Methylmercury Contamination of Terrestrial Spiders Living Along the Trinity River

Abstract

Methylmercury (MeHg) is a toxic environmental contaminant found in all waterbodies on Earth. Aquatic emergent insects, such as mosquitoes and midges, can transfer MeHg from waterbodies to terrestrial ecosystems. Terrestrial shoreline spiders consume emergent aquatic insects and become contaminated with MeHg. Methylmercury-contaminated spiders can pose a health risk to arachnivorous songbirds. Because shoreline spiders have MeHg concentrations that reflect MeHg contamination of nearby aquatic ecosystems and are an important source of MeHg to songbirds, they have been proposed as a biosentinel species that can be used to estimate MeHg contamination of waterbodies. In this study, I used long-jawed orb weavers (Tetragnatha sp.) as a biosentinel species to examine MeHg contamination in the Clear Fork and the West Fork of the Trinity River, Fort Worth, Texas. The objectives of this study were to: 1) evaluate MeHg contamination in long-jawed orb weavers from two forks of the Trinity River, and 2) determine if the concentrations of MeHg in the spiders pose a health risk to arachnivorous songbirds. I collected 101 and 105 spiders along the Clear Fork and the West Fork, respectively. All spiders were contaminated with MeHg, with spiders along the Clear Fork having higher concentrations of MeHg than spiders along the West Fork. Methylmercury in spiders increased with spider size along the Clear Fork. Concentrations of MeHg in spiders along the Clear Fork and the West Fork were high enough to pose a risk to the health of nestling arachnivorous songbirds.