Biosolids vs Bacon: An Easy Choice
I bet you thought that the problem with bacon was all that fat and salt. If you go back in time just a little bit, past the current concerns with high blood pressure, obesity and cholesterol, you will happen upon a time when concerns with bacon focused on potentially carcinogenic compounds in the bacon, namely nitrosamines. These concerns resulted in reduced nitrate concentrations in cured meat products, and with those reduced concentrations the nitrosamine concentrations have also dropped. With that, we are now able to feel guilty about enjoying bacon for many other reasons and may have even forgotten the days when bacon gave you cancer. Well, now thanks to new research from Rolf Halden’s group at Arizona State University’s Biodesign Institute, those same compounds are the new concern about biosolids. So, before you fry up some biosolids to go with your eggs over easy, read this library.
The library starts with an older paper that focuses on bacon. It turns out that nitrosamines are formed when nitrites react with amines, a component of many proteins. Like many of the other compounds we are now concerned about, nitrosamines come in different shapes and sizes. This is a name for a class of compounds, rather than for a specific compound. Nitrite was added to meats to preserve color and flavor and to prevent botulism. Concerns about the potential carcinogenicity of nitrites and nitrosamines prompted the USDA to reconsider how much nitrites were necessary to keep people safe from bacterial infections while simultaneously keeping them from getting cancer. It is important to keep the current paper in perspective, and this historic paper gets you started on that path.
From there we go to wastewater treatment. The second paper focuses on what happens when all of that nitrosamine from bacon and ham enters into the treatment plant. Much it seems goes away or at least decrease. One type of compound, NNitrosodimethylamine, decreased from the primary to the waste activated to the anaerobic digestion. Anaerobic digestion, particularly when carbon is added to the feedstocks, appears to degrade secondary amines. Not so bad, right?
In fact, if you go the 3rd paper, you’ll see where much of the focus on these compounds has been: drinking water and effluent treatment. It turns out that when you add chlorine to water with nitrogen in it, those same compounds that aren’t in bacon any more can be formed. This is a review paper and talks about alternative water treatment technologies, including UV and sunlight, as a way to degrade these compounds or to prevent them from forming in the first place. But we still do use a lot of chlorine to treat water.
Let us move on to the 4th paper. What happens when these compounds formed in water enter soils? The authors found that the compounds typically persist for 4 to 20 days. Degradation is enhanced at warmer temperatures and in cases of high levels of microbial activity. So, a well vegetated, high organic matter soil is a great place to degrade nitrosamines. The authors also point out that these compounds do not bind well and are susceptible to leaching.
And from here we go to the just released (thanks to Bill Toffey for sending me the link) paper about nitrosamines in biosolids. The authors tested preserved solids from the most recent national survey. They tested for 8 nitrosamines in 80 biosolids samples and were able to detect at least 1 in 88% of the samples. The most abundant compound was found at about 500 ng/g dry weight in the biosolids. For comparison, nitrosamines, in particular N nitrosopyrrolidine, had been found at about 100 ng/g (ppb) in bacon. Need I mention that the authors suggest that the results of their study indicate a need for increased research on the safety of land applied biosolids with respect to these compounds? But as we learned above, unless you are planning to consume your nitrosamines through direct ingestion of the biosolids, your risk of exposure is pretty darn low, as nitrosamines applied to land are neither high in concentration nor are they persistent.
I don’t know about you, but I’m thinking about bacon for breakfast.
Sally Brown, University of Washington