ABOUT 12 PERCENT of the total U.S. output of sludge — solids from sewage and wastewater — is used as fertilizer, and the trend is increasing. But there is growing concern that metals and pathogens (disease-causing microorganisms) present in the sludge may have detrimental health effects.

It is particularly attractive to use sludge as a fertilizer because it recycles nutrients and saves energy which would otherwise be spent producing chemical fertilizers. Using sludge as a soil amendment is also an ecological alternative to disposal in land fills or by incineration or ocean dumping (which is banned after 1981).

But the public generally rejects the idea of eating food grown with sludge fertilizer. Wanting to gain public acceptance, the wastewater industry has made some attempt to sprinkle the language of the technology with euphemisms, proposing that "sludge" become known as "solids;" that the term "sewage treatment plant" be replaced with "water reclamation plant;" and "sewage" become "used water." Nor is municipal sewage sludge made available as fertilizer without a proper name: it is "Metroloam" in Boston, "Nitrohumus" in Los Angeles, and "Milorganite" in Milwaukee.

Aside from the public reluctance to accept sludge fertilizer on aesthetic grounds, there is increasing concern about health risks, particularly from metals and pathogens.

Trace metals found in sewage sludge include cadmium, copper, nickel, zinc, lead and mercury. The greatest health risk appears to be that posed by cadmium. The levels of the other metals warrant monitoring but are not as great a concern because of their insignificant quantities, their bonding to soil particles, or the unlikelihood of their translocating in plants.

Cadmium, on the other hand, is known to accumulate in organs (especially the kidneys) and may cause damage. Cadmium levels, however, are likely to become elevated only in those persons who consume significant amounts of visceral meats from animals which were raised on foods produced on land fertilized with high cadmium-content sludges.

In general, the amount of metal uptake appears to depend on the type of soil, metal and plant involved. For instance, data indicate that for corn, soybeans and tomatoes, cadmium tends to concentrate more in the fruits than in the foliage. And while there are still some uncertainties about the passage of sludge contaminants through the food chain, at least one study recommends that those using sludge as a fertilizer for many years should monitor the cadmium level to keep it below 60 parts per million parts sludge and use proper soil management techniques.

Increased attention is being given to the potential pathogenic content of sludge. Wastewater has been known to support over 100 types of bacteria, viruses and parasites. One study examined lettuce and radish plants sprayed with sludge contaminated with polio virus; the virus survived 36 days. Most bacteria and viruses, though, are not as hardy, and are eliminated by sunlight and drying. Little information is available on the transmitting potential of parasites present in sludge fertilizer, and research continues in this area.

Because of the sludge processing and disposal policy of the Metropolitan Sanitary District of Greater Chicago (MSDGC), there do not appear to be any health problems associated with the sludge produced there. The MSDGC processed a daily average of 1.38 billion gallons of waste-water in 1980, resulting in 530 tons of dried sludge daily. Some of this was distributed free of charge under the name "Nu Earth" to golf courses, nurseries and other nonagricultural users. In 1980 about 99 tons of Nu Earth were distributed daily to users who agreed not to use it for agricultural applications and were subject to a follow-up inspection.

Sludge from MSDGC is used in an agriculture program in Fulton County. There, sludge is applied as a soil amendment for corn crops sold only as animal feed. According to Richard Lanyon, assistant director of research and development at MSDGC, the risk of pathogens is minimized because sludge is detained for a minimum of 10 days of anaerobic digestion, in accordance with federal regulations. And the concern of metal toxicity to man from eating animals which were fed on the corn is allayed by studies which indicate that "metals that are of concern, such as cadmium, do not accumulate in the muscle tissue," but are more apt to accumulate in organs, according to Lanyon.

But uncertainties about the safety of sewage prompted the Del Monte Corporation in 1979 to prohibit its growers from using sewage as a soil amendment. A general ban on the sludge remains in effect although variances are sometimes granted. According to Arthur Hansen, director of environment and consumer affairs of Del Monte, "We know that municipal sludge contains heavy metals . . . [that is our] number one concern." Hansen explained that Del Monte feels it needs more specific guidance about sludge usage than is offered by present guidelines from the U.S. Environmental Protection Agency (USEPA) and the Food and Drug Administration. Until more of this type of information is available, Hansen explained, Del Monte will continue the ban as a matter of policy "to assure . . . consumers a safe and suitable product."

July 1981/Illinois Issues/17

It was similar concern that last year prompted the Chicago-based Citizens for a Better Environment to petition the U.S. Consumer Product Safety Commission to ban consumer use of sewage sludge fertilizers and soil conditioners in lawns, gardens and other areas. The commission conceded that unrestricted home use of certain sewage sludge products may pose health problems, but denied the petition because the USEPA is drafting regulations for the distribution and marketing of sludge-derived fertilizers and soil conditioners.

Presently the marketing and distribution of sludge products go largely unregulated because the federal rules are still in the works and the majority of states do not make provisions in this area. According to Mike Flynn, Office of Solid Waste Management of the USEPA, it is unclear when the federal regulation will be established. "Right now there's no schedule for that regulation," said Flynn, who explained that it is in a state of flux because of the new administration. □

18/July 1981/Illinois Issues