Abstract
PurposeThe analysis covered the interaction of humic acids (HA) isolated from peats with the metazachlor using spectroscopic methods.Materials and methodsFive 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 discussionBased 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 E4/6 coefficient, was found in HA2 sample, while the smallest in HA3 sample. The addition of metazachlor to HA solutions reduced the values of E4/6 coefficient by 33 to 72%, while the values of hydrodynamic diameter by 4 to 32%. No significant changes were found between E4/6 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.ConclusionsThe particle sizes of HA molecules measured by E4/6 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.
Highlights
For many years, despite a number of controversies around the negative impact on the environment, the application of pesticides has been the most effective and modern method protecting crops against various threats of biotic origin (Aktar et al 2009)
The five peatlands have been selected for the research in the southern and northern parts of Poland (1—drainage peatland located in the Orava-Nowy Targ Basin area, 2, 3—mountain fens located in the Babiogórski National Park area, and 4, 5— fen and raised bog, respectively, located in the Dolna Odra Valley area)
Humic acids are heterogenic compounds developed by specific structures
Summary
Despite a number of controversies around the negative impact on the environment, the application of pesticides has been the most effective and modern method protecting crops against various threats of biotic origin (Aktar et al 2009). Since pesticides have been commonly used and their half-time is rather long, their residues can be found in every segment of the natural environment, including water (Tankiewicz et al 2010), soil (Aktar et al 2009), bottom sediments (Erkmen et al 2013), air (Zivana et al 2016), plants (Fantke et al 2011), and living organisms (Jayaraj et al 2016). Apart from their direct threat, the fact that pesticides reside in. They can be trapped in three-dimensional structures of organic matter (Oleszczuk 2007; Ukalska-Jaruga et al 2015)
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