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Sewage sludge compost poisons gardens 

Lax regulation endangers our nests and offspring

click to enlarge FILE PHOTO
For more than 10 years, SLO County has been wrestling with whether or how to allow spreading sewage sludge on land, due to the concentrations of toxic, carcinogenic, mutagenic, and infectious agents in the material.  These contaminants pose short- and long-term risks for public health, the environment, and agriculture.  Among those focused on local policy are the SLO County Board of Supervisors,  several county commissions and departments, agricultural and environmental organizations, and various advisory councils.


A recent incident highlighted the importance of exercising caution when exposing people, especially children, and plants and animals to the heavy metals, synthetic chemicals, pharmaceuticals, endocrine-disrupting compounds, and pathogens combined in sewage sludge.  As reported by New Times on Aug. 13 (“Real-world learning” by Kathy Johnston), Morro Bay High School grew vegetables in composted sewage sludge from the city’s sewage plant, planning to feed the produce to students through the cafeteria and home-economics classes.  Eight of the school garden’s ten raised beds contained 100 percent composted sewage sludge. The levels of cadmium, lead, molybdenum, and selenium in the material were high, compared to average uncontaminated agricultural soil in the state. 


After receiving some information about the risks involved, and a site visit by the author of this commentary, in late August the school returned the compost to the sewage plant and restarted the garden with natural soil amendments.


Sewage sludge contains a wide array of concentrated contaminants, the vast majority of which are unregulated, including such metals as beryllium, chromium and thallium; such chemicals as dioxins, PCBs, and pesticides; such hormones as progesterone and testosterone; such drugs as codeine, digoxin, and erythromycin; and various bacteria, viruses, protozoa, worm cysts, and fungi.  Exposure to these contaminants can occur through direct contact, inhalation of particles and gases, and ingestion of contaminated plants and water. 


Once spread on land, the synthetic chemicals and heavy metals in sewage sludge persist for decades and centuries, and accumulate with each successive application.  Federal, state, and local regulations place limits on only nine heavy metals and one pathogenic organism, and these are considered unsafe by many, including the Cornell Waste Management Institute, the state Farm Bureau, and the national Sierra Club.


Cadmium, for example, is a carcinogenic, endocrine-disrupting heavy metal toxic to the liver and kidneys, which is readily absorbed by root crops and leafy green vegetables.  The limit for cadmium (39 ppm) is 108 times the concentration found in background soil (0.36 ppm), and the amount in the Morro Bay compost (3.7 ppm) is 10.3 times that soil level.  Federal and state regulations allow cadmium soil concentration to build up to 20 ppm, which is 13 to 25 times higher than allowed in Ontario, Germany, Denmark, and Norway. In setting the limits on cadmium, and other metals, the U.S. Environmental Protection Agency did not consider exposure of children, dietary exposure, or simultaneous exposure to multiple contaminants, and it used a cancer risk factor 100 times less protective than it uses in water and air regulations. 


After the defeat of a plan to dump 50,000 tons of sewage sludge annually in San Miguel in 1998, the county took control of the activity from the state and federal governments.  Concurring with the recommendations of two county task forces, the board of supervisors imposed an interim moratorium ordinance to prevent an escalation in sewage sludge land application, and directed the drafting of an as yet incomplete permanent ordinance.


Neither the interim nor the permanent ordinance regulates amounts smaller than five cubic yards and both rely on obsolete federal standards that allow land application of highly contaminated sewage sludge. Both cap annual land application at historic levels (1,500 to 1,600 cubic yards) and, while the permanent ordinance would regulate sewage sludge and composts containing it, the interim ordinance does not regulate such composts. The proposed permanent ordinance would restrict applications exclusively to agriculturally zoned land used for growing food and feed, and for grazing.  This would permanently prevent organic farming on such land and marketing produce grown on it to such food processors as Heinz and Del Monte.  It fails to adequately protect the public, environment, property owners, and agribusiness from the risks of using sewage sludge as a soil amendment.


It appears that our county and schools need better policies to prevent the poisoning of our own nests and offspring.  The state Department of Education, which issued $2,500 grants to local schools in 2008 through its “Garden in Every School Program”, has no policy regarding the use of sewage sludge in school gardens.


Sewage sludge isn’t going away anytime soon, but spreading it on land poses a threat to the quality of our soil, water, food and air we may not immediately recognize.  In this situation, what you don’t know can hurt you, and those you care about.

Excellent resources with scientific and experiential information include:


Cornell Waste Management Institute (, Sludge Facts ( by Dr. Caroline Snyder, and Sewage Sludge Victims ( by Helane Shields.


As a member of both sewage sludge land application task forces convened by the county, the author of this article can also provide further information.


David Broadwater, of Atascadero, has been researching this topic and advocating protective policies for more than a decade. Contact him via the editor at


-- David Broadwater - Atascadero

-- David Broadwater - Atascadero


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