Tagged: sewage sludge
Contrarian friend Cliff White doesn’t share Lindsay Brown’s impatience with HRM Council’s decision to spend $50,000 studying the safety of fertilizer derived from the municipality’s sewage treatment plants.
Among other things, she mentions studies that go back eighty years. I’d suggest that studies going back even half that time wouldn’t be testing even half the chemicals, toxins, and metal compounds likely to be found in today’s sewage. Since any cursory search of the literature will show that not all of these products are removed at the treatment plant, three questions arise:
- First, how effective are our local sewage plants are in extracting heavy metals, toxins and other chemicals before it becomes sludge and then fertilizer?
- Second, what are the national and provincial standards for levels of these products in fertilizers?
- Finally, are these standards adequate to protect both the environment and human health?
A quick search of the literature will show that different countries have widely different standards in this regard, suggesting that this is a legitimate area for concern. Given the reasonable scientific concern regarding sewage sludge I don’t think a study of the local stuff is unwarranted.
In an earlier letter, Cliff forwarded information he extracted from a 2009 US EPA Report.
The sampling effort collected sewage sludge from 74 randomly selected publicly owned treatment works in 35 states. Samples were collected in 2006 and 2007. The TNSSS Technical Report provides results for 145 analytes, including:
- four anions (nitrite/nitrate, fluoride, water-extractable phosphorus),
- 28 metals,
- four polycyclic aromatic hydrocarbons,
- two semi-volatiles,
- 11 flame retardants,
- 72 pharmaceuticals, and
- 25 steroids and hormones.
Some analytes were found in all 84 samples, while others were found in none or only a few of the sewage sludge samples.
After the jump, more extracts from the report, detailing the number of samples in which various chemicals were found. That list will probably scare some readers. Certain environmentalists like to cite such lists precisely because they sound scary, and because they lend a false aura of scientific credibility to their arguments. Such lists are all but meaningless without two essential pieces of information:
- In what concentrations were the chemicals found? (For many chemicals, minuscule amounts are both routine and harmless.)
- What level of exposure to people, plants, or animals would result if the sludge were used for its intended purpose? (How much actually gets to people is the real worry, and Cliff’s list tells you nothing about that.)
To answer these questions, scientific risk assessors use a model known as source, pathway, receptor. In the case of a person who eats carrots grown in soil treated with fertilizer derived from composted sewage sludge, the sludge is the source, eating a carrot is the pathway, and the person is the receptor.
For each chemical, the risk assessor will determine the amount present in the sludge, and the amount that might make its way into a carrot and then into a person who eats the carrot. The risk depends on the actual exposure a person might experience. These calculations typically use ultra-conservative assumptions: the receptor is a developing child; the child eats only vegetables grown in soil treated with the fertilizer; Large amounts of fertilizer are used.
This is exactly the kind of analysis used to set allowable levels of Cliff’s scary sounding chemicals. Find the Canadian Council of Ministers of Environment (CCME) report on this process here [pdf]. Regular sampling confirms that composted Halifax sewage sludge meets these standards. Dozens of municipalities have safely used sewage sludge for decades, with less advanced equipment that that used in HRM. And let us not forget, Halifax’s sewage treatment plants solved a real environmental menace–the dumping of raw sewage into Halifax Harbour.
For all these reasons, real environmentalists should be delighted, and HRM Council should not waste public money pandering to anti-science zealots who will never be persuaded on this issue. Read more »
If the admirable Ellen Page* wants to contribute to the environment of her home province, she might consider pressuring the Dexter government to rethink its politically expedient decision to delay regulations to control mercury emissions from coal-fired power plants.
Mercury is a dangerous element with well-known impacts on human health, especially the health of young children. The province and Nova Scotia Power have known about their obligation to clean up mercury emissions for years, if not decades. [Disclosure: both NSP and the NS Govt. have been my clients.] The government’s decision to back away from that legislated commitment in the face of a threatened power rate increase came as a huge blow to morale in its Environment Department.
Power rates have been the third rail of Nova Scotia politics ever since they caused the defeat of Gerald Regan’s government in 1978. Darrell Dexter is nothing if not cautious, and he made the pragmatic decision to sacrifice a near-term improvement in public health for political longevity. That’s real politics, and a figure of Page’s stature could make a real contribution by weighing in on the side of health.
That would be a better use of her talents than opposing the productive recycling of biosolids, as she did in this appalling CBC-TV interview. Money quote:
I’m an advocate of hu-manure and utilizing our urine as a great nitrogen source for gardens and plants, but biosolids are very much not hu-manure… I like to refer to it as sewage sludge. It’s highly toxic. Look, I’m not a scientist, so I’ll say that obviously, but I’m a very concerned citizen and I’m worried because this is highly toxic material that is already being put on our land without the transparency of letting citizens of HRM and of Nova Scoti know.
To paraphrase, Page sympathizes with government’s desire to recycle human shit and urine, and she acknowledges that she brings no scientific expertise to the discussion, but she believes Halifax’s sewage sludge contains too many toxic contaminants, whose implications have not be fully disclosed to or discussed with residents.
No single word is more misused, in journalism and in environmentalism, than “toxic.” It’s a relative term that is almost invariably tossed about as an absolute. The public imagines that everything is either toxic or not toxic, whereas toxicologists and serious environmentalists know that virtually everything, including pure water, is toxic at sufficient dose. Dosis sola facit venenum. Dose is what determines risk.
Mercury is highly toxic at low doses. That’s why scientific risk assessment justifies spending lots of money (and political capital) to keep it out of our air. Untreated sewage also harms the environment, so most countries have stepped up efforts to remove solids from the waste stream. The question is what to do with them.
To answer the question, HRM built a biosolids processing plant at Aerotch Park to treat sewage sludge using the commercial N-Viro process. The HRM website has a description of the plant and the process, together with a schematic. The N-Viro Corporation website has a more detailed description of the process.
The provincial website offers a list of links on the use of biosolids throughout Canada, and a fact sheet on biosolids [PDF] (though the latter, frankly, is long on reassuring generalities and regrettably short on technical specifics.)
When the use of biosolids in Colchester County touched off a not-in-my-backyard furor a few years ago, the province held a public Biosolids Forum at which a variety of experts discussed their treatment and safety. (View their presentations.) Nova Scotia also established a broad-based committee to review provincial policy on agricultural use of biosolids. That led to revised and stricter guidelines [PDF] for biosolid use here.
The guidelines are worth a quick read. In contrast to the raw cow, pig, and chicken manure farmers apply freely to their lands, the HRM biosolids will be treated to kill pathogens. Samples from the plant will be tested regularly for fecal coliform, salmonella, Arsenic, Cadmium, Chromium, Cobalt, Copper, Mercury, Molybdenum, Nickel, Lead, Selenium, Zinc, dioxins, furans, and PCBs. The guidelines restrict the use of biosolids on farmland by proximity to 14 categories of land and land use, including watercourses, drinking water supplies, bedrock outcroppings, drainage ditches, roads, buildings, etc. The setbacks vary according to the slope of the land, and depth to groundwater and bedrock.
Want more information? The Food Action Committee of the Ecology Action Centre (an environmental group I belong to and support) has a short position paper [Word doc] opposing the agricultural use of biosolids, but it’s very general, and focuses on an alleged lack of transparency. The Canadian Council of Ministers of the Environment’s Biosolids Task Force has a website. A search of US educational websites for “biosolids safety agricultural use” yields 42 scientific papers; the same search on Canadian websites turns up 28.
Forums, task forces, stakeholder committees, websites, guidelines: Is it fair or accurate to describe all this as a lack of transparency?
On balance, HRM’s biosolids program offers a responsible way to recycle critical nutrients that would otherwise pose a pollution problem. Environmentalists ought to celebrate it, not oppose it.
One final note: Even by the lame standards of environmental reporting in Canada, the CBC’s treatment of this story is beyond disappointing. It took this unpaid blogger only a few hours to assemble the information and links included in this post, yet host Tom Murphy appeared to have no research at hand to contest Page’s wild claims about toxicity and non-transparency:
Murphy: But you know there is research out their suggesting, hey, it’s OK, and in this case the city put on, I think, about 25% of the manure they were using was this, so what do you say to that when they roll out the scientists to say it’s OK?
Page: At one point, doctors told us to smoke, so, you know what I mean?
So much for science. So much for journalism. I know television is conflict- and personality-driven, and by its nature must simplify complex issues, but this is negligent reporting by any standards.
* More disclosure: I like Ellen Page. In 2003, when we were just getting our little film series off the ground, she was generous enough to travel to Sydney to attend our Canadian premiere screening of Marion Bridge, in which she had a breakout role. I have tried to write this post in a way she might find persuasive, although I suppose she won’t. Should she want to respond, Contrarian’s space is hers.