Sewage Sludge has Super Powers that Protect Metals from Uptake into Plants!!

Heavy metals in sewage sludge (aka biosolids) and their potential for environmental impact has been a concern over the years, especially when it comes to recycling treated sewage sludge on farmland and composting it for home garden use.

This is exactly why I again enlisted the help of Rufus Chaney, a long-experienced USDA researcher on metals in biosolids and soils and plant uptake who worked for decades on this subject with a very long list of peer-reviewed journal articles. He even mentored another legend, Sally Brown with University of Washington who has also done some amazing work with biosolids, carbon sequestration, and greenhouse gas calculations (theme for another article).

It is important to recognize the difference between knowing that a metal or any other compound is present and knowing whether it is actually taken up by the plants that you may grow and eat. Nature can be very complicated in this way. Rufus to the rescue! He has worked with romaine lettuce as an indicator for highly sensitive crops - those that should up take the most bioavailable metals.

In the presentation below and the similarly titled peer-reviewed paper, the research compares control (unamended with biosolids soils) to biosolids amended soils which had received high rates of biosolids applications and contained significant concentrations of metals. Despite higher total soil cadmium, lettuce accumulation of cadmium was significantly lower in biosolids-amended soils than control soils that had never received biosolids. This was true for soils even decades after the applications occurred, meaning that the amazing biosolids properties stay in tact for as long as we can measure. You can see that the plants consistently accumulate more metals from the control soils even if there is a lot more of the metal present in the biosolids / sewage sludge.

I have heard Rufus present in person, and he is emphatic about the importance of the ratio of cadmium to zinc. If they are present in a ratio of 1:100, for instance, (for every one part cadmium there are 100 parts of zinc), then there will be a enough zinc to prevent the uptake of cadmium by the plant at any significant level; even protective of people eating large amounts of the lettuce. We often hear of a potentially similar "protection" mechanism in our bodies when we take zinc supplements to try to boost our immune systems during the flu season. Luckily, most biosolids have lots of zinc and iron (another protective metal that likes to bind with lots of compounds).

The implications of these finding go far beyond whether biosolids is safe to use in crops and home gardens. It means that biosolids have amazing assimilative and protective powers! For instance, urban soils often contain high levels of metals (from car brake pads, emissions, etc.). Biosolids have been added to these soils to remediate these contaminated soils so that inner city folks can again garden and play in the soils safely. Biosolids have been used to remediate mine tailings with high levels of metals. (Good fodder for future articles!)  

Another note from this study is that because of the tremendous success of modern industrial source control programs (they require prevention or treatment onsite at industries that discharge metals and other pollutants), modern biosolids - treated sewage sludges do not contain levels of metals that would be of concern for uptake. For instance, the metals in Orange County's sewage has been reduced by over 95% since the 1970's when the Clean Water Act began implementation. This equates to proportional reductions in the final biosolids - treated sewage sludge. The metals in these biosolids are significantly under the EPA's most restrictive criteria, which means they are so low that the cumulative loading is not of concern.

In other words, our nation has made great strides in cleaning up metals in the environment, which ensures that biosolids can be safely recycled to fertilize farms as well as turned into compost for home use. And our gardens and farms will actually be protected by the biosolids! Now that is Amazing!!

On a sad note, it is so unfortunate, disappointing, disheartening, and potentially an environmental disaster when fear and politics rule and biosolids are ban from use, forcing municipalities to use technologies with larger carbon footprints (it takes lots of energy to dry biosolids or refine into another product), and frankly, it’s a waste of significant resources. We are wasting precious non-renewable phosphorus that otherwise needs to be mined from the earth again to replenish fields. We put more pressure on farmers to turn to expensive, non-renewable, synthetic fertilizers. Banning biosolids is creating the environmental disaster that the politicians are ironically trying to prevent. 


VOICE YOUR SUPPORT! http://www.ipetitions.com/petition/biosolids/ 

Kukier chaney-2005-effect of biosolids on phytoavailability of cd

View more presentations from Deirdre Bingman.