Perfluorooctanesulfonic acid (PFOS)

July 6, 2018 | General

PFAS And Organic Residuals Management

Fears and uncertainties about PFAS trigger regulatory actions that damage biosolids recycling programs and composting facilities, rather than targeting the source of the chemicals. Part I

Ned Beecher and Sally Brown
BioCycle July 2018

PFAS Resources
• ATSR (Agency for Toxic Substances and Disease Registry
• ITRC (Interstate Technology Regulatory Council
• U.S. EPA

After decades of enjoying stain-free carpets, the compounds that keep your rugs clean are now a leading cause for concern in biosolids and composts. Per- and polyfluoroalkyl substances (PFAS) are a family of chemicals commonly used since the 1950s in carpets, furniture and other fabrics, cooking tools, outdoor clothing, paper products, firefighting foams, and numerous industrial applications. Despite their use for decades, we have only been able to routinely measure them in various matrices in parts per billion and parts per trillion for the last 15 years.
These compounds come in many shapes and sizes, with the common characteristic being carbon bonded to fluoride (C-F bond). The C-F bond is one of the strongest chemical bonds in nature. The PFAS class of compounds, designed to be stable by taking advantage of this bond, are made to be both hydrophobic and lipophobic. They repel water and grease in food packaging and fabrics — and they spread evenly and quickly — a major benefit in aqueous firefighting foams (AFFF). Their unique chemistry means some of them are ionized and soluble in water at or near neutral pH, so they migrate easily in soil pore water, surface water, and groundwater. In addition, unlike many other persistent contaminants, such as metals, PCBs, or flame retardants (e.g. PBDEs), they do not sorb as much to organic matter or other soil constituents. In humans and animals, they (especially the longer-chain versions) tend to bind to proteins and are found in blood serum and the liver. In humans, some have half-lives of four or more years.

Perfluorooctanoic acid (PFOA)

Perfluorooctanoic acid (PFOA)
Image: molekuul_be/


Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) — 8-carbon chain PFAS, a relatively longer chain — are the most common, best-studied, and possibly most toxic PFAS. Considerable public attention has been paid to PFOA and PFOS in recent years, including, most recently, in New Hampshire, Vermont, New York, New Jersey, Minnesota, and Michigan. Concerns have focused on impacts near industrial facilities and military sites that used PFAS, especially impacts on drinking water. Food and water are considered significant sources of PFAS found in humans, and there is evidence of probable correlations between some PFAS and some negative health outcomes and no probable correlations with other negative health outcomes.
In June, 2018, ATSDR, an agency within the U. S. Centers for Disease Control (CDC), released an updated draft Toxicological Profile for Perfluoroalkyls focused on PFOA, PFOS, and two other PFAS. Some say this review of the human health science clearly indicates a need for drinking water standards lower than the current U. S. Environmental Protection Agency (USEPA) screening level. However, much of the language in the report is hedging, indicating ongoing complexity and uncertainty about the extent and severity of risks to human health. The release of this new draft report at the time this article was going to press only heightens the importance of this topic and the perspective provided below. (Links to reports cited in online edition of this article.)
Because PFOA and PFOS have been ubiquitous in daily use for decades, wastewater, biosolids, digestates, and other residuals (e.g. residuals from recycled paper mills) typically contain single digit to tens of ug/kg (ppb) concentrations each of PFOA and PFOS. Many nonbiosolids composts include measurable levels (e.g. single digit ppb), which could be due to PFAS transferred to food scraps from food packaging.
Biosolids and paper mill residuals have received the most scrutiny so far, but food scraps composts and digestates are being evaluated as well. For example, preliminary data presented by PhD candidate Rooney Kim Lazcano and Dr. Linda Lee (Purdue University) at the Emerging Contaminants Summit 2018 in March (Lee and Lazcano, 2018) showed levels of PFAS in a wide variety of commercial organic residual products, including biosolids and nonbiosolids composts. It is important to note that the measurements were of the <2 millimeters (mm) fraction removed from materials with moisture contents of 5 to 55 percent (relatively dry materials), creating a high bias in the values in comparison to the actual materials. The combined total concentrations of 17 PFAS compounds ranged from about 35 to 200 ppb in biosolids-based products (including composts). In comparison, concentrations in food scraps composts (which included compostable serviceware as a feedstock) ranged from 30 to 75 ppb. Composts made from just yard and leaf waste showed concentrations of the same 17 PFAS totaling up to ~5 ppb.

Perfluorooctanesulfonic acid (PFOS)

Perfluorooctanesulfonic acid (PFOS)
Image: molekuul_be/

Table 1 includes a summary of levels of PFAS compounds in organic residuals and other matrices, as reported in the literature and measured recently (ug/kg or ppb, ND = non-detect). PFOA and PFOS are highlighted because they are currently the most studied and of greatest concern and regulatory scrutiny.

The Good News

Over the past 15 years, PFOA and PFOS have been largely phased out of use in the U.S. and Canada. Concentrations in various matrices are therefore diminishing. For example, in comparison to the low ppb concentrations found in biosolids today, in the 2000s, PFAS were found in concentrations of tens to hundreds of ppb, with a U.S. average of 34 ppb for PFOA and 403 ppb for PFOS. PFOA and PFOS likely still enter North America in some foreign-made goods, and PFOS can still be used in limited situations. But, in general, we can expect concentrations of these compounds in composts, paper mill residuals, and biosolids to continue to decrease over time.
As the phaseout has proceeded, alternative PFAS chemicals have been introduced, many of which are marketed to be less persistent, bioaccumulative, and problematic. These include the 6-carbon chain PFHxS and the 4-carbon chain PFBS, which some researchers claim are more persistent, if less toxic. However, some newer PFAS are longer or branched versions — precursors — some of which break down in the environment to the very stable forms PFOA and PFOS, i.e., they will not further break down and will persist in that form in the environment and biota for many years, even decades. Tests have shown higher levels of PFOA and PFOS exiting a wastewater treatment facility or in finished compost compared to the levels in wastewater influent or compost feedstock. This phenomenon is due, in part, to the breakdown of precursors.
Fortunately, despite the many troubling features of these chemicals, the primary significant concern for all PFAS related to organic residuals is with regards to the potential for PFAS to leach after they are applied to soils (Gottschall et al, 2017; Sepulvado et al., 2011) or, perhaps, with regards to run-off and surface water (Lindstrom et al., 2015). There is currently minimal regulatory concern with regards to inhalation, ingestion, dermal contact, or other possible organic residuals-related routes of exposure. Research and risk assessments have led to the most conservative (residential) soil screening levels being set at 500 ppb (New Hampshire standard) and 300 ppb (Maine and Vermont standards) for PFOA and PFOS in relation to these exposure routes. These levels are an order of magnitude higher than the levels of these chemicals in residuals products.

The Main Concern

Drinking water quality has been the focus of the most recent regulatory actions related to PFAS. In 2016, U. S. EPA created a public health advisory (PHA) level for PFOA and PFOS in drinking water of 70 ng/L (ppt) (7 in 100 billion) for the two chemicals separately or combined, which provides full protection from lifelong exposure for the most sensitive individuals and the most sensitive life stages. (The prior U. S. EPA advisory levels were an order of magnitude higher.) A few states (e.g. Minnesota, New Hampshire, New Jersey, and Vermont) have adopted the new PHA or lower drinking water enforcement standards or advisory levels. But most states have not adopted any state level PHA, relying instead on the U. S. EPA PHA screening value. This is due to the fact that these chemicals are ubiquitous in society and the environment and there is ongoing uncertainty about their fate, transport, and impacts.
Note that data on PFAS in any matrix other than drinking water is suspect and should be used for screening and educational purposes only. This is because the only U. S. EPA-approved method for PFAS is Method 537, rev. 1.1, which is specifically for drinking water only. U.S. EPA hopes to have methods for non-drinking waters and solids completed by sometime in 2019.
Some published literature shows some leaching of some PFAS to groundwater from biosolids land application sites at concentrations approaching the EPA PHA screening level for drinking water of 70 ppt. For example, Sepulvado et al. (2011) evaluated four varied sites where Chicago biosolids had been applied over several to many years (up to 2,218 Mg/ha cumulative application rate) and, in 2004-2007, found concentrations in the land applied biosolids ranging from 8 to 68 ppb PFOA and 80 to 219 ppb for PFOS, with soil levels linearly correlated with cumulative application rate. Some downward migration of PFAS was observed, with greater leaching of the short-chain versions. Gottschall et al. (2017) evaluated PFAS leaching to tile drain water and shallow groundwater from a one time 22 Mg/ha application of Ottawa biosolids in Ontario. The biosolids contained lower concentrations of PFOA (1.6 ppb) and PFOS (7.2 ppb). Levels in 2-meter groundwater reached 3 ng/L (ppt) for PFOA and 0.8 ppt for PFOS, while tile drainage water reached as high as 23 ppt for PFOA and 1.1 ppt for PFOS. These publications have caught the attention of stakeholders, and, as state regulators survey the landscape in their states for all potential sources of PFAS that may impact groundwater and drinking water, some have focused on wastewater, reclaimed water, biosolids, and other residuals.

Impact On Biosolids And Composts

Because of highly publicized PFAS contamination issues at industrial sites in Michigan, Minnesota, New Hampshire, New York, and Vermont in 2015–2016, scrutiny of PFAS sources has grown in the Northeast and upper Midwest, leading to examination of wastewater and biosolids/residuals as potential “sources” of groundwater (and possibly surface water) contamination. (These materials are not initial sources; they merely convey these chemicals from their everyday uses in modern society. Their presence in water systems and biosolids are not caused by water and wastewater management systems.) In 2017, regulatory agency staff in several of these states sampled some sites with relatively high cumulative loadings of biosolids and/or paper mill residuals, with the following results.

1. A farm where paper mill residuals were applied/disposed in the 1980s found levels of PFOS in the soil in 2017 to be as high as 878 ug/kg (ppb). The applied residuals were likely from a paper mill manufacturing PFAS-coated products. Despite high levels of PFOS in the soil, the farm’s drinking water source was elevated only to a total of 51 ppt PFOA and PFOS. However, farm milk showed PFOS as high as 690 ppt, possibly due to bioaccumulation in the cow from feed and water (although other potential contamination sources have not been thoroughly ruled out). Concerns about this site led other Northeast state regulators to quietly test milk at farms that have used a variety of biosolids with little industrial input for decades. No milk contamination was found.
2. A storm water collection pond at a composting facility that processes paper mill residuals as a feedstock had 240 ppt PFOA and PFOS; an on-site groundwater monitoring well totaled 160 ppt PFOA and PFOS. Alarmed, the state agency requested the facility stop distributing its compost. Given this action and the scrutiny, the provider of the paper mill residuals feedstock stopped delivering material, sending it to a landfill instead (at significantly higher cost). The composting facility graciously complied with the regulators’ requests, but had to lay off workers. A year later, negotiations have led to regulatory agency recognition that these residuals and composts are likely not a significant risk and business may be able to continue as it was before, albeit with PFAS monitoring of incoming feedstocks. But despite the negotiated agreement, uncertainty at the state regulatory agency has stalled further resolution, and, after a year and a half, compost sales continue to be on hold.
3. An old sand and gravel excavation site had been used for many years prior to the early 2000s for land application, composting, drying, and mixing of biosolids. Testing of monitoring well water found a total of PFOA and PFOS at 59 ppt under the site and 561 close by and downgradient. However, no nearby drinking water wells were found to be impacted.
4. A water resource recovery facility (WRRF) that had long used a monofill for disposal of its solids up until the 1990s tested water from downgradient monitoring wells, which revealed levels of PFOA and PFOS as high as 315 ppt combined. The monofill represents an extreme loading scenario. PFOA plus PFOS levels in groundwater under a nearby farm field where biosolids from that WRRF were applied over many years were found to be from 5 to 46 ppt. Groundwater dilution is likely playing a significant part in reducing PFAS levels in this site’s transmissive, sandy soil. The closest drinking water wells showed no PFOA or PFOS.
5. Tests of water from three wells (two deep and one shallow) at sites where composted, pelletized, and/or bulk cake biosolids — all Class A exceptional quality (EQ) — had been used annually for 10 years or more showed no detects in the deep wells and a minor (9 ppt) hit of PFOS only in the shallow well (and other potential PFOS sources, such as a neighboring fire station, could explain this hit).

PFAS Leaching Potential, Plant Uptake

The minimal local data collected to date regarding PFAS leaching potential and plant uptake appear to corroborate the findings of the few published studies. For the large majority of biosolids, composts, and paper mill residuals applied at typical agronomic rates, there is no evidence of PFAS leaching to groundwater in exceedance of regulatory standards. To date, no drinking water exceedance has been linked to biosolids or residuals application in the Northeast, although groundwater appears to have been impacted in a few worst-case situations.
At the same time, it appears likely that in those few cases where biosolids from WRRFs that had large, ongoing discharges from industries using PFAS as a major part of their operations (metal plating, manufacturing of PFAS, coating paper), have caused groundwater exceedances of the 70 ppt EPA public health advisory for drinking water. For example, there were drinking water exceedances in the Decatur, Alabama situation in the 2000s, where a 3M PFAS manufacturing facility was discharging PFAS to the local WRRF and the biosolids were applied to farm fields over several years (Lindstrom et al, 2011).
A similar industrially-impacted biosolids scenario (involving a metal finisher) has been discovered recently in Michigan. These situations are likely not common, and, now, with the phaseout of PFOA and PFOS, they are even less likely. Michigan has asked WRRFs to look upstream and identify businesses with significant PFAS use and assess the potential that they might impact wastewater effluent and biosolids quality. That approach makes sense, as an interim step, as the science continues to develop.
Attempts are being made to set limits for PFAS and PFOA in soils that will be protective of groundwater. For example, in January 2018, using EPA Regional Screening Level modeling, the Maine Department of Environmental Protection (MEDEP) adopted new screening levels for non-agronomic residuals of 2.5 ppb PFOA and 5.2 ppb PFOS. Though inappropriate for organic residuals, these screening levels could be applied, at MEDEP’s discretion, to biosolids and paper mill residuals, many of which would exceed these new screening levels. New York State has used 72 ppb for a total of PFOA and PFOS for screening feedstocks going to a composting facility in one permit situation. While such screening levels are what state regulators are starting to suggest in some cases (as in ME and NY), the science has not caught up, data are lacking for defensible risk modeling, and the resulting numbers may not be appropriate.
If PFAS are in soil, there is also the risk of them moving into plants. However, the research to date suggests that the concern for plant uptake is minimal. One study of the potential for plant uptake via biosolids applications (Blaine et al., 2013) showed that shorter chain PFAS were taken up by lettuce and tomatoes in pot studies, but not significantly in pilot or full-scale field trials. To date, research on plant uptake of PFAS has shown, noted the MN Department of Health, a “high leaching potential and high plant uptake rate of shorter-chain PFCs [PFAS]. In comparison, PFOS and PFOA in soil are not readily translocated through plants” (Scher et al., 2014).
While there is considerable research regarding some PFAS (e.g. PFOA and PFOS) in the environment and related fate, impacts, and treatments, little is focused on biosolids and residuals.
U. S. EPA is just now beginning to consider further research on PFAS related to biosolids and residuals land application. Meanwhile, additional questions need to be researched, such as the variables involved in leaching potential (soil type, organic carbon:water partitioning coefficient or Koc, pH, etc.) and other details that will allow robust modeling of leaching potential.

Part II of this article (August 2018) focuses on what biosolids and residuals managers, including composting facilities, can do to respond to questions and concerns about PFAS. This includes communicating with state regulatory authorities. 

Ned Beecher is Executive Director of NEBRA, the Northeast Biosolids and Residuals Association ( Sally Brown is a Research Associate Professor at the University of Washington in Seattle and a member of BioCycle’s Editorial Board.
Table 1. Levels of PFAS compounds in organic residuals and other matrices, as reported in the literature and measured recently (ug/kg or ppb, ND = non-detect).

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