When researching my last post on organic agriculture, I came across one restriction that I didn’t quite understand: no use of sewage sludge. I’ll admit that the words “sewage sludge” have a serious nose wrinkling effect on me, but should they? What is sewage sludge, and how is it used in conventional agriculture?
Also called biosolids, probably to reduce the aforementioned nose wrinkling, sewage sludge is the material removed from wastewater during its treatment. The residential component of wastewater is everything we flush down the toilet or pour down the drain. Human waste contains substances like nitrogen and phosphorous, which can be extremely valuable for fertilizing crops. Thus, using human waste that is removed from treated wastewater for agriculture could conceivably provide a disposal method for the ever-growing pile of human waste while simultaneously providing a natural and sustainable source of chemicals used for fertilizer. Despite the “yuck-factor”, it seems like utilizing biosolids in agriculture could be a good thing. So why is it banned under the National Organic Program?
The trouble is that human waste isn’t the only type of material that contributes to sewage sludge. Industrial waste products are combined with residential wastewater when entering the treatment facility. In addition, not all residential waste is natural, human waste. These additional sources can result in potentially harmful substances persisting through the treatment process and making it into sewage sludge.
According to a nationwide EPA study of sewage sludge , samples from all 74 treatment plants tested contained heavy metals, carcinogens, industrial chemicals like flame retardants, and even antibiotics, steroids, and hormones. Little is known about the affects of combining all of these substances in a vat of sludge and, when applied to farmland used for growing food or grazing land for animals that are eventually sent to slaughter, there is potential for food contamination. In addition, these materials may adversely affect farm workers and people living near farms in which sewage sludge is applied.
Concrete evidence is difficult to find mainly because there is little research (or even funding for research) on the direct or indirect health effects of using sewage sludge in agriculture. In addition, there is no standard method for reporting or compiling health complaints related to sewage sludge. Lack of research has led to a lack of evidence that sewage sludge negatively impacts human health, which is often used to justify weak regulation and a lack of comprehensive testing. Complaints about health effects from sewage sludge are often dismissed because there is no evidence that the sludge causes people to get sick. Of course, there is no evidence that sewage sludge is safe either.
Anecdotal evidence and one small scientific study  suggest that people in close proximity to farms that apply sewage sludge do experience adverse affects including skin ulcers, upper respiratory infections, and gastrointestinal issues – just to name a few. The study dealt with exposure to the less treated (Class B) type of sewage sludge, but even the better-treated version (Class A) may cause health problems, and both types are being used in agriculture.
Recently, sewage sludge made waves in the San Francisco Bay Area when the SF Public Utilities Commission gave away free fertilizer described as “organic biosolids compost” that was actually treated sewage sludge . The use of the word organic was considered misleading because it could be interpreted as being related to organic agriculture rather than simply including organic matter. The program was suspended after the Organic Consumers Association organized a protest at City Hall on March 4th, 2010. I checked the SFPUC website for more information on the biosolids program. No upcoming giveaways were mentioned, and I found no references to “organic” – merely free biosolids compost. They also note that biosolids are currently used on agricultural land in Solano and Sonoma counties in addition to the giveaways. The FAQ was an interesting read; they explain that biosolids are safe because they comply with EPA testing requirements. Unfortunately, the myriad substances found in the nationwide EPA study discussed above show that current regulations may be woefully inadequate in determining the safety of biosolids because many potentially harmful substances that are present in sewage sludge are unrestricted. In addition, the FAQ describes the biosolids program as strictly monitored and regulated, but many other sources suggest otherwise.
At present, to be certified organic, foods cannot be produced with sewage sludge. Until more research is done into the potentially harmful side effects of additional contaminants, or human wastewater is collected separately for use in creating biosolids, I’m glad there is an option to avoid food grown with sewage sludge. And with that, I’m off to the farmers market for some local, organic produce - sans sludge!
Sources (cited or summarized):
 EPA study website
 S. Khuder et al., 2007. Health Survey of Residents Living near Farm Fields Permitted to Receive Biosolids. Archives of Environmental and Occupational Health 62 (1): 5–11. doi:10.3200/AEOH.62.1.5-11
 Sourcewatch article on sewage sludge
NY Times article on the barriers to biosolids research
Science magazine article on EPA study
A good summary of sludge including several of the sources cited here can be found on the Wikipedia page on sludge.