Mercury concentrations in riparian spiders along three East Texas rivers and the health risk they pose to songbirds

Abstract

Mercury (Hg) is a global atmospheric pollutant that can be harmful to wildlife. Because methylmercury (MeHg) is only produced in aquatic ecosystems, it is assumed that Hg contamination poses a risk to aquatic but not terrestrial wildlife. Tetragnathid spiders transfer aquatic MeHg to terrestrial consumers and may contain high concentrations of MeHg that pose a threat to the health of songbirds that consume them. I collected tetragnathid spiders from 26 sites along three East Texas rivers, Black Cypress, Big Cypress, and Little Cypress Bayou, and determined their Hg concentrations. I then calculated potential Hg risk to four species of songbirds (American Robin, Eastern Bluebird, Carolina Wren, and Chickadee). Average site-specific MeHg concentrations in spiders ranged from 34.5 to 174 ng/g wet weight and were high enough to pose a risk to some songbirds. Mercury concentrations in spiders were significantly different between the rivers and lowest in Big Cypress Bayou