Background Nickel (Ni) phytomining operations cultivate hyperaccumulator plants ('metal crops') on Ni-rich (ultramafic) soils, followed by harvesting and incineration of the biomass to produce a high-grade 'bio-ore' from which Ni metal or pure Ni salts are recovered. Scope This review examines the current status, progress and challenges in the development of Ni phytomining agronomy since the first field trial over two decades ago. To date, the agronomy of less than 10 species has been tested, while most research focussed on Alyssum murale and A. corsicum. Nickel phytomining trials have so far been undertaken in Albania, Canada, France, Italy, New Zealand, Spain and USA using ultramafic or Ni-contaminated soils with 0.05-1 % total Ni. Conclusions N, P and K fertilisation significantly increases the biomass of Ni hyperaccumulator plants, and causes negligible dilution in shoot Ni concentration. Organic matter additions have pronounced positive effects on the biomass of Ni hyperaccumulator plants, but may reduce shoot Ni concentration. Soil pH adjustments, S additions, N fertilisation, and bacterial inoculation generally increase Ni phytoavailability, and consequently, Ni yield in 'metal crops'. Calcium soil amendments are necessary because substantial amounts of Ca are removed through the harvesting of 'bio-ore'. Organic amendments generally improve the physical properties of ultramafic soil, and soil moisture has a pronounced positive effect on Ni yield. Repeated 'metal crop' harvesting depletes soil phytoavailable Ni, but also promotes transfer of non-labile soil Ni to phytoavailable forms. Traditional chemical soil extractants used to estimate phytoavailability of trace e l em en ts a re of limi t ed us e t o p re dic t Ni phytoavailability to 'metal crop' species and hence Ni uptake.

The volume of e-waste is growing around the world, and, increasingly, it is being disposed of by export from developed to developing countries. This is the situation in Ghana, and, in this paper we address the potential consequences of such e-waste disposal. Herein, we describe how e-waste is processed in Ghana, and what the fate is of e-waste-chemical contaminants during recycling and storage. Finally, to the extent it is known, we address the prospective adverse effects of e-waste-related contaminants on health and aquatic life downstream from a large e-waste disposal facility in Accra, Ghana.In developing countries, including Ghana, e-waste is routinely disassembled by unprotected workers that utilize rudimentary methods and tools. Once disassembled,e-waste components are often stored in large piles outdoors. These processing and storage methods expose workers and local residents to several heavy metals and organic chemicals that exist in e-waste components. The amount of e-waste dumped in Ghana is increasing annually by about 20,000 t. The local aquatic environment is at a potential high risk, because the piles of e-waste components stored outside are routinely drenched or flooded by rainfall, producing run-off from storage sites to local waterways. Both water and sediment samples show that e-waste-related contaminant shave entered Ghana's water ways.The extent of pollution produced in key water bodies of Ghana (Odaw River and the Korle Lagoon) underscores the need for aquatic risk assessments of the many contaminants released during e-waste processing. Notwithstanding the fact that pollutants from other sources reach the water bodies, it is clear that these water bodies are also heavily impacted by contaminants that are found in e-waste. Our concern is that such exposures have limited and will continue to limit the diversity of aquatic organisms.There have also been changes in the abundance and biomass of surviving species and changes in food chains. Therefore, the need for actions to be taken to reduce entry of e-waste pollutants into Ghana's aquatic environment is real and is immediate.Heavy metals (e.g., lead, cadmium, copper and zinc) and organic pollutants (e.g.,PCDD/Fs and PBDEs) have been detected in the sediments of local water bodies in quantities that greatly exceed background levels. This fact alone suggests that aquatic organisms that live in the affected water bodies are highly exposed to these toxic, bio-accumulative, and persistent contaminants. These contaminants have been confirmed to result from the primitive methods used to recycle and process e-waste within the local environment.Only limited local data exist on the threats posed by these e-waste-related contaminants on nearby natural resources, especially aquatic organisms. In this review,we have addressed the potential toxicity of selected heavy metals and organic pollutants on aquatic organisms. Since there are no data on concentrations of contaminants in the water column, we have based our predictions of effects on pollutant release ra...

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The content of different Microcystis biochemical components (including total polysaccharides (TPS), proteins and RNA) were analyzed at different growth rates obtained under varying light intensities, temperatures and nutrient concentrations. Higher light intensity and temperature yielded a higher specific growth rate of Microcystis but the two different culture media did not significantly affect growth of Microcystis in the current study. The differences in the cellular content of TPS, protein and RNA at different temperatures (20 and 25 o C) were significant under both light intensities. The differences under different light intensities (30 and 60 µmol photons m-2 s-1) were significant at 25 o C but negligible when temperature was 20 o C. These phenomena suggested that temperature would be the limiting factor influencing the cellular processes when temperature was 20 o C. However, when temperature was 25 o C, the limiting factor was observed to be light intensity. The results also demonstrated that the content of TPS and RNA decreased, but the value of proteins increased with an increase in specific growth rate.