Sludge Watch ==> Ontario Farmer: Too Many Unknowns Make Biosolids Risky

[Maureen Reilly]

TOO MANY UNKNOWNS MAKE BIOSOLID APPLICATION RISKY

Ontario Farmer

Tuesday October 16, 2007

Pg. 20 B

Environment

“Urban contaminants that may exist in sewage sludge will be on your land 
forever, expert says”



By Jeffrey Carter

Ontario Farmer



Agricultural land is too important to take the chance of spreading sewage 
biosolids from the city, according to the director of the Cornell Waste 
Management Institute (CWMI),



There are just too many unknowns, Ellen Harrison says. Sewage biosolids are 
the residues of materials released into the sewers from a variety of sources 
including homes, industries, medical facilities, businesses and street 
runoff.



“Are you prepared to have contaminants spread on your soils that will 
basically be there forever?” Harrison asks.

“Often times, we just don’t know what the risks are.”

While Harrison says there are significant concerns attached to the heavy 
metals that are part of the sewage sludge, she’s even more concerned with 
the vast array of organic chemicals. These include PCBs (polychlorinated 
biphenyls) and brominated flame retardants.

The organic chemicals in sewage biosolids are not regulated in the United 
States, Harrison says.



In Ontario, there’s a reference to industrial organic contaminants in the 
Ontario government’s Guideline for the Utilization of Biosolids and Other 
Wastes on Agricultural Land:  “at present, little is known about  the 
effects of industrial organic contaminants contained in other wastes when 
applied to agricultural lands… As experience is gained and relevant 
research results reviewed, standards will be established.”



Harrison speaks to the question of organic chemicals in sludge in a paper 
published in 2006 by the scientific journal, Science in the Total 
Environment.  While there are tens of thousands of organic chemicals in use, 
data related to their presence in sewage sludge could only be found for 516.



“Evaluating the risks posed by individual chemicals, let alone mixtures, 
requires multiple assumption that can lead to unacceptably high levels of 
uncertainty.  Current limitation in our knowledge base regarding the amount 
and type of chemicals in sludges exacerbate this problem, as does the 
limited availability of fate and toxicity data,” Harrison and her 
colleagues write.



While Harrison is opposed to spreading sewage biosolids on agricultural land 
and on other properties, she has also been involved in publishing 
recommendations for those farmers who chose to do so.



A set of guidelines published this year by Rutgers University are more 
stringent than current U.W. regulations, Harrison says.  They include such 
suggestions as establishing a whole farm nutrient balance prior to applying 
any sewage biosolids and never spreading any sewage biosolids on soils used 
to grow vegetables and fruits.



The Ontario guidelines allow sewage biosolids to be spread on land used for 
vegetable and fruit production, 12 months or more before harvest.



Harrison was also involved in developing guidelines specific to dairy 
farmers in 2003.  These recommend that dairy farmers: become familiar with 
the potential interactions of copper, molybdenum, sulphur, iron and cadmium; 
avoid spreading sludge with concentrations of molybdenum or cadmium greater 
than 10 parts per million and obtain test results on a load-by-load basis 
for the sludge being spread.



Along with working at the waste management institute, Harrison is a senior 
extension associate with Cornell University’s Department of Crops and Soil 
Sciences.





For more information visit the CWMI web site at www.cwmi.css.cornell.edu .





ONTARIO FARMER, Tuesday October 16, 2007  Pg 20B