Case Study: Arsenic

Arsenic contamination of soil and water poses significant health risks to millions of people worldwide. Arsenic causes cancer, mutations and birth defects, and has been linked to the development of diabetes and problems with the immune system (NRC, 1977, 1999). Up to now, there has been no cost-effective method to clean up arsenic-contaminated soils, and the technologies currently used for the cleanup of arsenic-contaminated drinking water have significant drawbacks, such as high cost, generating high volumes of toxic sludge and brine, and low water recovery.

The edenfern™ forms the basis of a solar-powered (photosynthetic) technology that provides cost-effective, small-scale cleanup of arsenic-contaminated soil and surface, ground, and drinking water. Scientists from the University of Florida originally identified this fern (Ma et al., 2001), for which Edenspace has licensed exclusive rights for the cleanup of arsenic contaminated soil, sludge, and water.  Our research indicates that this fern accumulates an arsenic concentration, in the above ground plant tissue, more than 200-fold higher than any other plant species tested.  We have also examined time-dependent arsenic accumulation by edenfern™ and Boston fern (N. exaltata). Under the same growth conditions, edenfern™ accumulated significantly higher shoot arsenic concentration than Boston fern, a non-arsenic-accumulator. edenfern™, a perennial plant species, grows very rapidly in arsenic contaminated soil, regenerates substantial shoot biomass within three weeks following harvest the shoots, and accumulates consistent high arsenic concentrations in its shoots from successive harvesting.

Plant Species	Bioaccumulation Factor
B. juncea	62
Sunflower	25
N. exaltata	80
edenfern™	16,030

Table 1. Arsenic bioaccumulation factor for four plant species grown on an arsenic-contaminated soil with total soil arsenic concentration of 110 mg/kg.

To test the potential of edenfern™ to remove arsenic from drinking water, a phytofiltration system has been designed and used to investigate arsenic removal by the two fern species. edenfern™ removed arsenic from water rapidly, and reduced water arsenic concentration from 200 mg L-1 to less than 50 mg L-1 within two days, and completely removed arsenic from water in about 3 days. However, for the same experimental conditions, a non-accumulator fern (N. exaltata) removed arsenic from water much slowly except for the initial 24 h. For the same experimental period, the non-accumulator fern N. exaltata failed to reduce water arsenic concentration bellow the cleanup limit for arsenic in drinking water. The results demonstrate that edenfern™ is very effective in removal of arsenic from water.

Since plant cultivation and harvesting are relatively inexpensive processes, Edenspace's phytoremediation approach has significant cost saving advantages compared to other available technologies for treatment of arsenic-contaminated soil and water. Furthermore, phytoremediation does not generate toxic secondary waste since arsenic in the harvested biomass can be recycled. Arsenic phytoremediation should become a cost-effective and environmentally friendly cleanup method for most arsenic-contaminated soil and water worldwide.

Background on Arsenic

Arsenic is a major contaminant of soils and waters in the United States and other countries. Contamination of surface water, ground water, and drinking water by arsenic poses significant health risks to humans and animals. Arsenic is a known carcinogen and mutagen, is detrimental to the immune system, and contributes to skin, bladder, and other cancers (NRC, 1999).  According to the U.S. Geological Survey, in 24 percent of the counties in the United States where data are available, at least 10% of samples have arsenic concentration in water exceeding 10 µg L^-1, the World Health Organization’s arsenic limit in drinking water (Focazio et al., 1999). Approximately 6% of the US small public water-supply systems had water arsenic concentrations exceeding 10 µg L^-1, and 1% of such systems had concentrations exceeding 50 µg L^-1, the current US maximum limit of arsenic in drinking water (Focazio et al., 1999).  In some parts of the world, arsenic occurs naturally in groundwater. For example, a recent survey indicates that 80% of total area, and 40 million people, are at risk of arsenic poisoning in Bangladesh, where more than 7,000 patients are seriously affected by arsenic in drinking water (Karim, 2000).

Arsenic contamination of 50 µg L^-1 in drinking water may result in human cancer risks as high as 13 in 1000 (Pontius et al., 1994). Reductions in the maximum permitted contaminant levels in drinking water from 50 µg L^-1 to the range of 0.5 to 10 µg L^-1 (Jones et al., 1997) are under consideration.  Should the arsenic limit in drinking water decrease, the percentage of US small water-supply systems having water arsenic concentrations exceeding the limit will increase substantially. This will undoubtedly increase the costs for the treatment of arsenic-contaminated water in the nation. Other technologies currently used to clean arsenic-contaminated drinking water have significant drawbacks.

Sources and Transport of Contamination

Arsenic is a naturally occurring element in rocks, soils, and the waters in contact with them. Before 1968, inorganic forms of arsenic were used extensively in agriculture as insecticides and herbicides.  Frequent application at high rates of these chemicals caused significant arsenic accumulation in orchard soils. Inorganic forms of arsenic have since been replaced with organic forms because of their reduced phytotoxicity and overall environmental burden.  However, excessive additions of any arsenic compounds can cause pollution of nearby ground and surface waters (Duble et al., 1978).  Arsenic concentrations as high as 500 mg/kg have been reported in soils having a history of arsenic pesticide or herbicide applications. Such arsenic contaminated soils become a source of arsenic contamination in surface water, ground water, and drinking water. Environmental arsenic is still produced today as a result of various mining, industrial and manufacturing operations.  

Discuss Your Needs:

For further information on effective plant-based treatment of arsenic contaminated soils, groundwater, surface water, or drinking water, please contact: 
Michael Blaylock, Ph.D., Director [e-mail]

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