Continuous soil pollution mapping using fuzzy logic and spatial interpolation

Fuzzy classification combined with spatial prediction was used to assess the state of soil pollution in Isfahan region, central Iran. Total concentrations of cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), and cobalt (Co) were determined in 255 topsoil samples (0–20 cm) collected irregularly in a study area of 6800 km2. Heavy metals concentrations were grouped into four classes according to the optimum number of classes and fuzziness exponent using the fuzzy c-mean. Membership values were interpolated using ordinary kriging. To better visualize the results, a continuous colour index was calculated for each pixel of membership values by combining the colour mixture and composite colour map techniques. The result indicated that the topsoil was polluted with Pb and Cd in some parts of the study area, particularly in the centre of Isfahan city where the concentration were more than 50 and 4 mg kg−1, respectively. Continuous mapping revealed that concentrations of Zn, Cu, and Co were less than the pollution limits of 200, 50, and 25 mg kg−1, respectively. But their concentrations were significantly high in some parts of the study region. In addition, the continuous colour index procedure proved quite effective in visualizing the results of the fuzzy classification.