PRELIMINARY STUDIES ON ARSENIC AND PHOSPHORUS BIOAVAILABILITY IN CHEMICALLY AMENDED SOILS

A contaminant becomes a risk when it is bioavailable. Bioavailability is the readiness of a chemical compound or element to be taken up by living organisms. Arsenic, a naturally occurring carcinogen has been closely examined in recent years from the perspective of speciation and transport in both natural and anthropogenically-impacted soil systems. Arsenic-contaminated soil is one of the major sources of arsenic in drinking water. Therefore, to protect animal and human health, remediation of arsenic-contaminated sites has become a rather urgent issue. Although several ex-situ treatment methods are available for remediation of arsenic-contaminated soils, these are generally expensive and may cause damage to the ecosystem. Hence, novel in-situ chemical- and phyto-remediation techniques are becoming increasingly popular. One such potentially promising in-situ chemical remediation method is the application of water treatment residuals (WTRs) to lower arsenic bioavailability in contaminated soils. It has been demonstrated that WTRs have the capability of retaining phosphorus in soils. Since both arsenic and phosphorus exhibit similar chemical properties, it is assumed that arsenic, like phosphorus, will be retained by WTRs. However, application of WTRs to remediate arsenic in soils may simultaneously lower phosphorus bioavailability, thereby causing phosphorus deficiency in plants. A laboratory incubation study is in progress to identify the relationships between WTR application and arsenic/phosphorus bioavailability in an arsenical pesticide contaminated soil that has been fertilized with phosphorus. A sandy spodosol from the Immokalee series was amended with sodium arsenate, triple super phosphate and 3 WTRs, namely, Al-WTR, Fe-WTR, and Ca-WTR. Amended soils are being analyzed for bioavailable arsenic and phosphorus at four times, immediately after amendment, after 2 months of incubation, after 6 months of incubation, and finally, after 1y of incubation to study the effects of equilibration time on bioavailability of arsenic and phosphorus. Results from this study will provide preliminary information on potential applicability of low cost chemical amendments, such as WTRs in lowering arsenic bioavailability, and hence, human health risk from exposure to arsenic-contaminated soils.