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Introduction Treatment with biologics often leads to clearance of psoriasis. However, some patients do repeatedly fail to respond and/or lose an achieved response (treatment refractory) to the biologic, whereas other patients achieve excellent response to one biologic and remain clear of psoriasis for several years (super-responders). Objective To identify and characterize patients with treatment refractory psoriasis and patients who are super-responders to biologic treatment. Material and methods Patients registered in DERMBIO between January 2007 and November 2019 were included. Patients were categorized as being treatment refractory if they had had treatment failure to >= 3 biologics targeting >= 2 different pathways. Super-responders were patients treated with their first biologic for minimum 5 years without an absolute psoriasis area and severity index (PASI) > 3 between 6 months and 5 years of treatment. All remaining patients from DERMBIO served as comparators. Results In total, 3280 patients were included with a mean age of 45.0 years. 1221 (37%) of the patients were females. Of the included patients, 214 (6.5%) were categorized as treatment refractory and 207 (6.3%) were categorized as super-responders. Treatment refractory patients had higher mean body weight (100.6 kg vs. 90.6 kg, P < 0.0001) and higher mean BMI (32.2 vs. 29.4, P < 0.0001) compared with the rest of patients in DERMBIO. Super-responders had higher socioeconomic status and fewer comorbidities compared with the comparator group (P < 0.0001). Conclusion A small proportion of patients with psoriasis treated with biologics are either super-responders or treatment refractory. Treatment refractory patients have higher body weight, whereas super-responders have fewer comorbidities and higher socioeconomic status.

Saharan dust is an important phosphorus (P) supply to remote and oligotrophic parts of the oceans and American lowland tropical rainforests. Phosphorus speciation in aeolian dust ultimately controls the release and bioavailability of P after dust deposition, but the speciation in Saharan dust and its change during the trans-Atlantic transport remains unclear. Using P K-edge X-ray absorption near edge structure (XANES) spectroscopy, we showed that with increasing dust traveling distance from the Sahara Desert to Cape Verde and to Puerto Rico, about 570 and 4000 km, respectively, the proportion of Ca-bound P (Ca-P), including both apatite and non-apatite forms, decreased from 68-73% to 50-71% and to 21-37%. The changes were accompanied by increased iron/aluminum-bound P proportion from 14-25% to 23-46% and to 44-73%, correspondingly. Laboratory simulation experiments suggest that the changes in P speciation can be ascribed to increasing degrees of particle sorting and atmospheric acidification during dust transport. The presence of relatively soluble non-apatite Ca-P in the Cape Verde dust but not in the Puerto Rico dust is consistent with the higher P water solubility of the former than the latter. Our findings provide insights into the controls of atmospheric processes on P speciation, solubility, and stability in Saharan dust.

Silicic acid and soluble Fe are among the most abundant components in acid mine drainage. During the oxidation of Fe(II), the interaction between silicic acid and freshly formed Fe oxides might change the colloidal dynamics, altering surface charge properties. However, the effects of silicic acid on colloidal Fe oxides formed from acid mine drainage are not fully understood. In this work, we examined the colloidal dynamics of freshly formed Fe oxides in synthetic acid mine drainage (prepared from FeSO solution) under the effect of silicic acid as a function of changes in pH and ionic strength. The results demonstrate that through adsorption, silicic acid progressively slows oxidation and enhances the dispersion of freshly formed Fe oxides by shifting the surface charge toward more negative values. This effect was most prominent between pH 5 and 9. The current results demonstrate that silicic acid enhances the dispersion and transport of freshly formed Fe oxides and suggest that aggregation-based techniques for the treatment of Fe-rich drainage may require further consideration of this effect.

Understanding of the fate of phytolith in soils is important because of its role as an agronomical nutrient resource and for carbon sequestration. Accumulation of phytolith derived silica occurs in paddy soils when phytolith input, here through straw incorporation, is higher than silica removal through crop offtake, dissolution and leaching. Phytolith dissolution is thought to be the main reason for diminishing of phytolith derived silica in soil, with this dissolution being highly dependent on soil chemical properties. In this study, phytolith content from 78 paddy soils sampled in the Red River (RRD) and Mekong River (MRD) Deltas, Vietnam, were quantified and related to pH, electrical conductivity (EC), oxalate-extractable Al and Fe (Alox and Feox), organic carbon (OC) and clay content. Average phytolith contents within the topsoil (0–20 cm) were 4.8 ± 1.98 and 7.74 ± 2.97 mg g−1 for the RRD and MRD, respectively. Positive correlation coefficients obtained for Alox, OC, clay content and EC, implying that these parameters might enhance phytolith resistance to dissolution. Soil pH had a negative correlation coefficient with phytolith content. Lower pH and higher Alox content explained the predominance of the phytolith in the MRD compared to the RRD. Soil pH adjustment can be proposed as an active management strategy to maintain phytolith added Si, source for crops and for carbon sequestration.

Sequential chemical extraction has been widely used to study soil phosphorus (P) dynamics and inform nutrient management, but its efficacy for assigning P into biologically meaningful pools remains unknown. Here, we evaluated the accuracy of the modified Hedley extraction scheme using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy for nine carbonate-free soil samples with diverse chemical and mineralogical properties resulting from different degrees of soil development. For most samples, the extraction markedly overestimated the pool size of calcium-bound P (Ca-P, extracted by 1 M HCl) due to (1) P redistribution during the alkaline extractions (0.5 M NaHCO3 and then 0.1 M NaOH), creating new Ca-P via formation of Ca phosphates between NaOH-desorbed phosphate and exchangeable Ca2+ and/or (2) dissolution of poorly crystalline Fe and Al oxides by 1 M HCl, releasing P occluded by these oxides into solution. The first mechanism may occur in soils rich in well-crystallized minerals and exchangeable Ca2+ regardless of the presence or absence of CaCO3, whereas the second mechanism likely operates in soils rich in poorly crystalline Fe and Al minerals. The overestimation of Ca-P simultaneously caused underestimation of the pools extracted by the alkaline solutions. Our findings identify key edaphic parameters that remarkably influenced the extractions, which will strengthen our understanding of soil P dynamics using this widely accepted procedure.

Summary Aggregation properties of iron oxide particles have received much attention because of their environmental importance in soil and aquatic environments. The effects of silicic acid on the pH-dependent surface charges that govern the aggregation of goethite have received little attention. In this study we determined the effect of silicic acid as a function of pH and ionic strength (IS) on the aggregation of a synthetic goethite by a combination of particle-size analysis using dynamic light scattering and test tube experiments to quantify particles in suspension. We investigated silicic acid adsorption on goethite quantitatively by batch adsorption isotherms, and the changes in surface charge on the adsorption of silicic acid were identified by the zeta potential (ζ). Our results revealed that silicic acid can lead to a significant decrease in ζ. A change in the pHiep (iep: isoelectric point) from 8.5 to lower pH values, typically pH 4–5.5, in the presence of silicic acid suggests enhanced aggregation of goethite in the acidic pH range. At alkaline pH, both goethite and silicic acid were negatively charged because of strong deprotonation, and silicic acid adsorption promoted goethite dispersion. Ionic strength affected the aggregation of goethite by shifting ζ towards the iep and it can also obscure the role of silicic acid. Highlights Effect of silicic acid on surface charge and aggregation of goethite was investigated. Adsorption of silicic acid reduces ζ and allows goethite to aggregate at lower pH. Ionic strength can also affect aggregation of goethite by shifting ζ towards the isoelectric point. Silicic acid in soil might maintain goethite particles in an aggregated state.

In soils, dispersion is a crucial step preceding the loss of clay-sized particles by surface run-off and leaching, which in turn results in soil degradation. Despite the fact that silicic acid is common in soil solutions, its effect on aggregation stability of fine sized particles in soils has not been detailed. Here we examined the effect of silicic acid on dispersion of a kaolinitic soil clay fraction rich in Fe-oxides (8.5%) at different pH values by combining dynamic light scattering for particle sizing and test tube experiments for examination of particles in suspension. Adsorption of silicic acid on the clay fraction was characterized by batch adsorption experiments and effects on surface charge by zeta potential (ζ) measurements over a pH range from 2 to 11. We found that silicic acid adsorbed onto clay and co-existing Fe oxides, made ζ more negative, and thereby counteracted aggregation of the clay fraction. Silicic acid showed its most effectivity for maintaining dispersion at a pH range of 4 to 6. Beyond this pH range, dispersion was either strongly favored or prevented, and the effect of silicic acid on dispersion was obscured. Given the ubiquitous presence of silicic acid in soils, our findings regarding its impact on aggregation stability have important implication for conservation of acidic soils.

Rice plants assimilate both silicon (Si) and arsenic (As) from the soil solution and accumulate these elements in their tissues. While Si has been known as a major material that builds up a so-called phytolith structure throughout the plant body, the fate of As in rice plants is not fully understood. This study aims to clarify the possible encapsulation of As into the phytolith structure in rice straw or rice straw ash and to evaluate the dissolution properties of the encapsulated As. Rice straw contains up to ~12 mg As kg−1, which highlights this material as a sink and source of As that needs to be taken into account. The intensified heat treatments of rice straw could lead to an enrichment of As in the burned products, from which As is likely associated more tightly with the phytolith structure. We observed strong correlations of released As and Si, demonstrating that the release of As is tightly controlled by the dissolution of phytoliths. This means that phytoliths can contribute to the soil As pool, but this As source might be obscured because it is recalcitrantly lodged within the phytolith structure. This finding serves as a basis for further assessing the role of phytolith-encapsulated As rice paddy systems and for developing proactive practices to manage As-tainted straw.

• Vertical transport results in a potential loss of upto 10 ton Si ha −1 from paddy soils with two, annual rice-cropping cycles.

is missing (Short communication).