Adsorption of antiretroviral drugs, abacavir, nevirapine, and efavirenz from river water and wastewater using exfoliated graphite: Isotherm and kinetic studies.

In this work, exfoliated graphite was used to adsorb antiretroviral drugs from river water and wastewater. The exfoliated graphite was prepared from natural graphite by intercalating it with the acids and exfoliating it at 800 °C. It was characterized using Fourier Transform Infrared Spectroscopy which showed phenolic, alcoholic, and carboxylic functional groups between 1000 cm-1 and 1700 cm-1. Energy-dispersive X-ray spectroscopy results showed carbon as the main element with splashes of oxygen. The Scanning Electron Microscopy images showed increased c-axis distance between graphene layers after intercalation, which further increased after the exfoliation. The exfoliation resulted in elongated distorted cylinders, which were confirmed by the lower density (0.0068 g/mL) of exfoliated graphite material compared to the natural graphite (0.54 g/mL). The X-ray diffraction pattern showed the characteristics of hexagonal phase graphitic structure by the diffraction plane (002) at 26.74°. Raman spectroscopy results showed the natural graphite, graphite intercalated, and exfoliated graphite contained the D, G, D', and G' peaks at about 1350 cm-1, 1570 cm-1, 2440 cm-1, and 2720 cm-1, respectively indicating that the material's crystallinity was not affected by the modification. The highest antiretroviral drugs removal (95-99%), from the water was achieved with a solution pH of 7, an adsorbent mass of 30 mg, and an adsorption time of 30 min. The kinetic model and adsorption isotherm studies showed that the experimental data fit well in pseudo-second-order kinetics and is well explained by Freundlich's adsorption isotherm. The maximum adsorption capacity of the exfoliated graphite for antiretroviral drugs ranges between 1.660 and 197.0, 1.660-232.5, and 1.650-237.7 mg/g for abacavir, nevirapine, and efavirenz, respectively. The obtained removal percentages were 100% in river water, 63-100% in influent and 70-100% in effluent wastewater unspiked samples.

Case study on antiretroviral drugs uptake from soil irrigated with contaminated water: Bio-accumulation and bio-translocation to roots, stem, leaves, and fruits.

This study aimed to evaluate the potential of uptake of the commonly used antiretroviral drugs (ARVDs) in South Africa (abacavir, nevirapine, and efavirenz) by vegetable plants (beetroot, spinach, and tomato) from contaminated soil culture. The study results showed that all the studied vegetables have the potential to take up abacavir, nevirapine, and efavirenz from contaminated soil, be absorbed by the root, and translocate them to the aerial part of the plants. The total percentage of ARVDs found in the individual plant was mainly attributed to abacavir which contributed 53% in beetroot and 48% in spinach, while efavirenz (42%) was the main contributor in tomato. Abacavir was found at high concentrations to a maximum of 40.21 µg/kg in the spinach root, 18.43 µg/kg in the spinach stem, and 6.77 µg/kg in the spinach soil, while efavirenz was the highest concentrations, up to 35.44 µg/kg in tomato leaves and 8.86 µg/kg in tomato fruits. Spinach roots accumulated more ARVDs than beetroot and tomato however, the concentrations were not statistically different. Hydrophobicity was the main effect on the linearity, accumulation, and translocation of ARVDs. This study advances knowledge on the fate of ARVDs in agroecosystems, particularly in plant root - ARVD interaction and the resulting potentially toxic effects on plants. These results suggest that the quality of water used for crop irrigation needs to be assessed prior to irrigation to avoid vegetable plant pollution as contaminated water results in the contaminants uptake by plants. This may lead to the transfer of pollutants to the edible crops parts of and thus be unintentionally consumed by humans. More studies need to be continuously conducted to evaluate ARVDs bioaccumulation and their mechanism of uptake by other vegetables. The use of the pot-plant system can be recommended because it closely relates to the agricultural world.

Optimization and application of QuEChERS and SPE methods followed by LC-PDA for the determination of triazines residues in fruits and vegetables from Pietermaritzburg local supermarkets.

QuEChERS and solid phase extraction (SPE) methods were optimized and applied for the extraction of triazines in fruit and vegetables. These extraction methods are easy, effective, rugged and safe. Also, they have the ability to purify the extracts which leads to lower detection limits and higher recoveries of the analytes. The analysis were conducted using liquid chromatography coupled to photodiode array detector. The limits of detection and quantification ranged from 0.4 -1.4 µg/kg and 1.5 - 4.5 µg/kg, respectively, for QuEChERS and 0.3 - 1.8 µg/kg and 1.4 - 4.9 µg/kg respectively, for SPE. The recoveries ranged from 84 to 102% for QuEChERS and 76-119% for SPE, with relative standard deviation less than 20% for both methods. The fruits and vegetables analysed were apples, pears, carrots, potatoes, tomatoes, avocado, cucumber, spinach, bananas, and oranges. The concentrations detected ranged between 6 and 46 µg/kg in fruits and 4 - 84 µg/kg in vegetables. Simazine was detected in all fruits and vegetable samples except in pear, while terbutylazine was not detected in all samples analysed. Propazine and ametryn were only found in carrot while pear sample only had atrazine. The proposed methods proved to be sensitive and accurate indicating their applicability for detection and monitoring of the selected triazines in fruits and vegetables. However, QuEChERS can be recommended for routine analysis of these triazines due to its fewer extraction steps compared to SPE which is important for turn-around time.

Ultrasonic Followed by Solid Phase Extraction and Liquid Chromatography-Photodiode Array for Determination of Pharmaceutical Compounds in Sediment and Soil.

This work reports on the method optimization and application for quantitative analysis of non-steroidal anti-inflammatory drugs and anti-epileptic drug in soil and sediment samples. The analytes were extracted by ultrasonic extraction followed by solid phase extraction and quantified using liquid chromatographic coupled with photodiode array. The sensitivity of the method was determined based on the limit of detection and the limit of quantification which ranged between (0.010-0.027 µg/kg) and (0.025-0.049 µg/kg), respectively. The %recoveries of the method ranged between 74% and 112%. The concentrations obtained in real samples ranged from 0.055 to 0.426 µg/kg in sediment and 0.044-0.567 µg/kg in soil samples. The highest concentration was found for diclofenac in soil samples.

Method development and application for triazine herbicides analysis in water, soil and sediment samples from KwaZulu-Natal.

This study reports on the development and application of solid phase extraction (SPE) and ultrasonic extraction (UE) methods for the analysis of triazine herbicides in water, soil and sediment samples. The extraction parameters such as conditioning solvent, sample loading volume, eluting solvent, extraction time and sample mass were optimized due to their influence on the extraction efficiency of the analytes. To assess the applicability of the SPE and UE methods, spiked distilled water or soil samples were extracted and analyzed using an LC-PDA instrument. The recoveries obtained under optimum conditions were between 65-94% and 75-100% for SPE and UE, respectively. The relative standard deviations obtained were less than 0.36% for SPE and less than 4.6% for UE. The limit of detection (LOD) ranged from 0.026-0.084 µg/L for SPE and 0.0028-0.0083 mg/kg for UE. The limit of quantification (LOQ) was between 0.088-0.28 µg/L for SPE and 0.0089-0.028 mg/kg for UE. The concentrations of triazines were found to be between 0.96-7.4 µg/L and 0.79-15 µg/L in river water and wastewater effluent samples, respectively. In sediment samples, the triazine concentrations were found to be between 0.032-0.93 mg/kg, while in soil samples they were between 0.12-1.03 mg/kg.