This study evaluates the physico-chemical performance of Ordinary Portland Cement (OPC) when partially replaced with stone-cutting dust (SCD), limestone (LS) and natural pozzolana (NP), both individually and in ternary combinations. Blends were formulated with SCD and NP at 10-40% and LS at 5-20%, including optimized ternary mixtures. Tests focused on normal consistency, setting time and water sorptivity. Results showed that all supplementary cementitious materials (SCMs) increased normal consistency, from 28.0% in OPC to 35.0% at 40% substitution. Setting time was significantly extended in SCM-rich blends, with initial and final setting times reaching up to 250-260 minutes, compared to 100 and 180 minutes for OPC. This delay, especially in NP and SCD-rich mixtures, reflects reduced reactivity and higher water requirements. Water sorptivity improved in optimized ternary blends, with Mix H (10% SCD + 10% LS + 15% NP) showing the lowest sorptivity coefficient of 0.1666 g/cm2/hr0.5, compared to 0.1908 for OPC. These findings demonstrate that carefully balanced combinations of NP, LS and SCD enhance workability, provide longer setting windows and reduce water ingress, leading to improved durability. The results support the use of locally available materials in Kenya as sustainable and cost-effective alternatives for blended cement production.

The Schiff base ligands (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol (L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2), and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3) were immobilized onto mesoporous SBA-15 silica. The resultant adsorbents, 1-3, were investigated as potential adsorbents for Cr(VI), Cd(II), and Pb(II) cations from aqueous solution. Various parameters, such as pH, were varied to determine their influence on the metal cation removal capacity of adsorbent 1, where the highest removal efficiencies recorded were at pH 3 for Cr(VI) and Cd(II) cations of 64 and 62%, respectively, and pH 9 for Pb(II) at 99%. Compound 2 recorded efficiencies of 58, 66, and 93% and Compound 3 recorded 20, 88, and 55% for Cr(VI), Cd(II), and Pb(II), respectively. The adsorption nature of the metal cations was studied using 1 by employing several adsorption kinetic models, where the pseudo-second-order model recorded the highest R2 values for all the metal cations (R2 > 0.98) and adsorption capacities of 9.66, 9.25, and 74.7 mg/g for Cr(VI), Cd(II), and Pb(II) cations, respectively. To further study the nature of adsorption, various isotherms were utilized, where the Langmuir isotherm yielded the best fit for Pb(II) and Cr(VI) cations, recording adsorption capacities of 125 and 36.11 mg/g, respectively, while the Redlich-Peterson isotherm yielded the best fit for Cd(II) ion with an adsorption capacity of 16.63 mg/g.HIGHLIGHTSThere is a need for remediation of heavy metal-polluted water. Schiff base ligands (L1-L3) were immobilized onto mesoporous SBA-15 silica to afford three adsorbents 1-3. Adsorbents 1-3 yielded viable extractants for the remediation of environmental components polluted with heavy metals. pH, adsorbent dosage, contact time and initial metal concentration influenced the extraction ability of the adsorbents.

The Schiff base chelating ligands; (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol (L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2) and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3) were immobilized on Fe3O4 magnetic nanoparticles (MNPs) and utilized in the extraction of Cr(VI), Cd(II) and Pb(II) metal cations from aqueous solutions. The compounds synthesized, denoted as L1@ Fe3O4, L2@Fe3O4, and L3@Fe3O4, were characterized using FT-IR spectroscopy, TEM-SEM, VSM, and BET/BHJ techniques for analysis of functional groups, surface morphology, magnetic properties, and degree of porosity of the adsorbents, respectively. BET/BHJ technique confirmed the mesoporous nature of the compounds as their pore diameters ranged between 15 and 17 nm. The initial optimization conditions of pH, adsorbent dosage, initial metal concentration, and contact time on adsorption were studied using L1@ Fe3O4. The optimum efficiencies recorded were 68

The world’s growing population and industrialization have led to increased construction activities. This has increased the amount of waste aggregates which can be recycled in construction and cut the cost of infrastructure development. This study, therefore, reports the experimental findings for the effect of immobilizing Bacillus megaterium on the compressive strength and water absorption of laboratory prepared test mortar. Bacterial solution used in this work had a concentration of 1.0 × 107 cells/mL. The impact of recycled mortar impregnated with bacteria was studied after curing the specimens in water, saturated lime water, and 1.5% sulfuric acid. Compressive strength for test specimens cured in the three media was determined at the 2nd, 7th, 28th, and 56th day of curing. SEM analysis was done for mortars cured in acidic media and saturated lime water after curing for 28 days. The test results indicated that curing in water and saturated water improved the compressive strength, while the acidic medium lowered it. Recycled mortar is, therefore, an ideal material for immobilizing Bacillus megaterium before introduction into fresh concrete/mortar. The use of recycled mortar is a good strategy to reduce wastes from construction activities, save on the cost of construction materials, and enhance environmental conservation.

Pesticide use in Kenya plays a critical role in socio-economic development because its economy depends heavily on agriculture, which contributes to 30% of the GDP and accounts for 60% of export earnings. For agriculture and public health vector control, the country relies on pesticides, most of which (95%) are formulated products imported from China, India and Germany as the top exporters. In this chapter, we present the chemistry, manufacturing, importation and regulatory processes regarding pesticides in Kenya as well as their usage and impacts. All the various categories, organochlorine, organophosphate, carbamate, pyrethroid, neonicotinod insectides, as well as fungicides, herbicides and biopesticides, which are used in the country, are considered. A total of 1,447 and 157, which include formulations and active ingredients, respectively, for use in agriculture and public health sectors, with sufficient information on their usages and toxicities, are listed on the Pest Control Products Board (PCPB) database that is available to the public. A significant number of studies have been conducted in major agricultural regions, which have characterized pesticides, their toxicities, the types of crops and pests, the usage and human and environmental health risk indices, since the 2000, but the reports have not made any impacts on pesticide regulation, as some of the very toxic active ingredients, belonging to the WHO Class I and II, are still reported by farmers. However, a recent call from NGO’s made an impact in government and parliament, and a bill was introduced in 2020 with the aim of banning some of the toxic ones that have already been withdrawn from the EU market.

Reactions of 2-[f(2-hydroxyethyl)iminogmethyl]phenol (L1) and 2-[1-f2-(diethylamino)ethyliminogethyl]phenol (L3) with copper(II) nitrate yielded monometallic complexes [CuNO3(L1)] (1) and [CuNO3(L3)] (2), respectively. The solid-state structures of 1 and 2 confirmed the kappa(3)-O,N,O' and kappa(3)-O,N,N' tridentate binding mode of L1 and L3, respectively. The phenoxy-imino ligands 2-[f(2-hydroxyethyl)iminogmethyl]phenol (L1), 2-[f(2-(diethylamino)ethyliminogmethyl]phenol (L2), 2-[1-f2-(diethylamino)ethyliminogethyl]phenol (L3) and 2-[(2-mercaptoethylimino)methyl]phenol (L4) were also used as model chelating agents for liquid-liquid extraction of copper(II), zinc(II), cadmium(II) and lead(II) cations from water using dichloromethane as the organic solvent. The relative affinities of these chelating ligands for copper(II), zinc(II), cadmium(II) and lead(II) by liquid-liquid extraction were found to be in the order copper(II) > zinc(II) > cadmium(II) > lead(II) in line with the hard-soft acid-base interaction. The ligands L1-L4 showed extraction efficiencies ranging from 75% to 99% for copper(II), 72% to 97% for zinc(II), 64% to 87% for cadmium(II) and 51% to 74% for lead(II). The extraction protocol was successfully applied to sewage effluent. [GRAPHICS]

This paper reports study findings on the use of Lysinibacillus sphaericus (at 1.0 × 107 cells/ml concentration) to enhance and improve the physicomechanical and chemical properties of blended Ordinary Portland Cement (OPC). Blending was done separately with pulverized fly ash (PFA) and natural pozzolana (volcanic tuff) at substitution levels of 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Mortar prisms of dimensions 40 mm by 40 mm by 160 mm were prepared and cured for the 2nd, 7th, 28th, 56th, and 90th days using Lysinibacillus sphaericus solution as mixing water and curing media. Commercial OPC and PPC mortar prisms cast and cured using distilled water were used as controls. Results showed that prisms treated with bacteria exhibited the highest performance on compressive strength development. Further microstructure analysis of blended cement incorporated with Lysinibacillus sphaericus bacteria showed significant amounts of reacted secondary cementitious materials compared to samples without bacteria. Bacteria presence was also found to reduce water demand during mixing and setting times and exhibited low porosity in relation to samples without bacteria. These results showed that the presence of alkaliphilic bacteria in the blended cement resulted in synergistic effect in enhancing the physicochemical and mechanical properties.

Due to climate change and anthropogenic activities such as agriculture, mining, and urbanization, water contamination has become a very real modern problem. Modern solutions such as activated carbon, reverse osmosis, and ultrafiltration, among others, have been employed in the decontamination of water. These methods are, however, expensive to set up and maintain and therefore have proved a challenge to implement in developing countries. Zeolite materials exhibit excellent structural properties, such as high ion exchange capacity, porosity, and relative surface area, which make them attractive to water decontamination processes. However, conventional zeolites are expensive, and recent research has focused on utilizing low-cost materials such as agro-wastes and clays as raw materials for the synthesis of zeolites. This review aims to discuss the role of low-cost zeolites in their removal of heavy metals and the feasibility of agro-wastes and natural clays in the synthesis of zeolites. Recent research studies based on the synthesis of zeolites from clays and agro-wastes and their application in heavy metal removal have been reviewed and discussed. Agro-wastes such as rice husk ash and sugarcane bagasse ash and layered silicate clays such as kaolinite and smectites are particularly of interest to zeolite synthesis due to their high silica to alumina ratio. Zeolites synthesized through various methods such as hydrothermal, molten salt, and microwave irradiation synthesis have been discussed with their effect on the adsorption of various heavy metals.

Malaria a mosquito-borne disease caused by Plasmodium remains to be a main global burden despite concerted efforts to eliminate it. While diverse control strategies have been put in place for mosquito-borne diseases, vector control continues to be a critical component in infection prevention. Vector control majorly focuses on the eradication of mosquitoes using a variety of chemical insecticides that includes organochlorides, carbamates, organophosphates, and pyrethroids. The use of conventional insecticide-based as mosquito control strategies poses several challenges such as the widespread development of insecticide resistance, environmental damage concerns, and effects on non-target organisms. These challenges create a demand for the development and use of alternative pest control strategies that are sustainable, safer, and environmentally friendly to mosquito vector management. This review provides insight into alternative sustainable interventions for mosquito vector control in the form of biorational pesticides. Biorational pesticides are pesticides that have little or no effect on humans and environments and include entomopathogenic microorganisms, insect growth regulators, and endosymbiotic bacteria. It also puts into perspective their environmental impacts, benefits, and challenges. Further, countries like Sri Lanka, that are certified as malaria free by World Health Organization (WHO) incorporated the use of entomopathogenic bacteria, insect growth regulators and larvivorous fish in their national vector control programs leading to the successful elimination of malaria in 2016. We therefore highlight success stories of the countries that have implemented these interventions bringing out the lessons for countries that are battling malaria epidemics.

Microplastics are emerging threat contaminants that have been shown to provide toxic pollutants, either from the environment or from their inherent toxic monomers and additives, a pathway into the aquatic food web. In the present study, the occurrence, abundance, and composition of microplastic load in the surface water of Lake Naivasha (Kenya) was determined. The surface water physicochemical parameters were measured in situ; microplastic samples were collected using plankton net trawls and treated with H2O2 to decompose organic matter. The microplastic particles recovered were classified both by visual observation and by attenuated total reflection–Fourier transform infrared spectroscopy. The average microplastic concentration range in surface water was 0.183 ± 0.017 to 0.633 ± 0.067 particles/m2, with the mean concentration being 0.407 ± 0.135 particles/m2. Fragments, fibers, and films were identified and were mostly composed of polypropylene, polyethylene, and polyester. We also performed correlational analysis, which showed a strong positive association between microplastic quantity and turbidity, total nitrogen, and total phosphorus in the lake. The high variability in microplastic densities exhibited between the sampled locations was attributed to human activities, water and wastewater intake through rivers and tributaries, and the presence of local wind patterns responsible for the general water circulation. Our assessment adds to the growing documentation of microplastic presence in freshwater ecosystems, and provides a baseline for future monitoring and assessment in sediment and biota of Lake Naivasha and other Kenyan freshwater systems. Environ Toxicol Chem 2020;39:765–774. © 2020 SETAC

The German Academic Exchange Service (DAAD) and the National Commission for Science, Technology and Innovation (NACOSTI)

The inclusion of both zeolites X and zeolite Y significantly affected the dissipation of malathion in water. In the fresh water, malathion degradation followed a pseudo-first order kinetics with concomitant half-life dropping from 8.76 hours in fresh water to 4.44 and 6.65 hours up on the introduction of faujasite X and Y, respectively. Zeolite X had higher degradation efficiency as compared to the Y type. In pure fresh water, Malathion mainly hydrolyzed to form malathion monocarboxylic and dicarboxylic acids as the only degradation products. However, in the presence of zeolites X and Y, in addition to the degradation products obtained in the fresh water, dimethyldithiophosphate was also formed. Notably, all the degradation products obtained are environmentally benign compared to the parent malathion. Eventually, both the adsorption on the zeolite framework and zeolite catalyzed degradation processes contributed to the overall dissipation behavior of the malathion and its degradation products.