affect the preys resource independent of changes in the density of prey. We assessed the importance of predator identity in mediating the grazing effects of the freshwater snail Physa integra on its periphyton resources using field and mesocosm studies. Field observations showed that Physa used covered habitats more in ponds containing fish than in ponds containing crayfish or no predators at all. A field experiment confirmed that snail behavior depended on predator identity. Physa placed near caged pumpkinseed sunfish (Lepomis gibbosus) selected covered habitats, but Physa placed near caged crayfish (Orconectes rusticus) moved to the surface of the water. The effects of predator identity on periphtyon were then examined in a mesocosm experiment, using caged predators. Habitat use of Physa was similar to their habitat use in the field experiment. In the presence of caged sunfish, periphyton standing crop in covered habitats was reduced to 34% of the standing crop in the presence of crayfish. In contrast, periphyton in near-surface habitats was 110% higher in the presence of fish than in the presence of crayfish. Thus, the effects of predator identity on Physa behavior cascaded through the food web to affect the abundance and spatial distribution of periphyton.

Parasite–host elemental content and the effects of a parasite on host-consumer-driven nutrient recycling

Abstract. Parasites are ubiquitous members of ecological communities but have only recently been recognized as key players in broader interactions and ecosystem dynamics, such as foodweb structure and energy flow. Ecological stoichiometry provides a framework for placing parasites in an ecosystem perspective by considering elemental imbalances and their consequences. I measured the elemental content of trematodes and their gastropod hosts and then estimated the nutrient-recycling effects of parasitism. N∶P of all tissue types in trematodes of the freshwater pulmonate snail, Physa acuta, was similar to N∶P of gastropod gonadal tissue. However, N∶P of trematodes and gastropod gonads was lower than N∶P of other gastropod tissues, a result suggesting an elemental imbalance between parasite and host. N∶P of excreta of P. acuta increased with the N∶P content of their algal food, consistent with consumer-driven nutrient recycling theory. However, gastropods with patent infections of Trichobilharzia physellae excreted greater N∶P than did uninfected snails, a result indicating that infected and uninfected gastropods were functionally different. Overall, these results suggest a significant role for parasites in nutrient recycling.

Temperature and kairomone induced life history plasticity in coexisting Daphnia

We investigated the life history alterations of coexisting Daphnia species responding to environmental temperature and predator cues. In a laboratory experiment, we measured Daphnia life history plasticity under different predation risk and temperature treatments that simulate changing environmental conditions. Daphnia pulicaria abundance and size at first reproduction (SFR) declined, while ephippia (resting egg) formation increased at high temperatures. Daphnia mendotae abundance and clutch size increased with predation risk at high temperatures, but produced few ephippia. Thus, each species exhibited phenotypic plasticity, but responded in sharply different ways to the same environmental cues. In Glen Elder reservoir, Kansas USA, D. pulicaria dominance shifted to D. mendotae dominance as temperature and predation risk increased from March to June in both 1999 and 2000. Field estimates of life history shifts mirrored the laboratory experiment results, suggesting that similar phenotypic responses to seasonal cues contribute to seasonal Daphnia population trends. These results illustrate species-specific differences in life history plasticity among coexisting zooplankton taxa.

Spatial and temporal variability of zooplankton in a great plains reservoir

Seasonal and daily patterns of zooplankton populations are often predictable in natural lakes. Distinct zonation and geomorphic differences in reservoirs, however, make ecological extrapolations from lakes to reservoirs uncertain. We describe the spatial and temporal distribution of zooplankton, algae, and water clarity across reservoir zones and along a depth gradient in Glen Elder Reservoir, Kansas. Daphnia species were most abundant in the lacustrine zone, with D. pulicaria numerically dominant in early spring and D. mendotae dominant later in 1999 and 2000. Rotifers (Keratellaquadrata, Asplanchnaspp.) were dominant in the riverine zone in 1999, 2000, and 2001. Algal biomass was not significantly different between zones through most of the sampling periods, except late April in 1999 and mid-April in 2000. Chlorophyll a exceeded 81 μg l−1 in the lacustrine zone in mid- to late-April in 1999 and 2000, and exceeded 90μg l−1in the riverine zone in mid-April. Water clarity was significantly lower in the riverine zone in 1999 and 2000. Most zooplankton taxa had similar depth distributions at night and day, indicating a lack of diel vertical migration behavior on a large scale. However, in small scale (30 cm vertical enclosures) laboratory experiments, both D. pulicaria and D. mendotae occupied significantly deeper depths (>25 cm) under lighted conditions in the presence of fish chemical cues compared to shallow water (7–17 cm) under dark conditions and in the absence of fish cues. These contrasting results suggest that, as in other studies, Daphnia sense cues from predators and alter their depth in the water column on small scales without natural constraints on movement and choices. However, other factors in the reservoir such as wind-generated water movements and cues from other predators may prevent depth choices similar to those seen under controlled conditions. These results illustrate biotic and abiotic differences between riverine and lacustrine zones in a large reservoir, and contrast with Daphnia depth segregation and migration patterns in natural lakes.

Trematode infection alters the antipredator behavior of a pulmonate snail

Parasites can alter the behavior, life history, and morphology of their host. Many trematodes parasitize freshwater pulmonate snails, resulting in a reduction or the elimination of reproduction in those individuals. However, parasite effects on freshwater snail behavior are unclear. I measured trematode infection rates, size, and covered habitat use of the freshwater pulmonate snail Physa integra in a field survey of streams and ponds on Konza Prairie Biological Station. Then, in a laboratory experiment, I tested the hypothesis that behavioral decisions under the risk of predation differed between infected and uninfected P. integra. Infection rates ranged from 2% to 53% overall, but varied between snail size class and site of collection. Significantly fewer infected (7%) than uninfected P. integra (29%) were found under cover, but there was no difference in use of cover between snails infected with Paramphistomidae and Cathaemasiidae trematodes. A significantly greater proportion of larger snail size classes were infected than smaller size classes. In the laboratory experiment, habitat use by P. integra depended on predator presence and infection status. Significantly more uninfected snails used covered habitats in the presence of creek chub (Semotilus atromaculatus) than in the presence of crayfish (Orconectes nais) or in the absence of a predator. Significantly more uninfected snails used near-surface habitat in the presence of O. nais than in other treatments. However, in the presence of S. atromaculatus <20% of infected snails used cover compared to 60% of uninfected snails. Near-surface habitat use and crawlout behavior were also significantly higher among infected snails in crayfish and no predator treatments, suggesting that infected snails use near-surface habitats even when under predation risk. More detailed knowledge of this trematode–snail system is necessary, however, to determine if differences in habitat use between infected and uninfected snails is an adaptive manipulation of snail behavior by trematodes. Nevertheless, these results indicate that infection status affects the behavior of P. integra and may alter species interactions in freshwater benthic communities.

The effects of the psychiatric drug carbamazepine on freshwater invertebrate communities and ecosystem dynamics

Freshwater ecosystems are persistently exposed to pharmaceutical pollutants, including carbamazepine. Despite the ubiquity and recalcitrance of carbamazepine, the effects of this pharmaceutical on freshwater ecosystems and communities are unclear. To better understand how carbamazepine influences the invertebrate community and ecosystem dynamics in freshwaters, we conducted a mesocosm experiment utilizing environmentally relevant concentrations of carbamazepine (200 and 2000 ng/L). Mesocosms were populated with four gastropod taxa (Elimia, Physa, Lymnaea and Helisoma), zooplankton, filamentous algae and phytoplankton. After a 31 d experimental duration, structural equation modeling (SEM) was used to relate changes in the community structure and ecosystem dynamics to carbamazepine exposure. Invertebrate diversity increased in the presence of carbamazepine. Additionally, carbamazepine altered the biomass of Helisoma and Elimia, induced a decline in Daphnia pulex abundance and shifted the zooplankton community toward copepod dominance. Lastly, carbamazepine decreased the decomposition of organic matter and indirectly altered primary production and dissolved nutrient concentrations. Changes in the invertebrate community occurred through both direct (i.e., exposure to carbamazepine) and indirect pathways (i.e., changes in food resource availability). These data indicate that carbamazepine may alter freshwater community structure and ecosystem dynamics and could have profound effects on natural systems.