Many contemporary concerns for the environment were brought to our attention in 1962 by Rachel Carson (1907-1964) in her landmark book, Silent Spring. Carson was an ecologist with the U.S. Fish and Wildlife Service, and her warnings of the dire consequences of pollution with pesticides gave birth to a growing movement to regulate the release of biologically harmful chemicals into the environment. In 1970, Canada banned the application of the widely used organochlorine pesticide DDT, and two years later the U.S. followed suit. Since then, bald eagles, which were nearing extinction from exposure to DDT (and DDE, its toxic breakdown product), have been recovering gradually. Thanks to these regulatory actions, people and animals in the US and Canada are no longer at risk from exposure to this environmentally persistent synthetic pesticide. However, for every species saved, many more become threatened and endangered from human activities around the globe.
The ban on DDT did not end the threat from agricultural pollution. Other residual pesticides like toxaphene and dieldrin replaced DDT until they, too, were banned from general use. These were followed by a host of organochlorine pesticides, such as lindane, chlordane and endosulfan, that are still widely used around the world. A proliferation of non-residual pesticides, some more toxic than the organochlorine compounds they replaced, has added to the growing threat to our wildlife heritage. Also, many tropical countries still use DDT to control malaria mosquitoes, and some of this DDT is illegally diverted into agriculture. Since Silent Spring was published, the need to control toxic contamination has only become more urgent. Fortunately, new techniques to control agricultural chemicals and save wildlife are constantly being developed.
Agriculture is not the only source of organic pollutants. The impact of transportation and manufacturing sources is increasing as more and more countries industrialize. Although the US and other developed countries are now the main sources of many global contaminants, developing countries are beginning to enter the equation. For example, in South Asia industrial growth is in excess of 4-5% per year. New manufacturing facilities are making many products for worldwide distribution. Yet the regulatory framework needed to prevent contamination with toxic chemicals is not keeping up with the pace of industrialization.
The uninformed use of long-lived toxic chemicals can come back to haunt us many years after they have been discontinued. The polychloronated biphenols, or PCBs, are just such a present-day menace. They are chemically related to the organochlorine pesticides and are extremely persistent. PCBs have survived as hazardous waste residues from many products including sealants, caulkings, synthetic resins, rubber, paints, waxes, asphalt and flame retardants. Although these uses were banned since the early 1980s, PCBs continued to be used in closed electrical systems as coolants and liquid insulators. Old electrical transformers containing PCBs are a major disposal problem.One of the biggest ongoing controversies surrounds a group of hundreds of organic pollutants known as dioxins and their chemical relatives, the furans. Comprising one of the most toxic groups of chemicals known, dioxins are chlorinated byproducts from the manufacture of pesticides, preservatives, disinfectants, and paper. They are also produced by burning plastics and hydrocarbons at low temperatures. A source of concern is the pulp paper industry that discards expended chlorine bleaches. When the chlorine reacts with naturally occurring organic compounds in the waterways, dioxins are formed.
Not all of the pollutants that threaten our wildlife and wilderness ecosystems are complex synthetic compounds like the PCBs, dioxins and organochlorine pesticides. Radioactive elements and heavy metals like lead, mercury, cadmium and arsenic also contaminate waterways and soils. In North America, migratory birds are poisoned by ingesting lead from gunshot, fishing sinkers, and old paint chips in the environment. Some metals are toxic in their elemental form; others become more toxic when they are chemically reduced in nature. For example, the mercury used for mining gold in the Amazon River Basin changes to a highly toxic form, methyl mercury, which accumulates in fish and wildlife.
Environmental contaminants such as dioxin and lead are known to produce an astounding spectrum of damage to fish and wildlife. Chronic, low-level exposure to these toxic pollutants causes reduced fertility and hatching rates, birth defects, malformed genital organs, retarded growth, cancer, anemia, metabolic abnormalities, poor immune responses and neurological abnormalities. There is mounting scientific evidence that organic pollutants and some heavy metals interfere with the endocrine system of fetuses and young animals. Substances with these effects are called endocrine disruptors. Many pollutants with widespread global distribution are suspected to cause endocrine disruption.
Pollution may be in our backyards, but the problem is not just local. Wind drift, water runoff, groundwater leaching, sea currents and animal vectors move pollutants around the world, from continent to continent and sea to sea. For example, contaminants that originated in North America can be found in distant places like the South Pacific. With many economies expanding rapidly, air, water and biological dispersion insure that one area's local contamination will become tomorrow's global problem.
Biotechnology refers to the practical application of modern laboratory techniques such as recombinant DNA. Although most biotechnology research has been medical, more and more is being undertaken for agricultural and environmental uses. The term biological control usually refers to solutions found in nature that can replace synthetic chemicals in the environment. Since many biological control processes are being improved through biotechnology, it has become impractical to distinguish between the two. With proper attention to risk management, both natural and laboratory-enhanced "green technologies" have the potential to protect our wildlife heritage and reduce our chemical contamination of the environment.
Both heavy metals and persistent organic pollutants (POPs) are capable of accumulating in plants and animals. As they move up the food chain, these contaminants often increase in concentration and become more harmful to wildlife. Many species of bacteria, blue-green algae, mosses, ferns, and dicots are capable of absorbing POPs and heavy metals. By following the concentration of contaminants in specific plants, changes in environmental contamination can be monitored.
Many of the organisms useful for environmental monitoring can also be used for the biological destruction, detoxification and harvesting of POPs and heavy metals. The term for these biologically mediated clean-up functions is bioremediation. POPs and hydrocarbons can be destroyed by seeding soils with white rot fungi that degrade the contaminants. Heavy metals like lead can be removed by cultivating Indian mustard (Brassica juncea) on the contaminated soil after tying up the polluting element with the chelating agent EDTA. The harvested mustard stems and leaves are disposed of as hazardous waste. Water can be cleaned by a community of bacteria, blue-green algae, plants, and fish housed in an infrastructure known as a Living Machine. The organisms sequester heavy metals and break down various organic compounds that make the water unsuitable for wildlife habitat and human consumption.
Biosubstitution is the replacement of synthetic chemicals with biological alternatives. For example Bacillus thuringiensis (BT) is a soil bacterium that produces toxins that are short-lived in the environment and are non-toxic to people, wildlife, aquatic life and most beneficial insects. BT toxins are incorporated into biopesticidal products for agriculture and home gardens, and BT genes have been inserted into many food crops so they can produce their own insecticidal toxins. Plants (and animals) like BT corn are called genetically modified organisms, or GMOs. Another example of biosubstitution is the application of baculoviruses that infect and kill parasitic caterpillars. Genetic modification of the baculoviruses holds great promise for increasing their usefulness as natural pesticides. Integrated pest management (IPM) is the application of environmentally friendly cultivation practices that reduce the need for synthetic pesticides. In IPM, pesticides are applied only when harmful stages of the pests emerge. The cultivation of pest-resistant crop strains and the rotation of crop species help avoid the buildup of parasite populations. Biosubstitution is the most recent tool to be added to IPM for more sustainable agriculture.
All technologies can produce unanticipated negative repercussions. Assessing the environmental safety of biotechnologies can be especially difficult. New risks must be identified, quantified, and evaluated for their potential impact. GMOs may compete or cross with unmodified varieties, they may become weeds, or they may make pests hardier than ever by inducing new resistance to naturally occurring pesticides. Special consideration needs to be given to the release of GMOs in "centers of origin," as Mexico is for corn and China for soybeans. Complex genetic interactions between indigenous varieties and their wild relatives (such as corn and teosinte) may be altered by inadvertent crossing with GMOs. The successful use of biotechnology for agricultural and environmental applications will require vigilance and on-going management of the risks.
Pollution affects all species in the contaminated ecosystem, not just the large, conspicuous animals at the top of the food chain. When we use new biotechnology to solve environmental problems, we should also consider its potential impact on the entire ecosystem. With thoughtful use, biotechnology can have many positive effects on the diversity of species and habitats. Only by considering the ecosystem as a whole can we protect nature and shrink the growing list of endangered and threatened species.For instance, monarch butterflies overwinter in central Mexico. Today, deforestation and excessive tourism destroy their habitat. In the future, toxic chemicals like pesticides from surrounding agriculture will threaten their existence (unless we harness the potential of biotechnology to reduce chemical contamination of the biosphere.)
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