Arsenic Accumulation By Edible Aquatic Macrophytes.

Edible aquatic macrophytes grown in arsenic (As)-contaminated soil and sediment were investigated to determine the extent of As accumulation and potential risk to humans when consumed.  Nasturtium officinale (watercress) and Diplazium esculentum (warabi) are two aquatic macrophytes grown and consumed in Hawai'i.  Neither has been assessed for potential to accumulate As when grown in As-contaminated soil.  Some former sugarcane plantation soils in eastern Hawai'i have been shown to have concentrations of total As over 500 mg kg^-1.  It was hypothesized that both species will accumulate more As in contaminated soils than in non-contaminated soils.  N. officinale and D. esculentum were collected in areas with and without As-contaminated soil and sediment .  High soil As concentrations averaged 278 mg kg^-1, while background soil As concentrations were 1.6 mg kg^-1.  Average N. officinale and D. esculentum total As concentrations were 0.48 mg kg^-1 and 0.07 mg kg^-1, respectively, corresponding to hazard indices of 7.1 and 1.78.   N. officinale did not show properties of a hyperaccumulator, unlike previous studies where watercress was grown in As-contaminated water.  There was a slight correlation between high total As in sediment and soil and total As concentrations in watercress leaves and stems, resulting in a plant uptake factor of 0.044, an order of magnitude higher than previous studies.  D. esculentum  did not show signs of accumulating As in the edible fiddleheads.  Hawai'i is unique in having volcanic ash soils with extremely high sorption characteristics of As and P that limit release into groundwater.  This study presents a case where soils and sediments were significantly enriched in total As concentration, but the water As concentration was below detection limits.  The species of N. officinale and D. esculentum grown for consumption in As-contaminated soil presents a mild risk for human consumption.