Tight Bonds

Increasing concerns about perfluorinated compounds in groundwater is calling into question the safety of land application of biosolids as they are a potential source of leachable of these compounds. This battle is coming to a head in New England and Ned Beecher of NEBRA has been leading efforts to address concerns. This library will hopefully provide additional resources in that effort. Perfluorinated compounds have been covered twice before in this library; once in February 2014 and once in October 2010 (happy to make those libraries available as well).

I start the library with a bit of a rant. In reading the different articles- only some of which made it into the library it became clear yet again, that PFOS and PFOA -- the two forms of perfluorinated compounds that appear to be driving this concern -- have been around for decades, since the 1950s or 1960s. They are another case of a compound with concentrations in household dust and a range of household products that are far greater than in biosolids. They are found in people’s blood across the US and in wild animals across the world. Common household products that contain these compounds include food packaging, in particular for non-stick wrapping, stain resistant carpeting, and non-stick cookware. They are commonly used in firefighting foams and other industrial products.

These compounds are ubiquitous, and the concern goes to their chemical nature. These compounds are based on fluorine ions attached to carbon atoms. The bonds are very strong (hence the “tight bonds” title of this April library) and so are very resistant to degradation. Their utility lies in their solubility, so unlike prior organic contaminants like dioxins, they are readily mobile in soils. As with many of other organic compounds, they come in various forms with varying lengths. The longest compounds, PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid), are thought to be potentially the most harmful and have been banned from manufacture in the U.S., although they are still in use overseas and in imported products. While there is a great deal of concern over these compounds, the potential harmful effects associated with exposure are not clear, and in particular the NOAEL (no observed adverse effect level) is not known. Drinking water is considered to be a very sensitive exposure pathway, with concentrations of these compounds in drinking water apparently magnified in the exposed individual by a factor of 100 or so. In other words, we are talking about drinking water limits in the parts per trillion (ppt) range. Remember those good old days when we were worried about things like metals (ppm) and nutrients (parts per hundred, or %)?

One of the very difficult issues for us today are the big data gaps. The gap is particularly large when discussing whether land application of biosolids is a significant source of contamination to groundwater. Basic numbers would suggest that it is not. For example, the authors of article #3 in the library estimate that the sum of all of the perfluorinated compounds in biosolids in the U.S. totals less than 3500 kg per year. You then take into account that only about half of those are land applied. Put that into the context of how much water is consumed by the 324 million people in the U.S. and then consider what percentage of those are drinking well water impacted by biosolids…. Just saying. But for others, this is a current major issue. So, let’s get down to business and to the articles in the library.

The first article deals with soil adsorption of these compounds. As stated earlier, part of their value is their solubility, and they are considered to be highly mobile in soils. The authors review the range of lab studies that have determined adsorption of PFOS and PFOA to soils. This is then compared to real world conditions and partitioning. The authors conclude that the lab models are one to two log units off and UNDERESTIMATE retention time in soils. They are not saying that they won’t move, they are just saying that they move a lot more slowly than has been predicted. For part of this work, the authors consider concentrations in biosolids and wastewater effluent. So, slow down with the worry and the regulatory response.

The next article focuses right on groundwater in New England, Cape Cod to be exact. Here the authors examined groundwater PFOS and PFOA concentrations. There were two sources of contamination -- a fire fighting training site where compound rich foams had been sprayed for decades and effluent from a wastewater treatment plant where the effluent had been land applied for decades. Both sites have been inactive for about two decades, yet both are still sources of the compounds. Wastewater loading had ranged from 380 to 5,700 m3 per day from 1936 to 1995. As a result of high organic matter and oxides, both expected to be found in biosolids, and as a result of oxygenated conditions, also to be expected in soils, release of these compounds was slowed significantly. Concentrations of total compounds, of which over 50% consisted of PFOS or PFOA, in groundwater resulting from the effluent were 2.8 to 11 ppb. So, both of these don’t say that PFOS or PFOA won’t get into groundwater, however they say that soil retention is longer than predicted and that characteristics of biosolids will further slow this down. In addition, the Cape Cod study was a potential worst-case analysis, as effluent concentrations are comparable to biosolids and there was 30+ years of effluent irrigation at the same field as a source.

Let’s go to biosolids. Here you can count on Dr. Rolf Halden to provide survey data. Paper #3 includes data on biosolids concentrations from the 2001 national survey. PFOS was the most common with 403 ng/g, with PFOA coming in second at 34 ng gthose are ppb. This is meant as a useful reference.

The last two papers were the only ones that I could find that discuss what happens with these compounds when the biosolids are applied to land. The first of these (#4) is with Chicago biosolids and has Lak Hundal, formally of the MWRDGC, and Chris Higgins in Colorado as co-authors. The concentrations of PFOS (80 -219 ppb) and PFOA (8 - 68 ppb) in the biosolids were within the ballpark of what Halden had reported. Application rates for the biosolids were very high, up to 2218 Mg/;ha and included both short term and long term application sites. Concentrations of PFOS in the short term plots ranged from 2 - 11 ppb (here biosolids loading rates were up to 178 Mg/ha). What is most important here is the figure that shows that concentrations of PFOA and PFOS below 50 cm in the soil for both long-term and short-term sites, all with high loading rates (553-2218 Mg ha), are similar to the control soil. The authors conclude that the longer chain compounds are much less likely to leach than the shorter chain compounds.

The last study in the library is from Ed Topp’s group at Ag Canada. Topp was the subject of the March 2017 library. He does realistic studies of biosolids. Here, in a study that has been reported on previously, biosolids were applied to a tile drained field. Tile drainage is done to speed up water movement from soils to facilitate early planting. The PFOS (7.2 ppb) and PFOA (1.6 ppb) concentrations in the biosolids were well below what was reported by Halden (Note: Halden’s were samples from 2001, before the ban, and Topp’s are current, lower concentrations). Both compounds were detected in the control and biosolids-amended soils, with somewhat elevated concentrations in the biosolids-amended soils (PFOA about 0.1 ppb in control and up to 0.8 ppb in the biosolids, PFOS about 0.1 ppb in the control and between 0.2 and 0.4 ppb in the biosolids amended plot). PFOS was measured in tile drainage water in the control plot on one occasion and in the biosolids-amended plots twice with over ten sampling intervals. Concentrations were higher in the reference than in the biosolids. Groundwater showed one hit of PFOS for the reference (0.5 ppb), and the biosolids (0.8 ppb) with several sampling intervals showing no detects. For PFOA, three of the biosolids samples in tile drainage showed measurable concentrations ranging from >5 ppb to >25 ppb with many more non-detects. No PFOA was measured in the reference plot. Groundwater samples showed consistent measurable PFOA in the biosolids at concentrations ranging from 1.5 to 3 ppb with none detected in the reference area.

To me this gives some indication that the sky is not falling. These are useful compounds that we are likely better off not using. The limited data suggests that contributions to groundwater from agronomic use of biosolids that results in human exposure is not significant.

Sometimes you just get tired of being the low hanging fruit.