Heavy metal accumulation in deep sediment benthic invertebrates downstream from a historical mining district

Metal mining has resulted in substantial ecological impacts, with effects lasting long after mining activity has ceased. Metals can leach from abandoned mines and mining waste (i.e. "chat") into waterbodies, affecting the native biota and associated processes. Often, metals precipitate or otherwise leave the water column, depositing in deep sediments. These deep sediments can be densely populated with immature insects and other invertebrates; however, they are often ignored in the assessment of ecosystem impacts. Our study assessed heavy metal concentrations in common macroinvertebrates collected from deep sediments (>3 m depth) located downstream of Tar Creek, a stream draining Pb and Zn minefields in the historic Tri-State mining district (Oklahoma/Kansas/Missouri, USA). Macroinvertebrate, water, and sediment samples were collected at multiple sites in the Neosho River and Grand Lake in northeast Oklahoma (USA). The concentrations of 17 elements were determined using inductively coupled plasma optical emission spectroscopy. Higher concentrations of Zn were observed in invertebrates collected near the Neosho River-Tar Creek confluence than in invertebrates collected further downstream. Additionally, metal concentrations were higher in invertebrates than in the environmental samples collected, and higher than biological samples collected in previous studies. Although these concentrations appear to be sublethal, this study demonstrates the downstream spread of impact from the TCSS. Additionally, the study highlights the importance of including deep sediment fauna when assessing the impact of pollutants on aquatic ecosystems. These deep sediment assemblages can harbor high concentrations of metals, and through emergence reintroduce these pollutants to aquatic and terrestrial food webs.