Bioassessment of contaminant transport and distribution in aquatic ecosystems by chemical analysis of burrowing mayflies (Hexagenia)

Abstract

Burrowing mayfly nymphs (Ephemeroptera) inhabit and ingest fine-grained sediments and detritus that may be enriched with metals and persistent organic compounds. The burrowing nymphs can externally adsorb and internally assimilate these contaminants, providing a link for the food chain transfer of potentially toxic substances from sediments to organisms in higher trophic levels. The emergent adults are short-lived and do not feed, thus their gut contents do not contribute greatly to their total contaminant burden. These characteristics make Hexagenia spp. and certain other burrowing mayflies useful for assessing ecosystem contamination. General protocols are presented for the collection, processing and analysis of emergent mayflies to assess the spatial distribution and bioaccumulation of sediment-associated contaminants in aquatic ecosystems. Two essential components of this bioassessment approach are a network of on-site volunteers with the materials and instructions needed to correctly collect and store samples and quality assurance procedures to estimate the accuracy of chemical analyses. The utility of this approach is demonstrated with an example of its application to the Upper Mississippi River (USA). Determination of cadmium, mercury and polychlorinated biphenyl congeners in emergent Hexagenia bilineata from a 1250 km reach of this river revealed (1) several source areas of contaminants and ( 2 ) distinct patterns in the bioaccumulation (and apparent sediment-associated transport) of each residue on both small and large spatial scales.

Contaminants in the Upper Mississippi River: historic trends, responses to regulatory controls, and emerging concerns

“…3). In addition, the PCB congener composition of mayflies from the 375-km reach from Pool 2 through Pool 11 (data not shown) was very similar to that in mayflies from Pool 2 (Steingraeber & Wiener, 1995).…”

“…Thus, cadmium in fish is generally not considered a health risk to humans who eat fish. None of the five states bordering the Upper Mississippi River had fishconsumption advisories for cadmium as of Cadmium contamination of aquatic biota is greatest in the vicinity of industrialized metropolitan areas, as illustrated by the analyses of burrowing mayflies (Hexagenia bilineata Say, a benthic detritivore important in the riverine food web) and zebra mussels (Dreissena polymorpha Pallas, a filter-feeding, epibenthic bivalve) (Dukerschein et al, 1992;Beauvais et al, 1995;Steingraeber & Wiener, 1995;Cope et al, 1999). In 1988, mayflies were sampled after mass emergence events at 34 sites (25 navigation pools), extending 1,260 km from Little Falls, Minnesota, downstream to St. Louis, Missouri (Dukerschein et al, 1992).…”

“…Sampling locations are denoted by navigation pool, vertically scaled by river mile (main channel distance), and are shown in relation to three metropolitan areas bordering the river, Lake Pepin, and Little Falls, Minnesota (LF, upstream of the Twin Cities metropolitan area). Data are from Dukerschein et al (1992), Steingraeber et al (1994), and Steingraeber & Wiener (1995) cadmium and other contaminants that bind to particles. However, juvenile bluegills (Lepomis macrochirus Rafinesque) readily accumulated cadmium when exposed experimentally to 1000 mg/l of suspended contaminated sediment from the Upper Mississippi, Illinois, and Des Plaines rivers in 28-day tests (Cope et al, 1994).…”

“…Analyses of emergent female mayflies (H. bilineata) sampled in 1988 during mass emergence events on the Upper Mississippi River showed that PCB contamination of the aquatic food web was greatest in the vicinity of industrialized metropolitan areas (Steingraeber et al, 1994;Steingraeber & Wiener, 1995). In the Twin Cities Metropolitan Area, the total PCB concentration in mayflies increased nearly fourfold over an 18-km reach in Pool 2 and was greatest (3.9 to 4.1 lg/g dry weight) in samples from the middle and lower reaches of the pool (Fig.…”

Toxicity of Sediment Collected Upriver and Downriver of Major Cities Along the Lower Mississippi River

“…The presence of mayflies (Ephemeroptera) generally indicates acceptable habitat quality (Hubbard and Peters 1978). Mayflies are used in sediment toxicity testing (ASTM 1996) and have been used in habitat bioassessment and contaminant transport studies in the Mississippi River (Steingraeber and Wiener 1995). Hexagenia sp.…”