Fig. 3. SEM-EDX elemental dot maps of (a) Oxisol and (b) Ultisol soil samples. Light areas of the dot maps indicate elevated concentrations of a particular element. The first letter/s in the upper right-hand corner of each box represent/s the particular element of concern, Ka = K- excitation energy; Ma1 = M- 1 excitation energy, and the numbers correspond to the relative elemental intensities in counts per second.