On the face of it, there's no good reason for a gardener to object to sewage sludge (which we will henceforth call biosolids) in the garden. It's just manure, right? And if they can cook the salmonella and other microbes out of it–well, why not put the stuff to good use? Otherwise it just takes up space in a landfill.
Well–it's not that simple. Critics worry that everything we put down the drain and into our bodies–from antibiotics to vitamins to household cleaners to industrial solvents–could end up in the biosolids. The processing plants, after all, are designed to remove the living microbes but not necessarily the heavy metals and other nasty bits.
(I'm not trying to push books here, but if you want an overview of how a modern wastewater treatment plant works, check out The Ascent of the Worm, the last chapter of The Earth Moved.)
So the San Francisco Public Utilities Commission has, for years, distributed a composted biosolid product called SynaGro CV Compost–a name only a public official could come up with–and has tried to defend its product against criticism about heavy metals and other toxins.
And now the PUC has released a report comparing its product against a number of store-bought composts. They tested for 127 different contaminants–still not enough, according to critics, who also have questions about whether the right sorts of samples were taken.
But the study is interesting reading regardless, mostly because it shows the levels of lead, mercury, and other such things in compost products you might regularly buy–EB Stone, Kellogg, etc.
Read the study here. And answer me this–is there enough data in the world to reassure the public about the use of biosolids in gardens? What about in some kind of agricultural setting for non-food crops (like biofuel, fiber, etc). Or would you rather see it all go to the landfill? Discuss.