Just the remedy.
WHERE THERE'S MUCK there's brass" is a saying that could have been coined for environmental cleanup. Dealing ith hazardous wastes using conventional technologies is projected to cost around $1.7 trillion in the USA alone. But the most widely accepted conventional technologies for waste treatment such as incineration and landfill disposal all have serious drawbacks. Incineration creates air pollution and ash that has to be discarded. Disposal in a landfill does not treat waste, and space is decreasing as communities are more reluctant to have hazardous wastes in their neighbourhoods.
But what if there was an alternative that was cheaper, much less disruptive and which came with impeccable green credentials? Thankfully, there is.
Bioremediation and phytoremediation are the scientific names for processes which use bacterial microorganisms and plants to deal with pollutants ranging from toxic metals and TNT to oil and chemical weapons. These are methods which can almost completely degrade waste material with little or no toxic byproducts, and which also cost less. Bioremediation techniques have been successfully employed at more than 400 cleanup sites throughout the USA at a cost approximately 80-90 per cent lower than other cleanup technologies. It's no surprise then that US bioremediation revenues are climbing by between 15 and 20 per cent annually, and in 2000, estimated annual spending on bioremediation products is expected to top $500 million.
While bioremediation is a catch-all term for the use of bacterial cleanup agents, the use of plants splits four ways. Phytoextraction is the process by which metal-accumulating plants concentrate metals from the soil into the harvestable parts of the plant above ground, where it can be removed, dried and burned to metal-rich ash. It is a process University of Maryland plant researcher Rufus Chaney compares to harvesting hay. "Burning allows recovery and recycling of the metals. The ash is similar to commercial ore and could be sold as `Bio-Ore'," he suggests, adding green remuneration to remediation.
Rhizofiltration, meanwhile, refers to cleanup operations where plant roots absorb and concentrate toxic metals from polluted effluents, a process used particularly with water pollution. It is also possible for plants to immobilise metal residues in soil, a process called phytostabilisation. Phytovolitilisation, by contrast, is where plants take up metals (particularly selenium and mercury) and then release them into the atmosphere.
Proper studies using plants in environmental cleanup began in the late 1980s, but it was not until the early `90s that US company, Phytotech, took up the baton proffered by academic research and turned it into a corporation. However, the basic knowledge underpinning phytoremediation goes back further. That semi-aquatic plants like water hyacinth and duckweed drew up toxic metals such as lead and cadmium from contaminated waters was known in Russia at the dawn of the nuclear age in the 1950s, while the fact that plants such as the wild herb Alpine pennycress (Thlaspi caerulescens) thrived on zinc- and nickel-rich soils was used in the past by prospectors in the Alps and the US's Rocky Mountains to help find ore deposits.
The reason some plants should develop a liking for adding large doses of metal to their diet is now thought to be that its presence in their stems and leaves protects them against certain fungal diseases and chewing insects. But how plants do it is still something of a mystery. However, a recent discovery by researchers at the Plant Gene Expression Center in Albany, California, may have revealed the key in a gene for heavy-metal tolerance -- parents of Metallica fans please note -- which was found in a yeast, and dubbed `hmtl'. Many plants produce molecules called peptides that bind metals for storage in cell compartments called vacuoles, where plants either store things they need or dump things they don't. However, metal-loving plants also use organic acids (eg citric acid) to bind high levels of metals. The hmtl gene appears to prompt the manufacture of a protein that pumps more bound metals into vacuoles, like a sort of efficiency booster. If researchers can work out how to duplicate the hmtl gene's metalworking activities inside high yield crops these could be used as super metal scavengers. Initial trials with tobacco have hit snags, but the Albany team still predict we'll have gene-altered plant metal guzzlers within a decade.
Just as old-time miners used metal-accumulator plants to strike it rich, biotech companies are also seeing dollar signs. The bioremediation market in North America and Europe is projected to be at least $ lbn a year by the end of the century, while the use of phytoremediation against toxic metal contamination is expected to be worth around $400m a year as companies and government agencies move away from present methods such as excavation of soil for dumping in landfills or costly chemical processing that either removes metals or fixes them in the soil so they do not spread.
Despite the huge earning potential of bio- and phytoremediation, British companies have been painfully slow to grab a slice of the action, and it has been in the US that the new technology has been most welcomed with hard cash and research effort, spurred on by tough environmental legislation. The irony of this is that the first ever successful commercial demonstration of phytoremediation's potential, though it took place in the US, was actually a European Union-funded project under the control of two British academics, Alan Baker and Steve McGrath. The Pig's Eye Landfill in Minnesota was the battlefield, and Alpine pennycress the weapon -- a plant that can tolerate levels of zinc in its leaves 60 times higher than those which kill most plants. Bioengineered pennycress is now expected to quadruple the rate of metal uptake, cutting the time the plant would take to totally cleanse the Pig's Eye site from a present estimate of 16 years to just four.
Despite this pioneering British triumph, however, there are precious few UK counterparts to the rash of companies which have followed Phytotech into a boom industry. Throughout the US, phytoremediation is being used at a growing number of sites, pitching Indian mustard against lead in New Jersey, sunflowers against uranium-contaminated water in Ohio, and bulrush against selenium in California. Indian mustard (Brassica juncea) is also tackling the environmental devastation around the pig's ear of the nuclear industry, Chernobyl, confirming the plant's high profile in the phytoextraction armoury. In addition to being able to accumulate up to an amazing 60 per cent of its dry root weight as lead, Brassica has shown a tolerance for radionuclides such as strontium, caesium and uranium.
While plants are a powerful weapon against inorganic pollutants such as toxic metals, organic nasties such as oil are grist for microbial attack. Just as certain plants have adapted to dealing with metallic soils so some natural bacteria take advantage of the energy to be derived from oil and other hydrocarbons -- a sort of Ewing family of the bacterial world. Oil is, after all, a natural product, and what's good enough to power a car is also good enough to power a microbe. What's more, once the oil-loving bacteria have extracted the energy from hydrocarbons the formerly complex chains of molecules have been broken down into two harmless products, carbon dioxide and water. Even better, some bioremediating bacteria actually leave commercially useful by-products, such as sulphite-loving bugs that create methane. The basic processes used by bioremediating bacteria are also those behind fermentation, whose useful products include beer and wine.
Hydrocarbons present one of the two major challenges which are being dealt with by bioremediation, the other being dangerous military leftovers of the Cold War such as chemical weapons. It was, in fact, a military problem which led to the foundation of the modern bioremediation industry. When US forces in the Korean conflict of the early 1950s found their uniforms degrading unexpectedly in the moist, humid climate, Howard Worne was commissioned by the US government to look into this new threat and found that the culprit wasn't some new `Commie' weapon but a microorganism which could break down fabrics that had previously been thought non-biodegradable. Worne began investigating to see whether other microorganisms existed with similar powers, and he eventually isolated one which could degrade phenol, a common organic pollutant. His work was taken up by others, and the continuing search for more pollutant-busting bacteria has spurred on bioremediation since.
The search has taken scientists to some odd places. Until recently the most famous thing to come out of a whale's gut was probably Jonah, but Oregon State University toxicologist Morrie Craig might be about to change that. Intrigued by the tolerance of Alaska's bowhead whales to the large concentrations of oil and other industrial pollutants which have accumulated in their food chain, Craig began investigating the thousand-or-so species of bacteria that live in the leviathan's gut, and found himself staring at a bioremedial bonanza. Not only did he find bacteria which digested normally hard to break down oil carcinogens like napthalene and anthracene, but also ones that made short work of PCBs (polychlorinated biphenyl), industrial pollutants which have long been linked to cancer. Furthermore, the whale bacteria proved to be anaerobic, capable of converting the pollutants to non-toxic substances in the absence of oxygen, in contrast to aerobic bioremediating bacteria found in seawater which need oxygen to function. This would make the whale bacteria particularly useful in tackling oil that has seeped underground.
Craig's gut instincts have also hit pay dirt with a bacterium found in the stomachs of sheep and goats which has the unexpected ability to break down TNT, a common contaminant at munition sites. Craig's discovery was particularly timely, as other bacteria had only managed to break TNT down into other toxic substances. TNT is also facing the squeeze from a kind of fungi known as white rot fungus (WRF) which last year degraded more than 97 per cent of TNT in the soil at one US test site. Another weapons material, RDX, meanwhile, was bioremediated totally at the same site.
Research at America's Oak Ridge National Laboratory has also found amoebae-associated bacteria packing a powerful punch against weapons material, kicking butt against TNT and napalm in particular, as well as removing mercury from contaminated soil. The Pentagon, meanwhile, has found two new techniques to deal with 1,800 tonnes of mustard gas at a Maryland base and 1,400 tonnes of the nerve gas VX in Indiana in which bioremediation finishes off a course of treatment.
A more unexpected triumph for bioremediation came in 1993 when an Australian researcher, David Bourne, came across a member of the Sphingomonas bacterium which destroyed the poison in one of the most common blue-green alga, Microcystis. Blue-green algae are being increasingly linked with cancer in humans, and until now have proved difficult to deal with. Sphingomonas makes three enzymes which break down the most powerful toxin produced by Microcystis into harmless amino acids, holding out hope for dealing with deadly algal blooms that are an increasing hazard on summer waterways.
Not all pollutants have fallen to the mean green treatment. Fifty per cent breakdown is the best figure so far for dioxins. Some toxic wastes are difficult to degrade as microorganisms simply don't recognise them. Microorganisms evolve over millions of years, but if they are exposed to some relatively recent humanmade compounds, they do not have systems to efficiently degrade these waste compounds.
The answer could be genetically altered organisms. As yet, no genetically created bioremediation organisms have been licensed. But while scientists and authorities indulge in a delicate dance over issues of safety, an array of test projects are already in place in closed reactor systems worldwide. The future looks bright -- and clean.