Ecological implications of arsenic hyperaccumulation

Arsenic (As) is widely known for its use as a poison, pesticide, and for the contamination of soil and water across the world.  Due to increasing concerns in the exposure rates and cost of mitigation, new technologies are emerging that incorporate ecologically sensitive and cost effective solutions to remediate contaminated areas.  Pteris vittata is an As hyperaccumulating fern and potentially effective As phytoremediator.  While research continues on the efficacy of using these ferns to treat contaminated areas, there is also considerable interest in the functional advantages conferred by hyperaccumulation. 

One of the unexpected consequences of As hyperaccumulation is the re-enrichment of the top soil underneath the fern.  When the As rich fronds senesce, and fall to the ground, As is released back into the soil.  While this effect likely benefits the fern by deterring competitors it has unknown consequences on the environment.  We addressed this unknown by examining the specific relationship between soil As concentrations, invertebrate abundance and As accumulation within surface active invertebrates.  As soil As concentrations increased, overall invertebrate abundance decreased.  However, individual taxonomic groups (orders) differed in their direct response to soil As.  While every type of invertebrate had a higher As body load than the associated soil As concentrations, there was considerable variation in accumulation by taxonomic group.  These results have important connotations on the effect of environmental As on the environment.  While As can serve as a deterrent, we also found a caterpillar (Callopistria floridensis) that can accumulate As upwards of 4200ppm.  The major consequence is that sub-lethal concentrations of soil As can be accumulated by invertebrates and potentially redistributed around the environment with unknown consequences.