The aim of the research was to compare the effect of two types of organic sorbents-humic acid (HA) and biochar (BC)-in sorption-desorption processes of different polar pesticides, which residues are commonly present in arable soils and are potentially harmful for the environment. It also aims to advance the understanding of behavior of both ionizable and nonionizable pesticides in the presence of BC and HA in soils. Materials and methods Three different classes of pesticides were investigated: carbamates (carbaryl and carbofuran), phenoxyacetic acids (2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)), and aniline derivatives (metolachlor). Investigated humic acid was extracted by Shnitzer's method from topsoil horizon of arable Gleyic Phaeozem. Biochar was produced from wheat straw in gasification process at 550°C, remaining 30 s in the reactor. To obtain the experimental goal structural properties of both sorbents were determined and sorption-desorption experiments conducted. To the investigated organic matter samples (HA or BC), 10 or 15 mg L −1 pesticide solutions in 10 mM CaCl 2 were added and the mixtures were shaken for 24 h. Afterwards, the samples were centrifuged and supernatants analyzed by LC-MS/MS for the pesticide content. Analogous experiment was performed for desorption studies (samples refilled with 10 mM CaCl 2). Results and discussion Humic acids exhibited strong affinity for the ionic substances, for which high-percentage uptake (74.6 and 67.9% initial dose of 2,4-D and MCPA, respectively) was obtained. Retention of nonionic carbamates on HA was much weaker (35.4% of carbofuran and 10.2% of carbaryl sorbed). Sorption of carbamates to BC was significantly reduced (76.4-84.3%) by the alkaline hydrolysis. Metolachlor was bound comparably strong both by HA (72.9%) and BC (70.2%), although different mechanisms governed its sorption. Noticeable desorption occurred only in the case of 2,4-D bound to HA (over 50%), whereas other studied compounds were released from HA within the range of 4.4-10.8% of the dose sorbed. Oppositely to HA, desorption of all studied pesticides from BC was completely inhibited, except for 2,4-D (3.7% desorbed). Conclusions Investigated humic acid has high affinity to polar, ionic pesticides of high water solubility, which are sorbed via specific interactions with HA functional groups. Studied biochar, due to its moderately hydrophobic character, preferentially attracts nonionic pesticides of relatively high logP values and low water solubility. Hydrophobic bonding is postulated as a main mechanism of their attraction to BC. Besides sorbent structural properties, pH is the main factor governing sorption equilibria in the studied mixtures.

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were determined using FAAS; the N-NH 4 and N-NO 3 content was analysed using a SAN ++ SFA continuous flow colorimeter (Skalar Analytical B.V., Holland). The solubility index (I), presented as the percentage share of water-extractable forms of macro-and micronutrients in the total content, was calculated according to Eq. (1): p-macro-or microelement, pw-water-extractable form of element, pt-total content of the element. Statistical analysis. Results were statistically verified using Statistica 12.5. Means were compared by the Tukey test, at a confidence level of P < 0.05. Results and discussion pH and ec during composting. Changes in H + concentration were observed during composting of MSW, reflected by analysis of water solution pH (Table 1). The lowest pH values (6.9) were found for water extracts from raw material. During the composting process, the pH increased, with the highest values being observed at between 54 and 126 days. In the following phases of the composting process, a slight decrease in pH was observed (8.0-8.1), but the result was significantly higher than those observed in the first days of the composting process. The decomposition of organic matter, particularly its components like proteins, amino acids and peptides, causes the release of ammonium which contributes to an increase in pH 36. Changes in the EC of water extracts during the composting process were observed as well (Table 1). The values of this parameter depended on the length of the composting process, significantly decreasing with an increased in composting time. After about 54-70 days of composting, the EC value was about 2 mS/cm, and in the final phase it increased slightly to 2.15 mS/cm. From the 54th to 68th day of composting, we observed some stabilization of EC, and lower values with respect to that of the initial material, indicating a reduction in the amount of soluble salts in the matured compost. The results obtained, according to many authors 36,37 , suggest that the concentrations of soluble salts in the compost analysed here were in the range considered non-phytotoxic.

Humic substances, including humin fraction, play a key role in the fate of organic and inorganic xenobiotics contaminating the environment. Humin is an important fraction of humic substances, which has been the least studied to date. This is due to the difficulties connected with its isolation that pose a number of methodological problems. Methods of humin fraction isolation can be divided into following main groups: (1) digestion of mineral soil components with HF/HCl followed by alkali extraction of HA and FA; (2) alkali extraction of HA and FA followed by extraction of humin by different organic solvents; and (3) alkali extraction of HA and FA followed by HF/HCl digestion of mineral soil components. Nevertheless, each of these methods has different limitations. We described in detail a useful procedure of humin isolation, in which this fraction was not extracted, but isolated from the soil by removing its soluble organic and mineral components. A modified method of HA and FA extraction with 0.1 M NaOH, according to the International Humic Substances Society, was used in the first step. Then, the mineral components in the residue were digested with the 10% HF/HCl. Unlike the procedures oriented to increase the concentration of organic matter, samples were treated several times with the HF/HCl mixture until the mineral fraction was almost completely digested. The main assumption of the method modification was to obtain the highest yield with the lowest possible ash content, but without affecting humin chemical structure. The results showed that the proposed procedure is characterized by a high efficiency and recovery and, therefore, it can be used to isolate high amounts of humin from soil.

In 2019–2020, a study was conducted to evaluate the suitability of willow composts as a substrate or substrate component in tomato transplant cultivation. In 2019, 4-year-old chopped willow biomass (mostly chips <2 cm long) was formed into four compost prisms: S0—willow compost without additives; SN—willow compost with the addition of nitrogen; SF—willow compost with the addition of wood-decaying mycelium; and SFN—willow compost with the addition of wood-decaying mycelium and nitrogen. Willow compost was rated as a homogeneous substrate (S0, SN, SF, and SFN) and as a substrate component with peat (P), mixed in willow:peat ratios such as 25:75, 50:50, and 75:25, in the variants S0:P, SN:P, SF:P, and SFN:P. For reference, deacidified peat was used as a homogeneous substrate. The study showed that willow compost could be used as a renewable plant material replacing peat. The best parameters (plant height, leaf span, number of leaves, and especially the highest weight) were found in tomato transplants grown in the SF:P and SFN:P substrates and at a 25:75 ratio. It was found that the addition of nitrogen to the compost, in order to obtain a wide C:N ratio, negatively affected the initial growth of tomato plants.