Capacitance Determination for the Evaluation of Electrochemically Active Surface Area in a Catalyst Layer of NiFe-Layered Double Hydroxides for Anion Exchange Membrane Water Electrolyser

The determination of the electrochemically active surface area (ECSA) of a catalyst layer (CL) of a non-precious metal catalyst is of fundamental importance in optimizing the design of a durable CL for anion exchange membrane (AEM) water electrolysis, but has yet to be developed. Traditional double layer capacitance (Cdl), measured by cyclic voltammetry (CV), is not suitable for the estimation of the ECSA due to the nonconductive nature of Ni-based oxides and hydroxides in the non-Faradaic region. This paper analyses the applicability of electrochemical impedance spectroscopy (EIS) compared to CV in determining capacitances for the estimation of the ECSA of AEM-based CLs in an aqueous KOH electrolyte solution. A porous electrode transmission line (TML) model was employed to obtain the capacitance-voltage dependence from 1.0 V to 1.5 V at 20 mV intervals, covering both non-Faradic and Faradic regions. This allows for the identification of the contribution of a NiFe-layered double hydroxide (LDH) catalyst and supports in a CL, to capacitances in both non-Faradic and Faradic regions. A nearly constant double layer capacitance (Qdl) observed in the non-Faradic region represents the interfaces between catalyst supports and electrolytes. The capacitance determined in the Faradic region by EIS experiences a peak capacitance (QF), which represents the maximum achievable ECSA in an AEMCL during reactions. The EIS method was additionally validated in durability testing. An approximate 30% loss of QF was noted while Qdl remained unchanged following an eight-week test at 1 A/cm2 constant current density, implying that QF, determined by EIS, is sensitive to and therefore suitable for assessing the loss of ECSA. This universal method can provide a reasonable estimate of catalyst utilization and enable the monitoring of catalyst degradation in CLs, in particular in liquid alkaline electrolyte water electrolysis systems.

Six common behavioral trials and their relevance for perch performance in natural lakes

Behavioral traits measured in laboratory settings are commonly used when predicting ecological effects and evolutionary outcomes in natural systems. However, uncertainties regarding the relevance of simplified lab-based behavioral tests for complex natural environments have created doubts about the use of these tests within aquatic ecology and ecotoxicology. In this study, we scrutinize the assumption that fish performance in six commonly applied behavioral assays has relevance for in situ behavior, by comparing individual behavior tracked in both artificial laboratory settings as well as in two natural lakes. We show that: i) commonly measured behavioral traits of individual fish (Perca fluviatilis) have low predictive power for within-lake behaviors if interpreted alone, but that; ii) composite variables synthesized from several (six) behavioral assays explain important in situ measures such as swimming activity, dispersion, home-range size, and habitat preference. While our findings support recent criticisms against the use of single behavioral tests for predicting environmental effects, we provide empirical evidences suggesting that fish performances in multiple laboratory assays are highly relevant for fish behavior in nature.

No evidence of increased growth or mortality in fish exposed to oxazepam in semi-natural ecosystems

An increasing number of short-term laboratory studies on fish reports behavioral effects from exposure to aquatic contaminants or raised carbon dioxide levels affecting the GABA_A receptor. However, how such GABAergic behavioral modifications (GBMs) impact populations in more complex natural systems is not known. In this study, we induced GBMs in European perch (Perca fluviatilis) via exposure to a GABA agonist (oxazepam) and followed the effects on growth and survival over one summer (70days) in replicated pond ecosystems. We hypothesized that anticipated GBMs, expressed as anti-anxiety like behaviors (higher activity and boldness levels), that increase feeding rates in laboratory assays, would; i) increase growth and ii) increase mortality from predation. To test our hypotheses, 480 PIT tagged perch of known individual weights, and 12 predators (northern pike, Esox lucius) were evenly distributed in 12 ponds; six control (no oxazepam) and six spiked (15.5±4μgl^-1 oxazepam [mean±1S.E.]) ponds. Contrary to our hypotheses, even though perch grew on average 16% more when exposed to oxazepam, we found no significant difference between exposed and control fish in growth (exposed: 3.9±1.2g, control: 2.9±1g [mean±1S.E.], respectively) or mortality (exposed: 26.5±1.8individuals pond^-1, control: 24.5±2.6individuals pond^-1, respectively). In addition, we show that reduced prey capture efficiency in exposed pike may explain the lack of significant differences in predation. Hence, our results suggest that GBMs, which in laboratory studies impact fish behavior, and subsequently also feeding rates, do not seem to generate strong effects on growth and predation-risk in more complex and resource limited natural environments.

Bioaccumulation of five pharmaceuticals at multiple trophic levels in an aquatic food web - Insights from a field experiment

Pharmaceuticals derived from manufacturing and human consumption contaminate surface waters worldwide. To what extent such pharmaceutical contamination accumulates and disperses over time in different compartments of aquatic food webs is not well known. In this study we assess to what extent five pharmaceuticals (diphenhydramine, oxazepam, trimethoprim, diclofenac, and hydroxyzine) are taken up by fish (European perch) and four aquatic invertebrate taxa (damselfly larvae, mayfly larvae, waterlouse, and ramshorn snail), by tracing their bioconcentrations over several months in a semi-natural large-scale (pond) system. The results suggest both significant differences among drugs in their capacity to bioaccumulate and differences among species in uptake. While no support for in situ uptake of diclofenac and trimethoprim was found, oxazepam, diphenhydramine, and hydroxyzine were detected in all analyzed species. Here, the highest bioaccumulation factor (tissue:water ratio) was found for hydroxyzine. In the food web, the highest concentrations were found in the benthic species ramshorn snail and waterlouse, indicating that bottom-living organism at lower trophic positions are the prime receivers of the pharmaceuticals. In general, concentrations in the biota decreased over time in response to decreasing water concentrations. However, two interesting exceptions to this trend were noted. First, mayfly larvae (primarily grazers) showed peak concentrations (a fourfold increase) of oxazepam, diphenhydramine, and hydroxyzine about 30days after initial addition of pharmaceuticals. Second, perch (top-predator) showed an increase in concentrations of oxazepam throughout the study period. Our results show that drugs can remain bioavailable for aquatic organism for long time periods (weeks to months) and even re-enter the food web at a later time. As such, for an understanding of accumulation and dispersion of pharmaceuticals in aquatic food webs, detailed ecological knowledge is required.

Long-Term Persistence of an Anxiolytic Drug (Oxazepam) in a Large Freshwater Lake

Production and human consumption of pharmaceuticals result in contamination of surface waters worldwide. Little is known about the long-term (i.e., over decades) fate of pharmaceuticals in aquatic systems. Here, we show that the most prescribed anxiolytic in Sweden (oxazepam) persists in its therapeutic form for several decades after being deposited in a large freshwater lake. By comparing sediment cores collected in 1995 and 2013, we demonstrate that oxazepam inputs from the early 1970s remained in the sediments until sampling in 2013, despite in situ degradation processes and sediment diagenesis. In laboratory and pond experiments, we further reveal that therapeutic forms of oxazepam can persist over several months in cold (5 °C) lake water free from UV light. We conclude that oxazepam can persist in lakes over a time scale much longer than previously realized and that levels can build up in lakes due to both a legacy of past inputs and a growing urban population.