Lanthanum from a modified clay used in eutrophication control is bioavailable to the marbled crayfish (Procambarus fallax f. virginalis)

Environmental impacts of selected metal cations for phosphorus capture in natural waters: A synthesis

Cultural eutrophication from excessive human-related nutrient (phosphorus, P, and nitrogen, N) inputs is a major concern for water quality. Because P historically was regarded as the critical nutrient in controlling noxious algal/plant growth, P became the focus of "capturing" techniques, with emphasis on removal performance rather than environmental impacts. Here, we synthesize a literature review of known environmental effects linked to use of metal-cation-based P-capturing materials under eutrophic conditions in freshwaters. P-capturing materials with functional cations based on aluminum (Al), calcium (Ca), iron (Fe), lanthanum (La), and magnesium (Mg) were reviewed in terms of their ecotoxicity, persistence, and bioaccumulation-standard criteria used to evaluate environmental risks of chemical substances. We found very few published studies on environmental impacts of metal-cation-based P-capturing materials under eutrophic conditions. Available reports indicated that environmental effects vary depending on the selected material, dose, target organism(s), and experimental conditions. The Al-based materials had the potential to negatively impact various biota; several Fe-based materials caused various levels of toxicity in a limited group of aquatic organisms; La-based materials can bioaccumulate and some were linked to various harmful effects on biota; and Mg-based materials also adversely affected various organisms. The limited number of published studies underscores the need for further research to characterize the environmental impacts of these materials. Results can be used to guide future work and can assist resource managers in sustainable management strategies. Among various research needs, future assessments should assess the impacts of chronic exposures on sensitive species under realistic field conditions in eutrophic waters.

The effects of different doses of lanthanum-modified bentonite in combination with a submerged macrophyte (Vallisneria denseserrulata) on phosphorus inactivation and macrophyte growth: A mesocosm study

The combination of chemical phosphorus (P) inactivation and submerged macrophyte transplantation has been widely used in lake restoration as it yields stronger effects than when applying either method alone. However, the dose effect of chemical materials on P inactivation when used in combination with submerged macrophytes and the influences of the chemicals used on the submerged macrophytes growth remain largely unknown. In this study, we investigated P inactivation in both the water column and the sediment, and the responses of submerged macrophytes to Lanthanum modified bentonite (LMB) in an outdoor mesocosm experiment where Vallisneria denseserrulata were transplanted into all mesocosms and LMB was added at four dosage levels, respectively: control (LMB-free), low dosage (570 g m-2), middle dosage (1140 g m-2), and high dosage (2280 g m-2). The results showed that the combination of LMB dosage and V. denseserrulata reduced TP in the water column by 32%-38% compared to V. denseserrulata alone, while no significant difference was observed among the three LMB treatments. Porewater soluble reactive P, two-dimensional diffusive gradient in thin films (DGT)-labile P concentrations, and P transformation in the 0-1 cm sediment layer exhibited similar trends along the LMB dosage gradient. Besides, LMB inhibited plant growth and reduced the uptake of mineral elements (i.e., calcium, manganese, iron, and magnesium) in a dosage-dependent manner with LMB. LMB may reduce plant growth by creating a P deficiency risk for new ramets and by interfering with the uptake of mineral elements. Considering both the dose effect of LMB on P inactivation and negative effect on macrophyte growth, we suggest a "small dosage, frequent application" method for LMB application to be used in lake restoration aiming to recover submerged macrophytes and clear water conditions.

The role of bioturbation triggered by benthic macroinvertebrates in the effectiveness of the Floc & Lock technique in mitigating eutrophication

Anthropogenic activities have led to excessive loading of phosphorus and nitrogen into water bodies, leading to eutrophication and promoting the growth of cyanobacteria, posing a threat to the health of humans and aquatic animals. Techniques such as Floc & Lock have been developed to mitigate eutrophication by reducing phosphorus concentrations in water and preventing algal blooms. However, little attention has been given to the impact of phosphorus resuspension by sediment-associated organisms such as benthic macroinvertebrates, on the effectiveness of this technique. Here, we experimentally evaluated whether the presence of snails Melanoides tuberculata (Müller, 1774) and larvae of Chironomus sancticaroli (Strixino and Strixino, 1981) affects the efficiency of the Floc & Lock technique. Snails and chironomid larvae are benthic macroinvertebrates commonly found in high abundance in eutrophic reservoirs. Specifically, we tested the hypotheses that (i) the presence of benthic macroinvertebrates reduces the efficiency of coagulants and clays in removing phosphorus and algal biomass from the water column, and (ii) this effect is species-dependent, as some organisms such as the snails, revolve the substrate and resuspend sedimented particles, while other ones, such as chironomid larvae, aid in the removal of phosphorus from the water column by depositing them in the sediment. Our findings revealed that the impact of benthic macroinvertebrates on the effectiveness of the Floc & Lock technique is species-dependent. Chironomid larvae positively influenced the efficiency of the technique by aiding in the removal of total phosphorus, soluble reactive phosphorus, and algal biomass from the water column, depositing them in the sediment. In contrast, the presence of snails had the opposite effect, resulting in increased phosphorus concentration and algal biomass in the water. Surprisingly, the snails consumed the flocs formed by the coagulant and clay within a short time interval of 72 h, raising concerns due to the presence of toxic cyanobacterial biomass in these flocs. Our study emphasizes the importance of considering benthic macroinvertebrates and their impact on the effectiveness of eutrophication management techniques.

Response of sediment phosphorus partitioning to lanthanum-modified clay amendment and porewater chemistry in a small eutrophic lake

Sustained eutrophication of the aquatic environment by the remobilization of legacy phosphorus (P) stored in soils and sediments is a prevailing issue worldwide. Fluxes of P from the sediments to the water column, referred to as internal P loading, often delays the recovery of water quality following a reduction in external P loads. Here, we report on the vertical distribution and geochemistry of P, lanthanum (La), iron (Fe) and carbon (C) in the culturally eutrophied Lake Bromont. This lake underwent remediation treatment using La modified bentonite (LMB) commercially available as Phoslock™. We investigated the effectiveness of LMB in decreasing soluble reactive phosphorus (SRP) availability in sediments and in reducing dissolved fluxes of P across the sediment-water interface. Sediment cores were retrieved before and after LMB treatment at three sites representing bottom sediment, sediment influenced by lakeside housing and finally littoral sediment influenced by the lake inflow. Sequential extractions were used to assess changes in P speciation. Depth profiles of dissolved porewater concentrations were obtained after LMB treatment at each site. Results indicate that SRP extracted from the sediments decreased at all sites, while total extracted P (P_TOT) bound to redox-sensitive metal oxides increased. ³¹P NMR data on P extract reveals that 20-43% of total solid-phase P is in the form of organic P (P_org) susceptible to be released via microbial degradation. Geochemical modelling of porewater data provides evidence that LaPO_4(s) mineral phases, such as rhabdophane and/or monazite, are likely forming. However, results also suggest that La³⁺ binding by dissolved organic carbon (DOC) hinders La-phosphate precipitation. We rely on thermodynamic modelling to suggest that high Fe²⁺ would bind to DOC instead of La³⁺, therefore promoting P sequestrations by LMB under anoxic conditions.

Combining Old and New Tricks: The Study of Genes, Neurons, and Behavior in Crayfish

For over a century the nervous system of decapod crustaceans has been a workhorse for the neurobiology community. Many fundamental discoveries including the identification of electrical and inhibitory synapses, lateral and pre-synaptic inhibition, and the Na⁺/K⁺-pump were made using lobsters, crabs, or crayfish. Key among many advantages of crustaceans for neurobiological research is the unique access to large, accessible, and identifiable neurons, and the many distinct and complex behaviors that can be observed in lab settings. Despite these advantages, recent decades have seen work on crustaceans hindered by the lack of molecular and genetic tools required for unveiling the cellular processes contributing to neurophysiology and behavior. In this perspective paper, we argue that the recently sequenced marbled crayfish, Procambarus virginalis, is suited to become a genetic model system for crustacean neuroscience. P. virginalis are parthenogenetic and produce genetically identical offspring, suggesting that germline transformation creates transgenic animal strains that are easy to maintain across generations. Like other decapod crustaceans, marbled crayfish possess large neurons in well-studied circuits such as the giant tail flip neurons and central pattern generating neurons in the stomatogastric ganglion. We provide initial data demonstrating that marbled crayfish neurons are accessible through standard physiological and molecular techniques, including single-cell electrophysiology, gene expression measurements, and RNA-interference. We discuss progress in CRISPR-mediated manipulations of the germline to knock-out target genes using the ‘Receptor-mediated ovary transduction of cargo’ (ReMOT) method. Finally, we consider the impact these approaches will have for neurophysiology research in decapod crustaceans and more broadly across invertebrates.

Influence of temperature and pH on phosphate removal efficiency of different sorbents used in lake restoration

Phosphorus sorbents (PS) are viewed as a powerful tool to manage eutrophication. Here, we tested three commercially available PS - lanthanum-modified bentonite (LMB), aluminium-modified zeolite (AMZ) and aluminium salts (Al) on their capacity to chemically inactivate soluble reactive phosphorus (SRP) at six different temperatures (5 to 35 °C) and five pH values (6 to 10). We also evaluated if the SRP bound at a neutral pH would be released if pH increases to pH 10. Results showed that temperature affected the SRP binding behavior differently for each PS. For instance, the highest SRP binding capacities of LMB, AMZ and Al were 14.0, 29.9 and 251.1 mg P g^-1 at 30 °C, 35 °C and 30 °C, respectively; and the lowest was at 35 °C for LMB, 25 °C for AMZ and 20 °C for Al (6.3, 4.0 and 205.2 mg P g^-1, respectively). The pH also affected the SRP binding differently. When pH increased from pH 6 to pH 10, LMB and Al decreased their binding capacity from 10.0 to 4.9 and from 571.7 mg P g^-1 to 21.3 mg P g^-1, respectively. The SRP adsorption capacity of AMZ was similar at pH 7 and 10 (6.3 and 6.2 mg P g^-1). We observed that in high pH, LMB did not release the SRP precipitated. In contrast, AMZ and Al desorbed around 39%, and 71% of the SRP adsorbed when pH changed from 7 to 10. Abiotic factors such as pH should be considered when selecting the most promising material in lake restoration.

Highly Stable and Nontoxic Lanthanum-Treated Activated Palygorskite for the Removal of Lake Water Phosphorus

Nutrient pollution of surface water, such as excess phosphate loading on lake surface water, is a significant issue that causes ecological and financial damage. Despite many technologies that can remove available phosphate, such as material-based adsorption of those available phosphate ions, the development of a material that can trap them from the surface water is worth doing, considering other aspects. These aspects are: (i) efficient adsorption by the material while it settles down to the water column, and (ii) the material itself is not toxic to the lake natural microorganism. Considering these aspects, we developed a trace lanthanum-grafted surface-modified palygorskite, a fibrous clay mineral. It adsorbed a realistic amount of phosphate from the lake water (typically 0.13–0.22 mg/L). The raw and modified palygorskite (Pal) includes unmodified Australian Pal, heated (at ~400 °C) Pal, and acid (with 3 M HCl)-treated Pal. Among them, while acid-treated Pal grafted a lower amount of La, it had a higher adsorption capacity (1.243 mg/g) and a quicker adsorption capacity in the time it took to travel to the bottom of the lake (97.6% in 2 h travel time), indicating the adsorption role of both La and clay mineral. The toxicity of these materials was recorded null, and in some period of the incubation of the lake microorganism with the material mixture, La-grafted modified clays increased microbial growth. As a total package, while a high amount of La on the already available material could adsorb a greater amount of phosphate, in this study a trace amount of La on modified clays showed adsorption effectiveness for the realistic amount of phosphate in lake water without posing added toxicity.

Cyanobacterial Harmful Algal Blooms in Aquatic Ecosystems: A Comprehensive Outlook on Current and Emerging Mitigation and Control Approaches

An intensification of toxic cyanobacteria blooms has occurred over the last three decades, severely affecting coastal and lake water quality in many parts of the world. Extensive research is being conducted in an attempt to gain a better understanding of the driving forces that alter the ecological balance in water bodies and of the biological role of the secondary metabolites, toxins included, produced by the cyanobacteria. In the long-term, such knowledge may help to develop the needed procedures to restore the phytoplankton community to the pre-toxic blooms era. In the short-term, the mission of the scientific community is to develop novel approaches to mitigate the blooms and thereby restore the ability of affected communities to enjoy coastal and lake waters. Here, we critically review some of the recently proposed, currently leading, and potentially emerging mitigation approaches in-lake novel methodologies and applications relevant to drinking-water treatment.

The efficacy of Phoslock® in reducing internal phosphate loading varies with bottom water oxygenation

Eutrophication in lakes and reservoirs has prompted interest in using sediment capping technology to reduce the sediment contribution to internal nutrient loading. One such sediment capping technology is Phoslock®, a lanthanum-embedded clay, which can bind phosphate at the sediment surface and limit its diffusion into the water column. However, in well-oxygenated lakes, naturally occurring iron can bind phosphate by a similar mechanism. We sought to test the efficacy of Phoslock® in limiting phosphate (PO₄ ^3-) fluxes relative to untreated iron-rich lake sediment under conditions of bottom-water oxia and anoxia through laboratory batch core incubations of intact sediment cores from Jordan Lake, a reservoir in central North Carolina. We found that Phoslock® decreased phosphate fluxes relative to the control under anoxic conditions (7.5 ± 9.5 vs. 236 ± 74 µmol PO₄ ^3-•m^-2•d^-1), but provided no benefit relative to the control when the water column was oxygenated (4.5 ± 4.3 vs. 7.0 ± 11.4 µmol PO₄ ^3-•m^-2•d^-1). We also found that Phoslock® itself can act as a source of NH₄ ⁺ to Jordan Lake waters. Applied at recommended levels to the whole lake, Phoslock® addition would result in a pulse increase in water column NH₄ ⁺ concentrations of approximately 2.6 ± 0.8 μM (an increase of 10 to 275% compared to ambient).

Physiologists turned Geneticists: Identifying transcripts and genes for neuronal function in the Marbled Crayfish, Procambarus virginalis

The number of undergraduate researchers interested in pursuing neurophysiological research exceeds the research laboratory positions and hands-on course experiences available because these types of experiments often require extensive experience or expensive equipment. In contrast, genetic and molecular tools can more easily incorporate undergraduates with less time or training. With the explosion of newly sequenced genomes and transcriptomes, there is a large pool of untapped molecular and genetic information which would greatly inform neurophysiological processes. Classically trained neurophysiologists often struggle to make use of newly available genetic information for themselves and their trainees, despite the clear advantage of combining genetic and physiological techniques. This is particularly prevalent among researchers working with organisms that historically had no or only few genetic tools available. Combining these two fields will expose undergraduates to a greater variety of research approaches, concepts, and hands-on experiences. The goal of this manuscript is to provide an easily understandable and reproducible workflow that can be applied in both lab and classroom settings to identify genes involved in neuronal function. We outline clear learning objectives that can be acquired by following our workflow and assessed by peer-evaluation. Using our workflow, we identify and validate the sequence of two new Gamma Aminobutyric Acid A (GABAA) receptor subunit homologs in the recently published genome and transcriptome of the marbled crayfish, Procambarus virginalis. Altogether, this allows undergraduate students to apply their knowledge of the processes of gene expression to functional neuronal outcomes. It also provides them with opportunities to contribute significantly to physiological research, thereby exposing them to interdisciplinary approaches.

Lanthanum modified bentonite behaviour and efficiency in adsorbing phosphate in saline waters

Lanthanum-modified bentonite (LMB, commercially called Phoslock®) has been widely applied in freshwater systems to manage eutrophication. Little is known, however, about its behaviour and efficiency in binding filterable reactive phosphorus (FRP) in saline environments. We assessed if LMB would adsorb phosphate over a range of salinities (0-32 ppth) comparing the behaviour in seawater salts and equivalent concentrations of NaCl. Lanthanum release from the bentonite matrix was measured and the La species prevailing in saline environments were evaluated through chemical equilibrium modelling. We demonstrated that LMB was able to adsorb FRP in all the salinities tested. Filterable lanthanum (FLa) concentrations were similarly low (<5 μgL^-1) at all seawater salinities but considerably elevated, on occasion >2000 times greater in equivalent NaCl salinities. Mineralogical analysis indicates that La present in the clay interlayer was (partially) replaced by Na/Ca/Mg present in the seawater and a possible secondary P-reactive phase was formed, such as kozoite (LaCO₃OH) or lanthanite (La₂(CO₃)₃·8H₂O) that may be physically dissociated from the LMB. Geochemical modelling also indicates that most FLa dissociated from LMB would be precipitated as a carbonate complex. In light of the identification of reactive intermediate phases, further studies including ecotoxicologial assays are required to assess any deleterious effects from the application of LMB to saline waters.

Potential Hazard of Lanthanides and Lanthanide-Based Nanoparticles to Aquatic Ecosystems: Data Gaps, Challenges and Future Research Needs Derived from Bibliometric Analysis

Lanthanides (Ln), applied mostly in the form of nanoparticles (NPs), are critical to emerging high-tech and green energy industries due to their distinct physicochemical properties. The resulting anthropogenic input of Ln and Ln-based NPs into aquatic environment might create a problem of emerging contaminants. Thus, information on the biological effects of Ln and Ln-based NPs is urgently needed for relevant environmental risk assessment. In this mini-review, we made a bibliometric survey on existing scientific literature with the main aim of identifying the most important data gaps on Ln and Ln-based nanoparticles' toxicity to aquatic biota. We report that the most studied Ln for ecotoxicity are Ce and Ln, whereas practically no information was found for Nd, Tb, Tm, and Yb. We also discuss the challenges of the research on Ln ecotoxicity, such as relevance of nominal versus bioavailable concentrations of Ln, and point out future research needs (long-term toxicity to aquatic biota and toxic effects of Ln to bottom-dwelling species).

Removal efficiency of phosphorus, cyanobacteria and cyanotoxins by the "flock & sink" mitigation technique in semi-arid eutrophic waters

Geoengineering techniques have been used to control phosphorus and cyanobacteria in lakes promising greater and quicker chemical and ecological recovery. Techniques that use coagulants and clays to remove particulates and dissolved phosphorus from the water column have received great. In this study, bench-scale "flock & sink" assays were carried out to evaluate the efficiency of the coagulants aluminium sulphate (SUL), polyaluminium chloride (PAC) and chitosan (CHI), alone and combined with natural bentonite clays (BEN) and lanthanum-modified bentonite (LMB), to remove of phosphorus from a eutrophic reservoir in a semi-arid region of Brazil. In addition, the study seeks to assess the effects on the cyanobacteria density and the intra- and extracellular concentrations of cyanotoxins after the application of these geoengineering materials. The SUL and PAC coagulants effectively reduced the total phosphorus (TP), reactive soluble phosphorus (SRP), turbidity, chlorophyll-a, cyanobacteria density and intracellular microcystin, whereas CHI showed a low removal efficiency. Lanthanum-modified bentonite proved to be more effective than BEN; however, the application of the coagulants only was sufficient to successfully remove phosphorus and cyanobacteria from the water column. In addition, the efficiency of the "flock & sink" technique in cell removal varied among the cyanobacteria species. Small colonial species such as Aphanocapsa delicatissima, Merismopedia glauca and Merismopedia tenuissima were removed regardless of the treatment used, including those with CHI and BEN. As for the filamentous cyanobacteria, Cylindrospermopsis raciborskii, Geitlerinema amphibium, Planktothrix agardhii and Pseudanabaena catenata, removal was achieved only using PAC, SUL and LMB alone or when combined. The intracellular concentrations of saxitoxin and cylindrospermopsin and the extracellular fraction of these cyanotoxins and of microcystin were not influenced by the application of coagulants and clays. This indicates that cell lysis did not occur with the addition of the geoengineering materials. These results demonstrate that the "flock & sink" technique could be used for restoration of eutrophic waters.

A simple method to improve the adsorption properties of drinking water treatment residue by lanthanum modification

The loading of La can substantially enhance the adsorption capability of drinking water treatment residue (DWTR) for better recycling. Normally, the modification was based on incubation of DWTR and La solution at a certain ratio, following by solid-liquid separation and drying processes. This study attempted to simplify La loading procedures by adopting high ratio of DWTR and La solution to eliminate the solid-liquid separation, aiming to promote the potential actual production. According to the results of the short- (2 d) and long-term (30 d) P adsorption tests, the N₂ gas sorption and desorption analysis, the X-ray photoelectron spectroscopy analysis, and the metal fractionation, the substantial enhanced adsorption capability of the modified DWTR was maintained and the La loading mechanisms to DWTR changed little after eliminating solid-liquid separation processes during modification; typically, La loading increased the initial P adsorption rates from 1.00 (raw DWTR) to 6.08 and 6.03 mg g^-1 d^-1 for the modified DWTR with and without the separation processes. Furthermore, the DWTR before and after modification had little unfavorable effect on the survival of snail Bellamya aeruginosa, while eliminating the separation processes tended to reduce the bioavailability of Al, Fe, and La in the modified DWTR. These results demonstrated that solid-liquid separation was not the key step for DWTR modification and that the developed simple modification method was feasible for La loading to DWTR, promoting the beneficial recycling in environmental remediation.

Phosphorus removal by application of natural and semi-natural materials for possible recovery according to assumptions of circular economy and closed circuit of P

In the last few years the idea of circular economy has become essential. Thus, designing methods of nutrients removal should be based on using materials that make it possible to recover those nutrients. Recently, methods applied in wastewater treatment plants cannot provide optimal results; moreover, the application of commercial coagulants like ferric chloride and polyaluminum chloride can cause difficulties in potential recovery of phosphorus from sludge. Sorption materials, both natural and modified, are appearing as successful for wastewater treatment, especially for treatment wetland effluent. To pursue circular economy principles, the capacity of waste materials needs to be tested with regard to nutrients removal. If in addition a possibility to recover them appears, it will be possible to close the circuit. The aim of the investigation, according to HELCOM and EU Water Framework Directive recommendations, was to explore the possibility of ensuring good and stable quality of effluent by the application of natural materials for phosphorous removal with possible minimum energy and material consumption. The objective was to determine the sorption capacity of two selected materials (waste material and chemically modified material) in steady conditions. The research focused also on the time of mixing, a period of sedimentation of absorbent materials, and the influence of used materials on the basic parameters of the solution: pH, temperature, total suspended solids, conductivity, turbidity, and color. M1 was a waste material after thermal treatment of carbonate-siliceous rock in temperature above 700 °C (Rockfos®). Material M2 was lanthanum-modified bentonite, a material of anthropogenic origin. Both selected materials have shown a high ability to reduce phosphates concentration in synthetic wastewater. Sorption capacity of materials M1 and M2 were 45.6 mg/g and 5.6 mg/g, respectively.

Lanthanum-modified drinking water treatment residue for initial rapid and long-term equilibrium phosphorus immobilization to control eutrophication

This study presents an approach for developing inactivating materials to achieve an initial rapid and a long-term equilibrium P immobilization to control eutrophication based on drinking water treatment residue (DWTR), which is a byproduct of potable water production. By taking advantage of the long-term equilibrium P adsorption by DWTR, the La chemical properties, and the previous success of using La-modified bentonite clay (Phoslock^®), we used DWTR as a La carrier with different ratios to develop the specific materials. The La loading mechanisms, the potentially toxic effect of La-modified DWTR on snail Bellamya aeruginosa (within 120 d), and the short- and long-term (within 80 d) P immobilization characteristics of the modified DWTR were investigated to understand the performance of the developed materials. The results showed that La loading into DWTR was based on ligand exchanges and the formation of new particles; DWTR loaded with <5% La had no toxicity against the snail. Most importantly, the loading of 5% La to DWTR substantially enhanced the rapid immobilization capacity of DWTR, achieving an initial rapid and a long-term equilibrium P adsorption in aqueous solutions. This study promotes the beneficial recycling of DWTR and results in a win-win situation for lake restoration.

Assessment of possible solid-phase phosphate sorbents to mitigate eutrophication: Influence of pH and anoxia

Managing eutrophication remains a challenge to water managers. Currently, the manipulation of biogeochemical processes (i.e., geo-engineering) by using phosphorus-adsorptive techniques has been recognized as an appropriate tool to manage the problem. The first step in finding potential mitigating materials is conducting a sequence of upscaling studies that commence with controlled laboratory experiments. Here, the abilities of 10 possible solid-phase-sorbents (SPS) to adsorb P were examined. Four materials adsorbed P, and two of these materials were modified, i.e., a lanthanum-modified-bentonite (LMB) and an aluminum-modified-zeolite (AMZ), and had the highest adsorption capacities of 11.4 and 8.9mgPg^-1, respectively. Two natural materials, a red soil (RS) and a bauxite (BAU), were less efficient with adsorption capacities of 2.9 and 3.4mgPg^-1, respectively. Elemental composition was not related to P adsorption. Since SPS might be affected by pH and redox status, we also tested these materials at pH values of 6, 7, 8 and 9 and under anoxic condition. All tested materials experienced decreased adsorption capacities under anoxic condition, with maximum adsorptions of 5.3mgPg^-1 for LMB, 5.9mgPg^-1 for AMZ, 0.2mgPg^-1 for RS and 0.2mgPg^-1 for BAU. All materials were able to adsorb P across the range of pH values that were tested. The maximum adsorption capacities of LMB and RS were highest at pH6, AMZ was higher at a pH of 9 and BAU at a pH of 8. Thus, pH influenced P adsorption differently. Given the effects of pH and anoxia, other abiotic variables should also be considered. Considering the criteria that classify a useful SPS (i.e., effective, easy to produce, cheap and safe), only the two modified materials that were tested seem to be suitable for upscaling to enclosure studies with anoxic sediments.

Commercial silicate phosphate sequestration and desorption leads to a gradual decline of aquatic systems

Laboratory desorption behaviour, function and elemental composition of commercially marketed silicate minerals used to sequester phosphorus pollution as well as Zeolite, Smectite, and Kaolinite were determined to see whether their use by environmental scientists and water managers in eutrophic waterways has the potential to contribute to longer-term environmental impacts. As expected, lower phosphorus concentrations were observed, following treatment. However, data relating to desorption, environmental fate and bioavailability of phospho-silicate complexes (especially those containing rare earth elements) appear to be underrepresented in product testing and trial publications. Analysis of desorption of phosphate (P) was > 5 μg[P]/L for all three non-commercial samples and 0 > μg[P]/L > 5 for all commercial silicates for a range of concentrations from 0 to 300 μg[P]/L. Based on a review of bioaccumulation data specific to the endangered Cherax tenuimanus (Hairy Marron) and other endemic species, this is significant considering anything > 20 μg[La]/L is potentially lethal to the hairy marron, other crustaceans and even other phyla. Where prokaryotic and eukaryotic effects are underreported, this represents a significant challenge. Especially where product protocols recommend continual reapplication, this is significant because both the forward and reverse reactions are equally important. The users of silicate minerals in water columns should accept the dynamic nature of the process and pay equal attention to both adsorption and desorption because desorption behaviour is an inherent trait. Even if broader desorption experimentation is difficult, expensive and time-consuming, it is a critical consideration nonetheless.

Predator recognition of chemical cues in crayfish: diet and experience influence the ability to detect predation threats

Aquatic prey often alter their morphology, physiology, and/or behaviour when presented with predatory chemical cues which are heavily influenced by the diet of the predator. We tested the roles that diet and prey familiarity with predators play in the ability of prey to recognize predator threats. Odours from two fish, bass and cichlid fed a vegetarian, protein, heterospecific, and a conspecific diet, were collected and presented to virile crayfish in a choice arena. Our results show that crayfish altered their behaviour in the presence of odours containing conspecific, as opposed to heterospecific diets, but only from familiar predators. A reduced anti-predator response was measured with odours from an unfamiliar predator fed conspecific crayfish. Therefore, crayfish may be able to determine different threat levels based on the different dietary cues from a potential predator, but only when the prey have familiarity with the predators.

Bio-accumulation of lanthanum from lanthanum modified bentonite treatments in lake restoration

Lanthanum (La) modified bentonite (LMB) is one of the available mitigating agents used for the reduction of the phosphorus (P) recycling in eutrophic lakes. The potential toxicity of the La from LMB to aquatic organisms is a matter of concern. In this study the accumulation of La was investigated in the macrophyte Elodea nuttallii, in chironomid larvae and in several fish species during periods up to five years following in situ LMB applications. The application of LMB increased the La concentration of exposed plants and animals. During the first growing season following LMB applications, the La content of E. nuttallii increased 78 fold (3.98-310.68 μg La g^-1 DW) to 127 fold (2.46-311.44 μg La g^-1). During the second growing season following application, the La content decreased but was still raised compared to plants that had not been exposed. The La content of chironomids was doubled in the two years following LMB application, although the increase was not significant. Raised La concentrations in fish liver, bone, muscle and skin were observed two and five years following to LMB application. Liver tissues showed the highest La increase, ranging from 6 fold (0.046-0.285 μg La g^-1 DW) to ∼20 fold (0.080-1.886 μg La g^-1, and 0.122-2.109 μg La g^-1) two years following application and from 6 fold (0.046-0.262 μg La g^-1) to 13 fold (0.013-0.167 μg La g^-1) after five years in pelagic and littoral fish. The La content of the liver from Anguilla anguilla (eel) had increased 94 fold (0.034-3.176 μg La g^-1) two years and 133 fold (0.034-4.538 μg La g^-1) five years following LMB application. No acute and chronic effects of La accumulation were observed and human health risks are considered negligible. We advocate the long-term study of effects of La accumulation following future LMB applications.

Effects of combined flocculant - Lanthanum modified bentonite treatment on aquatic macroinvertebrate fauna

A low dose flocculant (FeCl₃), combined with lanthanum modified bentonite (LMB) as phosphate-binding agent, has been applied for eutrophication management in Lake De Kuil (The Netherlands). After the treatment, the state of the lake shifted from hypertrophic to mesotrophic. Although macroinvertebrate fauna is important for lake ecosystems, the knowledge of its response to this lake restoration method is fragmented and scarce. Because insight in the macroinvertebrate fauna response is important to assess future applications, pre and post application macroinvertebrate assemblages were identified in Lake De Kuil. The research was accompanied by a microcosm experiment in which the effects of LMB, FeCl₃ and LMB + FeCl₃ were studied on macroinvertebrate communities. Results show the reduction of macroinvertebrate numbers and taxa during the first month following the application. The number of Gastropoda was strikingly reduced one month after the application. One year after the application, the macroinvertebrate numbers and taxa exceeded the pre-application situation and Gastropoda and Oligochaeta prospered. The effects one month after the treatment are most likely due to the combination of physical impacts of the use of bentonite and chemical impacts of the use of FeCl₃, while effects after one year are likely attributed to the shift in trophic state of the lake.

Management of eutrophication in Lake De Kuil (The Netherlands) using combined flocculant - Lanthanum modified bentonite treatment

Eutrophication of Lake De Kuil (The Netherlands, 6.7 ha, maximum depth 9 m) has frequently caused cyanobacterial blooms resulting in swimming bans or the issue of water quality warnings during summer. The eutrophication was mainly driven by sediment phosphorus (P)-release. The external P-loading was in the range of the critical loading for phytoplankton blooms. Hence, the reduction of the internal P-loading provided a promising way to reduce cyanobacterial blooms. To mitigate the cyanobacterial blooms, the combination of a low dose flocculant (iron(III)chloride; Flock) and a solid phase phosphate fixative (lanthanum modified bentonite; Lock) was applied in May 2009. This combined approach both removed cyanobacterial biomass from the water column and also intercepted P released from the bottom sediments. Immediately after treatment, the Secchi depth increased from 1.5 m up to 5 m. Sediment P-release decreased from 5.2 mg P m(-2) d(-1) (2009) to 0.4 mg P m(-2) d(-1) (2010) but increased in later years. Mean summer concentrations of total P decreased from 0.05 mg L(-1) (1992-2008) to 0.02 mg L(-1) (2009-2014) and chlorophyll-a from 16 μg L(-1) (1992-2008) to 6 μg L(-1) (2009-2014). Mean summer Secchi depth increased from 2.31 m (1992-2008) to 3.12 m (2009-2014). The coverage of macrophytes tripled from 2009 to 2011. In the winter of 2010/2011 Planktothrix rubescens bloomed, but cyanobacterial biomass decreased during the summers after the Flock and Lock treatment in comparison to prior years. After the Flock & Lock the bathing water requirements have been fulfilled for six consecutive summers. As the sediment P-release has gradually increased in recent years, there is a risk of a reversion from the present mesotrophic state to a eutrophic state.

Eutrophication management in surface waters using lanthanum modified bentonite: A review

This paper reviews the scientific knowledge on the use of a lanthanum modified bentonite (LMB) to manage eutrophication in surface water. The LMB has been applied in around 200 environments worldwide and it has undergone extensive testing at laboratory, mesocosm, and whole lake scales. The available data underline a high efficiency for phosphorus binding. This efficiency can be limited by the presence of humic substances and competing oxyanions. Lanthanum concentrations detected during a LMB application are generally below acute toxicological threshold of different organisms, except in low alkalinity waters. To date there are no indications for long-term negative effects on LMB treated ecosystems, but issues related to La accumulation, increase of suspended solids and drastic resources depletion still need to be explored, in particular for sediment dwelling organisms. Application of LMB in saline waters need a careful risk evaluation due to potential lanthanum release.

Responses in sediment phosphorus and lanthanum concentrations and composition across 10 lakes following applications of lanthanum modified bentonite

A combined field and laboratory scale study of 10 European lakes treated between 2006 and 2013 with a lanthanum (La) modified bentonite (LMB) to control sediment phosphorus (P) release was conducted. The study followed the responses in sediment characteristics including La and P fractions and binding forms, P adsorption capacity of discrete sediment layers, and pore water P concentrations. Lanthanum phosphate mineral phases were confirmed by solid state (31)P MAS NMR and LIII EXAFS spectroscopy. Rhabdophane (LaPO4 · nH2O) was the major phase although indications of monazite (LaPO4) formation were also reported, in the earliest treated lake. Molar ratios between La and P in the sediments were generally above 1, demonstrating excess La relative to P. Lanthanum was vertically mixed in the sediment down to a depth of 10 cm for eight of the ten lakes, and recovery of La in excess of 100% of the theoretical aerial load indicated translocation of the LMB towards the deepest areas of the lakes. Lanthanum was generally recovered from bed sediment samples following sequential chemical extraction from the HCl fraction. Soluble reactive P (SRP) release experiments on intact sediment cores indicated conditions of P retention (with the exception of two lakes) by sediments, indicating effective control of sediment P release, i.e. between two and nine years after treatment.