TRANSPORT AND FATE OF CYANOBACTERIAL TOXINS IN SOIL AND GROUNDWATER: AQUIFER RECHARGE AND HUMAN HEALTH IMPLICATIONS

Shortages in the quantity and quality of groundwater in rapidly urbanizing areas have led to an increasing use of artificial recharge techniques to support sustainable aquifer management. Enhancement of aquifer recharge using surface water, however, carries with it the risk of contaminant impacts on groundwater quality. One group of contaminants of emerging concern are toxins produced by cyanobacteria. Cyanobacteria commonly proliferate in rivers, lakes, and reservoirs, where eutrophication caused by nutrient impacts from urban and agricultural runoff foster harmful algal blooms. Upon collapse of the bloom, released cyanotoxins can remain dissolved in the water column. Cyanotoxins pose a risk to human health and can bioaccumulate in food crops. Health risks are of particular concern for artificial recharge facilities where infiltrated water may subsequently be withdrawn for consumption or irrigation, such as riverbank filtration and stormwater harvesting systems.

We estimated the potential transport and fate of three cyanotoxins—microcystin-LR (MCLR), cylindrospermopsin (CYL), and anatoxin-a (ATX)—in several soils and in sand using batch sorption experiments (MCLR and ATX) and column experiments (MCLR and CYL). Column experiments indicate relatively little sorption of MCLR and CYL to sand, whereas during batch experiments ATX experienced substantial sorption to soils with textures ranging from sandy loam to clay. X-ray fluorescence and X-ray diffraction analyses suggest sorption of ATX was related to clay mineralogy. Additionally, column experiments indicate little degradation of CYL and substantial degradation of MCLR, which we hypothesize was predominantly due to biodegradation. Overall, under the given experimental conditions, results suggest that CYL has greater potential to migrate with flowing groundwater and persist within an aquifer, whereas MCLR and ATX have greater potential to be removed from groundwater by biogeochemical and physicochemical processes, respectively.

The potential impacts of cyanotoxins should be considered during planning, design, and operation of aquifer artificial recharge facilities, especially for aquifers that may serve as sources of water for human consumption, public-access landscape irrigation, or irrigation of food crops.