Thanks to Darrol and Lisa for contributing to the conversation about biosolids.
The study that Darrol cited last week was conducted on Class B biosolids, which are not available to the home gardener and under strict regulations. Class A biosolids have gone through a second treatment, usually involving heat, which would break things down further. These molecules are more stable than thought earlier, but they do break down, and there is ongoing research in the area. However, the chance that they have any effect on microbial populations is very slim. Most treatment plants (including the one I am most familiar with in Tacoma) are entirely biological in nature, meaning that there is a microbial population that keeps the whole thing running. If the microbes get sick and die off, it is a huge problem and the digesters need to be re-inoculated, much like sour-dough bread. This rarely happens, and it's an emergency situation if it does. My point being that triclosan and triclocarban, even while they enter into the treatment plants and break down slowly, do not kill off the microbes. There is also a vast body of research on using biosolids on nitrogen- fixing plants, and in one recent study on Alder, trees grew faster and had more nitrogen-fixing nodules when fertilized with biosolids. I can get you the research if you are interested. Yes, compounds break down into smaller and smaller compounds, many of which are not analyzed. There is constant, ongoing research into newer and smaller and previously undetectable compounds. But most people are not afraid of their yard-waste compost, even though it may have contained pesticides and herbicides (and the smaller and smaller compounds that came from them). Even if there are organic compounds in biosolids (or yard waste compost, or anything else for that matter) that have yet to been discovered and analyzed for risk, they are not the type of molecule that will be taken up by plants. They are large, hydrophobic, and will not go into the solution that plants take up. The soil is a good place for these compounds to get broken down further and further, rather than our waterways, for instance. Heavy metals will be taken up by plants to some degree (mostly leafy greens), and biosolids are heavily regulated and tested for these. Everyone comes to gardening for different reasons, and will all find the soil amendments that work best for each of us. I would still encourage everyone to consider using biosolids in the garden if a Class A product is available to you. Most people flush the toilet without thinking of the consequences of where all that organic matter will go. I encourage you all to investigate biosolids in your area and learn what type of program your city has, and where it is recycled. Kristen On Mar 14, 2008, at 1:11pm, Darrol Shillingburg wrote: > Thanks Kriste and others for the clear and interesting discussion - > there is another issue that is considered an emerging problem with > biosolids and is related to domestic as well as commercial sources. > That being the accumulations of antimicrobials found in the sludge > component and the high percentage of those compounds that survive > both anaerobic and aerobic processes. > > "Whats known and whats unknown" about this small molecule > contamination is what stopped me personally from using biosolids in > my own garden, and I think needs to be part of everyone's > considerations. My particular concern is introducing and > accumulating antimicrobial into the soil colony while not knowing > the effects those introduced compounds have on soil bacteria > (particularly the nitrogen fixing varieties), or knowing the > effects (or lack of) of soil bacteria on the introduced compounds - > which are designed to remain stable and functional. > > I have included a partial quote and some links for those interested > in pursuing the trail into current research. > > regards, > > Darrol > > A quote from: Science Observer Jan-Feb 2007 issue > http://www.americanscientist.org/template/AssetDetail/assetid/54434 > > “More than a million pounds of antimicrobial chemicals from soap > and other products flow into the nation's sewers every year. Do > these compounds pose a risk? Product manufacturers say no, pointing > to data that show only traces of the two most common > antibacterials, triclosan and triclocarban, in treated wastewater. > What happens to the remainder is less certain. The stock > explanation has been that the majority is broken down during the > treatment process. The fraction released into surface water was > thought to meet the same fate sooner or later. Thus, much of the > claim that these products are safe rested on the fact that they > were rendered harmless in treatment plants or just beyond. > New data puncture that conclusion: 50 percent of triclosan and 76 > percent of triclocarban remain unchanged by aerobic and anaerobic > digestion in a typical wastewater facility, according to a pair of > recent reports. This large intact fraction isn't going out with the > treated water—the old estimates are correct in that respect. > Rather, it is trapped in the sludge at the bottom of the treatment > tanks. Most of that sludge gets spread on the ground to fertilize > pasture, forests and human food crops.” > > http://toxics.usgs.gov/regional/emc/municipal_biosolids.html > http://pubs.acs.org/subscribe/journals/esthag-w/2006/sep/science/ > nl_composting.html > http://toxics.usgs.gov/highlights/earthworms.html >> >> >> -------------- next part -------------- An HTML attachment was scrubbed... URL: http://list.communitygarden.org/pipermail/community_garden_list.communitygarden.org/attachments/20080317/bf2d1839/attachment.html _______________________________________________ The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org To post an e-mail to the list: [email protected] To subscribe, unsubscribe or change your subscription: http://list.communitygarden.org/mailman/listinfo/community_garden_list.communitygarden.org
