Persistence of detectable insecticidal proteins from Bacillus thuringiensis (Cry) and toxicity after adsorption on contrasting soils.

Insecticidal Cry, or Bt, proteins are produced by the soil-endemic bacterium, Bacillus thuringiensis and some genetically modified crops. Their environmental fate depends on interactions with soil. Little is known about the toxicity of adsorbed proteins and the change in toxicity over time. We incubated Cry1Ac and Cry2A in contrasting soils subjected to different treatments to inhibit microbial activity. The toxin was chemically extracted and immunoassayed. Manduca sexta was the target insect for biotests. Extractable toxin decreased during incubation for up to four weeks. Toxicity of Cry1Ac was maintained in the adsorbed state, but lost after 2 weeks incubation at 25 °C. The decline in extractable protein and toxicity were much slower at 4 °C with no significant effect of soil sterilization. The major driving force for decline may be time-dependent fixation of adsorbed protein, leading to a decrease in the extraction yield in vitro, paralleled by decreasing solubilisation in the larval gut.

Adsorption on montmorillonite prevents oligomerization of Bt Cry1Aa toxin.

The adsorption of the insecticidal Cry1Aa protein from Bacillus thuringiensis (Bt-toxin) on a model clay surface was studied to understand the structural changes of the protein induced by the clay surface. We studied the adsorption of the monomeric and soluble oligomeric forms of the Cry1Aa toxin as a function of pH and ionic strength conditions on montmorillonite, which is an electronegative phyllosilicate. Cry1Aa secondary structure was determined from the amide I' FTIR absorption profiles. Accessibility to the solvent was determined by NH/ND exchange to characterize conformational flexibility of the different states of the Cry1Aa protein. The size distribution of Cry1Aa solutions was obtained by dynamic light scattering (DLS). From combined DLS and FTIR measurements, we conclude that montmorillonite traps the Cry1Aa toxin in its monomeric state, preventing the oligomerization of the protein. The oligomeric forms were adsorbed onto the clay without significant structural changes.

An overview of BORIS: Bioavailability of Radionuclides in Soils.

The ability to predict the consequences of an accidental release of radionuclides relies mainly on the level of understanding of the mechanisms involved in radionuclide interactions with different components of agricultural and natural ecosystems and their formalisation into predictive models. Numerous studies and databases on contaminated agricultural and natural areas have been obtained, but their use to enhance our prediction ability has been largely limited by their unresolved variability. Such variability seems to stem from incomplete knowledge about radionuclide interactions with the soil matrix, soil moisture, and biological elements in the soil and additional pollutants, which may be found in such soils. In the 5th European Framework Programme entitled Bioavailability of Radionuclides in Soils (BORIS), we investigated the role of the abiotic (soil components and soil structure) and biological elements (organic compounds, plants, mycorrhiza, and microbes) in radionuclide sorption/desorption in soils and radionuclide uptake/release by plants. Because of the importance of their radioisotopes, the bioavailability of three elements, caesium, strontium, and technetium has been followed. The role of one additional non-radioactive pollutant (copper) has been scrutinised in some cases. Role of microorganisms (e.g., K(d) for caesium and strontium in organic soils is much greater in the presence of microorganisms than in their absence), plant physiology (e.g., changes in plant physiology affect radionuclide uptake by plants), and the presence of mycorrhizal fungi (e.g., interferes with the uptake of radionuclides by plants) have been demonstrated. Knowledge acquired from these experiments has been incorporated into two mechanistic models CHEMFAST and BIORUR, specifically modelling radionuclide sorption/desorption from soil matrices and radionuclide uptake by/release from plants. These mechanistic models have been incorporated into an assessment model to enhance its prediction ability by introducing the concept of bioavailability factor for radionuclides.

Soil arsenic availability and the transfer of soil arsenic to crops in suburban areas in Fujian Province, southeast China.

The bioavailability, soil-to-plant transfer and associated health risks of arsenic in soils collected from paddy rice fields and vegetable fields in suburban areas of some major cities of Fujian Province were investigated. The total soil concentrations of arsenic ranged from 1.29 to 25.28 mg kg(-)(1) with a mean of 6.09 mg kg(-)(1). Available (NaH(2)PO(4)-extractable) arsenic content accounted for 0.7-38.2% of total soil arsenic and was significantly correlated with total soil arsenic content. For the vegetable soils, the available fraction (ratio of available As to total As) of arsenic decreased with decreasing silt (particle size 0.02-0.002 mm) and free iron (DCB extractable) contents and with increasing soil pH and organic matter content. The available fraction of arsenic in the paddy rice soils increased with increasing free iron and organic matter contents and decreasing soil pH and silt content. The correlation of NaH(2)PO(4)-extractable arsenic with the arsenic concentration of the vegetables was much better than that of total As. The transfer factor based on the soil available arsenic (TF(avail)) was chosen to compare the accumulation ability of the various crops. The TF(avail) values of rice grains (air-dried weight basis) ranged between 0.068 and 0.44 and were higher than those of the vegetables, ranging from 0.001 to 0.12. The accumulation ability of the crops decreased in the order of rice>radish>water spinach>celery>onion>taro>leaf mustard>fragrant-flowered garlic>pakchoi>Chinese cabbage>lettuce>garlic>cowpea>cauliflower>bottle gourd>towel gourd>eggplant. Daily consumption of rice and other As-rich vegetables could result in an excessive intake of arsenic, based on the provisional tolerable intake for adults for arsenic recommended by WHO.

Possible role of organic matter in radiocaesium adsorption in soils.

The aim of this review is to examine the hypothesis that organic matter decreases the adsorption of radiocaesium on clay minerals. The factors that determine radiocaesium mobility and bioavailability in soil are briefly outlined to show why a relationship between soil organic matter content and enhanced Cs bioavailability is paradoxical. In all the investigations reviewed the ionic compositions of both the solid and the solution phases have been strictly controlled. We show that the addition of organic matter to reference clay minerals causes decreases of up to an order of magnitude in the distribution coefficient of radiocaesium. Similarly, the chemical removal of organic matter from the clay-sized fraction of soil usually leads to an increase in Cs adsorption. We suggest that the nature of the organic matter and its interaction with mineral surfaces are as important as the amount present.

Diaphragmatic paralysis in motor neuron disease. Report of two cases and a review of the literature.

Two patients presenting with respiratory insufficiency had diaphragmatic paralysis secondary to adult-onset motor neuron disease (progressive spinal muscular atrophy). A review of the literature discloses seven similar cases, most of them reported in non-neurological journals.