Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

IMPLICATION OF PESTICIDES USAGE ON FRESHWATER FISH: A REVIEW

Pesticides play a significant role in improving food production through control against harmful pests with low labour and efforts while on the other hand are regarded as aquatic pollutants. These toxicants persist in aquatic environment and cause harmful effects to non- target organisms including fish. The development of pesticide tolerant species led to the need and use of varieties of pesticides with the risk of exposure to many compartments including water. Many pesticides have been proscribed for agricultural purposes by the regulatory agencies such as WHO (2020). However, It is unfortunate that many of these are sold in Nigeria or donated by donor agencies. The donated pesticides often become “obsolete” while in stock due to poor logistics and delays in receiving them at the point of need. The review on the classification, bioavailability, biotransformation, the direct and indirect effects of pesticides on freshwater fish was carried out. Biomarkers of pesticides toxicity that induce alterations in fish physiology were discussed; these include: behavioral changes such as erratic swimming, hyperactivity among other alterations. Other alterations include feeding behaviour, fluctuation in antioxidant enzyme activities, histology, haematology, growth performance and DNA damage.

Salinity Alters Toxicity of Commonly Used Pesticides in a Model Euryhaline Fish Species (Menidia beryllina)

Changing salinity in estuaries due to sea level rise and altered rainfall patterns, as a result of climate change, has the potential to influence the interactions of aquatic pollutants as well as to alter their toxicity. From a chemical property point of view, ionic concentration can increase the octanol–water partition coefficient and thus decrease the water solubility of a compound. Biologically, organism physiology and enzyme metabolism are also altered at different salinities with implications for drug metabolism and toxic effects. This highlights the need to understand the influence of salinity on pesticide toxicity when assessing risk to estuarine and marine fishes, particularly considering that climate change is predicted to alter salinity regimes globally and many risk assessments and regulatory decisions are made using freshwater studies. Therefore, we exposed the Inland Silverside (Menidia beryllina) at an early life stage to seven commonly used pesticides at two salinities relevant to estuarine waters (5 PSU and 15 PSU). Triadimefon was the only compound to show a statistically significant increase in toxicity at the 15 PSU LC50. However, all compounds showed a decrease in LC50 values at the higher salinity, and all but one showed a decrease in the LC10 value. Many organisms rely on estuaries as nurseries and increased toxicity at higher salinities may mean that organisms in critical life stages of development are at risk of experiencing adverse, toxic effects. The differences in toxicity demonstrated here have important implications for organisms living within estuarine and marine ecosystems in the Anthropocene as climate change alters estuarine salinity regimes globally.

Behavioural Responses and Mortality of Clarias gariepinus Juveniles Exposed to Acute Concentrations of Paraquat

Paraquat is the most common contact and non- selective herbicide for exterminating vegetative pest. Fish are ideal sentinels for detecting aquatic pollutants and are largely used as bio indicators of environmental pollution. This study is aimed to determine the behavioural changes, lethal concentrations (LCs) and mean lethal time (MLT) of paraquat exposed to Clarias gariepinus. A 96 hours renewable bioassay was conducted with various paraquat concentrations 0.0, 0.25, 0.50, 0.75, 1.0 and 1.25 mg/l. Behavioural changes and cumulative mortality were observed and recorded at 12, 24, 48, 72 and 96 hour. Behavioural changes such as air gulping, erratic swimming, loss of balance, excessive mucus secretion, discolouration and death were observed with severity increasing as concentration and duration of exposure increases. The LC50 values were decreased from 0.191mg/l (0.171 – 0.222) in 12 hour to 0.107mg/l (0.065 – 0.150) in 96 hour, while relative toxicity factor (TF) was increased from 1 to 1.79 times respectively. The 96hr MLT values were decreased from 91.18 hours (54.09-105.64) at the lowest concentration to 16.22 hours (9.06 – 25.15) at the highest concentration with relative toxicity time (RTT) increasing from 1 to 5.62 times. Herbicide should be apply with caution and studies on the sub lethal effects of paraquat on the haematological, biochemical and histological parameters of C. gariepinus juveniles will be necessary.

A comparative study of the degradation efficiency of chlorinated organic compounds by bimetallic zero-valent iron nanoparticles

The efficacy of zero-valent iron nanoparticles (nZVI) in degrading aquatic pollutants could be enhanced by the deposition of other metals on their surface. This article describes the synthesis of bimetallic...

A practical guide to unbiased quantitative morphological analyses of the gills of rainbow trout (Oncorhynchus mykiss) in ecotoxicological studies

Rainbow trout (Oncorhynchus mykiss) are frequently used as experimental animals in ecotoxicological studies, in which they are experimentally exposed to defined concentrations of test substances, such as heavy metals, pesticides, or pharmaceuticals. Following exposure to a broad variety of aquatic pollutants, early morphologically detectable toxic effects often manifest in alterations of the gills. Suitable methods for an accurate and unbiased quantitative characterization of the type and the extent of morphological gill alterations are therefore essential prerequisites for recognition, objective evaluation and comparison of the severity of gill lesions. The aim of the present guidelines is to provide practicable, standardized and detailed protocols for the application of unbiased quantitative stereological analyses of relevant morphological parameters of the gills of rainbow trout. These gill parameters inter alia include the total volume of the primary and secondary gill lamellae, the surface area of the secondary gill lamellae epithelium (i.e., the respiratory surface) and the thickness of the diffusion barrier. The featured protocols are adapted to fish of frequently used body size classes (300–2000 g). They include well-established, conventional sampling methods, probes and test systems for unbiased quantitative stereological analyses of light- and electron microscopic 2-D gill sections, as well as the application of modern 3-D light sheet fluorescence microscopy (LSFM) of optically cleared gill samples as an innovative, fast and efficient quantitative morphological analysis approach. The methods shown here provide a basis for standardized and representative state-of-the-art quantitative morphological analyses of trout gills, ensuring the unbiasedness and reproducibility, as well as the intra- and inter-study comparability of analyses results. Their broad implementation will therefore significantly contribute to the reliable identification of no observed effect concentration (NOEC) limits in ecotoxicological studies and, moreover, to limit the number of experimental animals by reduction of unnecessary repetition of experiments.

DETERMINING THE EFFECTS OF POLLUTANTS ON SOME TYPES OF MICRO ALGAE AND MYTILUS GALLOPROVINCIALIS (LAMARCK, 1819)

This study was conducted to determine the effects of aquatic pollutants on aquatic organisms. Izmit Bay, which is polluted both domestically and industrially, was chosen as the study area. Densely populated areas and industry are located around the Izmıt Bay. For this purpose, mussel and micro algae samples were taken from selected stations. In the study, salinity value was measured in the range of 22% - 28%. Water temperature, pH and conductivity varied from 9.20 – 25.01 ℃, 6.81 - 8.3, 30.42 - 45.11 µS/cm, dissolved oxygen values as minimum and maximum 4.62 – 12.61 mg l−1 were determined respectively. In heavy metal analyses Al, Mn, Zn, Cu, Pb, Cr, Ni, Cd and Fe) of seawater were determined in the study. As a result of the study, the highest heavy metal ratio in Mytilus galloprovincialis was determined to be iron. In the study, Oscilatoria sp., Ulnaria sp. and Nitzschia sp. taxa were determined as dominant. These species have high tolerance to aquatic pollution parameters.