Multielement Urban Geochemistry : Exporing the Expected, the Unexpected and the Unknown

Abstract: Urban areas are hot-spots for the human use of most elements. These elements are the building blocks of our various goods and chemicals and are used both purposely and in a more unaware fashion. There are many ways in which the elements get dispersed from the human use. Commonly acknowledged and evident processes of dispersion are point sources (e.g. industrial pollution), diffuse sources (e.g. traffic) and the past historic use of various chemicals. In fact everything ever produced is going to end up somewhere - it is just a matter of time. Soils and sediments are the main sinks for elements dispersed from the above and other sources. The importance of recognising the dispersion of elements lies in the well-known fact that many elements are toxic or potentially toxic. Due to the multitude of chemicals used in urban areas during time periods up to even thousand of years it can not be known exactly which elements are enriched at specific sites or in specific samples. Moreover, if the presence of a specific element is "unexpected" then it can lead to the element not being searched for (determined) at all. Due to this it is important that as many elements as possible are determined from samples with urban environmental concern.In this thesis multielement chemical analyses (mainly ICP-MS) are used to study the past, present and potential future dispersion of chemical elements, mainly in and around the small town of Jakobstad (Pietarsaari), Finland. The materials studied were till, boreal forest humus, various urban soils, street dust, lake sediments and sediment leachates. The results first of all show that multielement analytical methods are useful, if not totally necessary, in order to grasp the presence and dispersion of various elements from both natural and anthropogenic sources. This is especially important when dealing with the dispersion of toxic elements. The most important specific findings of this thesis are: the presence of reduced sulphur in natural lake sediments can lead to considerable leakage of many elements if the sediments are dredged and allowed to oxidise; that boreal forest humus can be used to track the past urban dispersion of various chemical elements; boron can be used to track wood fires from sedimentary profiles; that the use of red lead has caused extreme lead concentration in the topsoil from small-scale usage. This lead can be "invisible" and highly bioavailable to certain bacteria and most likely also to other organisms; that tungsten carbide is enriched in the urban humus and dust and dispersed to the environment from the studded tyres as < 0.1 -1.4 um particles.

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