Location: Watershed Physical Processes ResearchTitle: Physical, chemical, and mineralogical controls on retardation of anatoxin-a migration by sorption to natural soils with implications for groundwater protection
|HOBART, JUSTIN - Geosyntec|
|O'Reilly, Andrew - Andy|
|GIFFORD, JENNIFER - University Of Mississippi|
Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2022
Publication Date: 9/14/2022
Citation: Hobart, J.L., O'Reilly, A.M., Gifford, J.N. 2022. Physical, chemical, and mineralogical controls on retardation of anatoxin-a migration by sorption to natural soils with implications for groundwater protection. Water. 14(18):2869. https://doi.org/10.3390/w14182869.
Interpretive Summary: The migration of the potent toxin, anatoxin-a, into groundwater may be reduced in areas with silty or clayey soils. Anatoxin-a is produced by some cyanobacteria species—microscopic organisms naturally occurring in the environment—that can proliferate in rivers, lakes, and reservoirs. The toxin can be released upon the death of cyanobacteria causing fatalities of birds, cattle, and other animals when they ingest the contaminated water. Groundwater can become contaminated as these toxins move with water as the aquifer is recharged by infiltrating surface water through natural or artificial means. The amount of toxin dissolved in groundwater decreases and moves more slowly when the toxin is adsorbed to soil particles. Soils with textures ranging from sandy loam to clay were collected and tested for their ability to remove anatoxin-a from sites in Grenada County, Mississippi, resulting in anatoxin-a removals ranging from 85.0% to 92.2%. Results indicate that loamy, silty, or clayey soils would substantially slow migration of anatoxin-a. This information will enable scientists to identify types of soils that promote the transport or removal of anatoxin-a, thus providing a better understanding of the toxin in the environment. Practices can be developed by action agencies as a result of this study to incorporate silt and clay components that limit anatoxin-a migration, such as engineered soil amendments and filter media, which are also commonly used for the removal of many other pollutants.
Technical Abstract: Increasing prevalence of cyanotoxins in surface water bodies worldwide threatens groundwater quality when contaminated water recharges an aquifer through natural or artificial means. The subsurface fate of anatoxin-a (ATX) is not well studied. Laboratory batch experiments were performed to expand the current knowledge of ATX sorption affinities to geologic media, with a focus on natural soil (Vertisol, Ultisol, Alfisol, and Inceptisol) and physical, chemical, and mineralogical characteristics. For a range of aqueous ATX concentrations (0.3–14 µg/L), linear, Freundlich, and Langmuir isotherms fit observed data well (r2 = 0.92–1.00, RMSE = 0.4–6.3 µg/kg). Distribution coefficients (Kd) and retardation factors (Rf) values were computed for the linear isotherm, giving Kd of 22.3–77.1 L/kg and Rf of 62–256. Average percent removals were 85.0%–92.2%. The strongest predictors of Kd were kaolinite and smectite group mineral abundances and for Rf were smectite group and silt and clay abundances, described by bivariate linear regressions (r2 = 0.65 and 0.87, respectively). Results indicate that loamy, silty, or clayey soils—particularly Vertisols—would tend to substantially slow migration of ATX through natural soil systems. Where implemented as an amendment, such soils may enhance natural ATX attenuation processes during infiltration-based managed aquifer recharge.