Using delayed luminescence to characterize humic acids from lake sediments

Purpose

Using the delayed luminescence (DL) method, the photoluminescent properties of humic acids (HA) extracted from lake sediments were analyzed. Delayed luminescence is a promising technique for characterizing HA and other forms of organic matter of various origins. But information is insufficient regarding both its optimal operating conditions and also those environmental factors that control the chemical constitution of samples, which affects patterns of delayed luminescence.

Materials and methods

The research material was HA from lake sediments. Humic acid extractions were carried out using the method developed by the International Humic Substances Society. Studies on excitation and recording of DL intensity of HA solutions were carried out with the use of a specially designed device for continuous recording of photo-induced luminescence. The DL was excited with a monochromatic light at multiple wavelengths.

Results and discussion

The DL intensity depended on the wavelength of the exciting light. The highest DL intensity was obtained with excitation by blue light, the lowest DL intensity was observed with excitation by red light. Statistically significant differences among DL intensity were observed in the examined humic acids. These differences may be evidence of the variable quantitative and qualitative contributions of photoluminophores to the structure of the studied HA molecules as well as their different photochemical reactivities. For the blue- and green-excited DL intensity, statistically significant positive correlations were obtained with the elemental atomic ratio O:H and CQ coefficient. For the red-excited DL intensity, statistically significant positive correlations were obtained with the C and H content and H:C, C:N atomic ratios, while negative correlations were obtained with the free radical concentration.

Conclusions

Delayed luminescence depended on the wavelength of the exciting light. The DL intensity excited by blue and green light was different than the red light-excited DL intensity. The DL depended on the primary composition of sediments and the properties and structure of HA too. The grouping of HA showed that the HA formed in organic matter-poor, silicate-rich sediments had greater DL emission than did those extracted from sediments that were enriched in organic matter.

     

Studying of the interaction between peat humic acids and metazachlor using spectroscopy methods

Purpose

The analysis covered the interaction of humic acids (HA) isolated from peats with the metazachlor using spectroscopic methods.

Materials and methods

Five peatlands have been selected for the study in the southern and northern parts of Poland. Extraction of humic acids (HA1, HA2, HA3, HA4, and HA5) was performed using a procedure recommended by the International Humic Substances Society. Metazachlor 500 SC with metazachlor as a biologically active substance [2-chloro-N-(pyrazol-1-ylmethyl)acet-2′,6′-xylidide] has been used. HA have been assessed on the basis of their elemental composition. Spectroscopic techniques have been used to study the HA structure and their interaction with metazachlor including: UV-visible spectroscopy, dynamic light scattering, and delayed luminescence (DL)

Results and discussion

Based on their morphological and chemical properties, the studied peat soils can be classified as follows: (1) Eutric Murshic Sapric Histosols, (2) Eutric Sapric Histosols, (3) Eutric Hemic Histosols, (4) Eutric Fibric Histosols, and (5) Dystric Dranic Hemic Histosols according to the WRB guidelines (2015). Results showed that the largest particle size, measured by E_4/6 coefficient, was found in HA2 sample, while the smallest in HA3 sample. The addition of metazachlor to HA solutions reduced the values of E_4/6 coefficient by 33 to 72%, while the values of hydrodynamic diameter by 4 to 32%. No significant changes were found between E_4/6 after adding of metazachlor to HA solutions. The largest changes in DL intensity, excited both by blue and red light after herbicide addition, were observed in HA2 sample, which is characterized by the largest particle size, the highest oxygen content and CQ value as well as the lowest “aromatization rate” value.

Conclusions

The particle sizes of HA molecules measured by E_4/6 coefficient do not impact on the particle sizes of HA-herbicide systems measured by the same ratio. The delayed luminescence may become valuable, because it is simple, fast, and sensitive. Additionally, the results show minor errors comparing with chemical methods. This method may provide information about structure and nature of humic acids, as well as their photoreactivity. The using of delayed luminescence in studies of HA-pesticides interaction may enable us to better understand the luminescence properties of HA.

     

Optical characteristic of humic acids from lake sediments by excitation-emission matrix fluorescence with PARAFAC model

Journal of Soils and Sediments - The study aimed to find out whether fluorescence parameters of humic acids (HA), obtained from excitation-emission matrix (EEM) fluorescence spectra, could be used...     

Nitrogen Loss by Ammonia Volatilization in Cultivation of Olive Orchards Fertilized with Compost

Eurasian Soil Science - This study concentrated on drip-irrigated olive trees on Calcisols, Cambisols, and Luvisols. The olive trees were fertilized with compost spread in bands about 30 cm from...     

Mutual relations between PAHs derived from atmospheric deposition,enzymatic activity,and humic substances in soils of differently urbanized areas

Purpose

The aim of this study was to determine the mutual relations between polycyclic aromatic hydrocarbons (PAHs) originated from atmospheric emissions and enzymatic activity and humic substances in soils at differently urbanized area, on an example of the Lublin city, east Poland.

Materials and methods

The chosen areas represented three differently urbanized environments: old tenement houses and modern residential blocks, mixture of different building and rural landscape, and typical rural environment with smallholding farms, respectively. On each of the urban, suburban, and rural areas, one representative plot was chosen on fallow lands classified as luvisol derived from loess. The soil samples were collected from the top 25 cm layer. The following properties were determined: pH, organic carbon, total nitrogen, humic and fulvic acids, PAHs content (14 PAHs from US EPA list), and the activities of the following enzymes: dehydrogenases, acid phosphatase, alkane phosphatase, protease, and urease.

Results and discussion

Higher contents of organic C and total N were found in the rural soil samples. The share of humic acid was similar in all soils investigated, ranging from 19.38 to 25.27%, while fulvic acid values differ significantly between urban and rural areas. The urban soils indicated much lower share of fulvic acids (9.78–10.99%) than those of rural (29.02–29.32%). Consequently, the values of the C_HA:C_FA ratio of the urban soil were approximately two times higher than those of the rural soil. The results showed that both the rate of humification and the activity of dehydrogenases, acid phosphatase, alkaline phosphatase, and proteases in the soils increased in the following sequence: urban < suburban < rural.

Conclusions

The results showed that an increase of PAHs in the urbanized areas affect other soil properties. The phenanthrene/anthracene and fluoranthene/pyrene ratios pointed to coal combustion as the principal source of PAHs in the investigated soils. The PAH content in the urbanized area inhibit humification processes in the soil and the activity of dehydrogenases, acid phosphatase, alkaline phosphatase, and proteases.