Biomedical subjects

M Van Hees

Publications and source records attributed to M Van Hees.

9 recordsLinked to original sources

PubMed2006

Oxidative stress reactions induced in beans (Phaseolus vulgaris) following exposure to uranium.

The present study aimed to analyze the biological effects induced by bioaccumulation of uranium in Phaseolus vulgaris. Ten-day-old seedlings were exposed to 0, 0.1, 1, 10, 100 and 1000 microM U in diluted Hoagland solution. Following 1, 2, 4 and 7 days' exposure, plants were monitored for uranium uptake, biometric parameters, capacities of enzymes involved in the anti-oxidative defense mechanisms (GPOD, SPOD, GLUR, SOD, ICDH, G-6P-DH), glutathione (GSH) pool and DNA integrity. Uranium contents were up to 900-fold higher in roots (31-14,916 mg kg(-1) FW following 7 days' exposure to 0.1 and 1000 microM U, respectively) as compared to primary leaves (1-16 mg kg(-1) FW following 7 days' exposure to 0.1 and 1000 microM U, respectively). Uranium exposure did not significantly affect plant growth compared to the control. For all enzymes studied, except SOD, enzyme capacities in roots were slightly stimulated with increasing contaminant concentrations (though not significantly). For roots exposed to 1000 microM U, enzyme capacities were significantly reduced. Enzyme capacities in leaves were not affected by uranium treatment. Total and reduced GSH levels were higher in primary leaves of uranium (</=100 microM U) exposed plants than in control plants. When exposed to 1000 microM U, level of total and reduced GSH dropped. These results indicate that uranium can cause oxidative stress and cellular redox imbalance. Root DNA integrity was hampered at the highest external uranium concentration. For P. vulgaris the uranium toxicity threshold is expected to be between 100 and 1000 microM U.

Antioxidants↗

PubMed2006

Plant-induced changes in soil chemistry do not explain differences in uranium transfer.

A greenhouse experiment was set up with maize, ryegrass, Indian mustard, wheat and pea to evaluate to what extent differences in uranium (U) transfer factors can be explained by root-mediated changes in selected soil properties. The experiment involved an acid and an alkaline soil contaminated with (238)U. U soil-to-shoot transfer factors (TFs) ranged between 0.0005 and 0.021 on the acid soil and between 0.007 and 0.179 on the alkaline soil. Indian mustard showed the highest U uptake in shoots and maize the lowest. The root TFs, only available for the acid soil, ranged from 0.58 for maize and Indian mustard to 1.38 for ryegrass. The difference in U uptake between the two soils and the five plants was only partially explained by the different initial U concentrations in soil solution or differences in soil properties in the two soils. However, we obtained a significant relation for differences in shoot TFs observed between the two soils when relating shoot TFs with concentration of UO(2)(2+) and uranyl carbonate complexes in soil solution (R(2)=0.88). The physiological mechanisms by which root-to-shoot U transfer is inhibited or promoted seemed at least as important as the plant-induced changes in soil characteristics in determining soil-to-shoot TFs.

Plants↗

PubMed2006

Can we predict uranium bioavailability based on soil parameters? Part 1: effect of soil parameters on soil solution uranium concentration.

Present study aims to quantify the influence of soil parameters on soil solution uranium concentration for (238)U spiked soils. Eighteen soils collected under pasture were selected such that they covered a wide range for those parameters hypothesised as being potentially important in determining U sorption. Maximum soil solution uranium concentrations were observed at alkaline pH, high inorganic carbon content and low cation exchange capacity, organic matter content, clay content, amorphous Fe and phosphate levels. Except for the significant correlation between the solid-liquid distribution coefficients (K(d), L kg(-1)) and the organic matter content (R(2)=0.70) and amorphous Fe content (R(2)=0.63), there was no single soil parameter significantly explaining the soil solution uranium concentration (which varied 100-fold). Above pH=6, log(K(d)) was linearly related with pH [log(K(d))=-1.18 pH+10.8, R(2)=0.65]. Multiple linear regression analysis did result in improved predictions of the soil solution uranium concentration but the model was complex.

Adsorption↗

PubMed2006

Can we predict uranium bioavailability based on soil parameters? Part 2: soil solution uranium concentration is not a good bioavailability index.

The present study aimed to quantify the influence of soil parameters on uranium uptake by ryegrass. Ryegrass was established on eighteen distinct soils, spiked with (238)U. Uranium soil-to-plant transfer factors (TF) ranged from 0.0003 to 0.0340kgkg(-1). There was no significant relation between the U soil-to-plant transfer (or total U uptake or flux) and the uranium concentration in the soil solution or any other soil factor measured, nor with the U recovered following selective soil extractions. Multiple linear regression analysis resulted in a significant though complex model explaining up to 99% of variation in TF. The influence of uranium speciation on uranium uptake observed was featured: UO(2)(+2), uranyl carbonate complexes and UO(2)PO(4)(-) seem the U species being preferentially taken up by the roots and transferred to the shoots. Improved correlations were obtained when relating the uranium TF with the summed soil solution concentrations of mentioned uranium species.

Biological Availability↗

PubMed2005

Effect of K and bentonite additions on Cs-transfer to ryegrass.

Bentonite amendments are generally ineffective in reducing the soil-to-plant radiocaesium transfer but have previously been shown that bentonites in the K-form having been subjected to wetting-drying cycles had pronounced radiocaesium binding capacities. We have investigated the effect of wetting-drying (WD) on Radiocaesium Interception Potential (RIP) development in three K-bentonites and K-bentonite soil mixtures, using a variety of procedures: homogenisation of the bentonites with K through dialysis (K(B)), or partial transformation of the bentonite to the K-form in the presence of a solution of K2CO3 (K(L)) or in presence of solid K2CO3 (K(S)). Of the three strategies tested, addition of K2CO3 (solid) at a dose of 2 meq g(-1) clay and adding the K-bentonite mixtures to the soil resulted in the highest RIP increase after 20 WD cycles. The procedure giving the highest RIP yield is the most practical for further applications and was used in a pot experiment under greenhouse condition. When expressing the RIP increase of the soil-bentonite mixtures per unit bentonite added (RIP yield), 28- to 110-fold RIP increases were observed up to a value of approximately 60,000 meq kg(-1) (6 times higher than the RIP for illite). The beneficial effect following K-bentonite application was shown to be dependent both on a sorption enhancement effect (direct RIP effect) and fixation effects (indirect RIP effect). Greenhouse testing proved that the RIP effects observed in greenhouse could be predicted by making use of the sorption data from the laboratory tests. Optimum soil-amendment would be obtained with bentonites with high initial sorption RIP and a high sorption RIP increase when subjected to WD in the presence of potassium. Hypothised Transfer Factor (TF)-reductions of at least 10-fold could result when mixing approximately 1% bentonite, like Otay bentonite (RIP yield 99,000 meq kg(-1) after WD in presence of K if only fine particle size of <1mm considered) with the contaminated ploughing layer.

Bentonite↗

PubMed2005

Can barium and strontium be used as tracers for radium in soil-plant transfer studies?

Radium is one of the prominent potential contaminants linked with industries extracting or processing material containing naturally occurring radionuclides. In this study we investigate if 133Ba and 85Sr can be used as tracers for predicting 226Ra soil-to-plant transfer. Three soil types were artificially contaminated with these radionuclides and transfer to ryegrass and clover was studied. Barium is considered a better tracer for radium than strontium, given the significant linear correlation found between the Ra and Ba-TF. For strontium, no such correlation was found. The relationship between soil characteristics and transfer factors was investigated. Cation exchange capacity, exchangeable Ca+Mg content and soil pH did not seem to influence Ra, Ba or Sr uptake in any clear way. A significant relation (negative power function) was found between the bivalent (Ca+Mg) concentration in the soil solution and the Ra-TF. A similar dependency was found for the Sr and Ba-TF, although less significant.

Barium↗

PubMed2005

Fibre crops as alternative land use for radioactively contaminated arable land.

The transfer of radiocaesium, one of the most important and widespread contaminants following a nuclear accident, to the fibre crops hemp (Cannabis sativa L.) and flax (Linum usitatissimum L.) as well as the distribution of radiocaesium during crop conversion were studied for sandy soil under greenhouse and lysimeters conditions. Soil parameters did not unequivoqually explain the transfer factors (TF) observed. TFs to flax stems ranged from 1.34 to 2.80x10(-3) m2 kg(-1). TFs to seeds are about a factor of 4 lower. During the retting process for separating the fibres from the straw, more than 95% of the activity was removed with the retting water. For hemp, the TF to the stem was about 0.6x10(-3) m2 kg(-1). For hemp, straw and fibres were mechanically separated and TF to straw was about 0.5x10(-3) m2 kg(-1) and to fibres 1.0x10(-3) m2 kg(-1). Generally, the TFs to the useable plant parts both for hemp and flax, are low enough to allow for the production of clean end-products (fibre, seed oil, biofuel) even on heavily contaminated land. Given the considerable decontamination during retting, contamination levels in flax fibres would only exceed the exemption limits for fibre use after production in extreme contamination scenarios (>12,300kBq m(-2)). Since hemp fibres are mechanically separated, use of hemp fibres is more restricted (contamination <740kBq m(-2)). Use of stems as biofuel is restricted to areas with contamination levels of <250 and 1050kBq m(-2) for flax and hemp, respectively. Use of seeds for edible oil production and flour is possible almost without restriction for flax but due to the high TFs to seed observed for hemp (up to 3x10(-3) m2 kg(-1)) consumption of hemp seed products should be considered with care.

Biodegradation, Environmental↗

PubMed2004

Phytoextraction for clean-up of low-level uranium contaminated soil evaluated.

Spills in the nuclear fuel cycle have led to soil contamination with uranium. In case of small contamination just above release levels, low-cost yet sufficiently efficient remedial measures are recommended. This study was executed to test if low-level U contaminated sandy soil from a nuclear fuel processing site could be phytoextracted in order to attain the required release limits. Two soils were tested: a control soil (317 Bq 238U kg(-1)) and the same soil washed with bicarbonate (69 Bq 238U kg(-1)). Ryegrass (Lolium perenne cv. Melvina) and Indian mustard (Brassica juncea cv. Vitasso) were used as test plants. The annual removal of soil activity by the biomass was less than 0.1%. The addition of citric acid (25 mmol kg(-1)) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15,000 and 10,000 kg ha(-1), respectively, up to 3.5% and 4.6% of the soil activity could be removed annually by the biomass. With a desired activity reduction level of 1.5 and 5 for the bicarbonate-washed and control soil, respectively, it would take 10-50 years to attain the release limit. However, citric acid addition resulted in a decreased dry weight production.

Biodegradation, Environmental↗

PubMed2001

A metabolic derivation of tritium transfer coefficients in animal products.

Tritium is a potentially important environmental contaminant originating from the nuclear industry, and its behaviour in the environment is controlled by that of hydrogen. Animal food products represent a potentially important source of tritium in the human diet and a number of transfer coefficient values for tritium transfer to a limited number of animal products are available. In this paper we present an approach for the derivation of tritium transfer coefficients which is based on the metabolism of hydrogen in animals. The derived transfer coefficients separately account for transfer to and from free (i.e. water) and organically bound tritium. A novel aspect of the approach is that tritium transfer can be predicted for any animal product for which the required metabolic input parameters are available. The predicted transfer coefficients are compared to available independent data. Agreement is good (R2=0.97) with the exception of the transfer coefficient for transfer from tritiated water to organically bound tritium in ruminants. This may be attributable to the particular characteristics of ruminant digestion. We show that tritium transfer coefficients will vary in response to the metabolic status of an animal (e.g. stage of lactation, diet digestibility etc.) and that the use of a single transfer coefficient from diet to animal product is inappropriate. It is possible to derive concentration ratio values from the estimated transfer coefficients which relate the concentration of tritiated water and organically bound tritium in an animal product to their respective concentrations in the animals diet. These concentration ratios are shown to be less subject to metabolic variation and may be more useful radioecological parameters than transfer coefficients. For tritiated water the concentration ratio shows little variation between animal products ranging from 0.59 to 0.82. In the case of organically bound tritium the concentration ratios vary between animal products from 0.15 (goat milk) to 0.67 (eggs).

Animals↗