Emerging Contaminants from the Microscopic Perspective: The Effects of Perfluoroalkyl Substances on a Common Soil Microbe Tess S. Weathers, Christopher P. Higgins, Jonathan O. Sharp Hydrologic Science and Engineering, Civil and Environmental Engineering, Colorado School of Mines Contact Email:
[email protected]
PFAS Background
Introduction
Methods
• Widespread detection: • Synthetic molecules – Groundwater • Widespread use: – Hydro- and lipophobic tails – Packaging – Surface water – Micelle formation – Non-stick coatings – Wastewater treatment • Perfluorocarboxylic acids – Pesticides plant sludge (e.g. PFOA) – Aqueous film– Wildlife • Perfluoroalkyl sulfonates forming foams (e.g. PFOS) – Humans
Due to their historical co-application at fire training areas, poly- and perfluoroalkyl substances (PFASs) and hydrocarbon fuels can co-occur in groundwater. The interactions between PFASs and microbes has not been investigated, nor has the transport behavior of PFASs in active bioremediation settings.
• Single point Koc values are larger for sorption to cellular organic carbon (orange) than for soil organic carbon (blue) • Koc increases with increasing chain length, except for short chain acids
Objectives • Explore the effects of PFASs on Rhodococcus jostii RHA1 in batch systems – Are toluene degradation rates impacted by PFAS presence? – Are RHA1 induction times (reflecting enzymatic effects) impacted by PFAS presence? – Does the presence of PFASs impact RHA1 growth? – Does RHA1 express stress when exposed to PFASs? • Measure single point organic carbon sorption coefficients (Koc) for PFASs onto cells • Provide predictions for PFAS transport in upscaled environments F F F F F F O
No PFAS
With PFAS
• Above: Flocculation is evident in the batch setup (left), with light microscopy (middle), and with scanning electron microscopy (right)
10 μm
F
• Above: Flocculation is apparent at concentrations as low as 1 mg/L after two days of growth. All scale bars represent 100 µm. • Left: Up-regulation of a propane mono-oxygenase enzyme, a potential stress indicator, increases with increasing PFAS concentration
O-‐ F F
With PFASs
No PFASs
Toluene 4.0 ± 0.2 4.4 ± 0.1 Grown
Induc1on Time (hr) With PFASs
No PFASs
-‐-‐
-‐-‐
LB Grown 2.8 ± 0.9 3.1 ± 0.2 3.7 ± 0.3 3.7 ± 0.2
F F F F F F F F O
F F
F F
S F F
F F
F F
F F O
O-‐
Implications for PFAS Transport • Consider 2 fully saturated soils contaminated with PFOA: Cellular logKoc = 3.09, Soil logKoc = 1.89 150 µg cellular organic carbon per gram of soil
fw
foc
Surface Soil 4.5%
Aquifer Sediment 0.5%
ρb (g/cm3)
0.9
1.5
Sorbing only to soil
8.54%
34.0%
Sorbing to soil and cells
0.17%
0.11%
Sorbing only to cells
0.18%
0.11%
• Cellular presence may significantly reduce PFOA in the aqueous phase • Potential reduced mobilization in groundwater
Exploring the Perspective: Future Studies • Columns • Flow-through systems • Traditional stress genes • Redox conditions • Biogeochemical hydrologic modeling
Conclusions
• Toluene concentration over time depicts similar rates and induction times for both growth conditions (average ± standard deviation shown)
F F
F
Results: PFASs and Toluene Degradation Degrada1on Rate (mg/L/hr)
RHA1, sodium azide
PFAS Sorption to Cellular Surfaces
• Right: Growth with high concentrations of PFASs causes RHA1 to flocculate, requiring protein as a measure for growth instead of optical density • Protein content is roughly the same regardless of no or high levels of PFAS
10 μm
Toluene Degradation Sorption to Cellular Buffer, toluene Surfaces
0-10 mg/L each • Each batch system contains LB Media, RHA1 PFAS, LB, RHA1 carboxylic acids with 4 to 11 Optical density, carbon chains and protein sulfonates with 4, 6, and 8 50 µg/L sampled carbon chains. PFASs were each over time RT-qPCR, OD, PFAS, 10 mg/L measured using LC-MS/MS and protein after No 10 mg/L of RHA1 grown on buffer each PFAS and toluene with GC-FID. PFASs each PFAS 2 days toluene or LB
Results: RHA1 Growth and Potential Stress Response
1 cm
Growth and Stress
LB Grown
Toluene Grown
PFAS has been shown to preferentially sorb to cellular organic carbon over soil organic carbon. Additionally, the presence of PFASs in batch systems containing RHA1 does not affect toluene degradation or induction, although RHA1 exhibits increased flocculation and prmA expression with increasing PFAS concentrations. Continued remediation of co-contaminants is promising, while PFAS transport may be retarded by increased biofilm formation.
Acknowledgements: Special thanks to the CSM GEM Lab and funding from SERDP ER-2126
