There are numerous scientific studies that document the benefits of
appropriate applications of non-toxic biosolids on agricultural land used
for crop production. Such non-toxic uses of biosolids are readily
acheivable with the current quality of biosolids produced by many wastewater
treatment plants in the US today. Scientifically based criteria for
appropriate land and crop uses are available in each of the states. The US
EPA has established standards for heavy metal content of biosolids that will
be land applied. States may have even more stringent standards that the
federal ones, but not less stringent. For information on biosolids within
the jurisdiction of concern to you, consult the state agency (usually called
Dept. of Environment, Dept. Natural Resources, Dept. of Solid Waste,
Environmental Protection Dept. or some variation thereof). You might
inquire about which chemical compounds are measured and assessed in
biosolids from the area(s) you are concerned about. Several agencies and
departments are detecting exceedingly minute levels of toxic compounds;
levels that are not associated with unacceptable risk.
One notable, recent study of possible interest is cited in the following
news report. Others are also available from most university libraries and
many agronomy, soil science, and crop science departments at state
universities throughout the US. - Pat Millner
******************************
ARS News Service
Agricultural Research Service, USDA
Don Comis, (301) 344-2748, dcomis@asrr.arsusda.gov
May 18, 1998
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A 20-year study of growing crops with municipal sewage sludge offers solid
evidence that the practice is safe and beneficial to crops and soil.
A common concern about sewage sludge or "biosolids" is that it will put
toxic heavy metals in food crops. But soil scientist Robert H. Dowdy says
that won't happen if the sludge is used correctly. Dowdy works at the
Agricultural Research Service's Soil and Water Management Unit at St.
Paul,
Minn. He participated in the municipal sewage sludge study, which tracked
corn and reed canary grass growth on a 40-acre watershed near Rosemount,
Minn., where biosolids were applied annually.
Each fall after the corn harvest, biosolids were injected into the soil in
a liquid suspension. The result: No extra metals showed up in the corn or
grass, except slightly higher levels of zinc. The zinc levels were well
within safety guidelines and can even be beneficial as dietary nutrients.
The biosolids raised the soil's organic matter content more than did
commercial fertilizer used for comparison, according ARS biochemist C.
Edward Clapp. Crop yields were slightly higher with the biosolids.
Biosolids hold a slow-release form of nitrogen that is less likely to be
lost to surface water or groundwater. Like commercial fertilizers, farmers
should apply biosolids only at the rate at which crops can take up the
nutrients.
Recycling biosolids also helps return carbon to the soil, rather than
losing it to the atmosphere as carbon dioxide during incineration or
composting.
On cornfields in the study during the last four years, the applied
biosolids supplied an average of 314 pounds per acre of nitrogen (N), 216
pounds phosphorus (P) and 20 pounds potassium (K) annually. On the grass,
433 pounds of nitrogen, 134 pounds phosphorus, and 18 pounds potassium
were
applied annually. These biosolids, respectively, had a 2-2-0 and 7-2-0
nutrient (N-P-K) content, considerably lower than most commercial
fertilizers.
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Scientific contact: Robert H. Dowdy, Soil and Water Management Research
Unit, St. Paul, Minn., phone (612) 625-7058, fax (612) 625-2208,
bdowdy@soils.umn.edu.
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