Soil pH changes induced by contamination by magnesium oxides dust

In this paper we evaluate the environmental impact of dust emission from a magnesite calcination factory during the last 40 years over an area of abou t 600 ha in northern Spain. Our study aimed to determine the contamination levels through the spatial modifications induced on the soil pH by depositi on of the dust, mostly composed of magnesium oxides. A soil survey of the a rea has been conducted by collecting soil samples at three different depths (0-2, 2-32 and 32-52 cm) following a square grid pattern. Our survey has e videnced an important and general pH increase of the soils. Thus, from orig inal values of around 7, pH reaches alkaline values of above 9.5. IDRISI GI S techniques have been used to analyse and represent the spatial distributi on of the pH values. Variations in the expected concentric circular pattern of soil pH distribution appear to be related to climatic factors, such as precipitation. wind direction and intensity. Also topography affects pH dis tribution through its 'screen' effect. The contamination levels in the area have a strong environmental impact responsible for the abandonment of some agricultural lands. Copyright (C) 2000 John Wiley & Sons, Ltd.