Ted Peterson wrote:
The use of biosolids/sludge is, in most cases, far safer than the accepted
use of chemical inputs that are certified as "organically" safe. There are
a number of fearmongers who have made good livings out of scaring people
with the threat of monsters growing out of their wastes. Human wastes are
no more dangerous than any other monogastric animal's.
[Tom Jaszewski] From the fear mongers at Cornell (sarcasm intended!)
http://cwmi.css.cornell.edu/Sludge/dairysludge.pdf
Soil pH Change
Application of non-alkaline sewage sludges, if continued over a number of
years, can be expected to lower
soil pH, the result of the acidifying effect of S and N mineralization. It
is important to monitor pH and add
lime to prevent pH from falling below about 6. Low pH allows certain metals=
,
notably Cd, Cu, Ni and Zn to
become more plant-available and thus potentially harmful.
Sewage sludge-lime mixtures are commonly used as limestone substitutes on
farms. The "lime" component
of these materials is much more alkaline (pH 11-12) than standard limestone
(pH 8.0-8.5), and reacts more
rapidly with soils because of higher solubility and fine particle size. Thi=
s
more rapid reaction creates the
short-term potential for "overliming" if applied at comparable rates to
ground limestone, especially if the
material is applied unevenly. The harmful effects of overliming (soil pH >
7.5) include crop deficiency of
manganese. In addition, the alkaline soil pH increases the plant uptake of
Mo, an element that can cause
disease in ruminants. Rechecking pH is essential.
METALS IN SLUDGES
Concentrations of Cd, mercury (Hg), lead (Pb), Ag, Sn and a number of other
metals are higher (often
much higher) in sewage sludge products than the concentrations of these
metals in human waste or manure.
The debate about the advisability of applying sewage sludges to farmlands
has centered for decades on the
degree of risk that would be incurred by increasing the levels of
potentially toxic metals in soils in our farms
and gardens.
Table 3 illustrates the fact that long-term farm application of sludges wit=
h
"typical" metal concentrations
increases the topsoil concentrations of some or all of the elements listed.
Most of the metals listed in Table
3 are relatively immobile in the soil, and are likely to persist for
decades, or even centuries, following
application. The concern with excessive metal buildup in soils is that some
of the metals (Cd, Hg, Pb) are
particularly zootoxic (cumulatively toxic to animals and humans), whereas
other metals (Cu, Ni, Zn) are
known to be phytotoxic (damaging to crops).
Farm Family Health/Workers
Farmers and farm workers working with sludges and on sludged fields should
be aware that Class B sludges
contain pathogens. While manures also contain pathogens of human concern,
the number of different
pathogens likely to affect humans is far higher in sewage sludges. The
National Institute for Occupational
Safety and Health recently issued guidance for workers that suggests hygien=
e
practices to minimize risks of
infection from sludge handling.
Conclusions
Since the banning of disposal of sludges by dumping into the ocean, more
wastewater treatment plants are
looking to farmlands for the disposition of sewage sludges. Use of sludges
on dairy farms has both short
and long-term benefits and risks which a farmer should carefully assess.
Sludges from different wastewater
plants can have very different properties and quality, so specific knowledg=
e
of the sludges that may be
applied to a particular farm is needed to make appropriate decisions.
Management practices and precautions
can reduce risks, so if sludges are used, consideration should be given to
how they are applied. A farmer
choosing to use sludges should be clear as to why and how the materials wil=
l
be used.
Sludge Spread on Fields Is Fodder for Lawsuits
By JENNIFER 8. LEE The New York Times
http://www.nytimes.com/2003/06/26/national/26SLUD.html
Critics are skeptical that the E.P.A. can objectively assess the program,
given its promotion of sludge since it set new regulations in 1993 under th=
e
Clean Water Act. For example, a 1994 E.P.A. brochure says that biosolids ma=
y
"protect child health." The brochure cites a study showing that animals tha=
t
ingest "biosolid-treated soil and dust may have a decreased absorption of
lead into the blood stream, thus lessening the potential for lead-induced
nerve and brain damage." A researcher with the Sierra Club, Caroline Snyder=
,
said, "Instead of protecting the public, they are right there in there with
industry promoting the practice." One of the agency's most senior scientist=
s
left as a result of a dispute over sludge research. In May, the agency
terminated the scientist, David Lewis, a 32-year veteran who had published
an article in the journal Nature raising questions about the agency's sludg=
e
research. "To me, of all the environmental issues, this is Mount Everest,"
said Dr. Lewis, who won the agency's top science award in 2000.
The Labor Department ruled in 1996 and 1998 that the E.P.A. had retaliated
against him for whistle-blowing. Other groups say the E.P.A. research
proposal is not rigorous enough. "It's not looking at health outcomes," sai=
d
Ellen Harrison, the director of the Cornell Waste Management Institute, who
helped write the National Research Council report. Ms. Harrison said most o=
f
the research was being done by groups with a history of promoting sludge.
"There has to be a change in the way that E.P.A. operates," she said, "so
that it's not just lining up the same old guys." Copyright 2003 The New Yor=
k
Times Company
Received on Sun Dec 26 2004 - 17:41:24 EST