Dear EarthTalk: I want to garden this spring without using chemicals. Are there any safe, non-toxic garden herbicides?
—D. Muller, Jackson, MS
There are now several natural herbicides on the market. One of the most effective natural ingredients is corn gluten meal, a yellow powder that is a waste product of the corn milling process. While the meal has been used in dog, fish and other animal foods for years, it has only recently been marketed as a natural herbicide. As researchers at Iowa State University's (ISU) Horticulture Department discovered, the material naturally inhibits the growth of seeds" initial root systems, while doing no harm to already established plants.
ISU researchers say that once vegetables or flowers have their first true leaves, corn gluten meal can be safely and effectively applied to kill weeds. ISU scientists also note that, because corn gluten meal is high in nitrogen, it is beneficial to surrounding plants, doubling as a fertilizer.
It has been reported that corn gluten meal is particularly effective against dandelions, pigweed, crabgrass, plantain and curly dock. ISU scientists suggest an application rate of 20 pounds per 1,000 square feet and they say the product remains effective for five to six weeks. Researchers say that corn gluten meal should be applied to lawns about three to five weeks before weeds begin to grow.
The U.S. Environmental Protection Agency's (EPA) Office of Pesticide Programs urges people to decrease the amount of chemical herbicides used to battle weeds. There are already more than 865 active ingredients registered for use in pesticides, herbicides and fungicides. About 350 pesticide products, including herbicides, are used on the foods we eat and to ward off pests from our homes and pets. But pesticides and herbicides often contain toxic substances that are harmful to human and ecological health.
ChemFree+ is one brand of herbicide that uses corn gluten meal. Available from Chem Free Lawns, it is advertised as both a natural weed control and fertilizer for lawns and gardens, harmless to people, pets, groundwater, insects and soil microorganisms. Comparable products include Dynaweed, from the American Natural Products Company, and "A-Maize-N," from Planet Natural.
CONTACT: Chem Free Lawns, (952) 473-2127, www.chemfreelawns.com; American Natural Products Company, (800) 221-7645; www.americanatural.com; Planet Natural, (800) 289-6656; www.planetnatural.com; Iowa State University's Horticulture Department, (515) 294-2751, www.hort.iastate.edu; U.S. Environmental Protection Agency, Office of Pesticide Programs, (703) 305-5440, www.epa.gov/pesticides.
Dear EarthTalk: What are PCBs, and how do they harm the environment?
—Dale Roach, Waterford, MI
Polychlorinated biphenyls (PCBs) are various man-made mixtures of chlorinated compounds that were first made by the Swann Chemical Company back in 1880. PCBs were once considered a "miracle product" for manufacturers because of their water insolubility, high tolerance for heat, and chemical stability. This led to their widespread use in the making of products such as inks, dyes, paints, adhesives, carbonless papers, lubricants, flame-retardants, surface coatings and sealants, and industrial fluids.
As early as 1936, the harmful effects and health risks of PCBs were known, and today they are well documented. PCBs cause cancer in studies using animals, and are therefore classified by the U.S. Environmental Protection Agency (EPA) as probable human carcinogens. PCBs also cause liver, kidney and nervous system disorders, as well as developmental and reproductive abnormalities.
Most insidious is that PCBs increase in concentration as much as 1,000-fold as they move up the food chain. This "bioaccumulation" is of special concern in areas where wildlife and humans consume PCB-contaminated fish. Because of such harmful effects, the EPA banned PCBs in 1977, but PCB problems are far from over.
In one highly publicized case, two General Electric (GE) plants in upstate New York dumped 1.3 million pounds of PCBs into New York's Hudson River between 1947 and 1977. Although the dumping ceased more than 25 years ago and concentrations have declined since, they have stabilized at levels that are significantly higher than those considered safe for human consumption of fish. According to Riverkeeper, a New York-based environmental organization, large quantities of PCBs remain concentrated in sediment in northern portions of the Hudson, and are found in fish and wildlife throughout the river's ecosystem.
Forty so-called PCB “hot spots" have been identified in a six-mile stretch directly downstream from the two GE plants, and in February 2002 the EPA decided to proceed with a comprehensive cleanup of the Hudson River. The plan calls for removing 100,000 pounds of PCB contaminated sediments from the Upper Hudson River by dredging, a plan that will cost GE $460 million. GE has contested the ruling, arguing that its efforts should be limited to conducting the design of the cleanup, estimated at approximately $30 million, and preventing additional PCB contamination.
PCBs from GE have also contaminated the Housatonic River in Massachusetts and Connecticut, leading to its listing by the group American Rivers as one of "America's Most Endangered Rivers of 2004."
CONTACTS: Environmental Protection Agency, (202) 260-1876, www.epa.gov/pbt/pcbs.htm; Hudson Riverkeeper, (800) 21-RIVER, www.riverkeeper.org; General Electric, (203) 373-3476, www.ge.com; American Rivers, (202) 347-7550, www.amrivers.org.