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Assessment of Plant Uptake, Transport and Leaching Models and their Suitability for PFAS
Nava Garisto1, Christopher Shepherd2, Erika Houtz2, Kacie Clark2, Elham Arbaban1, Paul Anderson2
1Arcadis Canada Inc.
2Arcadis US
The objective of this presentation is to discuss the challenges of selecting environmental fate and transport models suitable for predicting PFAS concentrations in groundwater (e.g., due to leaching from soil) and in plants. The objective of this study is to evaluate fate and transport models and soil-to-plant transfer factors that can be used to predict PFAS concentrations in groundwater and plants, respectively. These can be used in risks assessment for estimation of exposure to PFAS.  

Per- and polyfluoroalkyl substances (PFAS) are used in a large variety of industrial processes and are present in many common household items. As a result, PFAS are regularly introduced into the environment from a variety of sources. Many PFAS are present in wastewater treatment plant residuals and may contaminate soil, surface water, and groundwater following land application. Understanding the fate and transport of PFAS in soil is a critical step in assessing potential effects on human health and the environment. PFAS in soil and/or groundwater can enter the food chain through uptake by plants leading to potential exposure of human and ecological receptors. The general public is exposed to PFAS mostly through diet. PFAS have been detected in vegetables, fruits and grains in Europe and North America. Modeling the uptake and accumulation of PFAS in plants is therefore also important.

PFAS fate and transport in the environment is complex and is influenced by many factors including hydrologic processes, soil properties, total organic carbon content, surface charge, soil and water pH, redox, PFAS concentrations, polyfluorinated compound transformation rates, and the structural features of individual PFAS. Therefore, selection of environmental fate and transport models suitable for predicting PFAS concentrations in leachate, and plants is quite challenging. In this study, we reviewed publicly available models that could potentially be used to predict PFAS concentrations in groundwater, and plants resulting from soil leaching. Each model reviewed was evaluated for: basic function; intended or most common usage; availability; and, applicability to PFAS. The models were then evaluated for their overall suitability to predict PFAS fate and transport through leaching process. This information can be used by various industries, municipalities, regulators and other stakeholders to: 1) select models for fate and transport of PFAS; 2) identify key parameters necessary to model PFAS fate and transport; 3) considerations for modeling; and, 4) describe information gaps to refine PFAS modeling. Dependence on PFAS chain length and functional groups is also discussed.

The study also focuses on plant uptake modeling. Readily available, comprehensive plant uptake models have been developed mainly for neutral persistent organic pollutants. Simple models of bioaccumulation using soil to plant transfer factors for edible parts of plants or root vegetables can provide an estimate of PFAS concentrations in plants despite variability in uptake among plant species and in soil characteristics. In this study, literature-based soil to plant transfer factors were compiled for perfluoroalkyl carboxylic acids (PFCA) (C4 to C10) and perfluoroalkane sulfonic acids (PFSA) (C4, C6, C7, C8 and C10) for several types of crops and under various soil characteristics. Generic soil to plant transfer factors were derived in this study for several plant types including root vegetables, leafy vegetables, grains and fruits where data permitted. This can be used in environmental risks assessment for estimation of dietary exposure to PFAS.

Dr. Nava Garisto, National Discipline Leader and Risk Group Manager, Arcadis Canada Inc.
Dr. Nava Garisto is an internationally recognized risk expert. She is a National Discipline Leader and a Risk Group Manager at Arcadis Canada Inc. with 30 years of project experience managing large scale and complex environmental risk projects in Canada and internationally.

Nava has developed human health and ecological risk assessments for a variety of industries and contaminated sites, including PFAS contaminated sites (airports, sludge-amended soils, industrial sites), nuclear generating stations and fuel refining and manufacturing and sites of potential future waste disposal, former refineries and municipal works.

Nava has managed projects related to asset risk ranking, fate and transport modelling, geochemistry/hydrogeochemistry and spill risk assessment. She has developed risk estimates as strategic tools for making cost-effective risk-management decisions including recent projects on risk from releases to groundwater and the aquatic environment in both freshwater lakes and the marine environment.

Nava participates, as a member of the Canadian Standards Association (CSA) N288 Committee, in the development of fate and transport models and plant uptake models for use in contaminated site risk assessment. She is a co-author of the CSA Standard on Environmental Risk Assessment (N288.6). She was a member of Environment Canada advisory committee on priority substance list and ASTM on PFAS.

Generation of Bioaccumulation Factors for PFAS in Aquatic Ecosystems
Andrew Mitchell and Karl Bowles
RPS Group
The objective of this presentation is to generate discussion and consideration of the use of bioaccumulation factors in the context of what we have learned in Australia.  

Environmental contamination with per- and polyfluoroalkyl substances (PFAS) has received increasing interest in the early 21st century, since identification of PFAS in human blood and animal tissues globally. The use of PFAS in aqueous film forming foams (AFFF) for training and fighting hydrocarbon fires has received particular attention, as this has proved an important route to the environment in Australia and abroad.

The Australian Department of Defence (Defence) is undertaking a nationwide program to investigate and manage PFAS contamination from legacy AFFF use on Defence sites. Investigations have been undertaken at 28 sites across the country using an accelerated tiered process responsive to community and regulator expectations to rapidly assess the extent and associated risks from contamination by PFAS compounds. Investigations focussed on migration and exposure pathways, and as a result have collected information about soils, waters and biota under different environmental conditions.

A range of aquatic biota, such as riparian or aquatic vegetation, fish and crustaceans, were sampled and analysed for both ecological and human health risk assessment at sites where a likely exposure pathway was identified. While the studies were not specifically designed for developing an understanding of PFAS trophic transfer, the resulting large publicly available data set is nevertheless a unique and highly valuable source of information.

Using a geospatial approach to data analysis, bioaccumulation factors were calculated for PFAS in sampled biota for a range of surface water ecologies and climatic settings. The bioaccumulation factors were then aggregated and compared against published values.

A total of 1,691 biota and 1,202 water samples were used to derive 1,171 bioaccumulation factors at 58 sample locations once the data were filtered. Factors were derived for perfluorohexane sulfonate (PFHxS), perfluoroheptanesulfonic acid (PFHpS), perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA) and 6:2 fluorotelomer sulfonate (6:2 FTS) in fish tissue.

Results/Lessons Learned.
The bioaccumulation factors were found to be highly variable between different species and different locations. Measures of central tendency were generally lower than published values.

The many factors affecting bioaccumulation highlight the value of a well-considered conceptual site model and site-specific investigations with repeated monitoring of relevant environmental media, including biota, through different seasons. The variability of the factors draws into question the derivation of water quality guidelines based on a generic bioaccumulation factor.

Andrew Mitchell, Executive Project Director, RPS Group
Andrew Mitchell currently leads a technical policy team in supporting the Australian Department of Defence in its investigation and management of PFAS contamination arising from legacy use of AFFF. He has a Bachelor of Environmental Engineering, a Master of Public Administration and over 20 years’ experience in solving environmental problems in regulation, government and consulting.

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