Genetic engineering in the improvement of plants for phytoremediation of metal polluted soils

Metal concentrations in soils are locally quite high, and are still increasing due to many human activities, leading to elevated risk for health and the environment. Phytoremediation may offer a viable solution to this problem, and the approach is gaining increasing interest. Improvement of plants by genetic engineering, i.e. by modifying characteristics like metal uptake, transport and accumulation as well as metal tolerance, opens up new possibilities for phytoremediation. So far, only a few cases have been reported where one or more of these characteristics have been successfully altered; e.g. mercuric ion reduction causing improved resistance and phytoextraction, and metallothionein causing enhanced cadmium tolerance. These, together with other approaches and potentially promising genes for transformation of target plants are discussed.     

Cu accumulation in the earthworm Dendrobaena veneta in a heavy metal (Cu, Pb, Zn) contaminated site compared to Cu accumulation in laboratory experiments

Earthworms (Dendrobaena veneta) were exposed to heavy metal contaminated soil from a field site under both laboratory and field conditions. In the laboratory study, D. veneta were analysed for Cu after 2 weeks' exposure. The tissue Cu concentration (Cu(W)) increased proportionally with the total extractable soil Cu content (Cu(T)) in soils that contained less than 150 mg Cu kg(-1). In D. veneta exposed to soils containing more than Cu(T) = 150 mg kg(-1), however, we observed no further increase in Cu(W). In a 64-m(2) field plot at a contaminated site, 81 soil samples were taken and analysed for Cu, Pb, Zn and pH. In June 1994, 1000 D. veneta were homogeneously distributed in the plot and sampled after 1, 2 and 5 weeks to analyse for Cu. Additionally, 2000 D. veneta were introduced in September 1994 and sampled after 1, 2 and 4 weeks. At locations where earthworms were removed, the soil Cu content was estimated by disjunctive kriging. Cu concentration factors (ratio of Cu(W) to Cu(T)) in the field experiment were in excellent agreement with those of the laboratory experiment. This indicates that, with a sufficiently high sampling density, it may be feasible to predict earthworm Cu accumulation in the field using a concentration factor determined in the laboratory.     

Kinetics of mass and DNA decomposition in tomato leaves

This laboratory study investigated the kinetics of leaf and DNA content decomposition in two varieties of tomato (Palmiro and Admiro) after incubation in soil for 35 days. Results revealed that the decrease of dry matter in leaves in both varieties did not follow a single exponential function and was better described by a double exponential model. Composite half-decrease times were 3.4 and 2.4 days for Palmiro and Admiro respectively. The same pattern was observed for DNA mass loss, although this was closer to a single exponential model with composite half-decrease times of 1.5 and 1.4 days. Genomic analysis showed that DNA in dried leaves at room temperature (not inoculated in the soil), remains intact or presents a weak degradation, and DNA extracted from leaves inoculated in non-sterile soil showed degradation after two days. These results indicate that before release an important quantity of DNA may be degraded inside plant tissues during decomposition in soil.     

Microbial reduction of sulfate injected to gas condensate plumes in cold groundwater

Despite a rapid expansion over the past decade in the reliance on intrinsic bioremediation to remediate petroleum hydrocarbon plumes in groundwater, significant research gaps remain. Although it has been demonstrated that bacterial sulfate reduction can be a key electron accepting process in many petroleum plumes, little is known about the rate of this reduction process in plumes derived from crude oil and gas condensates at cold-climate sites (mean temperature <10 degrees C), and in complex hydrogeological settings such as silt/clay aquitards. In this field study, sulfate was injected into groundwater contaminated by gas condensate plumes at two petroleum sites in Alberta, Canada to enhance in-situ bioremediation. In both cases the groundwater near the water table had low temperature (6-9 degrees C). Monitoring data had provided strong evidence that bacterial sulfate reduction was a key terminal electron accepting process (TEAP) in the natural attenuation of dissolved hydrocarbons at these sites. At each site, water with approximately 2000 mg/L sulfate and a bromide tracer was injected into a low-sulfate zone within a condensate-contaminant plume. Monitoring data collected over several months yielded conservative estimates for sulfate reduction rates based on zero-order kinetics (4-6 mg/L per day) or first-order kinetics (0.003 and 0.01 day(-1)). These results favor the applicability of in-situ bioremediation techniques in this region, under natural conditions or with enhancement via sulfate injection.     

Intercomparison of reactive transport models applied to UO2 oxidative dissolution and uranium migration

Oxidative dissolution of uranium dioxide (UO₂) and the subsequent migration of uranium in a subsurface environment and an underground waste disposal have been simulated with reactive transport models. In these systems, hydrogeological and chemical processes are closely entangled and their interdependency has been analyzed in detail, notably with respect to redox reactions, kinetics of mineralogical evolution and hydrodynamic migration of species of interest.Different codes, where among CASTEM, CHEMTRAP and HYTEC, have been used as an intercomparison and verification exercise. Although the agreement between codes is satisfactory, it is shown that the discretization method of the transport equation (i.e. finite elements (FE) versus mixed-hybrid FE and finite differences) and the sequential coupling scheme may lead to systematic discrepancies.     

Oyster Contamination with Human Noroviruses Impacted by Urban Drainage and Seasonal Flooding in Vietnam

This study investigated the level of norovirus contamination in oysters collected at a lagoon receiving urban drainage from Hue City for 17 months (August 2015–December 2016). We also investigated the genetic diversity of norovirus GI and GII in oyster and wastewater samples by using pyrosequencing to evaluate the effect of urban drainage on norovirus contamination of oysters. A total of 34 oyster samples were collected at two sampling sites (stations A and B) in a lagoon. Norovirus GI was more frequently detected than GII (positive rate 79 vs. 41%). Maximum concentrations of GI and GII were 2.4 × 10⁵ and 2.3 × 10⁴ copies/g, respectively. Co-contamination with GI and GII was observed in 35% of samples. Norovirus GII concentration was higher at station A in the flood season than in the dry season (P = 0.04, Wilcoxon signed-rank test). Six genotypes (GI.2, GI.3, GI.5, GII.2, GII.3, and GII.4) were identified in both wastewater and oyster samples, and genetically similar or identical sequences were obtained from the two types of samples. These observations suggest that urban drainage and seasonal flooding contribute to norovirus contamination of oysters in the study area.     

Major challenges of integrating agriculture into climate change mitigation policy frameworks

Taking the European Union (EU) as a case study, we simulate the application of non-uniform national mitigation targets to achieve a sectoral reduction in agricultural non-carbon dioxide (CO₂) greenhouse gas (GHG) emissions. Scenario results show substantial impacts on EU agricultural production, in particular, the livestock sector. Significant increases in imports and decreases in exports result in rather moderate domestic consumption impacts but induce production increases in non-EU countries that are associated with considerable emission leakage effects. The results underline four major challenges for the general integration of agriculture into national and global climate change mitigation policy frameworks and strategies, as they strengthen requests for (1) a targeted but flexible implementation of mitigation obligations at national and global level and (2) the need for a wider consideration of technological mitigation options. The results also indicate that a globally effective reduction in agricultural emissions requires (3) multilateral commitments for agriculture to limit emission leakage and may have to (4) consider options that tackle the reduction in GHG emissions from the consumption side.