Chapter Seven
EFFECTS OF SLUDGE ON SOILS AND CROPS
AND GROUNDWATER
The NRC's third point considers the:
(3) effects on soils, crop production, and ground
water;
The NRC report concluded the, "Treated municipal
wastewater effluent and sludge resemble normal
irrigation water and manures. Although they may contain
some exotic compounds and fertilizer elements in
different proportions than ideal fertilizer, they
present no significant hazard to agricultural soils,
crops, or the environment if they are applied in
quantities commensurate with crop needs." (p. 83)
If it is true that wastewater and sludge present no
hazard, why did NRC point out the potential hazards.
1. "Organic matter in sludge and wastewater can impede
infiltration and aeration by temporarily plugging
the soil surface." (p. 69)
2. "Following organic matter decomposition, trace
elements [pollutants] from wastewater and sewage are released
and form sparingly soluble reaction products. These
trace elements include arsenic, cadmium, copper,
cobalt, nickel, lead, selenite-selenium, molybdate-
molybdenum, and others. Because of their sparingly
soluble nature and their limited uptake by plants,
they tend to accumulate in the surface soil and
become part of the soil matrix (McGrath et al.,
1994). With repeated applications of wastewater,
and particularly with sludges, these elements could
accumulate to levels of toxic to plants (Chang et
al. 1992) and soil organisms (Mcgrath et al.,
1994). They could also accumulate in crops where
they could, in turn, build up to potentially
harmful levels in humans, domestic animals, and
wildlife that consume the crops (Logan and Chaney,
1983)." (p. 70-71)
3. "The accumulation of metals following long-term
applications of sewage sludge has been observed to
reduce levels of microbial biomass (Brookes et al.,
1986b) In a long-term field experiment that
compared sludge-amended soils to manure-amended
soils, (McGrath et al. (1994) reported microbial
biomass levels in the high metals sludge treated
soils to be approximately half of the manure-
treated soils." In effect, it is only half as good
as our ancestors fertilizer, even if there were no
hazardous substances in it.
4. "Nitrate pollution of ground water is often
reported as an effect of excessive application of
conventional fertilizer to crops (Hallberg and
Keeney 1993)."
The EPA also reports that nitrates can build up in
cattle fodder to excessive levels, which will kill
cattle.
The report also notes that, "Yield and crop quality
have been harmed by excess nitrogen in many crops,
including tomatoes, potatoes, citrus, and grapes (Bouwer
and Idelovitch, 1987)" (p. 66)
What will this do to humans who eat the produce?
Moreover, the NRC report found that: "The
application of wastewater effluents to soil may pose
some risk of ground water contamination by viruses and
bacteria: however," they also noted, "that risk can be
minimized by adequate disinfection of reclaimed
wastewater and by slow infiltration rates." (p. 9)
Wastewater effluent is the cleanest treated water
from a treatment plant which normally is returned to the
rivers and lakes and yet the NRC report found that it
could contaminate the soil and ground water at a depth
of almost 100 feet.
Yet, some cities are now selling the effluent to
water lawns based on the premise that if it is clean
enough to return to our rivers and lakes, it is clean
enough to put on lawns. However, according to Corpus
Christi Wastewater Superintendent Wayne Cockcroft, as
reported in the Corpus Christi Caller Times, "It's very
clean water that's suitable for outdoor use,"... "But
even when a lawn has been watered with effluent, we
encourage people not to let their children play on the
lawn until the water has soaked into the ground. There
is always a chance that a child could get his hands wet,
put it in his mouth and get an upset stomach."
If the NRC report found that 25 groups of both
viruses and bacteria in the effluent may contaminate the
ground water, what makes Cockcroft think the worse thing
that could happen to a child is an upset stomach?
And if the clean effluent could contaminate ground
water, why would the EPA allow "clean" sludge with
extremely high levels of toxic and hazardous substances
(3,000 ppm for chromium is an example) and 98 percent
water to be dumped within 30 feet of a lake or river?
Yet, the same sludge with less liquid can not be put in
a part 503 landfill, because it may contaminate the
groundwater. According to the EPA's preamble to the 503
regulation, "Sewage sludge with a high (in this case,
high is 600 ppm of Chromium) concentration of certain
organic or metal pollutants may pose human health
problems when disposed of in sludge only landfills
(often referred to as monofills) {part 503, surface
disposal}, or simply left on the land surface, if the
pollutants leach from the sludge into ground water.
Therefore the pollutant concentrations may need to be
limited or other measures such as impermeable liners
must be taken to ensure that ground water is not
contaminated." (FR. 58, 9259)
Furthermore, why didn't the NRC report question the
EPA for raising the pollutant limits for lead from those
in the proposed part 503 of 300 ppm, the acceptable risk
level for children, to 840 ppm? According to the NRC
Preface, the EPA risk assessment standards were the
primary purpose of the study.
Furthermore, the NRC report did not address what
will happen to crop safety when the land loading limits
are reached for any one of the pollutants in sludge.
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Review of National Academy of Science's (NAS) 1996 literary review report by
its National Research Council (NRC) Committee :
"Use of Reclaimed Water and Sludge in Food Crop Production"
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