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[GreenYes] biosolids

Concerns & Risks

* _Trace elements_
* _Toxic chemicals_
* _Pathogens_ (

* _Odors_ (
* _Storm water run-off_
* _Groundwater contamination_
* _Truck traffic_

Despite over 30 years of research which shows that, when conducted according
to regulations, the land application of biosolids is safe, concerns remain
over soil and groundwater contamination from trace elements, toxic chemicals
and potentially harmful disease causing organisms (pathogens). In response to
these concerns, _EPA_ ( conducted a comprehensive risk
assessment that evaluated the health risk to the general population as well
as to a highly exposed individual, such as a person who would have direct
contact with biosolids land application sites for a lifetime. To date, there have
been no documented negative human cases where a biosolids program met all
the federal and state requirements.
Finally, odors associated with the land application of biosolids are
considered more of a nuisance than a health problem. Odors are oftentimes the most
objectionable aspect of biosolids use on neighboring farms.
_Trace elements_ ( (heavy
Historically, industries disposed of their liquid wastes to the sanitary
sewer system, Consequently, highly industrialized cities and places with certain
industrial activities such as metal plating factories, produces sewage
sludges with high metal concentrations. However, since the late 1970s,
pretreatment requirements have been established and implemented to require such
facilities to reduce or remove the metal constituents before they enter the sanitary
sewer system. This has resulted in significantly decreased levels of heavy
metals in biosolids. Between the national surveys of biosolids in the late
1970s and the survey from the late 1980s (both conducted by _EPA_
( ), the average lead level decreased from 969 mg/kg to 134 mg/kg.
Nickel levels decreased from 135.1 mg/kg to 42 mg/kg, and cadmium levels from 69
mg/kg to 7 mg/kg.
Furthermore, _EPA_ ( conducted a comprehensive risk
assessment for pollutants in biosolids that are land applied. The risk
assessment evaluated risks to human health as well as ecological risks (to animals and
plants) through 14 exposure pathways for land application. Current
regulations based on the risk assessment, set forth conservative pollutant limits and
other requirements that protect public health and the environment.
_top of page_ (
Toxic chemicals
Certain toxic chemicals that do not volatilize or decompose during treatment
may concentrate in biosolids. Residues from the chemicals have declined over
the past 20 years. Benzene for example was detected in 93% of biosolids
samples in a survey conducted during the late 1970s, but in only 3% of samples
from the late 1980s. Detection of persistent pesticides such as chlordane,
dieldrin, heptachlor, and hexachlorobenzene were detected in 16% of the 1970s
samples, but none of the 1980s samples. These declines are due to pretreatment,
chemical bans and the phasing out of chemicals.
In developing current regulations, EPA considered about 200 toxic organic
compounds. After conducting extensive risk analyses on the 31 that were the
most threatening, the agency concluded that they appeared so rarely, or at such
low concentrations that they did not need regulations.
_top of page_ (
A major public health and environmental concern associated with land
application of sewage sludge is the effect of pathogens on humans and animals.
Municipal wastewater generally contains four major types of human pathogenic
(disease-causing) organisms: bacteria, viruses, protozoa and helminthes
(parasitic worms). The potential for exposure diminishes over time as environmental
conditions such as heat, sunlight, desiccation, and other microorganisms
destroy pathogens that may be present in biosolids.
In order to be approved for land application, biosolids must have been
treated to reduce the number of pathogenic organisms. There are two classes of
pathogen treatment, referred to as Class A and Class B. Class A pathogen
treatment is the most rigorous and this biosolids can be applied to any land
including lawns, gardens and areas freely accessible to the general public. There
are no site restrictions so biosolids that meet Class A standards are treated
and handled with the same care as regular fertilizers and soil conditioners.
Class B biosolids receive less rigorous treatment. While safe to land apply,
there are site restriction pertaining to harvest of plants, use of the land
for grazing, and public access.
_top of page_ (
Many of the odors associated with biosolids are reduced during the treatment
process. As organic materials breakdown, odors are released. Thus is the
case with biosolids, which like other manures, will release odors. The method of
biosolids treatment also affects odors. Lime stabilized biosolids will have
a slightly sweet ammonia odor. Digested biosolids will have a more organic
aroma. In most cases, odors dissipate after several days, similar to animal
_top of page_ (
Storm water runoff
Biosolids absorbed to soil particles may runoff from land applied fields
into nearby streams and surface waters. In order to prevent water pollution,
site restrictions are required. These include maintaining buffers along
waterways and surface waters and restricting slopes where biosolids can be applied to
less than 15%. [Diagram of buffers]
_top of page_ (
Groundwater contamination
The Biosolids Use regulations required at least 18 inches of soil depth to
bedrock or groundwater. In this way, the soil acts as a protective layer to
filter nutrients from entering to groundwater. Furthermore, biosolids
application rates are limited to the plant available nitrogen, which can be used by
the crop. In this way, there are no excess nitrates to leach into the
Bacteria and pathogens in biosolids tend to adhere to the biosolids amended
soils because of the organic nature of biosolids. This clinging mechanisms
prevents potentially disease causing organisms from entering the groundwater
while keeping them near the surface where sunlight, temperature, dryness and
naturally occurring organisms destroy them.
_top of page_ (
Truck traffic
Biosolids are delivered to the site in tractor-trailers for cake biosolids
or tanker trucks for liquid biosolids. Each tractor-trailer contains
approximately 20 wet tons of biosolids (15 % - 35 % solids). Application rates
generally equate to about one tractor trailer truckload per acre. Therefore a
fifty-acre field could receive about 50 truckloads of biosolids resulting in heavy
truck traffic during the spreading operation. Truckers are required to abide
by Virginia Department of Transportation requirements. Contractors designate
haul routes which avoid residential roads whenever possible. Also, land
application operations usually occur during working hours when most people are at
work and school to minimize inconvenience caused by the trucks.
_top of page_ (
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