Macrophytes are creatures with low versatility and cannot stay away from any mix of streamflow, nutrient accessibility, and other physical and chemical attributes that impact their survival in the aquatic system. Sampling for macrophytes in Chanchaga River was conducted monthly for a 6-month period (May - October 2019). Sampling stations were selected at approximately equal distance along the streamline, the aquatic vegetation were surveyed, and some environmental variables were analysed using standard methods. Results obtained indicated that temperature ranged from 24.6-28.4°C; pH 6.4 -9.7; Electrical conductivity 28.0-79.0μS cm-1; Total dissolved solids 16-75 mg L-1; Dissolved oxygen(DO) 1.3-5.2 mg L-1; Nitrate 0.217-0.654 mg L-1; Phosphate 0.084-0.211 mg L-1; Biological oxygen demand (BOD) 0.89-5.4 mg L-1 and total alkalinity 8.00-11.00 mgL-1 for the study period. A total of eleven (11) macrophyte species belonging to ten genera and eight families were identified during the entire study. Variations in terms of families showed that Araliaceae was the most abundant followed by Poaceae, while Cyperaceae had more species throughout the study period. The high frequency of Araliaceae, Cyperaceae, and Poaceae families suggests that the environmental characteristics favour these species. We propose the use of Cyperus digitatus, Cyperus papyrus and Mimosa spp. as macrophytes indicators of organic pollution in Chanchaga River.

The Pearl River Estuary (PRE), the largest estuary in Southern China, historically has suffered from metal contamination as a result of inputs from different riverine discharges. Determining the sources of metals accumulation in local aquatic flora and fauna remains a great challenge for this estuarine system with complex water circulation. In this study, Zn isotope ratios were measured in local oysters (Crassostrea hongkongensis) collected at 8 locations in the estuary on four occasions from 2014 to 2018, to better understand and assess the contamination sources. The results showed no significant differences (p < 0.05) in δ⁶⁶Zn values in oysters among the four sampling dates within individual sites. However, approximately a 0.67‰ (range from -0.66‰ to 0.01‰) difference in average δ⁶⁶Zn values was consistently found in oysters collected from the east side of the estuary compared to the west side, despite their comparable Zn concentrations. A mixing model was subsequently used to estimate the relative contributions from various sources to the δ⁶⁶Zn values in these oysters. The mixing model predicts that zinc derived from the dissolved fraction (approximately 80 %) was the dominant uptake pathway for oysters collected at the east shore whereas approximately 50 % of the Zn in oysters collected at the west shore was derived from the particulate fraction. The mixing model also was used to estimate the relative impacts of fresh versus saline water on the measured δ⁶⁶Zn values. Contributions from these two sources also varied between the east and west shores. This study presents the first data for Zn isotope ratios in oysters from the PRE, providing new insight for using Zn isotope ratios in oysters as a powerful tracer of sources in a complex estuarine system.

Aquatic plant biomass like Iris pseudacorus can be used as electron donor to improve denitrification performance in subsurface constructed wetlands. However, the phenomenon that the nitrogen removal rate declined in the terminal stage restricted the utilization of litters. In terms of this problem, this study investigated the performance of the used biomass through alkali treatment on nitrogen removal and analyzed the effect of alkali treatment on the component and structure of biomass and microbial community. The results showed that the alkali-treated biomass could further enhance the nitrogen removal by nearly 15% compared with used ones. The significant damage of cell walls and compact fibers containing cellulose and lignin through alkali treatment mainly resulted in the improvement of carbon release and nitrogen removal. With the addition of alkali-treated biomass, the richness index of microbes was higher compared with other biomass materials. Furthermore, the abundance of denitrification related genera increased and the abundance of genera for nitrification was maintained. Based on these finds, a mode of a more efficient Iris pseudacorus self-consumed subsurface flow constructed wetlands was designed. In this mode, the effluent total nitrogen could be stabilized below 5 mg L⁻¹ for nine months and the weight of litters could be further cut down by 75%. These findings would contribute to efficient utilization of plant biomass for nitrogen removal enhancement and final residue reduction in the wetlands.

140 contaminants belonging to various classes (organochlorine and organophosphorus pesticides, pyrethroid insecticides, carbamates, fungicides, acaricides, herbicides, synergists, insect growth regulators, polychlorobiphenyls, polycyclic aromatic hydrocarbons) were simultaneously analysed by GC-MS/MS in marine sediments, aquatic plant leaves and fish tissues samples. A total of 260 samples from five stations along the coast of Tunisia were evaluated. The results highlight that only 28 residues (12 polychlorobiphenyls, 8 organochlorine pesticides, 7 polycyclic aromatic hydrocarbons and triphenyl phosphate) were detected at levels higher than relative LOQ values. The amounts in sediment samples were compared with Sediment Quality Guidelines (SQGs) showing that the values are acceptable and no toxic effect is expected on aquatic organisms. A little variation of contaminant residues in sediment samples among coastal stations was recorded. Namely, with respect to almost all polychlorobiphenyls and organochlorine pesticides, higher values were recorder in summer. With respect to almost all polycyclic aromatic hydrocarbons, higher values were recorder in autumn. Aquatic plant leaves showed a residue accumulation higher than that of other compartments of marine system. The data about fish samples (Sparus aurata and Sarpa salpa, the two most frequently caught fish species at five sites on the central coast of Tunisia) do not pose direct hazard to human health because values were lower than protection limits.

Plastic pollution is the biggest threat to marine ecosystem owing to its high rates of disposal and low recovery from the environment. Due to inefficiency in degradation, most of plastic is fragmented into microplastics that are reported as ubiquitous toxicants in marine environment. The abundance of toxic microplastics in marine ecosystem causes adverse impacts on aquatic flora and fauna including oceans, lakes, rivers, coastal areas, and seas. This aggravates its toxicity and induces genomic instability, oxidative stress and disruption of marine organisms. Hence, it is necessary to understand the potential sources, types and behaviour of microplastic in marine environment. In this review, considering the pollution of aquatic ecosystem, major contributors of microplastics in marine environment along with their classification are brought out. Also, behaviour mechanisms of microplastics including physical, chemical and biological behaviours together with their ecological and toxicological impacts on marine ecosystem are illustrated. Finally, the remediation measures to combat against toxic microplastic pollution in aquatic ecosystem are highlighted to bring out an instant remedy for the environment.

This paper reviews the current state-of-the-art, limitations, critical issues, and new directions in freshwater plant ecotoxicology. We selected peer-reviewed studies using relevant databases and for each (1) publication year, (2) test plant species, (3) reference plant group (microalgae, macroalgae, bryophytes, pteridophytes, flowering plants), (4) toxicant tested (heavy metal, pharmaceutical product, hydrocarbon, pesticide, surfactant, plastic), (5) experiment site (laboratory, field), and (6) toxicant exposure duration. Although aquatic plant organisms play a key role in the functioning of freshwater ecosystems, mainly linked to their primary productivity, their use as biological models in ecotoxicological tests was limited if compared to animals. Also, toxicant effects on freshwater plants were scarcely investigated and limited to studies on microalgae (80%), or only to a certain number of recurrent species (Pseudokirchneriella subcapitata, Chlorella vulgaris, Lemna minor, Myriophyllum spicatum). The most widely tested toxicants on plants were heavy metals (74%), followed by pharmaceutical products and hydrocarbons (7%), while the most commonly utilized endpoints in tests were plant growth inhibition, variations in dry or fresh weight, morpho-structural alterations, chlorosis, and/or necrosis. The main critical issues emerged from plant-based ecotoxicological tests were the narrow range of species and endpoints considered, the lack of environmental relevance, the excessively short exposure times, and the culture media potentially reacting with toxicants. Proposals to overcome these issues are discussed.

The use of silver nanoparticles (AgNPs) in commercial products has increased due to their antibacterial properties and their impacts on the environment must be investigated. This scenario has motivated the conduction of this study, which relates different factors that affect the toxicity of AgNPs to the aquatic plant Lemna minor such as size, accumulation, concentration, and dissolution of AgNPs. To this end, synthesized AgNPs measuring 30, 85, and 110 nm were added into the culture medium to observe toxicity for 30 days. The mapping by SEM showed that the smallest AgNPs can translocate from roots to leaves due to its mobility and internalization. As predicted by the Ostwald equation, the solubility for 30-nm AgNPs increased almost 3 times at the end of 30 days, while for 85 and 110 nm size nanoparticles, after 7 days, the solubility decreased due to “Ostwald ripening” process. Plant mortality was assessed and, after 1 month, the size of 30 nm was the most toxic with negative growth in all studied concentrations, with 60% mortality in the worst case. The concentration of 50 μg mL⁻¹ was toxic in all sizes with negative growth in the period. Therefore, the investigation of AgNPs’ toxicity needs to consider a different factor to better understand their effects on aquatic plants and the environment.

Parboiling rice mills produce a large amount of wastewater. The effluent from the rice mill contains high concentration of organic and inorganic compounds. Continuous discharge of this wastewater from rice mills could be a major cause of eutrophication of the water bodies, leading to a robust and undesirable growth of vegetation and algal bloom. Eutrophication leads to deoxygenation of water bodies, resulting in the mortality of aquatic flora and fauna. It is therefore very important to treat wastewater and ensure safe disposal. There are various types of processes already in existence, but the most important thing is to select a cost-effective technique. Phytoremediation technique has shown promising results for low-income countries like India. It is useful for the small-scale industrial and domestic wastewater treatment. It is a slow process, requiring a large area of land. It is an eco-friendly approach and ideal for rural areas where there is ample land availability. This paper addresses the techniques used by various researchers for rice mill wastewater treatment and also focuses on reusing and recycling of waste from rice mills. The performance of every technique is discussed in detail with its specific advantages and disadvantages. This paper also focuses on the advanced techniques of water treatment with valuable by-products such as silica, activated adsorbent, electricity and methane gas.