Spatial prediction of the concentration of selenium (Se) in grain across part of Amhara Region, Ethiopia.

Grain and soil were sampled across a large part of Amhara, Ethiopia in a study motivated by prior evidence of selenium (Se) deficiency in the Region's population. The grain samples (teff, Eragrostis tef, and wheat, Triticum aestivum) were analysed for concentration of Se and the soils were analysed for various properties, including Se concentration measured in different extractants. Predictive models for concentration of Se in the respective grains were developed, and the predicted values, along with observed concentrations in the two grains were represented by a multivariate linear mixed model in which selected covariates, derived from remote sensor observations and a digital elevation model, were included as fixed effects. In all modelling steps the selection of predictors was done using false discovery rate control, to avoid over-fitting, and using an α-investment procedure to maximize the statistical power to detect significant relationships by ordering the tests in a sequence based on scientific understanding of the underlying processes likely to control Se concentration in grain. Cross-validation indicated that uncertainties in the empirical best linear unbiased predictions of the Se concentration in both grains were well-characterized by the prediction error variances obtained from the model. The predictions were displayed as maps, and their uncertainty was characterized by computing the probability that the true concentration of Se in grain would be such that a standard serving would not provide the recommended daily allowance of Se. The spatial variation of grain Se was substantial, concentrations in wheat and teff differed but showed the same broad spatial pattern. Such information could be used to target effective interventions to address Se deficiency, and the general procedure used for mapping could be applied to other micronutrients and crops in similar settings.

Cadmium uptake, translocation and tolerance in the hyperaccumulator Arabidopsis halleri.

Arabidopsis halleri is a well-known zinc (Zn) hyperaccumulator, but its status as a cadmium (Cd) hyperaccumulator is less certain. Here, we investigated whether A. halleri can hyperaccumulate Cd and whether Cd is transported via the Zn pathway. Growth and Cd and Zn uptake were determined in hydroponic experiments with different Cd and Zn concentrations. Short-term uptake and root-to-shoot transport were measured with radioactive 109Cd and 65Zn labelling. A. halleri accumulated > 1000 mg Cd kg(-1) in shoot dry weight at external Cd concentrations >or= 5 microm, but the short-term uptake rate of 109Cd was much lower than that of 65Zn. Zinc inhibited short-term 109Cd uptake kinetics and root-to-shoot translocation, as well as long-term Cd accumulation in shoots. Uptake of 109Cd and 65Zn were up-regulated, respectively, by low iron (Fe) or Zn status. A. halleri was much less tolerant to Cd than to Zn. We conclude that A. halleri is able to hyperaccumulate Cd partly, at least, through the Zn pathway, but the mechanisms responsible for cellular Zn tolerance cannot detoxify Cd effectively.

Field evaluation of Cd and Zn phytoextraction potential by the hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri.

Field trials were undertaken to investigate the effect of the application of metal mobilizing agents, different sowing strategies and length of growing season on the extraction of Cd and Zn from soils by Thlaspi caerulescens and Arabidopsis halleri. None of the mobilizing agents used enhanced metal accumulation by T. caerulescens. Between 1998 and 2000, on average across plots where Cd or Zn exceeded allowable limits, T. caerulescens removed 1.3 and 0.3% of the total soil Cd and Zn. In one season when T. caerulescens was grown for 14 months, 21.7 and 4.4% of the total soil Cd and Zn was removed. This was larger than values found when T. caerulescens was grown for 4 months. A. halleri accumulated similar concentrations of Zn, but lower Cd concentrations than T. caerulescens. The results indicate that metal phytoextraction using T. caerulescens can be used to clean up soils moderately contaminated by Cd.

Field evaluation of in situ remediation of a heavy metal contaminated soil using lime and red-mud.

We evaluated the effectiveness of lime and red mud (by-product of aluminium manufacturing) to reduce metal availability to Festuca rubra and to allow re-vegetation on a highly contaminated brown-field site. Application of both lime and red mud (at 3 or 5%) increased soil pH and decreased metal availability. Festuca rubra failed to establish in the control plots, but grew to a near complete vegetative cover on the amended plots. The most effective treatment in decreasing grass metal concentrations in the first year was 5% red mud, but by year two all amendments were equally effective. In an additional pot experiment, P application in combination with red mud or lime decreased the Pb concentration, but not total uptake of Pb in Festuca rubra compared to red mud alone. The results show that both red mud and lime can be used to remediate a heavily contaminated acid soil to allow re-vegetation.

Trace metal leaching through a soil-grassland system after sewage sludge application.

To determine whether sludge applications to soil would lead in the short term to toxicity to plants and trace metal leaching to ground water, we studied the fate of some trace and major elements in a brown soil-meadow system just after repeated sewage sludge applications. The main pathways were quantified over a 37-mo period with undisturbed monolith lysimeters including two controls, four lysimeters treated with 3 x 100 m3 ha-1, and four with 3 x 400 m3 ha-1 of sewage sludge. In drainage waters the effect was limited in time and, in the case of NO3-N and Cl, delayed by 1 to 4 mo and lasted several months before returning to background conditions. Nickel and Cu concentrations in solution increased also after sludge application and had not return to background conditions after 20 mo. Trace metal concentrations did not reach toxic levels in herbage and N, Cu, Cd, and Zn concentrations were correlated with the first sludge input only. Calculated over a 37-mo period, total element output was significantly increased for Ca, NO3-N, and Ni only, because of the time-dependent response to sludge application and high variability between replicates. Output was maximal for Cd, with 1.5% of total input for the 100 m3 ha-1 treatment. Particulate matter in drainage water accounted for an average of 20% of trace metal leaching. The main long-term risk was the rapid increase in trace metal concentrations in the topsoil, which may eventually lead to toxic levels in herbage.

Phytoremediation of heavy metal-contaminated soils: natural hyperaccumulation versus chemically enhanced phytoextraction.

A pot experiment was conducted to compare two strategies of phytoremediation: natural phytoextraction using the Zn and Cd hyperaccumulator Thlaspi caerulescens J. Presl & C. Presl versus chemically enhanced phytoextraction using maize (Zea mays L.) treated with ethylenediaminetetraacetic acid (EDTA). The study used an industrially contaminated soil and an agricultural soil contaminated with metals from sewage sludge. Three crops of T. caerulescens grown over 391 d removed more than 8 mg kg(-1) Cd and 200 mg kg(-1) Zn from the industrially contaminated soil, representing 43 and 7% of the two metals in the soil. In contrast, the high concentration of Cu in the agricultural soil severely reduced the growth of T. caerulescens, thus limiting its phytoextraction potential. The EDTA treatment greatly increased the solubility of heavy metals in both soils, but this did not result in a large increase in metal concentrations in the maize shoots. Phytoextraction of Cd and Zn by maize + EDTA was much smaller than that by T. caerulescens from the industrially contaminated soil, and was either smaller (Cd) or similar (Zn) from the agricultural soil. After EDTA treatment, soluble heavy metals in soil pore water occurred mainly as metal-EDTA complexes, which were persistent for several weeks. High concentrations of heavy metals in soil pore water after EDTA treatment could pose an environmental risk in the form of ground water contamination.

Hen's eggs with retarded gas exchange. I. Chorioallantoic capillary growth.

The diffusing capacity of the hen's egg for carbon monoxide (D tau co) increases during incubation, reflecting the development of the chorioallantoic circulation. Previous work showed that the increase in D tau co could be diminished by incubating eggs in a 60% oxygen environment. The present work explored the effects of impeding gas exchange on the development of D tau co. Half the shell area was covered during incubation by a removable neoprene membrane which limited D tau co by approximately 20%. No difference could be detected between the D tau co values (measured with the membrane removed) of these eggs and control eggs incubated in the same 21% oxygen environment without a neoprene membrane. We conclude that the development of the chorioallantoic circulation is at its maximum under normal conditions of incubation and cannot be accelerated by restricting gas exchange.