Surface modification of Ag-CdO with polyaniline for the treatment of 3',3″,5',5″-tetrabromophenolsulfonphthalein (BPB) under UV-visible light irradiation.

The quality of natural waters could be deteriorated by organic pollutants which can impose a risk to the ecosystem as well as human health. These organic contaminants are often needed to be removed with adequate techniques. In this study, the photocatalysts of CdO nanoparticles (NPs), Ag-CdO nanocomposites (NCs), and Ag-CdO/polyaniline (PANI) NCs were successfully synthesized in order to investigate their degradation performance against 3',3″,5',5″-tetrabromophenolsulfonphthalein (bromophenol blue, BPB) dye. The crystal structure, functional groups, morphological change, and degradation efficiency of as-synthesized photocatalysts were characterized using XRD, FTIR, SEM and UV-Visible spectroscopic techniques respectively. The SEM result showed that the surface morphology of the nanomaterials seems the agglomerated micron-scaled grains as compared to CdO NPs and Ag-CdO NCs. The FT-IR spectrum demonstrated the absorption peaks which strongly confirmed that Ag-CdO NCs surface was successfully modified with PANI. The highly sharp and intensive XRD patterns attributed to the cubic structure for CdO NPs and Ag-CdO NCs structures with decreasing crystalline size from 40.58 nm to 36.43 nm and 10.29 nm upon CdO NPs photocatalyst surface treatment with Ag metal and PANI. The decreased particle size brought about to narrow the bandgap from 2.76 eV to 1.61 eV and 1.58 eV respectively. Among the synthesized photocatalysts, Ag-CdO/PANI NCs exhibited the best degradation efficiency of 97.30 % at pH 6, 10 ppm concentration of dye, 0.140 g of catalyst load, and 210 min irradiation time. Moreover, the kinetics of photodegradation of model dye at optimum conditions followed pseudo-second order reaction with the rate constant of 8.56 × 10-2 M-1min-1. The results suggested that, the developed treatment method for this particular dye could be applicable for the treatment of wastewater samples containing acidic dyes.

Ecological effects of imidacloprid on a tropical freshwater ecosystem and subsequent recovery dynamics.

This study aimed to investigate the effect of imidacloprid on structural (invertebrates and primary producers) and functional (organic matter decomposition and physicochemical parameters) characteristics of tropical freshwaters using acute single species and mesocosm studies performed in Ethiopia. The recovery of affected endpoints was also studied by using a mesocosm study period of 21 weeks. Our acute toxicity test showed that Cloeon dipterum (96-h EC50 = 1.5 µg/L) and Caenis horaria (96-h EC50 = 1.9 µg/L) are relatively sensitive arthropods to imidacloprid. The mesocosm experiment evaluated the effects of four applications of imidacloprid with a weekly interval and the results showed that the macroinvertebrate and zooplankton community structure changed significantly due to imidacloprid contamination in mesocosms repeatedly dosed with ≥0.1 and ≥ 0.01 µg/L, respectively (time weighted average concentrations of 112 days (TWA112d) of ≥0.124 and ≥ ≈0.02 µg/L, respectively). The largest responses were found for C. dipterum, C. horaria, Brachionus sp. and Filinia sp. Chlorophyll-a concentrations of periphyton and phytoplankton significantly increased in the ≥0.1 µg/L treatments levels which are indirect effects as a result of the release of grazing pressure. A significant, but quantitatively small, decrease of organic matter decomposition rate was observed in mesocosms treated with repeated doses of 1 µg/L (TWA112d of 2.09 µg/L). No recovery was observed for the macroinvertebrates community during the study period of 21 weeks, but zooplankton recovered after 9 weeks. We observed spatio-temporal related toxicity differences between tropical and temperate aquatic taxa, with tropical taxa generally being more sensitive. This suggests that use of temperate toxicity data for the risk assessment of imidacloprid in tropical region is not recommended.

Biological and chemical monitoring of the ecological risks of pesticides in Lake Ziway, Ethiopia.

Lake Ziway, a freshwater lake located in Ethiopia, is under the pressure of pesticide and nutrient pollution due to agricultural activity and urbanization. This study has analysed concentrations of insecticides, fungicides and nutrients in water and sediment samples of Lake Ziway taken in the wet and dry season at 13 sites expected to be under different environmental stress and assessed their expected ecological impacts. Malathion, dimethoate, metalaxyl, diazinon, chlorpyrifos, fenitrothion and endosulfan were detected in more than half of the water samples, while diazinon, α-cypermethrin and endosulfan were frequently detected (>25%) in sediment samples. Higher levels of physicochemical parameters were observed at sample locations proximate to agricultural and urban activities. Risk quotients (RQ) and multi-substance Potentially Affected Fraction (msPAFRA) were calculated to assess the ecological risk of individual and mixture of pesticides, respectively. The majority of the pesticides detected in the water of the lake showed a potential acute risk (RQ > 1), specifically the insecticides chlorpyrifos, λ-cyhalothrin and α-cypermethrin for which high potential acute risks were calculated using a 2nd tier risk assessment. Levels of pesticides in sediment showed low ecological risks. Arthropods and fishes are expected to be highly affected by mixtures of pesticides (msPAFRA = < 1-80%) detected at locations that are proximate to smallholders' farms, and receive largescale farms' wastewater and at sites where inflow rivers join the lake. Macroinvertebrates based redundancy analysis showed the effectiveness of EPT richness to assess ecological status of the lake. Training for smallholder farmers on pesticides safety and usage, and implementation of improved effluent management mechanisms by floriculture farms are urgently needed intervention measures to reduce the pollution.

Distribution of microplastic and small macroplastic particles across four fish species and sediment in an African lake.

Pollution with microplastics has become an environmental concern worldwide. Yet, little information is available on the distribution of microplastics in lakes. Lake Ziway is one of the largest lakes in Ethiopia and is known for its fishing and drinking water supply. This study aims to examine the distribution of plastic particles, of all sizes (micro- and small macro-plastics) in four of the major fish species of the lake and in its shoreline sediment. The gastrointestinal tracts analysis showed that 35% of the sampled fishes ingested plastic particles. The median number of particles per fish was 4 (range 1-26). Benthic (Clarias gariepinus) and benthopelagic (Cyprinus carpio and Carassius carassius) fish species were found to contain a significantly higher number of plastic particles in comparison to the planktivorous fish species (Oreochromis niloticus). More fishes ingested plastic particles in the wet compared to the dry season. The maximum plastic size (40 mm fibre) was found in C. carpio. Estimated median mass of plastic particles in fish was 0.07 (0.0002-385.2) mg/kg_ww. Fish and sediment samples close to known potential sources of plastic particles had a higher plastic ingestion frequency (52% of the fish) and higher plastic concentration compared to the other parts of the lake. The median count and mass of plastic particles measured in sediment of the lake were 30,000 (400-124,000) particles/m3 and 764 (0.05-36,233) mg/kg_dw, respectively, the upper limits of which exceed known effect thresholds. Attenuated total reflection (ATR) - Fourier-transform infrared (FTIR) spectroscopy showed that polypropylene, polyethylene and alkyd-varnish were the dominant polymers in fishes and in sediment. The plastic particles size distributions were Log-linear and were identical for plastic particles found in fish and in sediment, suggesting strong benthic-pelagic coupling of plastic particles transfer.

The neonicotinoid imidacloprid shows high chronic toxicity to mayfly nymphs.

The present study evaluated the acute and chronic toxicity of imidacloprid to a range of freshwater arthropods. Mayfly and caddisfly species were most sensitive to short-term imidacloprid exposures (10 tests), whereas the mayflies showed by far the most sensitive response to long-term exposure of all seven arthropod species tested (28-d EC10 values of approximately 0.03 µg/L). The results indicated a high aquatic risk of chronic exposure of imidacloprid to mayflies.