This study proposes a method, backpropagation (BP) neural network, for interpolating missing values in daily precipitation time series. Firstly, the BP neural network is adopted to interpolate missing daily rainfall data at three selected stations in Yantai, Shandong, China. Then, the temporal and spatial variations in precipitation extremes across Shandong are analyzed by utilizing the complete daily rainfall dataset derived from accurate propagation at 24 meteorological stations. The results show that the long-term trends in five selected extreme precipitation indices calculated from interpolated daily rainfall data are generally consistent with those from original nonmissing values. And the spatial patterns of trends in precipitation extremes also show better performance for BP neural network approach in interpolating missing daily rainfall gaps. Those suggest that this BP neural network algorithm can obtain a good fit in terms of space-time variability of regional precipitation extremes, in case that the correlation coefficients between the target stations with missing values and reference stations with complete daily rainfall dataset are relatively large. These findings could be crucial for investigating regional frequency of heavy rainfall and water resource management.

Sorption of antibiotics to clay minerals is a key process controlling their transport and fate in environment. In this study, the effects of pH, ionic strength, and Cu(II) on ofloxacin (OFL) sorption to kaolinite were investigated by batch sorption experiments. The results of sorption edge experiments suggested that OFL sorption to kaolinite was pH and ionic strength dependent. Cation exchange was a major contributor to the sorption of OFL⁺ to kaolinite. The decreased OFL sorption with increasing ionic strength indicated the formation of outer-sphere complexation. When solution pH was lower than 7.0, Cu-OFL complexes facilitated OFL sorption through electrostatic attraction or formation of kaolinite-Cu-OFL and kaolinite-OFL-Cu ternary surface complexes. However, existence of free Cu(II) cation in solution competed for sorption sites, and thus suppressed OFL sorption. When solution pH was higher than 7.0, Cu(II) existed as Cu(OH)₂, and the Cu-OFL complexes in aqueous phase and solid phase (precipitation) enhanced OFL removal efficiency from solution. The results imply that Cu(II) effects should be taken into account in the evaluation of OFL mobility in environment.

Phosphate discharged in agricultural drainage causes water quality degradation on local, regional, and national scales. Iron oxyhydroxide filter materials can potentially remove the soluble phosphate present in drainage waters. Laboratory saturated column experiments and preliminary small-scale field tests were carried out to evaluate the effectiveness and efficiency of a synthetic goethite iron oxyhydroxide (α-FeOOH) filter material for phosphate treatment. Original iron oxyhydroxide filter material (SG-IOH-O) and the same filter material regenerated with sodium hydroxide (SG-IOH-R) were assessed. Results of replicated laboratory experiments showed that columns packed with SG-IOH-O or SG-IOH-R almost totally removed phosphate (>98%) from drainage waters spiked with an additional 1 or 10 ppm phosphate-P (PO₄-P). The column experiments with SG-IOH-O or SG-IOH-R additionally indicated that contact times of only 10 to 15 s were sufficient for near complete removal of phosphate from drainage water spiked with 1 ppm PO₄-P. In an initial small-scale filter treatment system field test with SG-IOH-O, percent phosphate removal averaged 89% in the first 200 days, which then decreased to an average 40% phosphate removal in the last 80 days. Following this initial field test, two field tests, one with SG-IOH-O and the other with SG-IOH-R, were conducted concurrently over a period of 193 days, with the SG-IOH-O system phosphate removal averaging 75%, while the SG-IOH-R system phosphate removal averaged 34%. This study’s findings support possible goethite iron oxyhydroxide filter material use for drainage water phosphate treatment; however, larger-scale field investigations are needed, particularly with modified regeneration procedures.

Mesoporous silica with wormhole framework structure (HMS-OH) and its amine-functionalized material (HMS-NH₂) were prepared through an electrically neutral assembly pathways, post-grafting process of 3-aminopropyltriethoxysilane (APTES), respectively. Their adsorption behaviors toward cationic dyes as well as heavy metal ions in aqueous system and the capture capacities for CO₂ molecules all have been investigated. As-synthesized HMS-OH showed a high removal efficiency and rapid sorption rate to cationic dyes because of large surface area and versatile pore structure. HMS-NH₂ exhibited better heavy metal ions and more CO₂ gas sorption capacities due to the intrinsic property of amine groups grafted on the surface. The adsorption isotherms of methylene blue (MB) onto HMS-OH, Cu(II) onto HMS-NH₂ were fitted with Langmuir model and kinetic processes followed well the pseudo-second order pattern. There results revealed that both HMS-OH and HMS-NH₂ had a potential application in the treatment of cationic dyes, heavy metal ions, and greenhouse gas CO₂.

Benzalkonium chloride (BAC) loaded to montmorillonites (Mt) or organomontmorillonites (OMt) generates a functional material that can be incorporated to several systems (polymers, paints, etc) as a controlled release bactericide. Understanding the BAC adsorption sites on these adsorbents is of high importance to clarify their adsorption/desorption characteristics in aqueous media or other solvents. In this work, a thorough study about the adsorption/desorption properties of Mt and OMt with regards to BAC is presented, in order to evaluate further BAC release with the consequent aquatic environment contamination. In this work, the BAC adsorption on two different sites is demonstrated: the interlayer space and the external surface. Depending on BAC concentration in water, sorption of BAC at Mt occurred in two steps. At adsorbed amount <0.5 mmol g⁻¹, there was an Mt interlayer expansion of 0.49 nm with no change of the external charge. At adsorbed amount >0.5 mmol g⁻¹, there was a new interlayer expansion attaining 0.75 nm and the external charge shifted to positive value. In the case of OMt, the introduction of BAC produced changes in the interlayer structure and in the external surface charge. BAC desorption was strongly dependent on the type of Mt or OMt and extraction solvent, knowledge of which will allow its safe use in environmental friendly technological applications.

Little is known about the potential toxicity of Cu nanoparticles (nCu), Cr nanoparticles (nCr), and their mixtures to aquatic organisms. To fill this gap, a comprehensive toxicity assessment was conducted using Daphnia magna as a test organism, including a 48-h acute toxicity test, a 21-day chronic test, and a feeding experiment. Four biomarkers were estimated after exposure to nCu, nCr, and their mixtures for 7 days, including acetylcholinesterase (AChE), catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST). The results at all endpoints showed that nCu was more toxic than nCr. The 48-h median lethal concentration values of nCu and nCr were 0.63 and 1.57 mg/L, respectively. Significant inhibition of reproduction and growth of D. magna was found, and the intrinsic rate of natural increase was a sensitive parameter for nCu and nCr during the 21-day exposure. A concentration-dependent decrease in filtration and ingestion was observed which was consistent with inhibition of reproduction and growth of D. magna. The biochemical responses revealed an increase in GST activity and decrease in AChE activity, while SOD and CAT activities were increased at low concentrations and decreased at high concentrations for all exposures. Collectively, our results confirmed that nanoscale Cu and Cr can exert negative effects at different levels on D. magna.

The process for extracting sugarcane juice (Saccharum officinarum) represents the point of greatest contamination in sugarcane mills. Sodium dithiocarbamate also known as metam-sodium or MS is added to inhibit the growth of microorganisms especially Leuconostoc mesenteroides which is responsible for forming polysaccharides. Metam-sodium, upon decomposition, produces highly toxic byproducts. According to literature, under acidic conditions, MS is hydrolyzed resulting in methylamine (MA), CH₃NH₂, and carbon disulfide (CS₂), and in dilute alkaline solutions, MS produces an oxidation reaction characterized by the formation of elemental sulfur (S) and methyl isothiocyanate (MITC). In this paper, it was studied how MS decomposes to MITC and/or MA considering the effects of the matrix (methanol and water); of temperature (4 and 25 °C); of processing time (0, 1, 2, 3, 4 days); and of pH (4.0, 4.5, 7.0). A second experimental design considering the effects of the matrix (water and sugarcane juice); of temperature (4, 25, 35, 45 °C); of processing time (30, 300 min); and of pH (4.0, 4.5, 7.0) was derived from the results obtained considering MITC and/or MA formation. According to the statistical analysis of these results (p < 0.05), the order of the influential factors was as follows: time > matrix > pH > temperature. Results also indicated that the water matrix at pH = 4.5 and 45 °C had the lowest degradation rate (k), with a value of 8.82 day⁻¹, while for the sugarcane juice matrix at the same pH and temperature conditions was larger, with a k value of 30.07 day⁻¹. These results show that the matrix is also important for the degradation of dithiocarbamate to MITC and to MA.

Aluminum/iodine pentoxide (Al/I₂O₅) composites are currently receiving much attention for their capabilities as potential anthrax combatants. Their high halogen gas release, coupled with high temperature evolution from combustion, renders them effective in bacterial deactivation. Despite extensive research on the energetic capacities of these compounds, limited information is currently available in relation to their potential environmental (non-target) effects. We evaluated the effects of Al/I₂O₅ on aquatic (Daphnia magna) and terrestrial (Eisenia fetida, Acheta domesticus) invertebrates, as well as alfalfa (Medicago sativa) seed germination. Polytetrafluoroethylene (PTFE, or DuPont Teflon® MP1150) was examined concurrently to assess whether observations were general to halogen, or element specific. Our observations were based on mortality and reproduction (hatchability) for the terrestrial and aquatic assays. In all Al/I₂O₅ assays, mortality was concentration dependent, ranging from 0% mortality in the control samples to partial and complete mortality in the contaminated cases. The PTFE assays showed no mortality at all contaminant concentrations. At a maximum Al/I₂O₅ contaminant concentration of 1000 μg/g (ppm), 100% mortality was observed in cricket assay conducted in sand within 72 h exposure and earthworm assay conducted in soil within 4 days exposure. In the aquatic assay, a water concentration of 200 μg/mL (ppm) caused 100% mortality to D. magna in less than 12 h. The effect of aluminum/iodine pentoxide on earthworm cocoon hatching success was also determined. At soil concentrations ≤ 400 μg/g, hatching success for earthworm cocoons was equivalent to control (un-contaminated) soil; above this concentration, hatching success was reduced by a factor of 2. Alfalfa germination tests were performed at a single contaminant concentration of 1000 μg/g. This soil concentration was completely inhibitory to seed germination.

Groundwater composition may have a pronounced impact on long-term performance of permeable reactive barriers (PRBs). Here, batch and column experiments were conducted to investigate the effects of humic acid (HA) on Cr(VI) removal by pyrite in systems containing cations such as Ca²⁺ and Mg²⁺. HA was observed to have inhibitory effect on Cr(VI) uptake by pyrite under the experimental conditions studied (e.g., pH 3 to 8). HA sorbed onto pyrite surface and thus (1) competed against Cr(VI) for pyritic surface sites and/or (2) increased electrostatic repulsion between Cr(VI) and pyrite. In systems with HA and Ca²⁺/Mg²⁺, the Cr(VI) uptake by pyrite decreased drastically relative to HA alone due to the aggregation of HA with Ca²⁺/Mg²⁺. The formation of such HA aggregates/precipitates blocked Cr(VI) ions to reach its binding sites, thereby resulting in a substantial decrease in Cr(VI) uptake. Overall, the results have major implications for proper design and operation of PRBs with pyrite as the reactive material.

In Portugal, the industrial production of phosphate fertilizers, has been dealing with a specific raw material—north African phosphate rock—with a high content of trace metals and natural radioactive elements mainly from the ²³⁸U decay series. A disabled phosphate plant located in the vicinity of the river Tejo estuary has produced phosphoric acid for several decades (1950–1989) and dumped tons of phosphogypsum (PG) on retention lagoons, formerly decanted and deposited into a stockpile. This paper deals with the assessment of radionuclides, rare earth elements (REEs) and heavy metals transfer to plants (fam. Plantaginaceae, Plantago sp.) and mosses (fam. Bryaceae, Bryum sp.) growing naturally on the PG pile. In Plantago sp., the concentration ratio (CR, plant tissue/PG) was 0.187 for ²²⁶Ra and 0.293 for ²¹⁰Pb. The translocation factor (TF, aerial parts/roots) was 0.781 for ²²⁶Ra and 0.361 for ²¹⁰Pb. In contradiction to the high CR, the leachability of ²²⁶Ra from PG was low, lower than 2%. The results confirmed the role of mosses as biomonitors. A high quantity of contaminants collected in its biomass confirmed the hypothesis of their significant transport by air and rain water. High concentrations of heavy metals (As, Cd, Zn, W) in samples collected on the stockpile are an evidence of their transport from former industrial zones in the surroundings and present even more important risk for public health and environment than natural radionuclides and REEs from the PG stockpile.