Compounds of Concern (COCs)… Fading Away Slowly

This month we go back to focusing on peer reviewed science. The general focus is on degradation of ‘contaminants of concern,” COCs, in field-applied biosolids. COCs are known also by various euphemisms, e.g., TOrCs (Toxic Organic Compounds), microconstituents, and CECs (Compounds of Emerging Concern).

The library starts with an article that was forwarded to me – please feel free to do this. When an article is sent, I take that to mean that it is a topic of interest. Anyway, the article reports research on degradation of COCs in biosolids that were applied in Eastern Colorado. Low (agronomic) rates of biosolids were sparingly incorporated into a field that was planted to dryland wheat. The authors measured 57 COCs, including detergent metabolites, fragrances, pesticides, fire retardants, polycyclic aromatic hydrocarbons, steroids, oils and fuels and disinfectants. In other words, all the stuff you’d find in a trip around your house. They also measured 19 pharmaceutical compounds, but did not report results because so few were detected. The researchers sampled the biosolids prior to application, at application and over a time course following application. They measured biosolids post application by collecting dry pieces of biosolids on the soil surface (you can bet that they got a grad student to do that!). Concentrations of COCs were also measured in the soils at both surface and depth concentrations. Results are generally reported as how many detects rather than concentrations of particular compounds. Wheat roots, leaves and grain were also tested. They sampled a neighboring farm where no biosolids had been applied. They basically found that the wheat was the same in both locations, with some compounds detected, primarily in the root tissue. Many compounds were identified at both the control and the biosolids sites. Most compounds went away or were really close to the detection limits to begin with. A few lingered. The authors suggest that a few also moved through the soil profile, namely 3- beta- coprostanol, HHBC and triclosan. These were detected on day 468 post application for generally 2 analyses at generally less than 10x the minimum reporting limit. 3- beta coprostanol is a metabolite of cholesterol, HHBC stands for hexahydro-hexamethyl cyclopenta-benzopyran, which is an ingredient in fragrances (not the Henderson Hills Baptist Church, as Google would suggest). Triclosan, or TCS, is an anti-microbial compound. As I read the supporting information with the actual numbers, concentrations of these were typically below detection or are reported as ‘Estimated’ values. So let’s see what other studies say about persistence of these compounds in biosolids amended soils.

The next study was co-authored by Rolf Halden, now at the U of AZ and not considered a friend of biosolids. The study presents results from his time in Baltimore. Here, anaerobically digested biosolids were added to a soil at a ratio of 1:2 (the paper awkwardly does not specify if this was by volume or by dry weight). The mixtures were placed outside for 3 years in large pots and sampled over time. The authors note that this is well above agronomic loading rates but represents rates that you would see at a forest application site. Apparently they have not spent time in the Northwest. Anyway, they monitored degradation of a range of compounds and generally found that most, including TCS, degraded over time, but at rates that were much slower than were predicted in lab studies. Can this really be true? Let’s go to Australia to find out.

The third study in the library is from a well done PhD thesis by a now Dr. Langdon. Here, degradation of compounds, including 4 nonylphenol, 4-t- octylphenol and bisphenol A, were monitored in soils to which anaerobically digested biosolids were applied at 25 and 45 t/ha or about 10 and 18 t/acre. Again, the authors note that, while degradation did occur, it took much longer than lab studies had predicted, 2.5x longer for bisphenol A and 10-20 times longer for the two other compounds.

This is not good news.

For the 4th study, we go to some good news to temper the longer than expected persistence observed in the first three studies. This study is co-authored by Tom Young, who presented at Biofest several years back. Here, the focus is on the impact of TCS on soil microbes. Degradation was also measured. As with the other studies, the biosolids appeared to slow degradation of TCS in comparison to breakdown of the compound added to plain soil. However, the biosolids also mediated the toxicity of the compound to soil microorganisms with a beneficial and stimulating effect on populations. The authors attribute this to the good stuff in biosolids -- the carbon and nutrients. It is also important to note that this paper also contradicts the finding of the study from Duke University that was the focus of the library two months ago. So, the good in biosolids from the perspective of soil microbes far outweighs the bad.

Nevertheless, the longer than expected persistence of many of these compounds in the environment is not a great thing. And, that brings us to the last paper, also authored by Halden. Here he argues that it is time to ban two antimicrobials, TCS and TCC, and find safer alternatives. He points out that while these compounds may be useful in medical settings, they have no benefit in your household soap and toothpaste. On this point, I couldn’t agree more with Dr. Halden.

Sally Brown, University of Washington