Currently, there are many different interpretations in the literature of what a circular economy is and how it functions. As cities are still facing challenges to become fully sustainable, the need for a comprehensive analysis of how the circular economy can be implemented in urban areas is increasing. This article aims at outlining circular cities by their key characteristics and to further explore and provide a framework for fostering circularity at the city level. In order to achieve this goal, we performed a systematic review and analyzed key papers published in the field of circular economy to determine how circular economy practices form circular cities. We discovered that cities play a focal role in facilitating the transition towards circularity through the closing of the loops, recirculation, technical innovation, policy elaboration and citizens’ support. However, city policymakers are still uncertain about how a circular city looks like and what its purpose is, as views are ranging from a strategic ambition to a niche concept of a smart city. Such uncertainty brings challenges, especially in the transition phase that many cities are in at the moment. This further implies that circular economy applied at the urban level still needs effort and innovation to successfully pass the transition phase from the linear economy. Therefore, lastly, we developed a framework model that can be adapted in other cities to facilitate their transition to circular cities.

It is a well–known fact that heavy metal pollution in sediments causes serious problems not only in the Danube basin, but also in the large and small adjacent river streams. A suitable method for assessing the level of heavy metals and their toxicity in sediments is the calculation of pollution indices. The present research aims to assess heavy metal pollution in the Lower Danube surface sediments collected along the Danube course (between 180 and 60 km) up to the point where the Danube River flows into the Danube Delta Biosphere Reserve (a United Nations Educational, Scientific and Cultural Organization—UNESCO, protected area). In addition, this monitored area is one of the largest European hydrographic basins. Five heavy metals (Cd, Ni, Zn, Pb, Cu) were analyzed in two different seasons, i.e., the autumn of 2018 and the spring of 2019, using the Inductively Coupled Plasma Mass Spectrometry (ICP– MS) technique. Our assessment of heavy metal pollution revealed two correlated aspects: 1. a determination of the potential risks of heavy metals in sediments by calculating the Potential Ecological Risk Index (RI), and 2. an evaluation of the influence of anthropogenic activities on the level of heavy metal contamination in the surface sediments, using three specific pollution indices, namely, the Geo–Accumulation Index (Igeo), the Contamination Factor (CF), and the Pollution Load Index (PLI). The results of this pioneering research activity in the region highlighted the presence of moderate metal (Ni and Cd) pollution and a low potential ecological risk for the aquatic environment.

The aim of the present paper is to quantify water quality in the Lower Danube Region by using a series of multivariate techniques and the Water Quality Index (WQI). In this paper were measured 18 parameters upstream and downstream the city of Galati along the Danube River, namely: pH, Dissolved Oxygen (DO), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), N-NH₄⁺, N-NO₂⁻, N-NO₃⁻, N total, P-PO₄³⁻, SO₄²⁻, Cl⁻, Fe-total, Cr-total, Pb²⁺, Ni²⁺, Mn²⁺, Zn²⁺, As²⁺, in the interval winter 2013–winter 2016. The samples were either analyzed on the field, or sent for testing to the laboratory. The physicochemical parameters mentioned above were analyzed in accordance with the Romanian and International standards in force. The WQI was calculated according to Weighted Arithmetic Water Quality Index Method. The interdependencies between the selected physicochemical parameters were used for determining potential sources of pollution. Monitoring water quality dynamics in the period mentioned above favoured a series of relevant conclusions about the anthropic influence on water quality. Water quality was assessed by processing the measurements results, by calculating the water quality index (WQI), and by using the principal component analyses (PCA) and the response surface method (RSM) with the aim of correlating the indices for the physico-chemical parameters.

This review highlights recent advances in the development of electrochemical sensors and biosensors for detecting pharmaceutical contaminants in water samples, including surface water, wastewater, and bottled water. The electrode modification materials—such as nanomaterials, conductive polymers, and eco-friendly nanocomposites—have shown notable improvements in sensor sensitivity and selectivity, enabling the detection of various pharmaceutical compounds, including diclofenac, ibuprofen, antibiotics, and hormones. Future research directions suggest the use of eco-friendly nanocomposites, the development of multiplexed platforms for simultaneous contaminant detection, and the integration of sensors into portable devices for in situ monitoring. Additionally, integrating biosensors with specific biomolecules and IoT technology can expand their applicability, enabling continuous and efficient water quality monitoring, thus supporting public health and environmental protection.

This paper retrieves an optical 1–soliton solution to a model that is written as a concatenation of the Lakshmanan–Porsezian–Daniel model and Sasa–Satsuma equation. The method of undetermined coefficients obtains a full spectrum of 1–soliton solutions. The multiplier approach yields the conserved densities, which subsequently lead to the conserved quantities from the bright 1–soliton solution.

Plastics are becoming common environmental pollutants. Plants behave as access routes for plastics in the trophic chain since they can adsorb particles through their roots or on their surfaces. In this review, various methods for sample preparation and analytical methods for plastic isolation and identification from vegetables, fruits, and their seedlings were discussed. The effects that plastic particles have on them were also addressed. All of the studies offer convincing proof that micro and nano plastics already exist in fruits and vegetables, or can easily enter into their seedlings and have a variety of effects. Since most studies have been conducted under strictly controlled conditions using standard plastics, more tests under more environmentally realistic conditions are required to ensure that literature studies are applicable. Also, more fruits and vegetables need to be tested to identify the number of plastics currently there that, when consumed, could harm human health.