Do contaminants compromise the use of recycled nutrients in organic agriculture? A review and synthesis of current knowledge on contaminant concentrations, fate in the environment and risk assessment.

Use of nutrients recycled from societal waste streams in agriculture is part of the circular economy, and in line with organic farming principles. Nevertheless, diverse contaminants in waste streams create doubts among organic farmers about potential risks for soil health. Here, we gather the current knowledge on contaminant levels in waste streams and recycled nutrient sources, and discuss associated risks. For potentially toxic elements (PTEs), the input of zinc (Zn) and copper (Cu) from mineral feed supplements remains of concern, while concentrations of PTEs in many waste streams have decreased substantially in Europe. The same applies to organic contaminants, although new chemical groups such as flame retardants are of emerging concern and globally contamination levels differ strongly. Compared to inorganic fertilizers, application of organic fertilizers derived from human or animal feces is associated with an increased risk for environmental dissemination of antibiotic resistance. The risk depends on the quality of the organic fertilizers, which varies between geographical regions, but farmland application of sewage sludge appears to be a safe practice as shown by some studies (e.g. from Sweden). Microplastic concentrations in agricultural soils show a wide spread and our understanding of its toxicity is limited, hampering a sound risk assessment. Methods for assessing public health risks for organic contaminants must include emerging contaminants and potential interactions of multiple compounds. Evidence from long-term field experiments suggests that soils may be more resilient and capable to degrade or stabilize pollutants than often assumed. In view of the need to source nutrients for expanding areas under organic farming, we discuss inputs originating from conventional farms vs. non-agricultural (i.e. societal) inputs. Closing nutrient cycles between agriculture and society is feasible in many cases, without being compromised by contaminants, and should be enhanced, aided by improved source control, waste treatment and sound risk assessments.

Early diagenetic behavior of arsenic in the sediment of the hypersaline Maharlu Lake, southern Iran.

Arsenic (As) is a toxic element can experience phase and speciation changes during the early diagenesis of sediments across the sediment-water interface, affecting its mobility and toxicity. Maharlu Lake is a hypersaline lake in Southern Iran that today receives significant inflow from urban, industrial and agricultural wastewater. A 1-m core was sampled from the lake sediment in an area far away from the major inflows. We performed a semi-quantitative analysis of the elemental composition, and a quantitative analysis of the total As concentration, pH, loss on ignition, water content, salt content, and grain size distribution to characterize changes in sediment composition with depth and their influence on the variability of As partitioning and speciation. Nine characterized lithologies were selected for a sequential As extraction analysis to study the vertical variations in phase and speciation of As in the heterogenic lithologies. Total As concentrations range from 1.0 µg g-1 to 13.6 µg g-1. As is present mostly in HNO3 and HCl extractable fractions with As5+ being the predominant species. As3+ was mostly found in phosphate and NH2OH·HCl extractable fractions. The concentration of mobile As fractions generally decrease with depth. It seems that the As stored in volatile sulfides and very poorly crystalline Fe and Al hydr-oxides in the shallow sediment transforms to sulfides phases during burring. Our findings show that the mobility and toxicity of As decreases during early diagenetic processes in Maharlu lake. However, the As can be remobilized either via changes in the redox conditions in the lake.

Visualizing the dynamics of soil aggregation as affected by arbuscular mycorrhizal fungi.

Stable soils provide valuable ecosystem services and mechanical soil stability is enhanced by the presence of arbuscular mycorrhizal fungi (AMF). Soil aggregation, which is the major driver of mechanical soil stability, is often treated as a static phenomenon, even though aggregate turnover is continually ongoing. In fact, some breakdown of macroaggregates is necessary to allow new aggregate formation and inclusion of new organic matter into microaggregates. We determined how aggregate turnover times were affected by AMF by tracking movement of rare earth elements (REE), applied as their immobile oxides, between aggregate size classes, and using X-ray fluorescence microscopy to spatially localize REEs in a sample of aggregates. Here we show that AMF increased large macroaggregate formation and slowed down disintegration of large and small macroaggregates. Microaggregate turnover was increased in the presence of AMF. Internal aggregate organization suggested that although formation of microaggregates by accretion of soil to particulate organic matter is common, it is not the only mechanism in operation.

Pathophysiology of severe forms of falciparum malaria.

We studied 26 patients with severe falciparum malaria who were admitted to an ICU in Namibia. The pathophysiologic effects on various organ systems are documented and the mortality associated with organ failure is reported. Patients with three or more organ failures showed a high mortality, especially when pulmonary or renal failure occurred. Predicted mortality based on the Acute Physiology and Chronic Health Evaluation II scoring system was 34% compared to an actual mortality of 38%.

G-protein alpha-subunits in cytosolic and membranous fractions of human neutrophils.

In plasma membranes of human neutrophils, we identified two major pertussis toxin substrates of 40 kDa Mr with pI values of 5.30 and 5.37. Only the acidic of the two substrates was also present in neutrophil cytosol. Two-dimensional tryptic peptide maps revealed a high degree of homology of cytosolic and particulate substrates. Purified G-protein beta gamma-complex stimulated pertussis toxin-catalyzed [32P]ADP-ribosylation of membranous and cytosolic substrates of neutrophils less than 2-fold and 6-fold, respectively. Hydrodynamic properties of the cytosolic substrate strongly suggested that it exists as a monomer. Purified G-protein beta gamma-complex increased the s20,w value of the cytosolic substrate from 3.3 S to 4.0 S. The GTP analogue, guanosine 5'-O-(3-thiotriphosphate), promoted the release of pertussis toxin substrates from plasma membranes. An antiserum raised against a sequence specific for the Gi2 alpha-subunit reacted with 39-40 kDa proteins in plasma membranes and with an apparently single 40 kDa protein in cytosol. We conclude that neutrophil cytosol contains monomeric Gi2 alpha-subunits which--by interacting with hydrophobic beta gamma-complexes--may reversibly bind to the plasma membrane.