Kartering av kadmiumhalt i matjord med portabelt röntgenfluorescensinstrument

University essay from SLU/Dept. of Soil and Environment

Author: Elin Laxmar; [2018]

Keywords: Cd; jord; kärna; PXRF; markkartering;

Abstract: Cadmium (Cd) is a nonessential heavy metal that can be toxic to living organisms even in small amounts. Cd occurs naturally in all type of soils but have also been added trough soil amendments and atmospheric fallout. Cd can cause osteoporosis, endometrial cancer, and can accumulate in liver and kidneys where it causes damage if the intake is too large. Non-smokers are exposed to Cd mostly by eating vegetable-based food. To be able to plan the reduction of Cd in food, soil with high respectively low levels of Cd must be identified. Therefore, it´s of great value to develop simple and cost-effective methods of measurement. The purpose of this degree project was to evaluate the possibility of using a portable x-ray fluorescence instrument (PXRF) to be able to estimate the content of Cd in the topsoil in a fast and cheap manner. The method was tested in different scales, on national and local levels, in winter wheat and soil samples to evaluate what it takes for the instrument to provide the correct data. PXRF measuring as a method to map Cd at a regional level was tested on soil samples from a national material with existing soil and grain analysis collected from several different geographic areas. This was supplemented with sampling and analysis of soil and grain from two conventional agricultural fields in Skåne, one with expected high content of Cd and one with expected low content. It is not possible to measure Cd directly with PXRF, since the Cd levels in arable land normally are so low that the instrument cannot detect them. Therefore, a couple of other elements were measured both on a national and local level. The difference between measurements on dry and moist soil was also studied. PXRF-data were used to estimate the Cd content of the soil samples with regression analysis and the estimated value was validated by comparing it to laboratory data. The elements that were used in the regression analysis (Zr, Sr, Rb, Zn, Fe, Mn, Cr, V, Ti, Ca, K och Ba) were those who were measurable with PXRF on all samples. The results show a clear pattern on how the Cd level in soil correlates with elements that are analyzed with PXRF, for example zinc and vanadium, which makes it possible to develop a general model to predict Cd content in soil. This means that it is possible to estimate the content of Cd in soil by measuring other elements, in a fast and rather cheap way. There is also a correlation, albeit weaker, between elements measured by PXRF on soil samples and the content of Cd in the grain. No obvious differences were found when comparing measurements on moist and dry soil. This could lead to the development of better factual basis to be used when developing action packages that in the extension can result in methods to decrease the content of Cd in products that are used in food.

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