Assessment and source quantification of heavy metal(loid)s in surface water using multivariate analyses from the Saigon River, Vietnam.

The metal concentration in surface water of a river could be affected by season, position, and oceanic process such as tide. The current study aimed to (1) examine the heavy metal(loid) concentration in surface water from the Saigon River as affected by the combination of season, tide, and position and (2) apportion and quantify pollution sources. Ninety-six surface water samples were collected from 13 sites on the River in four campaigns (rainy season + ebb tide, rainy season + flood tide, dry season + ebb tide, and dry season + flood tide). Eight heavy metal(loid)s (Al, B, Bi, Fe, Mn, Pb, Sr, and Zn) were measured and subjected to multivariate analyses. Three-way ANOVA showed that in the rainy season, the total concentration of the metal(loid)s (TCM) in two tides was not clearly different from each other while in the dry season the TCM was significantly higher during the ebb tide than during the flood tide. Principal component analysis/factor analysis and Pearson correlation matrix showed that the TCM could be derived from three main sources, grouped into anthropogenic activities such as industrial, agricultural, and domestic wastes from inside Ho Chi Minh city, and natural origins from lowland area and acid sulfate soil. Three pollution sources explained 70% and 68% of the total variance of TCM in the rainy and dry seasons, respectively. In brief, the metal(loid) concentration was significantly affected by the season and tide and the pollution sources could be derived from inside Ho Chi Minh City and from lowland areas beyond the river estuary.

Modeling and Prediction of the Covid-19 Cases With Deep Assessment Methodology and Fractional Calculus.

This study focuses on modeling, prediction, and analysis of confirmed, recovered, and death cases of COVID-19 by using Fractional Calculus in comparison with other models for eight countries including China, France, Italy, Spain, Turkey, the UK, and the US. First, the dataset is modeled using our previously proposed approach Deep Assessment Methodology, next, one step prediction of the future is made using two methods: Deep Assessment Methodology and Long Short-Term Memory. Later, a Gaussian prediction model is proposed to predict the short-term (30 Days) future of the pandemic, and prediction performance is evaluated. The proposed Gaussian model is compared to a time-dependent susceptible-infected-recovered (SIR) model. Lastly, an analysis of understanding the effect of history is made on memory vectors using wavelet-based denoising and correlation coefficients. Results prove that Deep Assessment Methodology successfully models the dataset with 0.6671%, 0.6957%, and 0.5756% average errors for confirmed, recovered, and death cases, respectively. We found that using the proposed Gaussian approach underestimates the trend of the pandemic and the fastest increase is observed in the US while the slowest is observed in China and Spain. Analysis of the past showed that, for all countries except Turkey, the current time instant is mainly dependent on the past two weeks where countries like Germany, Italy, and the UK have a shorter average incubation period when compared to the US and France.

Seasonal, spatial variation, and pollution sources of heavy metals in the sediment of the Saigon River, Vietnam.

The current study was conducted to (1) examine seasonal and spatial distribution of heavy metals and metalloid in sediment from the Saigon River and (2) apportion and quantify their pollution sources. Ninety-six sediment samples were taken in the rainy and dry season on 13 sampling sites, distributed over the lower reaches of the River, to analyze for exchangeable concentration of 11 heavy metals and metalloid (Al, B, Cd, Co, Fe, In, Mn, Ni, Pb, Sr, and Zn), pH, EC, organic carbon content, and particle-size distribution. Generally, the concentration of 11 elements was ranked in the order Mn > Al > Fe > Zn > Sr > In > B > Ni > Co > Pb > Cd. Hierarchical cluster analysis grouped 13 sampling sites into two parts based on the similar concentration of the 11 elements. Three-way analysis of variance showed that the total exchangeable concentration of 11 elements was significantly higher in the rainy season than in the dry season and in the upper part than in the lower part of the river. Principal component analysis/factor analysis and correlation analysis revealed that three pollution sources (PS) may contribute to enriching the 11 examined elements in the sediment. These sources included (PS1) from catchment through water erosion over natural areas, explaining 83%, (PS2) mixed sources from catchment through water erosion over agricultural fields and inside Ho Chi Minh City, accounting for 6%, and (PS3) mixed sources from lowland areas, explaining 7.8% of the total variance of the elements. In brief, the sediment concentration of 11 metals and metalloid varied with season and space and three major pollution sources from river catchment, inside Ho Chi Minh City, and lowland contributively enriched the elements in the sediment of the River.

Structure of a new usnic acid derivative from a deacylating Mannich reaction: NMR studies supported by theoretical calculations of chemical shifts.

In a conventional Mannich reaction using piperidine, hydroxypiperidines, morpholine, and N-methylpiperazine with usnic acid, a deacetylation was observed resulting in a substitution at C-2, a loss of an acetyl group, and a Mannich base with a stabilized enol. The enol has a hydrogen bond to the nitrogen of the secondary amine. The structure was investigated by nuclear magnetic resonance and deuterium isotope effects on 13 C chemical shifts as well as with density functional theory calculations to study the changed hydrogen bond pattern. It was found that the hydrogen bond involving the OH-9 group in chloroform forms a strong hydrogen bond than in usnic acid itself and that this hydrogen bond becomes even stronger in the more polar solvent, dimethylsulfoxide. Tautomerism was observed in the Mannich base as demonstrated by deuterium isotope effects on chemical shifts. The position of the tautomeric equilibrium depends on the solvent, and the position of the equilibrium governs the strength of the OH-9…O═C hydrogen bond.