The effects of biochar aging on rhizosphere microbial communities in cadmium-contaminated acid soil.

Biochars are widely used in the remediation of Cd-contaminated soils. However, changes in the bacterial communities in the rhizosphere contaminated with Cd in response to biochar aging are poorly studied. Addressing this gap in knowledge is important to improving micro-ecological services on healthy growth of plants with mitigation strategies against Cd contamination. An aging experiment (270 days) was conducted with biochars derived from poultry litter and sugar-gum wood added to a Cd-contaminated acid soil. Bacterial communities in the rhizosphere of Brassica rapa and bulk soils were investigated after 1, 90 and 270 days of biochar aging. There was no significant difference (P > 0.05) in bacterial Shannon and Simpson indices between the control and biochar treatments. However, compared to the no-Cd control, the addition of Cd decreased the relative abundances of Firmicutes, Chloroflexi and Acidobacteriota but increased those of Actinobacteriota and Proteobacteria. Poultry-litter biochar had the largest effect on bacterial community composition, especially in the rhizosphere. Aging of poultry-litter biochar increased the abundance of Armatimonadota over time more than the sugar-gum-wood biochar, which was attributed to a lower pH and higher bioavailability of Cd in the sugar-gum-wood biochar treatment. The addition of poultry-litter biochar to the contaminated soil mitigated the bioaccumulation of Cd by increasing soil pH and restoring soil bacterial ecology in contaminated acid soils over time.

Biochar aging alters the bioavailability of cadmium and microbial activity in acid contaminated soils.

The effects of biochar aging on heavy-metal bioavailability and microbial activity are not fully understood. This study determined the effect over 270 days of poultry-litter biochar (PBC) and sugar-gum-wood biochar (SBC) on the bioavailability of Cd and microbial activity in acidic soils differing in organic matter content. Soil basal and substrate-induced respirations, microbial properties, Cd bioavailability and plant Cd bioaccumulation were evaluated at 1, 30, 90 and 270 days. The addition of PBC decreased Cd bioaccumulation by 81% and 85% while SBC decreased bioaccumulation by 47% and 56% in high (Chromosol) and low (Sodosol) organic matter soils, respectively, at Day 1. By Day 270, Cd bioaccumulation significantly (P < 0.05) increased in SBC-amended soils but decreased in PBC-amended soils. The addition of PBC increased both basal and substrate-induced microbial respirations compared to the other treatments over 270-day aging. However, SBC increased microbial biomass C compared to the PBC after Day 30. Aging decreased microbial respiration and biomass C in biochar-amended soils. It is concluded that Cd bioaccumulation increased in SBC-amended soils during aging whereas the PBC decreased Cd bioaccumulation and that the selection of biochar is important to enhance remediation efficiency in the long term.

Mechanisms for the removal of Cd(II) and Cu(II) from aqueous solution and mine water by biochars derived from agricultural wastes.

The capacity of biochars derived from agricultural wastes to remove Cd(II) and Cu(II) from aqueous solution and contaminated mine water was evaluated using laboratory-based batch sorption experiments. To examine immobilization of heavy metals, biochars produced in a commercial-scale mobile pyrolizer from feedstocks: poultry litter; lucerne shoot; vetch shoot; canola shoot; wheat straws; and sugar-gum wood, were tested in a liquid-based system. Biochars were characterized by FTIR, XPS and XRD before and after the mine water treatment. Lucerne biochar had the highest Langmuir sorption capacity of Cd(II) (6.28 mg g-1) and vetch-derived biochar had the highest Cu(II) sorption capacity (18.0 mg g-1) at pH 5.5. All the biochars exhibited higher sorption capacity for Cu(II) than for Cd(II). The smaller ionic radius and higher electronegativity of Cu(II), and the PO43-, CO32- and N-containing functional groups of biochars enhanced their binding affinity. The results demonstrated that poultry litter-derived biochar was effective at removal of the Cd(II) and Cu(II) from mine water up to the levels recommended by the World Health Organisation. The results revealed that precipitation with CO32- and PO43-, complexation with -OH and -COOH groups and electrostatic interaction with O-containing surface functional groups were the main mechanisms involved in the removal of multi-metals by biochars, and that selection of feedstock materials for biochar production is important to maximise remediation of multi-metals in contaminated water.

Efficacy of woody biomass and biochar for alleviating heavy metal bioavailability in serpentine soil.

Crops grown in metal-rich serpentine soils are vulnerable to phytotoxicity. In this study, Gliricidia sepium (Jacq.) biomass and woody biochar were examined as amendments on heavy metal immobilization in a serpentine soil. Woody biochar was produced by slow pyrolysis of Gliricidia sepium (Jacq.) biomass at 300 and 500 °C. A pot experiment was conducted for 6 weeks with tomato (Lycopersicon esculentum L.) at biochar application rates of 0, 22, 55 and 110 t ha-1. The CaCl2 and sequential extractions were adopted to assess metal bioavailability and fractionation. Six weeks after germination, plants cultivated on the control could not survive, while all the plants were grown normally on the soils amended with biochars. The most effective treatment for metal immobilization was BC500-110 as indicated by the immobilization efficiencies for Ni, Mn and Cr that were 68, 92 and 42 %, respectively, compared to the control. Biochar produced at 500 °C and at high application rates immobilized heavy metals significantly. Improvements in plant growth in biochar-amended soil were related to decreasing in metal toxicity as a consequence of metal immobilization through strong sorption due to high surface area and functional groups.

Iodine in commercial edible iodized salts and assessment of iodine exposure in Sri Lanka.

BACKGROUND: Iodine is an essential micronutrient used by the thyroid gland in the production of thyroid hormones. Both excessive and insufficient iodine intakes can cause thyroid diseases thus harmful to the human body. Inadequate iodine intake by human body causes Iodine Deficiency Disorders (IDD) and hypothyroidism. Excessive iodine intake causes Iodine Induced Hyperthyroidism (IIH). Universal Salt Iodization (USI) is the most effective way of preventing IDD. This study determined the concentrations of iodine species in commercial edible salt products, the stability of iodine at different conditions and iodine exposure at the consumer level. METHODS: The iodine contents of six commercial edible iodized salts were determined qualitatively and quantitatively for both iodide and iodate. Thereafter, the first three products of highest iodine contents, the stability of iodide at exposed to air and heat was measured after 24 hours. Risk assessment of exposure was done at four levels considering the WHO estimation. RESULTS: Results revealed that all of the salt products have excess iodine that is above the fortification level of 15-30 mg kg(-1) level in Sri Lanka. Iodide stability was reduced at the average percentages of 13.1, 10.7 and 11.3. The iodate loss percentages were 0, 5.7 and 0 at open air. The iodide loss percentages at the temperature of 50 °C were 4.6, 7.8 and 8.6 while at 100 °C, loss percentages were 11.1, 11.4 and 15.9 for the same salt products. The iodine exposure at lower consumption during cooking ranged 244.4-432.2 µg/day while 325.9-576.3 µg/day for medium consumption, 407.4-720.4 µg/day for moderate high salt consumptions and 488.8-864.4 µg/day for high salt consumptions. As a total 95.8 % cases can cause IIH and only 4.1 % of them can provide optimal iodine nutrition in a population. Iodine exposure without cooking ranged 305.5-540.3 µg/day for low salt consumption, 407.4-720.4 µg/day for medium consumption and 509.2-900.5 µg/day for moderate high consumption and 611.1-1080.6 µg/day for high salt consumptions. CONCLUSIONS: All of the incidents (100 %) of consumption without cooking at the household level can cause excessive iodine intake and IIH in a population.