BIOAVAILABILITY OF ARSENIC AND PHOSPHORUS IN A SANDY SOIL AMENDED WITH WATER TREATMENT RESIDUALS

Arsenic (As) is classified as Group A carcinogen. Human exposure to As occurs through both anthropogenic and natural sources. Arsenic occurs naturally in rocks, soils and waters. It is also found in abundance in agricultural soils with a history of arsenical pesticide application. Bioavailability is an important factor in assessing human health risk from exposure to environmental As, and hence, As remediation depends on an estimation of bioavailable As concentration. Remediation of As can be performed by ex-situ or in-situ methods. Ex-situ treatments are extremely expensive and generally result in destruction of the ecosystem under remediation. Therefore an in-situ method of soil-As remediation using water treatment residuals (WTRs) was evaluated in the reported study. Recent studies showed that WTRs has the ability to adsorb phosphorus (P). Since As and P are chemical analogs, it is assumed that As can be similarly retained by WTRs. The 2 major hypotheses of this study are: (1) WTRs decrease human bioavailability of soil-As via hysteretic adsorption onto variable-charge mineral components, such as amorphous Fe/Al-oxides, (2) Phosphorus competes with As for sorption sites, thereby rendering some As bioavailable, which would have otherwise been adsorbed. A laboratory incubation study is currently in progress to study the ability of WTRs to reduce phosphorus and As bioavailability in soil contaminated with arsenical pesticides and fertilized with triple super phosphate (TSP). A sandy Spodosol from the Immokalee series, FL was amended with sodium arsenate pesticide, 3 WTRs (Al-, Fe-, and Ca-WTR) and TSP. Arsenic and P bioavailability studies are being conducted 3 times: immediately after spiking with pesticide, fertilizer and WTRs (0-time), after 6-months and 1 year of equilibration. Arsenic concentration is being measured using a Graphite Furnace Atomic Absorption Spectrophotometer. Results obtained from the 0-time and 6-month studies show that the bioavailability of As was lowered significantly by Fe-WTR and Al-WTR applications despite the presence of phosphorus. These preliminary results indicate that WTRs can be used to lower As bioavailability and hence, to lower human health risk from exposure to As contaminated systems.