Measuring in-stream retention of copper by means of constant-rate additions

The Biosorption of Copper(II) Using a Natural Biofilm Formed on the Stones from the Metro River, Malang City, Indonesia

Biofilm is the predominant habitat of microbes in aquatic ecosystems. Microhabitat inside the biofilm matrix is a nutrient-rich environment promoted by the adsorption of nutrient ions from the surrounding water. Biofilms can not only adsorb ions that are nutrients but also other ions, such as heavy metals. The ability of biofilm to attract and retain heavy metals, such as copper(II), makes biofilms a promising biosorbent for water pollution treatment. The present study analyzes the characteristics of copper(II) adsorption by biofilms naturally formed in the river. The biofilms used in this study grow naturally on the stones in the Metro River in Malang City, Indonesia. Methods to analyze the adsorption characteristics of copper(II) by biofilms were kinetics of the adsorption and adsorption isotherm. The maximum adsorption amount and the adsorption equilibrium constant were calculated using a variant of the Langmuir isotherm model. In addition, the presence of the functional groups as suggested binding sites in biofilm polymers was investigated using the Fourier transform infrared (FTIR) analysis. The results indicate that copper(II)’s adsorption to the biofilm is a physicochemical process. The adsorption of copper(II) is fitted well with the Langmuir isotherm model, suggesting that the adsorption of copper(II) to a biofilm is due to the interaction between the adsorption sites on the biofilm and the ions. The biofilm’s maximum absorption capacity for copper(II) is calculated to be 2.14 mg/wet-g of biofilm, with the equilibrium rate constant at 0.05 L/mg. Therefore, the biofilms on the stones from river can be a promising biosorbent of copper(II) pollution in aquatic ecosystems.

The role of microplastics biofilm in accumulation of trace metals in aquatic environments

Microplastics are one of the major contaminants of aquatic nature where they can interact with organic and inorganic pollutants, including trace metals, and adsorb them. At the same time, after the microplastics have entered the aquatic environments, they are quickly covered with a biofilm - microorganisms which are able to produce extracellular polymeric substances (EPS) that can facilitate sorption of trace metals from surrounding water. The microbial community of biofilm contains bacteria which synthesizes EPS with antimicrobial activity making them more competitive than other microbial inhabitants. The trace metal trapping by bacterial EPS can inhibit the development of certain microorganisms, therefore, a single microparticle participates in complex interactions of the diverse elements surrounding it. The presented review aims to consider the variety of interactions associated with the adsorption of trace metal ions on the surface of microplastics covered with biofilm, the fate of such microplastics and the ever-increasing risk to the environment caused by the combination of these large-scale pollutants - microplastics and trace metals. Since aquatic pollution problems affect the entire planet, strict regulation of the production, use, and disposal of plastic materials is needed to mitigate the effects of this emerging pollutant and its complexes could have on the environment and human health.

Translocation of Epipelic Biofilms and Their Short-Term Responses to Urbanization Impacts in Nutrient Rich Streams

Stream biofilms are among the first to react to environmental degradation, since their structural and functional characteristics are tightly linked to the physicochemical variables in the water and sediment. The objectives of this research were to study the differences in chlorophyll-a, bacterial density and metabolism endpoints of epipelic biofilms in nutrient-rich streams under different physical-chemical conditions in the stream water in relation to changes in urbanization, and to measure the short-term responses (up to 72 h) in the biofilm when translocated to more urbanized sites. For these purposes, chlorophyll-a, bacterial density, biofilm respiration (electron transfer activity) and O2 consumption were measured in epipelic biofilms in nutrient-rich streams exposed to different levels of urbanization after a 30 day colonization. Afterward, biofilms were translocated downstream to more polluted sites, and sampled to identify any fast occurring changes to be considered as potential indicators of environmental degradation. Results show that in the nutrient-rich streams studied, the structural characteristics of the biofilm were linked to urbanization, and even after a short time following the translocation, chlorophyll-a and bacterial density varied, reflecting the environmental degradation. On the other hand, metabolic variables were highly variable and produced inconsistent results when representing an increase in urbanization.

Arsenic Transfer from As-Rich Sediments to River Water in the Presence of Biofilms

The influence of epipsammic biofilms on As release from river sediments was evaluated in a microcosm experiment where biofilms were grown on sediments containing 106 mg kg−1As, collected in the Anllóns River, and compared with control systems without biofilms. The As transfer to the water column was low (<0.11% of total As in the sediment) and was further reduced by 64% in the presence of biofilms.AsVwas the predominant species in the overlying water in both systems.AsIIIconcentration was higher (up to 12% of total dissolved As) in the control systems than in the systems with biofilms, where this species was almost absent. This fact is of toxicological relevance due to the usually higher mobility and toxicity of the reducedAsIIIspecies. Control systems exhibited higher As mobility in water, in sulphate solution, and in weak acid medium and higher bioavailability in diffusive gradient in thin films (DGT) devices. Arsenic retained by the biofilm was equally distributed between extracellular and intracellular compartments. Inside the cells, significant concentrations ofAsIII, monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) were detected, suggesting that active methylation (detoxification) processes are occurring in the intracellular compartment.

Experimental evaluation of the contribution of acidic pH and Fe concentration to the structure, function and tolerance to metals (Cu and Zn) exposure in fluvial biofilms

An indoor channel system was colonised with fluvial biofilms to study the chronic effects of high Fe and SO4(2-) concentrations and acidic pH, the water chemistry in the surrounding streams of Aljustrel mining area (Alentejo, Portugal), and their contribution to community (in)tolerance to metal toxicity by short-term experiments with Cu and Zn. Biofilms were subjected to four different treatments during 8 weeks: high Fe and SO4(2-) concentrations (1 mg Fe l(-1)+ 700 mg SO4(2-) l(-1)) and acidic pH, high Fe and SO4(2-) at alkaline pH; lower Fe and SO4(2-) at acidic pH: and lower Fe and SO4(2-) concentrations at alkaline pH as negative control. During chronic exposure, acidic pH affected growth negatively, based on low values of algal biomass and the autotrophic index, high values of the antioxidant enzyme activities and low diversity diatom communities, dominated by acidophilic species (Pinnularia aljustrelica) in acidic treatments, being the effects more marked with high Fe and SO4(2-). Co-tolerance to metals (Cu and Zn) was also shown in biofilms from the acidic treatments, contrasting with the higher sensitivity observed in the alkaline treatments. We can conclude that the Aljustrel mining area acidic environment limits algal growth and exerts a strong selection pressure on the community composition which is in turn, more tolerant to metal exposure.

The use of antioxidant enzymes in freshwater biofilms: temporal variability vs. toxicological responses

This study aims to investigate the potential of antioxidant enzyme activities (AEA) as biomarkers of oxidative stress in freshwater biofilms. Therefore, biofilms were grown in channels for 38 days and then exposed to different concentrations (0-150 μg L(-1)) of the herbicide oxyfluorfen for 5 more weeks. Under control conditions, the AEA of biofilms were found to change throughout time with a significant increase in ascorbate peroxidase (APX) activity during the exponential growth and a more important role of catalase (CAT) and glutathione reductase (GR) activities during the slow growth phase. Chronic exposure to oxyfluorfen led to slight variations in AEA, however, the ranges of variability of AEA in controls and exposed communities were similar, highlighting the difficulty of a direct interpretation of AEA values. After 5 weeks of exposure to oxyfluorfen, no clear effects were observed on chl-a concentration or on the composition of other pigments suggesting that algal group composition was not affected. Eukaryotic communities were structured clearly by toxicant concentration and both eukaryotic and bacterial richness were reduced in communities exposed to the highest concentration. In addition, during acute exposure tests performed at the end of the chronic exposure, biofilms chronically exposed to 75 and 150 μg L(-1) oxyfluorfen showed a higher CAT activity than controls. Chronic exposure to oxyfluorfen provoked then structural changes but also functional changes in the capacity of biofilm CAT activity to respond to a sudden increase in concentration, suggesting a selection of species with higher antioxidant capacity. This study highlighted the difficulty of interpretation of AEA values due to their temporal variation and to the absence of absolute threshold value indicative of oxidative stress induced by contaminants. Nevertheless, the determination of AEA pattern throughout acute exposure test is of high interest to compare oxidative stress levels undergone by different biofilm communities and thus determine their antioxidant capacity.

Light history modulates antioxidant and photosynthetic responses of biofilms to both natural (light) and chemical (herbicides) stressors

In multiple stress situations, the co-occurrence of environmental and chemical factors can influence organisms' ability to cope with toxicity. In this context, the influence of light adaptation on the response of freshwater biofilms to sudden light changes or to herbicides exposure was investigated by determining various parameters: diatom community composition, photosynthetic parameters, chlorophyll a content, antioxidant enzyme activities. Biofilms were grown in microcosms under sub-optimal, saturating, and high light intensities and showed already described characteristics of shade/light adaptation (community structure, photosynthetic adaptation, etc.). Light history modulated antioxidant and photosynthetic responses of biofilms to the stress caused by short-term exposure to sudden light changes or to herbicides. First biofilms adapted to sub-optimal light intensity (shade-adapted) were found to be more sensitive to an increase in light intensity than high-light adapted ones to a reduction in light intensity. Second, while light history influenced biofilms' response to glyphosate, it had little influence on biofilms' response to copper and none on its response to oxyfluorfen. Indeed glyphosate exposure led to a stronger decrease in photosynthetic efficiency of shade-adapted biofilms (EC(50) = 11.7 mg L(-1)) than of high-light adapted communities (EC(50) = 35.6 mg L(-1)). Copper exposure led to an activation of ascorbate peroxidase (APX) in biofilms adapted to sub-optimal and saturating light intensity while the protein content decreased in all biofilms exposed to copper. Oxyfluorfen toxicity was independent of light history provoking an increase in APX activity. In conclusion this study showed that both previous exposure to contaminants and physical habitat characteristics might influence community tolerance to disturbances strongly.

Fluvial biofilms: A pertinent tool to assess beta-blockers toxicity

Among increasingly used pharmaceutical products, beta-blockers have been commonly reported at low concentrations in rivers and littoral waters of Europe and North America. Little is known about the toxicity of these chemicals in freshwater ecosystems while their presence may lead to chronic pollution. Hence, in this study the acute toxicity of 3 beta-blockers: metoprolol, propranolol and atenolol on fluvial biofilms was assessed by using several biomarkers. Some were indicative of potential alterations in biofilm algae (photosynthetic efficiency), and others in biofilm bacteria (peptidase activity, bacterial mortality). Propranolol was the most toxic beta-blocker, mostly affecting the algal photosynthetic process. The exposure to 531microg/L of propranolol caused 85% of inhibition of photosynthesis after 24h. Metoprolol was particularly toxic for bacteria. Though estimated No-Effect Concentrations (NEC) were similar to environmental concentrations, higher concentrations of the toxic (503microg/L metoprolol) caused an increase of 50% in bacterial mortality. Atenolol was the least toxic of the three tested beta-blockers. Effects superior to 50% were only observed at very high concentration (707mg/L). Higher toxicity of metoprolol and propranolol might be due to better absorption within biofilms of these two chemicals. Since beta-blockers are mainly found in mixtures in rivers, their differential toxicity could have potential relevant consequences on the interactions between algae and bacteria within river biofilms.

Effects of chronic copper exposure on fluvial systems: linking structural and physiological changes of fluvial biofilms with the in-stream copper retention

Long-term metal exposure is known to be responsible for a large variety of structural and functional changes in periphyton communities which allow these communities to adapt to metal-polluted conditions. This study aimed to link the changes that chronic copper (Cu) exposure causes on the structure and physiology of fluvial biofilms with the efficiency of the river systems in retaining phosphate and Cu. The effects of a chronic Cu exposure on the structure, physiology and induction of Cu tolerance of the community were evaluated by comparing this community with a non-exposed one. Results showed that periphyton chronically exposed to Cu had lower algal biomass, higher proportion of green algae, lower proportion of brown algae, and higher EPS content per unit of biomass than the un-exposed community. In addition, the chronically-exposed community showed a Cu content (both total and intracellular Cu content) ten times higher than the un-exposed community. While in-stream phosphate retention was not markedly influenced by chronic Cu exposure; Cu retention was clearly reduced, as was shown by a reduction in Cu retention efficiency (Cu-S(w)) and demand (Cu-Vf). The chronically-exposed periphyton, in spite of having high intracellular Cu concentration, showed similar photosynthetic efficiency than the un-exposed community and showed a higher Cu tolerance. It indicated that this community was acclimatized to Cu exposure and that this acclimatization was probably linked to the ability to detoxify and immobilize metals. These observations suggest that the fate of Cu in fluvial ecosystems will be influenced by the exposure history of the system. The results from this study indicate that metals will travel longer distances in metal-polluted streams compared to pristine systems having effects on water quality farther downstream.