Bioaccessibility of polycyclic aromatic hydrocarbons in activated carbon or biochar amended vegetated (Salix viminalis) soil.

The aim of the present study was to determine the effect of activated carbon (AC) or biochars on the bioaccessibility (Cbioacc) of polycyclic aromatic hydrocarbons (PAHs) in soils vegetated with willow (Salix viminalis). The study determined the effect of willow on the Cbioacc PAHs and the effect of the investigated amendments on changes in dissolved organic carbon (DOC), crop yield and the content of PAHs in plants. PAH-contaminated soil was amended with 2.5 wt% AC or biochar. Samples from individual plots with and without plants were collected at the beginning of the experiment and after 3, 6, 12 and 18 months. The Cbioacc PAHs were determined using sorptive bioaccessibility extraction (SBE) (silicon rods and hydroxypropyl-ß-cyclodextrin). Both AC and biochar caused a decrease in the Cbioacc PAHs. Immediately after adding AC, straw-derived biochar or willow-derived biochar to the soil, the reduction in the sum of 16 (Σ16) Cbioacc PAHs was 70.3, 38.0, and 29.3%, respectively. The highest reduction of Cbioacc was observed for 5- and 6-ring PAHs (from 54.4 to 100%), whereas 2-ring PAHs were reduced only 8.0-25.4%. The reduction of Cbioacc PAHs increased over time. Plants reduced Cbioacc in all soils although effects varied by soil treatment and PAH. Willow grown in AC- and biochar-amended soil accumulated less phenanthrene than in the control soil. The presence of AC in the soil also affected willow yield and shoot length and DOC was reduced from 53.5 to 66.9% relative to unamended soils. In the biochars-amended soil, no changes in soil DOC content were noted nor effects on willow shoot length.

The concentration and changes in freely dissolved polycyclic aromatic hydrocarbons in biochar-amended soil.

The presence of polycyclic aromatic hydrocarbons (PAHs) in biochars hinders their environmental use. The aim of this study was to determine the freely dissolved (Cfree) PAH content in soil amended with biochar in a long-term (851 days) field experiment. Biochar was added to the soil at a rate of 30 and 45 t/ha. The addition of biochar to the soil resulted in a decrease in Σ13 Cfree PAHs by 25 and 22%, in the soil with the addition of biochar at the rate of 30 and 45 t/ha, respectively. As far as individual PAHs are concerned, in most cases a reduction in Cfree was also observed (from 3.6 to 66%, depending on the biochar rate). During the first 105 days of the experiment, the content of Σ13 Cfree in the biochar-amended soil significantly decreased by 26% (30 t/ha) and 36% (45 t/ha). After this period of time until the end of the experiment, no significant changes in Cfree were observed, regardless of the biochar rate. However, the behavior of individual PAH groups differed depending on the number of rings and experimental treatment. Ultimately, after 851 days of the experiment the content of Σ13 Cfree PAHs was lower by 29% (30 t/ha) and 35% (45 t/ha) compared to the beginning of the study as well as lower by 40% (30 t/ha) and 42% (45 t/ha) than in the control soil. The log KTOC coefficients calculated for the biochar-amended soils were higher immediately after adding biochar and subsequently they gradually decreased, indicating the reduced strength of the interaction between biochar and the studied PAHs. The obtained results show that the addition of biochar to soil does not create a risk in terms of the content of Cfree PAHs.

Persistence of polycyclic aromatic hydrocarbons (PAHs) in biochar-amended soil.

In the present study the persistence of polycyclic aromatic hydrocarbons (PAHs) applied with biochar to acidic soil (loamy sand) was studied in two and half year field experiment. An experiment was carried out in three experimental plots (15 m(2) each). The biochar was introduced in the following doses: soil without fertilization - control (C-BC00), soil with 30 t ha(-1) (B-BC30) and soil with 45 t ha(-1) (A-BC45) of biochar. Biochar addition to soils resulted in an increase in the PAHs content from 0.239 µg g(-1) in control soil to 0.526 µg g(-1) and 1.310 µg g(-1) in 30 and 45 t ha(-1) biochar-amended soil respectively. However during the experimental period the PAHs content decreased to a level characteristic for the control soil. The highest losses of PAHs were observed during the first 105 days of the experiment. Three and four rings PAHs were the most susceptible for degradation and leaching. Migration of PAHs from 0-10 cm to 10-20 cm soil horizon was also observed.

An ecotoxicological evaluation of soil fertilized with biogas residues or mining waste.

This paper presents an ecotoxicological evaluation of soil fertilized with biogas digestate (BD) or mining waste (MS). The study was performed under pot experiment conditions. BD was added at a dose of 1.5 and 3% to the soil. MS was applied at a dose of 10 and 20%. Samples were collected at the beginning of the experiment and after 180 and 360 days from the start of the study. In addition, a parallel experiment with the addition of CaO was done. This was designed to eliminate the adverse effect of low soil pH on the test organisms. A battery of ecotoxicological tests was used based on tests with plants (Phytotoxkit F), microorganisms (Microtox), and crustaceans (Daphtoxkit F). In most cases, the obtained results showed that the investigated wastes had a stimulating effect on the growth of Lepidium sativum roots. The highest content of BD was an exception since it inhibited the growth of L. sativum roots. After adding BD and MS, both the luminescence of Vibrio fischeri and the mortality of Daphnia magna was at a similar level to that in the control soil. An exception was the significant increase in the mortality of D. magna after 48 h for soil with 3% BD. The tests performed after 6 and 12 months showed that, with time, the toxicity of the waste-amended soil fluctuated, but ultimately decreased in most cases compared to the control. The effect of the addition of CaO on the examined toxicity parameters was different and depended on the experimental variant.