MARCH 2017 RESEARCH UPDATE

MARCH 2017 RESEARCH UPDATE

Much can be said of the world north of the 49th parallel, I mean besides that of handsome, young Justin Trudeau. Perhaps the biggest asset, at least from the biosolids perspective, is a scientist named Ed Topp.

Ed Topp is a scientist with Agriculture Canada based in Ontario. His work spans multiple topics, but he has done extensive work on pharmaceuticals and personal care products (PCPPs) in biosolids-amended soils. What makes his work refreshing is that it is typically done with a unique combination of scientific rigor and common sense. He looks at biosolids and fields as they are used and farmed. He does not resort to claiming impending doom to elicit interest in his work. And while he often finds minimal risks associated with appropriate use of biosolids, when there is a hazard or a concern he has no qualms about calling it out. His work has appeared in this library on multiple occasions. However, this is the first library that exclusively features papers that he has co-authored. The focus on the library is some of his more recent publications and those that deal with PCPPs in biosolids-amended soils.

The first paper goes back to a well-established field site where biosolids had been applied and wheat was grown. The site is tile-drained. This means that ditches have been dug to facilitate water drainage from the soil during Spring thaw. Warmer soils allow for earlier planting, and draining snow-melt from soil is one way to help soils warm quickly. For this article, the authors are looking at the behavior of brominated flame retardants (PBDE) and perfluoroalkyl acids in groundwater, tile drainage, soil and wheat grain following biosolids applications. Flame retardants you likely recognize. Perfluoroalkyl acids (PFAA) are substances commonly found in microwave popcorn bags and carpets. They have been viewed as a contaminant of concern in biosolids and were the focus of unsuccessful arguments against land application in the recent Kern County case. For both classes of compounds the rates added with the 22 Mg/ha of biosolids were greater than rates added from air deposition. Biosolids added about 0.05 kg/ha of PBDEs, while air deposition adds 0.00047 kg/ha. Biosolids added 0.0014 kg/ha of PFAAs, while the air adds 0.00033 kg/ha. For comparison, a typical weight of the top 15 cm of soil is 2000 Mg, or 2,000,000 kg. The PFAAs were more frequently detected in the biosolids soils in comparison to the control and concentrations did not decrease over time. This was true, too, for flame retardants, but concentrations of some did decrease over time. PBDEs were found at low ng/L concentrations in some of the groundwater samples for both the control and the biosolids plots and at greater frequency in the biosolids plots. Detects of PBDEs were more frequent in the tile drainage water with almost all samples <1 ppb. Due to high variability, very little of these detects were statistically significant, with increases only significant in tile drainage water. Even so, those levels were below those levels associated with ecological toxicological thresholds for acute exposure and then only for a minority of the sampling points. Nothing was detected in the wheat grain.

From here we move on to Dr. Topp’s research into antimicrobials triclocarban (TCC) and triclosan (TCS) and uptake by garden crops and soybeans in both pot trials and a field study. So as not to take too much of your reading time and cut to the chase, TCC and TCS were detected in plant shoots midway through the growing cycle for some of the plants, but concentrations decreased by the time they were ready for harvest. Between the two compounds, concentrations got as high as 5.7 ng/g dry weight. The researchers conclude that concentrations of TCS and TCC in the edible portion of plants grown on biosolids-amended soils represents a ‘negligible exposure pathway to humans,’ or less than 0.5% of the acceptable daily intake, even if you eat your vegetables.

If any amount of TCC and TCS is too much and you are worried about carbamazepine and naproxen as well, then read the third paper. Dr. Topp’s focus here is on whether these compounds degrade more quickly in soils if the biosolids are surface applied or tilled in. Radioactive labeled compounds were added to the biosolids-amended soil, and soils were maintained in special cores in buckets filled with soil in the field. Research results showed that soil incorporation makes TCC, TCS and naproxen degrade more quickly. Nearly 60% of the TCS and 90% of naproxen were gone in about 120 days for the subsurface samples. About 20% of the TCC went away in the same time. While nearly 50% of the carbamazepine went away, degradation of this drug went as fast for surface applied as with incorporated compound.

So yes, these compounds are present, but at low concentrations with no realistic evidence of environmental risk. From here we move on to Dr. Topp’s research into antimicrobials triclocarban (TCC) and triclosan (TCS) and uptake by garden crops and soybeans in both pot trials and a field study. So as not to take too much of your reading time and cut to the chase, TCC and TCS were detected in plant shoots midway through the growing cycle for some of the plants, but concentrations decreased by the time they were ready for harvest. Between the two compounds, concentrations got as high as 5.7 ng/g dry weight. The researchers conclude that concentrations of TCS and TCC in the edible portion of plants grown on biosolids-amended soils represents a ‘negligible exposure pathway to humans,’ or less than 0.5% of the acceptable daily intake, even if you eat your vegetables. If any amount of TCC and TCS is too much and you are worried about carbamazepine and naproxen as well, then read the third paper. Dr. Topp’s focus here is on whether these compounds degrade more quickly in soils if the biosolids are surface applied or tilled in. Radioactive labeled compounds were added to the biosolids-amended soil, and soils were maintained in special cores in buckets filled with soil in the field. Research results showed that soil incorporation makes TCC, TCS and naproxen degrade more quickly. Nearly 60% of the TCS and 90% of naproxen were gone in about 120 days for the subsurface samples. About 20% of the TCC went away in the same time. While nearly 50% of the carbamazepine went away, degradation of this drug went as fast for surface applied as with incorporated compound. So, yes, these compounds can be detected. Most compounds were mineralized, with little plant uptake. But what if you are a tiny animal and the soil is your home? We focused on soil microbes in a library last year. Dr. Topp focuses on soil fauna from both a short-term and a long-term timescale in the 4th paper in the library. The authors focused on earthworms, nematodes and enchytraeids and looked at sites up to 96 months post application. They found a population boost, a positive response that lasted up to about 44 months, one that is ‘typical’ for organic amendments. In the one site that was examined at 96 months, biosolids had been applied three times and the site was left fallow after the last application. That 96 months was 8 years after the last biosolids application. The authors found differences in worm populations, but those differences were attributed to agricultural management. Researchers did find less diversity and structure in the nematode population in the biosolids site compared with the control, but they are not sure why. They called this ’weak‘ evidence for any long- term negative effect.

The last article of the library is a review paper with Dr. Topp as a co-author that goes through the different classes of pharmaceuticals and what we know about their degradation and potential harm in soil ecosystems. This is a good reference to help you make sense of these hundreds of compounds that are available both by prescription and over the counter above and below the 49th parallel, though likely for substantially less money above. I hope for all of us that Dr. Topp continues with his work. If he does, you will certainly find it here.

Sally Brown, University of Washington