03/15/13

Microconstituents - Recent Research in the News

Notable research continues regarding pharmaceuticals, personal care product chemicals, nanoparticles, and other "microconstituents" in biosolids and what impacts, if any, they may have.  NEBRA covered this topic in a May, 2011 Info Update.

While past research focused on measuring microconstituents in biosolids, the most recent research efforts are focused on impacts, especially plant uptake.  See past NEBRA coverage here and here, including efforts to reduce drugs down the drain.

Recently, biosolids-borne nanoparticles of silver, zinc, and cesium have been a topic of concern.  In a paper by Colman, fresh nanoparticles were mixed directly into biosolids just prior to simulated land application and plant uptake was found.  Greg Kester expresses the concerns of biosolids researchers regarding the research design: the nanoparticles did not go through "any typical sludge treatment and did not become an integral component of the biosolids matrix. This is somewhat analogous to the old flawed metal salt pot studies used as the basis for the originally proposed 503 rules. Behavior is very different when the nanoparticles are subjected to actual sewage sludge treatment as they would be when entering a wastewater treatment plant." 

A similar study by Priester et al. erroneously implied significant potential uptake in soybean after biosolids application.  Several leading biosolids researchers severely critiqued that study (contact NEBRA for details).

Lombie et al. conducted more representative studies (2012, 2013) of silver nanoparticles (widely used nanoparticles) passing through wastewater treatment processes. Kester explains: "These papers found that all nanoparticles studied converted, through treatment, to silver... sulfides which are much less plant available, non-reactive, and much less toxic.

"Interestingly, one of the authors of the Coleman paper evaluated the biosolids from the wastewater plant with the highest silver concentration (856 mg/kg) from the US EPA Targeted National Sewage Sludge Survey (2009) and found it was all as silver sulfide (Kim et al 2010). 

"Therefore, while more work will always be recommended on these emerging constituents, the papers getting the headlines do not merit undue concern and the earlier papers represent a much more robust experimental design and pertinent and valid conclusions."

Most recently, Science Direct reported on Canadian research evaluating micropollutant uptake from soil fertilized with biosolids.  Again, as with nanoparticles, a realistic biosolids land application scenario found much less concern than spiked and other greenhouse or pot studies:

"Several recent greenhouse studies have established the potential for uptake of human pharmaceuticals from soil fertilized with municipal biosolids into a variety of crops. In the present study, a field experiment was undertaken to evaluate the uptake of organic micropollutants from soil fertilized with municipal biosolids at a regulated application rate into tomatoes, carrots, potatoes and sweet corn produced under normal farming conditions. The vegetables were grown according to farming practices mandated by the province of Ontario Canada, the key feature being a one-year offset between biosolid application and the harvest of crops for human consumption. Biosolids at application, and crop samples following harvest were analyzed for 118 pharmaceuticals and transformation products, 17 hormones or hormone transformation products, and 6 parabens. Analyte concentrations in the biosolids were consistent with those detected in other surveys. Eight of the 141 analytes were detected in one or two crop replicates at concentrations ranging from 0.33 to 6.25 ng/g dry weight, but no analytes were consistently detected above the detection limit in all triplicate treated plots. Overall, this study suggests that the potential for micropollutant uptake into crops under normal farming conditions is low."

In related news, in December, the U. S. Drug Enforcement Agency (DEA)  proposed new rules that would allow for easier local collection of unused medicines.  The comment period for these rules closed in mid-February.  DEA has led efforts nationwide to collect and properly dispose of such compounds.

Late-breaking news: MN Governor ends state agency use of products containing triclosan as of June 30, 2013.  Story.