Adsorption experiments using both monosodium methanearsonate (MSMA) and its inorganic degradation by-product species As(+5), as sodium arsenate Na2AsO4, were conducted to evaluate the sorptivity of these constituents to various fractions of soil samples taken from the West Palm Beach Country Club. Adsorption data were analyzed with common isotherm equations (i.e., Linear, Freundlich, Langmuir) to determine Kd for each arsenic (As) species/soil fraction. Simulations using a one-dimensional pesticide transport model, PRZM 2.0, were completed to evaluate possible dissolved concentrations of arsenic at the water table interface under 8 different application scenarios for the soil profile found at the sample site.
All contaminant/soil systems displayed a linear sorptivity relationship (R2 ranging from 0.8262 to 0.9779) with Kd values (units of L/g) ranging from 0.0102 to 0.2295. Results also indicate As(+5) had a higher affinity for the soil fractions than MSMA. PRZM-2.0 predicted concentrations of dissolved arsenic at the water table interface from 0.04 to 1018 ppb within 1 month from only 1 application. Florida's MCL for dissolved as in groundwaters is 50 ppb.
It is recommended that the registration and use of MSMA be re-evaluated as it may impact ground water quality at golf courses or other sandy aquifer systems.