Growers who follow U.S. Environmental Protection Agency (EPA) rules in applying sewage sludge as fertilizer to their land may be inadvertantly endangering human health, the environment and the future productivity of their own crops, an analysis by the Cornell University Waste Management Institute has found.
"The potential for widespread use of sludge on agricultural and residential land, the persistence of many pollutants which remain in soils for a very long time and the difficulty of remediation" warrant tougher rules than the federal EPA and most state environmental agencies have established, the university-based institute states in a new report.
Some states, including New York, have regulations in place that are more strict than the EPA's "Part 503" rules, and producers and applicators of sludge products in those states must follow the applicable state regulations. However, no state's regulations are as strict as those recommended by the Cornell institute, or as restrictive as sludge-application regulations in some European countries and the Canadian province of Ontario.
The August 1997 publication of "The Case for Caution: Recommendations for Land Application of Sewage Sludge and an Appraisal of the U.S. EPA's Part 503 Sludge Rules" follows the earlier issuance of a bulletin from Cornell Cooperative Extension. That bulletin urged greater caution in sludge application to agricultural lands -- and no sludge or sludge compost whatsoever on home gardens.
Explaining why a university-based organization is so vocal in opposing federal agency rules, institute Director Ellen Z. Harrison said: "We believe that the soil, water and crop conditions make these federal rules particularly inappropriate in New York state and the Northeast. As the land-grant university for New York state, it is Cornell's role to address this issue.
"We're not making a case for prohibition of sewage sludge in agriculture, but rather for more restrictive rules," said Harrison, one of three report authors (along with Murray B. McBride and David R. Bouldin, professor and professor emeritus, respectively, in the Department of Soil, Crop and Atmospheric Sciences at Cornell).
"Clearly there are societal benefits to recycling this material and potential benefits for agricultural productivity," said Harrison, a geologist. "But we are concerned that the EPA -- in setting rules that are far less protective than those of many other nations -- has made many overly optimistic or simplistic assumptions about contaminant impacts. We need to take a closer look at the contents of sewage sludges and the conditions under which they are applied before we make decisions that will affect agricultural productivity and human health, as well as the health of the environment for years to come."
Also known as biosolids, sewage sludges are the byproduct of municipal sewage-treatment processes. Separating liquids from treated sewage yields wastewater effluents and truckloads of an organically rich material -- and a waste-disposal problem for municipalities. Until ocean dumping was outlawed, New York City and some other municipalities hauled sewage sludge off-shore. Two legal alternatives, incineration and landfilling, cost municipalities money. Land application of sewage sludge offers an attractive option because municipalities can sell the material, or at least contract with haulers to remove the material at lesser cost to taxpayers.
However, sewage sludge contains more than organic matter and agriculturally useful chemicals like nitrogen and phosphorus. Depending on what households, businesses and industries are flushing down the drains -- and what is leaching from miles of pipes in every city -- untreated sewage includes a mixture of heavy metals (such as lead, mercury and cadmium) and toxic organic chemicals (such as PCBs), as well as pathogens (including bacteria, viruses, protozoa and other parasites) from fecal matter.
Some sewage-treatment processes kill most pathogens, but heavy metals and other contaminants are concentrated in the dewatered sludge. Humans and other animals potentially can be exposed by contacting sludge contaminants on the surface of soils and plants, through ground- and surface-water movement of contaminants, and by eating plants that are grown in soils with heavy metals and other contaminants.
The Cornell Waste Management Institute's report lists 14 reasons why the EPA's sludge rules may not adequately protect human health and the environment. Among them:
- Contrary to EPA analysis, contaminants might find their way into drinking water, according to analysts at Cornell. They concluded that low mobility of contaminants is predicted by unrealistic laboratory simulations of water moving through soil packed in columns, rather than soil with natural channels created by worms, roots and other "macropore" processes. A Cornell study published in 1997 found metals in water percolating from fields where sludge was applied more than a decade earlier. Application of sludge according to EPA rules could possibly result in a violation of drinking-water standards in private wells, the report said.
- Sewage sludge contains phytotoxic (or plant-damaging) metals, such as copper, zinc and nickel that accumulate in soil and can reduce yields of the same crops the fertilizer is supposed to help. High concentrations of these metals also harm soil microorganisms that contribute to plant growth, while other metals in sludges can create dietary imbalances in animals that graze on plants growing in sludge-treated soil.
- Consumers who follow the USDA's diet recommendations are eating more plant-based foods than the EPA assumes -- and may be consuming more heavy metals than the EPA predicts, the Cornell analysts found. They said the EPA's risk-assessment for heavy metals in fruits, vegetables and grains is incorrect because it based on the "average American" diet of the l970s rather than the current American diet or the USDA-recommended diet with even more vegetables, fruits and grains. For example, the "EPA diet" has only one-fifth the amount of leafy vegetables (potentially a major source of dietary cadmium, a toxic metal, when grown in some sludge-amended soils) as the USDA-recommended diet. And the USDA diet contains 16 times the amount of fruit that the EPA assumes Americans are eating.
- The EPA does not require labeling of sludges and sludge products. Without labels, the Cornell institute suggested, consumers may assume that all sludge-based products are alike, when in fact the levels of contaminants and other properties vary widely.
The "Case for Caution" report includes more protective recommendations for farmers and for applicators of sewage sludge, as well as suggestions for stricter policies and regulations on the state and federal levels and advice for home gardeners who already have applied sludge products. The Cornell institute was established in 1987 to address environmental and social issues associated with waste management through research, education and outreach.