Water Remediation: PVA-Based Magnetic Gels as Efficient Devices to Heavy Metal Removal

Scientific and technological researches are devoted to obtain materials capable of retaining different kinds of pollutants, contributing to contamination solutions. In this context, hydrogels have emerged as great candidates because of their excellent absorption properties as well as good mechanical, thermal and chemical properties. More specifically, ferrogels (magnetic gels) present the extra advantage of being easily manipulated by a permanent magnet. Here, we present the results derived from the application of ferrogels as efficient tools to extract heavy metal pollutants from wastewater samples. The gels were prepared following the method of freezing and thawing of a polyvinyl alcohol aqueous solution with magnetic nanoparticles coated with polyacrylic acid. Ferrogels were fully characterized and their ability to retain Cu²⁺ and Cd²⁺, as model heavy metals, was studied. Thus kinetics and mechanisms of adsorption were evaluated and modeled. The concentration of MNPs on the PVA matrix was key to improve the adsorption capability (approximately the double of retention is improved by the MNPs addition). The adsorption kinetics was determined as pseudo-second order model, whereas the Langmuir model was the most appropriate to explain the behavior of the gels. Finally reuse ability was evaluated to determine the real potential of these materials, the ferrogels demonstrated high efficiency up to about five cycles, retaining about 80–90% of their initial adsorption capability. All the results indicated that the materials are promising candidates able to compete with the commercial technology regarding to water remediation.     

A method for the assessment of light-induced oxidative stress in embryos of fucoid algae via confocal laserscan microscopy

A method was developed for measurement of active oxygen production in embryonic stages of the brown seaweed Fucus spiralis, using the label CM-DCFH-DA. Active oxygen species convert the label into the green fluorescent CM-DCF (exc/em 488/530 nm) that is detected via confocal laserscan microscopy and quantitative image analysis. Loading of the label did not harm the embryos; loading efficiency was age-independent, and the esterases needed for conversion to CM-DCFH were not inhibited by the effective UV dose (2 W m⁻²) applied in the experiments. After correction for daily variation of the laser power, and calibration with DCF standard solutions, this automated analysis of confocal images rendered active oxygen concentrations in fucoid embryos (μM DCF). An experiment was designed for the assessment of active oxygen production following irradiance stress in the light-sensitive embryos. Dim-light-acclimated, 1-, 2- and 4-day-old embryos were transferred for 60 min to defined high-light conditions (4π-irradiance 300 μmol photons m⁻² s⁻¹), optionally without UV radiation, including UVA, or including UVA plus UVB. PSII yield measurements (PAM fluorometer) were carried out in order to assess the degree of photoinhibition under these light conditions. The imposed light stress initially caused a rapid decrease of the PSII yields (Φ_P). With increasing embryo age, minimum Φ_P values attained under light stress remained higher. Consequently, electron transport rates (ETR) would increase with embryo age, i.e., with the development of their photosynthetic apparatus. Active oxygen production increased with ETR, and when UVB was included, relatively greater amounts of active oxygen were produced. A slow, second-phase decrease of Φ_P under light stress that was proportional to active oxygen production indicated that some photooxidative damage was caused, in particular during UVB exposure. Recovery from light stress was a rapid process in the absence of UVB; in such cases Φ_P was almost restored to the initial values within 60 min. The relative state of recovery of Φ_P was correlated with both the effective UV dose and active oxygen production rate (DCF). Recovery was slowest in embryos exposed for 60 min to an experimental UVB dose, which was representative of a situation at low tide, on a sunny day. The results suggest that active oxygen may cause an in situ inhibition of growth of the earliest life stages of F. spiralis. Received: 26 January 2000 / Accepted: 4 September 2000     

The response of sea scallop (Placopecten magellanicus) veligers to a weak thermocline in 9-m deep mesocosms

We examined the vertical distributions of scallop (Placopecten magellanicus) veligers in deep (0.6 m diameter, 9.5 m deep) polyethylene mesocosms from December 1991 to January 1992. In the mesocosms temperature stratification varied from 0 to 1.5 °C. Profiles of vertical distribution revealed several repeated patterns. Peaks in veliger numbers often appeared at the water surface and just above the thermocline. Higher density patches were seen below the surface peaks, and revealed the presence of bio-convective cells. Distribution away from these discontinuities was usually even. Distribution of veligers was affected by thermoclines above 1.0 °C. Responses to thermoclines varied with larval age and time of day, and 28 to 30 d veligers passed in both directions through a 1.5 °C thermocline. We conclude that larval behaviour is a major determinant of whether veligers pass through a thermocline. Kinematic viscosity may play a role in perception of temperature changes. Two potential consequences of such behaviour are (1) remaining in more productive upper water layers, where feeding opportunities are enhanced, and (2) increased horizontal transport in the region of the thermocline, which may enhance recruitment. Received: 15 May 1996 / Accepted: 11 May 2000     

Population Persistence and Offspring Fitness in the Rare Bellflower Campanula cervicaria in Relation to Population Size and Habitat Quality

Abstract: Data from several animal species and a few plant species indicate that small populations face an elevated risk of extinction. Plants are still underrepresented in these studies concerning the relation between population size and persistence. We studied the effect of population size on persistence among natural populations of the rare bellflower Campanula cervicaria in Finland. We monitored 52 bellflower populations for 8 years and found that the mean population size decreased from 24 to 14 during this period. Small populations with ≤5 individuals were more prone to losing all fertile plants than were larger ones. Reduction in population size was nevertheless unrelated to the degree of population isolation, measured as the distance to the nearest known population. To test the hypothesis that offspring fitness is lower in small populations, we germinated bellflower seeds from different-sized populations in a laboratory and found that seed germination ability was independent of population size. The seedlings raised from seeds of small populations grew faster than those taken from larger populations. Population size was negatively related to the amount of shade in the habitats. In conclusion, decreasing population sizes of C. cervicaria seemed not to be caused by lowered germination ability or growth rate in small populations; rather, population size reductions appeared to be due to closing of vegetation in the habitats.     

Does risk of intraspecific interactions induce shifts in prey-size preference in aquatic predators?

Interactions between foragers may seriously affect individual foraging efficiency. In a laboratory study of handling time, prey value and prey-size preference in northern pike and signal crayfish, we show that risk of intraspecific interactions between predators does not affect handling time or value of prey. However, the presence of agonistic intraspecific interactors shifts prey-size preference in these predators. Neither northern pike nor signal crayfish foraging alone show a prey-size preference, while pike foraging among conspecifics prefer small prey, and crayfish foraging in groups prefer large prey. We ascribe the different outcomes in prey preference to differences in susceptibility to interactions: northern pike under risk avoid large prey to avoid long handling times and the associated risk of interactions, while signal crayfish foraging among conspecifics may defend themselves and their prey during handling, and thus select prey to maximise investment. In addition, the value of pike prey (roach) is low for very small prey, maximises for small prey, and then decreases monotonically for larger prey, while crayfish prey (pond snail) value is low for very small prey, has a maximum at small prey, but does not decrease as much for larger prey. Therefore, a large and easily detected snail prey provides a crayfish with as much value as a small prey. We conclude that interaction risk and predator density affect prey-size preference differently in these aquatic predators, and therefore has different potential effects on prey-size structure and population and community dynamics. Received: 4 October 1999 / Revised: 20 March 2000 / Accepted: 27 May 2000