No abstract

No abstract

No abstract

Arsenic concentrations in a much larger fraction of U.S. groundwater sources will exceed the maximum contaminant limit when the new 10 microg L(-1) EPA standard for drinking water takes effect in 2006. Thus, it is important to develop remediation technologies that can meet this new standard. Phytoremediation of arsenic-contaminated groundwater is a relatively new idea. In this research, an arsenic-hyperaccumulating fern, commonly known as Chinese Brake fern (Pteris vittata L.), was grown hydroponically to examine its effectiveness in arsenic removal from what is believed to be herbicide-contaminated groundwater. One plant grown in 600 mL of groundwater effectively reduced the arsenic concentration from 46 to less than 10 microg L(-1) in 3 days. Re-used plants continued to take up arsenic from the groundwater, albeit at a slower rate (from 46 to 20 microg L(-1) during the same time). Young fern plants were more efficient in removing arsenic than were older fern plants of similar size. The addition of a supplement of phosphate-free Hoagland nutrition to the groundwater had little effect on arsenic removal, but the addition of phosphate nutrition significantly reduced its arsenic affinity and, thus, inhibited the arsenic removal. This study suggested that Chinese Brake has some potential to remove arsenic from groundwater.

No abstract

No abstract

Phosphate rock (PR) is an important mineral resource with numerous uses and applications in agriculture and the environment. PR is used in the manufacture of detergents, animal feed, and phosphate (PO43–) fertilizers. Leaching or runoff losses from PR products like PO43– fertilizers, animal feeds, and detergents could cause eutrophication of surface waters enriched in PO43– by these losses. Although direct application of PR reduces pollution by acting as a slow-release fertilizer, its effectiveness is limited by several factors. The major limitation of PR in direct application is its low solubility, which reduces its availability for soil reactions or plant uptake. Strategies used to increase the effectiveness of directly applied PR are based on increasing acidity, as this increases PR solubility. The application of PR in agriculture may have adverse effects because it contains hazardous elements that could be transferred to the soil through the application of fertilizers, especially after long term use. Chemical analysis of PR obtained from top PR-producing countries, however, shows that hazardous elements contained therein are below tolerable limits for PO43– fertilizers. Studies have also reported that the radionuclides in PR do not pose any radiological risk. The presence of these elements in PR can be put to positive use if they are extracted before they are applied to farmlands. This makes PR a source of rare earth metals and radionuclides that could be used in technological development and as a future energy source. The affinity of PR for metals makes it a useful adsorbent for the removal of metals from aqueous solutions and an excellent material for metal immobilization in contaminated soils. PR is a very important finite resource but its applications have adverse environmental implications.

Selenium (Se), an essential nutrient for animals and humans, occurs as selenoproteins in enzymes. It is very important in animal nutrition because it functions as an anti-oxidant assisted by vitamin E. Se deficiency is a major problem which can be reduced or prevented by supplementation with inorganic or organic sources of Se. However, excessive supplementation and consumption of Se accumulating plants may lead to Se toxicity and animal poisoning. Minimal lethal dose for animals range between 1.5 to 8 mg kg-1 Se live body weight and maximum tolerable concentration of Se in forages is 5 mg kg-1. Se deficiency in animals also depends greatly on Se content of forages and soils. Se deficient soils contain less than 0.6 mg kg-1 and can be fertilized to increase Se content of forages or pastures for animals. Forages are classified as adequate, marginally deficient and deficient in Se and contain 0.2, 0.1-0.199 and <0.1 mg kg-1 Se respectively. Silages can also be fortified with selenium to meet the requirements for Se in animals. The requirements of Se for animals need to be met to provide adequate animal and human nutrition.