Trace elements pose a challenge to our ability to understand their dis-tribution in that they occur naturally. Trace elements may accumulate in a system due to geological and chemical factors other than pollution, or through indirect effects caused by human activities such as land use changes. In order to fully understand these effects, data sets across a large temporal and spatial range are required, however most modern pollution monitoring programs were only instituted in the 1970s or later. In this study, mussel shells from prehistoric, historic and modern collections were analyzed as proxies of trace metal accumulation in the Illinois River system. Shells were found to have almost no variation between species collected at the same site. Prehistoric shells consistently accumulated higher concentrations of Mn and Zn, but lower concentrations of As, Co, Cu and Ni. The elements Cd, Co, Cu and Ni were found to have increased over the past 120 years, while Mn decreased. One potentially confound-ing factor was that older populations of shells were significantly older and larger than larger collections. However, allometric relationships were not consistently significant and had little effect on temporal trends. In contrast, allometric relationships had a large effect on analysis of the spatial gradient along the Illinois River mainstem due to strong allometric effects at the uppermost and lowermost sites. Overall, modern shells indi-cated higher downstream concentrations of As, Co, Mn and Ni. Elements that varied spatially in no direction was Co, Cu, Ni and Zn. Large scales in the watershed and bivalve populations have clearly occurred over time. These changes are clearly expressed in the concentrations of elements such as Mn, which accumulates in higher concentrations in older shells. Other elements show clear elevation over a prehistoric baseline and vary in time and space, such as As, Co, Cu and Ni. Finally, another set of elements appears to be extremely conservative with little temporal or spatial differences. This set includes Fe and Cd, which while commonly associated with pollution appears in shells at extremely consistent con-centrations. This study can serve as a model for future investigations into trace metal concentrations in bivalve shells and works towards a greater understanding of the manner in which they vary in both space and time.
|Original language||English (US)|
|Title of host publication||7th Society of Environmental Toxicology and Chemistry World Congress/Society of Environmental Toxicology and Chemistry North America 37th Annual Meeting, 6-10 November 2016, Orlando, Florida|
|State||Published - 2016|