Bioaccumulation trends of arsenic and antimony in a freshwater ecosystem affected by mine drainage

Abstract

Environmental context The food web behaviours of As and Sb are poorly understood. We compare As and Sb bioaccumulation in a contaminated freshwater ecosystem. Metalloid accumulation decreased with increasing trophic level. Bioprecipitated minerals in microbial mats represent a direct route of uptake (by ingestion) of metalloids to tadpoles, which contained the highest concentrations ever reported. We demonstrate food web bioaccumulation, but not biomagification, of As and Sb. We also report an unexpectedly high tolerance of tadpoles to metalloid toxicity. Abstract We compared As and Sb bioaccumulation and biomagnification when these metalloids co-occurred at varying environmental concentrations in a stream and wetlands near a contaminated mine site in Idaho (USA). We measured As and Sb concentrations in water and substrate samples, and in tissues of organisms representing several trophic levels. Bioaccumulation of both As and Sb was observed in stream organisms with the following trend of bio-diminution with increasing trophic level: primary producers>tadpoles>macroinvertebrates>trout. We also note reductions in metalloid concentrations in one of two stream remediation reaches engineered within the past 17 years to ameliorate metalloid contamination in the stream. Several wetlands contained thick microbial mats and were highly populated with boreal toad tadpoles that fed on them. The mats were extremely contaminated (up to 76564mgkg–1 As and 675mgkg–1 Sb) with amorphous As- and Sb-bearing minerals that we interpret as biogenic precipitates from geomicrobiological As- and Sb-cycling. Ingested mat material provided a direct source of metalloids to tadpoles, and concentrations of 3867mgkg–1 (As) and 375mgkg–1 (Sb) reported here represent the highest whole body As and Sb levels ever reported in living tadpoles. The bulk of tadpole metalloid burden remained in the gut despite attempts to purge the tadpoles prior to analysis. This study adds to a number of recent investigations reporting bioaccumulation, but not biomagnification, of As and Sb in food webs. Moreover, our results suggest that tadpoles, in particular, may be more resistant to metalloid contamination than previously assumed.