Can Periodic Cicadas be used as a Biomonitor for Arsenical Pesticide Contamination?

Widespread use of arsenical pesticides on fruit crops, particularly apple orchards, during the first half of the 20th century is a significant source of arsenic to agricultural soil in the Mid-Atlantic region. Cumulative application rates may be as high as 37 Kg/hectare of arsenic in orchard areas. Brood X 17-year periodic cicadas (Magicicada spp.) emerged at densities up to 30,000 or more individuals per hectare in orchard and forest habitats during May-June, 2004, in Clarke and Frederick Counties, Virginia and in Berkeley and Jefferson Counties, West Virginia. These cicadas were sampled to evaluate the bioavailability of arsenic in orchard and non-orchard reference site soils. Potentially toxic elements, such as arsenic and other heavy metals bind to sulfhydryl groups, and thus may accumulate in keratin-rich tissues, such as cicada nymphal exuviae and adult exoskeletons. These cicadas feed on plant roots underground for 17 years before emerging to molt into their adult form. Adult cicadas have very limited dispersal, rarely traveling more than 50 m in a flight. As such, their body and exoskeleton keratin has potential value as a biomonitor for arsenic and other metals that is spatially referenced to local conditions for the duration of time the nymphs live in the soil. This study addresses the following research questions: (1) do the soils in and adjacent to orchard sites where arsenical pesticide was used contain elevated concentrations of arsenic and other metals relative to likely background conditions?; (2) can periodic cicadas be used as an easily sampled biomonitor measuring bioavailability of pesticide residues in soils?; and (3) do the concentration levels of arsenical pesticide residues in periodic cicadas emerging from contaminated orchard sites pose a dietary threat to birds and other wildlife that preferentially feed upon cicadas during emergence events?