What contaminants lurk in sewage sludge (biosolids) compost? Watch out if you EAT more than 60 pounds per day!!! Wanna see the data?

The EPA's "503" regulations that was the most thorough health risk assessment ever completed for any material looks at many complex pathways of exposures (including direct ingestion). They looks at many organic (and inorganic) compounds. After oodles of analyses they determined that only the main heavy metals were contained in high enough concentrations to regulate.

Since then, many of the large urban areas have reduced metals 90% lower than they were in the 1970's when some of the original sewage sludge safety and plant uptake studies were done. The sewage sludge (biosolids) have an amazing simulative capacity and binding capacity that holds on tightly to the metals and other constituents that are present so they are not bioavailable to plants. Then the biosolids go above and beyond and have the ability to remediate (further incorporating even more metals). See early post.

Yes there are metals present in sewage sludge (biosolids). Some may see the data and the numbers may appear to be high. But we have to consider these binding properties of biosolids. PRESENSE DOES NOT EQUAL AVAILABLE TO PLANTS OR THE ENVIRONMENT. This has been demonstrated for decades now and even aging biosolids (sewage sludge) does not "release" these contaminents that they hold so tightly.  

I found this memo on the internet (re-uploaded to Scribed). It gets to some of the questions of other modern organic chemical contaminents in sludge. San Francisco had a wonderful compost program that made compost available to local gardeners. This memo was written in response to attacks from a group that was concerned about what's in their compost.

You'll see the organic contaminents listed are in extremely tiny concentrations that would not be measureable if plants do updake. The memo mentions that dioxins were proposed by EPA in 1999 and then they decided that the risk was so low they didn't need to regulate them. The memo shows the TEQ (toxicity equivalency) in parts per TRILLION. One part per trillion is ONE-TWENTIETH of a drop of water in an Olympic-size swiming pool!

The memo shows that ALL available soil amendments (adding organic matter to your soil along with macro and micro nutrients and beneficial microbes) are comparable in the levels of contaminents they contain. These are very, very low numbers. And I've seen previous reports that show that synthetic fertilizers and any other products will also be in the same ranges. But synthetic fertilizers are not renewable and carbon sequestering (climate change benefits) like biosolids-base products.

One part per trillion (1 ppt) is a proportion equivalent to one-twentieth of a drop of water diluted into an Olympic-size swimming pool. http://en.wikipedia.org/wiki/Parts-per_notation 

There is nothing "clean" in our world. Technology has brought us ultra-low detection limits, so we are finding "contaminents" everywhere (chemical and microbial). We have to consider the levels at which they are present. Very very low levels do not pose health risks. The EPA has done the most thorough risk assessment on biosolids (and these other products on the shelves have similar contents - animal products probably have higher levels of steriods and anti-biotics but they probably are not availabe to the plants).

As Sally Brown recently stated (July 2011 BioCycle article), people are more worried about micro-constituents in the world and missing the big picture of climate change. That is something real, big, and most people don't believe that's true despite the unequivocal science that says it's happening. Biosolids sequesters massive amounts of carbon to the soil to help prevent climate change, but all the debates about contaminents are forcing many biosolids managers to energy options that just add to carbon emissions rather than sequestering in the soil.