Soil, water, and pasture enrichment of antimony and arsenic within a coastal floodplain system

Moderate levels of enrichment with environmental contaminants, such as arsenic (As) and antimony (Sb), have received less attention than gross contamination related to obvious point sources of pollution. Within the Macleay floodplain of north-eastern NSW it was found that approximately 90% of the floodplain is enriched in As and Sb, and 6-8% of the floodplain contains As and Sb levels greater than current Australian soil environmental investigation levels. Variation in surface and depth distributions indicated flood deposition of As and Sb across major environmental floodplain environments, with highest accumulation in modern swamp depositional environments. The soil enrichment was reflected by pasture uptake (up to 6.4 and 2.2 mg kg(-1) for As and Sb, respectively) and elevated surface water concentrations (up to 10 and 21 times drinking guideline values and 2.9 and 6.9 times freshwater trigger values for protection of 95% of species for As and Sb, respectively) of these metalloids. Significant relationships between pasture and total soil levels imply higher relative availability than is typical at grossly contaminated sites. Implications for metalloid mobility and availability in acid sulfate soil environments in the floodplain are discussed.