We present a study on the radioactivity of selected Croatian agricultural soils that vary considerably with respect to geological background; physical, chemical, and biological characteristics; soil type; land use; and soil management. Our investigation is focused on the main naturally occurring radionuclides (⁴⁰K, ²³⁸U, ²²⁶Ra, ²³²Th, ²³⁵U) and ¹³⁷Cs as the most threatening long-lived anthropogenic radionuclide. We find that the radioactivity level is not influenced by the application of different soil amendments, at least in moderate quantities, and that no effect of soil management can be detected as well. In contrast, geological and location-specific properties influence radionuclide content in soil, especially regarding the naturally occurring ones. Moreover, physical and chemical soil properties such as texture and soil adsorption complex, respectively, seem to be the main factors regarding fixation of ¹³⁷Cs in soil. Calculated dose rates for external exposure to the gamma radiation originating from soil have been found to be generally low, except for two locations where they are higher but not at a level that would lead to health problems for workers on the field.

The textile industry is responsible for the disposal of a large volume of effluents containing synthetic dyes, which are considered to be highly toxic compounds for both human health and the environment. The aim of the present study was to test potential use of a renewable, low-cost product—Luffa cylindrica in disk and powder form—as adsorbent material for the treatment of textile effluents containing dyes. Saccharomyces cerevisiae cells were also immobilized on L. cylindrica to increase the adsorbent capacity. Batch experiments were conducted for the evaluation of the removal of the azo dye Direct Red 23. The Langmuir, Freundlich, and Temkin isotherms were used for a better interpretation of the data. The results showed that adsorption is more efficient at acidic pH and all adsorbent materials best fit the Langmuir model, indicating the formation of a monolayer. The isotherm results also demonstrated that the materials immobilized with the yeast had a greater sorption rate, but the cell-free L. cylindrica powder had a higher adsorbate/adsorbent interaction. The comparison with a spectrophotometrically defined standard revealed that the powder without and with yeast cells was able to achieve an acceptable removal rate of the dye from the solution. Moreover, the difference in adsorption between the powder without and with yeast cells was very small. Thus, the application of the cell-free L. cylindrica powder is economically more feasible. The findings demonstrate the potential use of L. cylindrica powder as an adsorbent for the treatment of effluents containing textile dyes.

The microbial diversity from a fluidized bed reactor (FBR) for nonionic surfactant linear alcohol ethoxylate (LAE – Genapol® C100) degradation was determined by 454-pyrosequencing analysis. The FBR was operated with a hydraulic retention time of 18 h for 163 days and fed with synthetic substrate supplemented with yeast extract and LAE. The system was operated in two stages: (I) 80 mg/L of sucrose in synthetic substrate plus 107.4 ± 47.3 mg/L LAE and (II) synthetic substrate without sucrose and 97.9 ± 37.7 mg/L of LAE. By using 454 pyrosequencing, 14,325 sequences with an average length of 225 bp were generated. Proteobacteria phyla predominated in support material (sand) biofilm, while for the biomass from the phase separator, there was a prevalence of Acidobacteria phyla. Furthermore, many reads were related to genera of degraders of LAE and other nonionic surfactants (Desulfosporomusa, Syntrophomonas, Desulfobulbus, Geobacter, Dongia, etc.). Higher diversity and equitability indices were obtained for the biomass from the phase separator. The use of sucrose (C₁₂H₂₂O₁₁) as co-substrate for LAE degradation favored the microbial diversity in the support material and in the phase separator, indicated by the Shannon-Wiener (H′) index. The removal of sucrose from the synthetic substrate definitely altered the microbial community but did not influence the LAE efficiency removal.

This work studies the degradation of safranin T (SF, a recalcitrant pollutant) by an electrochemical process and three photochemical advanced oxidation technologies (TiO₂ photocatalysis, UV/H₂O₂, and photo-Fenton). The degradation routes of each process were elucidated initially. Based on the mineralization extent, improvement of the treated solutions’ biodegradability, and energy consumption, the most suitable process was identified. Interestingly, in the electrochemical system, safranin T was efficiently eliminated through electrogenerated HOCl. In contrast, the popular photo-Fenton process was unable to degrade SF. Moreover, the pollutant was refractory to highly energetic UV₂₅₄ irradiation. Meanwhile, the UV/H₂O₂ and TiO₂ photocatalysis processes removed SF slowly. Interestingly, the electrochemical system produced biodegradable solutions. Furthermore, the electrical energy consumption (EC) for the 100% removal of SF showed that the electrochemical process only spent 0.04 and 0.06% of the EC needed by TiO₂ photocatalysis and UV/H₂O₂, respectively. Therefore, the fast SF degradation, the high biodegradability intensification, and the very low energy consumption evidenced the relative advantages of the electrochemical process for the remediation of water containing safranin T. Finally, to obtain a deeper understanding of SF degradation by the electrochemical system, an analysis of structural transformations was made. It was found that the electrogenerated HOCl initially attacked the central azine and the aromatic amines on SF. Subsequently, aliphatic compounds were formed, which due to their biodegradable character could be completely eliminated by a conventional biological system or discharged into natural media.

The accumulation of ash, heavy metals, and polycyclic aromatic hydrocarbons (collectively called potential accumulating substances, PAS) was evaluated to ascertain the stability of lysis–cryptic growth sludge reduction process (LSRP) for municipal sludge treatment. One sequencing batch reactor (SBR) incorporated with homogenization was run to test the LSRP and another SBR as a control. The continuous monitoring results for 2 months showed that the ash and heavy metals slightly increased, and the polycyclic aromatic hydrocarbons decreased by 18.0%, indicating that there may be negligible accumulations during the LSRP. Their accumulations met pattern I, as demonstrated by statistical analysis, proving no PAS accumulation for LSRP. This was further confirmed by sludge activity and system performance. Moreover, the mechanism for no PAS accumulation was discussed. It was concluded that the LSRP was stable with no worries about PAS accumulation under the operational conditions.

Heavy metals are considered toxic to humans and ecosystems. In the present study, heavy metal concentration in soil was investigated using the single pollution index (PIi), the integrated Nemerow pollution index (PIN), and the geoaccumulation index (Igeo) to determine metal accumulation and its pollution status at the abandoned site of the Capital Iron and Steel Factory in Beijing and its surrounding area. Multivariate statistical (principal component analysis and correlation analysis), geostatistical analysis (ArcGIS tool), combined with stable Pb isotopic ratios, were applied to explore the characteristics of heavy metal pollution and the possible sources of pollutants. The results indicated that heavy metal elements show different degrees of accumulation in the study area, the observed trend of the enrichment factors, and the geoaccumulation index was Hg > Cd > Zn > Cr > Pb > Cu ≈ As > Ni. Hg, Cd, Zn, and Cr were the dominant elements that influenced soil quality in the study area. The Nemerow index method indicated that all of the heavy metals caused serious pollution except Ni. Multivariate statistical analysis indicated that Cd, Zn, Cu, and Pb show obvious correlation and have higher loads on the same principal component, suggesting that they had the same sources, which are related to industrial activities and vehicle emissions. The spatial distribution maps based on ordinary kriging showed that high concentrations of heavy metals were located in the local factory area and in the southeast-northwest part of the study region, corresponding with the predominant wind directions. Analyses of lead isotopes confirmed that Pb in the study soils is predominantly derived from three Pb sources: dust generated during steel production, coal combustion, and the natural background. Moreover, the ternary mixture model based on lead isotope analysis indicates that lead in the study soils originates mainly from anthropogenic sources, which contribute much more than the natural sources. Our study could not only reveal the overall situation of heavy metal contamination, but also identify the specific pollution sources.

The effect of exogenously applied citric acid (CA) on phytoextraction and antioxidant defense was analyzed using willow species (Salix viminalis, S. alba, and S. matsudana) grown in soil contaminated with cadmium (Cd). Citric acid has been used as a chelating agent for the purpose of accelerating the solubility of Cd in soil and enhancing the phytoextraction of selected plants. Willows were exposed to 6 mg/kg of Cd, following the same with citric acid (20 mM/kg soil). Results revealed a positive effect of citric acid in mobilization of accumulated Cd from roots to shoots and leaves. The addition of citric acid alleviated Cd toxicity by helping plants to overcome oxidative stress, through CA’s chelating properties and the increased activity of antioxidant enzymes. Different protection strategies were evident through modification of activities of antioxidant enzymes such as catalase (CAT), ascorbate-peroxidase (APx), and guaiacol peroxidase (GPx) in young versus mature leaves in plants exposed to Cd. Furthermore, results revealed that addition of citric acid may be beneficial in the reduction of the negative effect of Cd stress on photosynthesis. The efficiency of coupling phytoextraction with the chelating agents represents a good strategy for decreasing damages caused by cadmium and has good potential in decontamination of a polluted environment.

Electrokinetics (EK) was investigated as a possible technique for in-situ treatment of leachable chromium at a built site contaminated with chromium ore processing residues (COPR). A preliminary EK experiment was carried out at the laboratory scale on an undisturbed COPR core sample. Methods applied for material and pore water characterization before and after EK treatment addressed physical aspects by laser diffraction granulometry, pycnometry and pore water content, mineralogical aspects by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and chemical aspects by inductively coupled plasma-atomic emission spectroscopy and atomic absorption spectroscopy for elemental composition, spectrophotometry for Cr(VI) analysis, and potentiometry for pH determination. EK was run at 1 V/cm with no external constraints on current intensity. The EK experiment reached an extraction of 72% of the total leachable Cr(VI) after only 10 days of treatment and 84% after 20 days. Material texture, composition, and pH remained similar. These results indicate that EK presents a potential solution for extracting leachable Cr(VI) from COPR sites. The impounded COPR material appeared to be heterogeneous in composition at all scales, from field to lab sample, adding to the challenge of in-situ treatment.

Diclofenac (hereafter DCF) is an extensively used anti-inflammatory drug; therefore, it is found in many sewage treatment plant effluents and it is one of the most usually reported environmental pharmaceutical contaminants. In this work, the degradation of diclofenac in pure water under UV light was studied, and the influence of some variables, such as humic acids (HA), nitrate anions (NO₃⁻) and titanium dioxide (TiO₂) on DCF photodegradation was investigated. The experimental activity was carried out in a batch reactor of 100 mL equipped with fixed UV light of 254 nm and an irradiation intensity of 400 mJ/m². Diclofenac initial concentration was equal to 10 mg/L in pure water, and its removal was evaluated by varying HA concentration in the range 10–20 mg/L and NO₃⁻ concentration in the range 25–50 mg/L. Furthermore, the heterogeneous catalysis with TiO₂ (1–50 mg/L) was studied. Temperature in all experiments was kept constant at 20 °C. Experimental results show that while HA have a significant influence on DCF photodegradation, nitrate and titanium dioxide seem to be ineffective, at least in the tested conditions. Finally, DCF photolysis modelling was carried out and a pseudo-first-order kinetic model was used.

Petroleum hydrocarbon, a complex mixture including aliphatic and aromatic hydrocarbons, is known to have negative effects on the environment. We determined the effectiveness of persulfate (PS) (5% w/w) activated using 1% (w/w) of various types of soil minerals, goethite (α-FeOOH), hematite (Fe₂O₃), magnetite (Fe₃O₄), maghemite (γ- Fe₂O₃), manganese oxide (MnO₂), and zeolite (clinoptilolite) to treat petroleum hydrocarbon-contaminated soil. Total petroleum hydrocarbon (TPH) was 4200 ± 124 mg kg⁻¹. The TPH removal efficiency was in the order: Fe₃O₄ > MnO₂ > γ-Fe₂O₃ > Fe₂O₃ > α-FeOOH > clinoptilolite. When the PS dosage and the moisture content of the soil increased, the degradation rate (k ₒbₛ) of TPH removal increased; on the other hand, lowering the pH increased the k ₒbₛ of TPH removal. The PS oxidation of TPH was optimized using response surface methodology (RSM). The interactive effects of three factors, namely, persulfate dosage (X ₁), pH (X ₂), and soil moisture content (X ₃), were investigated. The optimum removal of TPH by PS oxidation activated using 1% (w/w) magnetite was obtained at 5.5% (w/w) PS and 85% (w/w) moisture content at an initial pH of 4.5. However, the soil treated by PS showed a negative effect on soil health. The germination of mung bean (Vigna radiata (L.) R. Wilczek) and the CO₂ release for the treated soil were low, indicating that toxicity had occurred in the treated soil. To restore the treated soil, adding a soil amendment, like CaCO₃, fly ash, or crop residue, was able to improve plant growth and soil microbial activity.